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Macrophages in the embryo and beyond: Much more than just giant phagocytes
Abstract
Originally recognized as an essential part of the innate and acquired immune systems, macrophages emerged as omnipresent and influential regulators of embryo- and organo-genesis, as well as of tissue and tumor growth. Macrophages are present essentially in all tissues, beginning with embryonic development and, in addition to their role in host defense and in the clearance of apoptotic cells, are being increasingly recognized for their trophic function and role in regeneration. Some tissue macrophages are also found to posses a substantial potential for autonomous self-renewal. Macrophages are associated with a significant proportion of malignant tumors and are widely recognized for their angiogenesis-promoting and trophic roles, making them one of the new promising targets for cancer therapies. Recent expression profiling of embryonic macrophages from different tissues revealed remarkable consistency of their gene expression profiles, independent of their tissue of origin, as well as their similarities with tumor-associated macrophages. Macrophages are also capable of fusion with other cells in tissue repair and metastasizing tumors, as well as with each other in the immune response and osteoclastogenesis. genesis 46:447–462, 2008. © 2008 Wiley-Liss, Inc.
... Macrophages, recognized as one of the most versatile cell types within the immune system, fulfill indispensable roles in maintaining overall physiological equilibrium. Their paramount function centers around phagocytosis, an intricate process through which they engulf and digest a diverse array of entities, encompassing microbial invaders, detritus from deceased cells, and even cancerous cells [10]. However, the multifaceted contributions of macrophages extend far beyond phagocytosis. ...
... Silibinin, a polyphenolic flavonoid and a major component of milk thistle extract was found to have strong anti-inflammatory properties, as demonstrated in this study The research showed that silibinin effectively inhibited phagocytosis, a key inflammatory function of macrophages responsible for engulfing and digesting foreign and endogenous substances to protect the host from pathogens and cancer cells [10]. The study utilized E coli bioparticles to assess phagocytosis, and the results indicated that silibinin dose-and time-dependently inhibited this process ( Figure 3A). ...
... Silibinin, a polyphenolic flavonoid and a major component of milk thistle extract, was found to have strong anti-inflammatory properties, as demonstrated in this study. The research showed that silibinin effectively inhibited phagocytosis, a key inflammatory function of macrophages responsible for engulfing and digesting foreign and endogenous substances to protect the host from pathogens and cancer cells [10]. The study utilized E. coli bioparticles to assess phagocytosis, and the results indicated that silibinin dose-and timedependently inhibited this process ( Figure 3A). ...
This study investigated the effects of silibinin, derived from milk thistle (Silybum marianum), on lipopolysaccharide (LPS)-induced morphological changes in mouse macrophages. Silibinin was treated at various doses and time points to assess its effects on macrophage activation, including morphological changes and phagocytosis. Silibinin effectively inhibited LPS-induced pseudopodia formation and size increase, while unstimulated cells remained round. Silibinin’s impact on phagocytosis was dose- and time-dependent, showing a decrease. We explored its mechanism of action on kinases using a MAPK array. Among the three MAPK family members tested, silibinin had a limited effect on JNK and p38 but significantly inhibited ERK1/2 and related RSK1/2. Silibinin also inhibited MKK6, AKT3, MSK2, p70S6K, and GSK-3β. These findings highlight silibinin’s potent inhibitory effects on phagocytosis and morphological changes in macrophages. We suggest its potential as an anti-inflammatory agent due to its ability to target key inflammatory pathways involving ERK1/2 and related kinases. Overall, this study demonstrates the promising therapeutic properties of silibinin in modulating macrophage function and inflammation.
... Macrophages, being the most diverse cells of the immune system, play critical roles in maintaining homeostasis. Their hallmark function is phagocytosis, which involves engulfing and digesting various foreign and endogenous objects, including microbial pathogens, dead cell debris, and cancer cells [10]. Macrophages also play a role in recruiting other lymphocytes and regulating adaptive immune responses. ...
... Silibinin, a polyphenolic flavonoid and a major component of milk thistle extract, was found to have strong anti-inflammatory properties, as demonstrated in this study. The research showed that silibinin effectively inhibited phagocytosis, a key inflammatory function of macrophages responsible for engulfing and digesting foreign and endogenous substances to protect the host from pathogens and cancer cells [10]. The study utilized E. coli bioparticles to assess phagocytosis, and the results indicated that silibinin dose-and time-dependently inhibited this process (Figure 3a). ...
... Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 July 2023 doi:10.20944/preprints202307.0826.v110 ...
This study investigated the effects of silibinin, derived from milk thistle (Silybum marianum), on lipopolysaccharide (LPS)-induced morphological changes in mouse macrophages. Silibinin was treated at various doses and time points to assess its effects on macrophage activation including morphological changes and phagocytosis. Silibinin effectively inhibited LPS-induced pseudopodia formation and size increase, while unstimulated cells remained round. Silibinin's impact on phagocytosis was dose- and time-dependent, showing a decrease. We explored its mechanism of action on kinases using a MAPK array. Among the three MAPK family members tested, silibinin had a limited effect on JNK and p38 but significantly inhibited ERK1/2 and related RSK1/2. Silibinin also inhibited MKK6, AKT3, MSK2, p70S6K, and GSK-3β. These findings highlight silibinin's potent inhibitory effects on phagocytosis and morphological changes in macrophages. We suggest its potential as an anti-inflammatory agent due to its ability to target key inflammatory pathways involving ERK1/2 and related kinases. Overall, this study demonstrates the promising therapeutic properties of silibinin in modulating macrophage function and inflammation.
... Macrophages are pivotal for maintaining homeostasis and executing the hallmark function of phagocytosis, which involves the engulfment and digestion of various foreign and endogenous entities, such as microbial pathogens, dead cell debris, and cancer cells [5]. Additionally, macrophages is important in adaptive immune responses. ...
... GSE effectively inhibited phagocytosis in LPS-stimulated RAW264.7. Phagocytosis is a key host defense and inflammatory function of macrophages, which involves engulfing and digesting various foreign and endogenous objects for protection against microbial pathogens and cancer cells [5]. A phagocytosis assay using E. coli bioparticles revealed a dose-and time-dependent inhibition of phagocytosis by GSE (Fig. 3). ...
... Macrophages are myeloid linage cells involved in innate immune responses that have historically been viewed as terminally-differentiated phagocytic cells that primarily exhibit pro-inflammatory phenotypes 1 . Fate-mapping studies now indicate that macrophages involved in the regulation of J o u r n a l P r e -p r o o f tissue homeostasis have distinct origins, which we will herein refer to as tissue-resident and recruited macrophages [2][3][4] . Most tissue-resident macrophages derive from the yolk sac or fetal liver during embryonic development and migrate to their final site prior to the end of gestation, whereas recruited macrophages derive from circulating monocytes that continue to differentiate from hematopoietic stem cells during the organism's lifetime [3][4][5] . ...
... Fate-mapping studies now indicate that macrophages involved in the regulation of J o u r n a l P r e -p r o o f tissue homeostasis have distinct origins, which we will herein refer to as tissue-resident and recruited macrophages [2][3][4] . Most tissue-resident macrophages derive from the yolk sac or fetal liver during embryonic development and migrate to their final site prior to the end of gestation, whereas recruited macrophages derive from circulating monocytes that continue to differentiate from hematopoietic stem cells during the organism's lifetime [3][4][5] . Monocytes that highly express Ly6c have pro-inflammatory and antimicrobial activity and accumulate at sites of inflammation, while monocytes with low levels of Ly6c expression are considered to be patrolling monocytes that crawl along and survey the vasculature and participate in early inflammatory and tissue repair responses 6 . ...
Macrophages are typically identified as classically activated (M1) macrophages and alternatively activated (M2) macrophages, which respectively exhibit pro- and anti-inflammatory phenotypes, and the balance between these two subtypes plays a critical role in the regulation of tissue inflammation, injury, and repair processes. Recent studies indicate that tissue cells and macrophages interact via the release of small extracellular vesicles (EVs) in processes where EVs released by stressed tissue cells can promote the activation and polarization of adjacent macrophages which can in turn release EVs and factors that can promote cell stress and tissue inflammation and injury, and vice versa. This review discusses the roles of such EVs in regulating such interactions to influence tissue inflammation and injury in a number of acute and chronic inflammatory disease conditions, and the potential applications, advantage and concerns for using EV-based therapeutic approaches to treat such conditions, including their potential role of drug carriers for the treatment of infectious diseases.
... Tissue-resident macrophages are highly abundant in all organs, including the skin, gastrointestinal tract, lymphoid organs, and lungs. Macrophage populations are aptly named according to the tissue in which they reside, as well as their function; for example, Kupffer cells refer to macrophages in the liver, microglia in the brain, and alveolar macrophages in the lung [4,9]. In general, all macrophages share several important functions: (1) they play a role in tissue development and maintenance; ...
... (2) tissue surveillance and sampling; and (3) pathogen clearance, antigen presentation, inflammation resolution, and tissue repair. Depending on the organ or tissue localization, macrophages may fulfill several of these tasks and, as such, comprise highly heterogeneous cell populations with various phenotypes and functions [9]. Macrophages are also known for their plasticity, as they may undergo phenotype switching in response to various stimuli [4,10]. ...
Chronic inflammation is inextricably linked to cardiovascular disease (CVD). Macrophages themselves play important roles in atherosclerosis, as well as acute and chronic heart failure. Although the role of macrophages in CVD pathophysiology is well-recognized, little is known regarding the precise mechanisms influencing their function in these contexts. Long non-coding RNAs (lncRNAs) have emerged as significant regulators of macrophage function; as such, there is rising interest in understanding how these nucleic acids influence macrophage signaling, cell fate decisions, and activity in health and disease. In this review, we summarize current knowledge regarding lncRNAs in directing various aspects of macrophage function in CVD. These include foam cell formation, Toll-like receptor (TLR) and NF-kβ signaling, and macrophage phenotype switching. This review will provide a comprehensive understanding concerning previous, ongoing, and future studies of lncRNAs in macrophage functions and their importance in CVD.
... Interestingly, erythrocytes in these colonies were not of primitive origin, as they did not express embryonic globins but rather a unique combination of hemoglobins (see Table 1). Later, we purified HPP-CFCs based on their [29]; Bertrand et al. [30]; Ovchinnikov [66] expression of multiple surface markers. At E10-E10.5 in the mouse embryo, we showed that all EMPs were contained in the CD45 lo cKit + AA4.1 + YS cell subset [29]. ...
... Csf1r, the receptor for Csf1 (also known as M-CSF) and for Interleukin-34, is exclusively expressed by cells from the monocytic/macrophage lineage [65]. By establishing the Csf1r-GAL4/UAS-ECFP transgenic mouse, Ovchinnikov and colleagues showed that macrophages already reach all tissues as early as E9, including the brain rudiment and the epidermis, among others [66]. At E9, we previously showed that EMPs have not started their differentiation into any lineage yet [30]; therefore, these early macrophages can only represent the progeny of the primitive macrophages lineage. ...
In most vertebrates, the yolk sac (YS) represents the very first tissue where blood cells are detected. Therefore, it was thought for a long time that it generated all the blood cells present in the embryo. This model was challenged using different animal models, and we now know that YS hematopoietic precursors are mostly transient although their contribution to the adult system cannot be excluded. In this review, we aim at properly define the different waves of blood progenitors that are produced by the YS and address the fate of each of them. Indeed, in the last decade, many evidences have emphasized the role of the YS in the emergence of several myeloid tissue-resident adult subsets. We will focus on the development of microglia, the resident macrophages in the central nervous system, and try to untangle the recent controversy about their origin.
... Male albino mice (6-8 weeks old) were used to isolate primary bone marrowderived macrophages (BMDMs) [35]. ...
... Macrophages are specialized immune cells found in all body organs, whose role is to phagocytose antigens, foreign material, cancer cells, and cellular debris [1]. In addition to their primary role in regulating the innate immune response, tissue macrophages keep tissue homeostasis and niche-specific functions. ...
Muscularis macrophages are a newly discovered population of macrophages distributed within the smooth muscle layers of the gastrointestinal tract. Muscularis macrophages are emerging as essential cell keepers of homeostatic gastrointestinal function, and when affected, can lead to functional gastrointestinal disorders. In this chapter, we briefly introduce the phenotype, the distribution of muscularis macrophages, and the difference compared with other tissue-resident macrophages. We next describe how they contribute to normal gastrointestinal function by interacting with cells required for gastrointestinal motility, such as enteric neurons. Finally, we highlight the increasing pieces of evidence suggesting the contribution of muscularis macrophages to gastrointestinal function diseases, such as gastrointestinal inflammation, gastroparesis and post operative ileus.
... Toutefois, leurs rôles sont pléiotropes et ces cellules sont impliquées dans la résolution de l'inflammation, dans la cicatrisation des plaies et des tissus après une infection ou une blessure ainsi que lors de la présentation de l'antigène (Duffield et al., 2013;Martinez et al., 2009;Wynn et al., 2013). Concernant leur origine, les monocytes sanguins en circulation étaient considérés comme étant les précurseurs exclusifs des macrophages tissulaires (van Furth and Sluiter, 1986 (Gordon and Taylor, 2005;Ovchinnikov, 2008). De nombreuses études en ont conclu que la localisation anatomique des macrophages dicte leur hétérogénéité en termes de fonction (Gordon and Taylor, 2005). ...
L'interleukine-10 (IL-10) est une puissante cytokine anti-inflammatoire produite par la plupart des cellules de l'immunité innée et adaptative et dont les monocytes en sont une cible majeure. La liaison de l'interleukine-10 à son récepteur initie une signalisation intracellulaire impliquant STAT3 ce qui induit l'expression de gènes codant pour des facteurs anti-inflammatoires. Du fait de son action immuno-modulatrice, l'IL-10 a été considérée comme un outil thérapeutique intéressant dans les maladies les maladies inflammatoires aigües ou chroniques, et les maladies auto-immunes ayant une composante inflammatoire. Cependant l'administration de l'IL-10 n'a montré que peu d'efficacité dans diverses situations pathologiques telle que la polyarthrite rhumatoïde (PR). La difficulté pourrait être liée à la complexité du foyer inflammatoire où la présence de multiples cytokines pourrait affecter la signalisation de l'IL-10. Dans ce contexte l'objectif de la thèse était de déterminer si le TNFα, une cytokine pro-inflammatoire majeure, pouvait altérer la signalisation de l'interleukine-10 dans les monocytes humains et de déterminer mécanismes sous-jacents, impliquant la NADPH oxydase 2 (NOX2) acteur important de la signalisation cellulaire et dont le TNFα en est agoniste, ainsi que l'impact potentiel dans les situations inflammatoires pathologiques, telle que la PR, en utilisant un modèle expérimental murin. Nos résultats montrent que le TNFα interfère avec la signalisation de l'IL-10 en induisant une déphosphorylation rapide de STAT3 dans les monocytes humains. La déphosphorylation de STAT3 induite par le TNFα se traduit par une diminution de la capacité de l'IL-10 à induire l'expression de SOCS3 un facteur anti-inflammatoire majeur. La diminution de la phosphorylation de STAT3 impliquait une phosphatase SHP1 / 2 car l'utilisation du NSC-87877, un inhibiteur de SHP1 / 2, empêche l'action inhibitrice du TNFα sur la signalisation de l'IL-10. Dans les monocytes stimulés par le TNFα la SHP1 est activée alors que la SHP2 ne l'est pas, suggérant l'implication de SHP1 et non pas celle de SHP2 dans la déphosphorylation de STAT3. L'activation de SHP1 par le TNFα est dépendante de NOX2 car nous avons observé que le diphénylèneiodonium, un inhibiteur de NOX2, supprime l'activation de SHP1 et la déphosphorylation de STAT3 déclenchée par le TNFα. De plus, H2O2 a reproduit l'action inhibitrice du TNFα sur la signalisation de l'IL-10. Par ailleurs, l'activation de SHP1 par les FRO dans les monocytes stimulés par le TNFα est médié par la tyrosine kinase Lyn connue pour être régulée par oxydation. Enfin, l'inhibiteur SHP1/2, NSC-87877, a atténue l'arthrite induite par les anticorps de collagène (CAIA) chez la souris. Ces résultats révèlent que le TNFα perturbe la signalisation de l'IL-10 en induisant la déphosphorylation de STAT3 via l'axe NOX2-ROS-Lyn-SHP1 dans les monocytes humains et que l'inhibition de SHP1/2 in vivo protège contre la CAIA. Cette nouvelle découverte pourrait expliquer la résistance à l'IL-10 dans l'arthrite et pourrait être utile pour exploiter l'IL-10 dans l'immunothérapie.
... In contrast, an alternatively pattern of stimuli such as interleukin 4 (IL-4) causes the polarization towards anti-inflammatory M2-like macrophages. This macrophage phenotype is involved in tissue repair and remodeling processes and other processes contributing mainly to the resolution of inflammation and regeneration [4][5][6][7][8]. Importantly, disturbances in controlled macrophage polarization may ultimately lead to maladaptive immune responses that cause severe tissue damage, fibrosis and cancer, or contribute to severe inflammatory conditions such as sepsis [9]. ...
Macrophages are important cells of the innate immune system that play many different roles in host defense, a fact that is reflected by their polarization into many distinct subtypes. Depending on their function and phenotype, macrophages can be grossly classified into classically activated macrophages (pro-inflammatory M1 cells), alternatively activated macrophages (anti-inflammatory M2 cells), and non-activated cells (resting M0 cells). A fast, label-free and non-destructive characterization of macrophage phenotypes could be of importance for studying the contribution of the various subtypes to numerous pathologies. In this work, single cell Raman spectroscopic imaging was applied to visualize the characteristic phenotype as well as to discriminate between different human macrophage phenotypes without any label and in a non-destructive manner. Macrophages were derived by differentiation of peripheral blood monocytes of human healthy donors and differently treated to yield M0, M1 and M2 phenotypes, as confirmed by marker analysis using flow cytometry and fluorescence imaging. Raman images of chemically fixed cells of those three macrophage phenotypes were processed using chemometric methods of unmixing (N-FINDR) and discrimination (PCA-LDA). The discrimination models were validated using leave-one donor-out cross-validation. The results show that Raman imaging is able to discriminate between pro- and anti-inflammatory macrophage phenotypes with high accuracy in a non-invasive, non-destructive and label-free manner. The spectral differences observed can be explained by the biochemical characteristics of the different phenotypes.
... The role of these primitive Mac was long believed to consist essentially in tissue remodeling and phagocytosis of dead cells. As early as E9, primitive Mac colonize all tissues, starting from the brain [98]. They comprise the predominant Mac population in most organs until E13.5, but are later replaced by monocyte-derived Mac, with one notable exception: brain microglia [97]. ...
Our knowledge of the complexity of the developing hematopoietic system has dramatically expanded over the course of the last few decades. We now know that, while hematopoietic stem cells (HSCs) firmly reside at the top of the adult hematopoietic hierarchy, multiple HSC-independent progenitor populations play variegated and fundamental roles during fetal life, which reflect on adult physiology and can lead to disease if subject to perturbations. The importance of obtaining a high-resolution picture of the mechanisms by which the developing embryo establishes a functional hematopoietic system is demonstrated by many recent indications showing that ontogeny is a primary determinant of function of multiple critical cell types. This review will specifically focus on exploring the diversity of hematopoietic stem and progenitor cells unique to embryonic and fetal life. We will initially examine the evidence demonstrating heterogeneity within the hemogenic endothelium, precursor to all definitive hematopoietic cells. Next, we will summarize the dynamics and characteristics of the so-called “hematopoietic waves” taking place during vertebrate development. For each of these waves, we will define the cellular identities of their components, the extent and relevance of their respective contributions as well as potential drivers of heterogeneity.
... On the other hand, in lymphatic infiltrations present in the affected tissue, the GPx8 was absent. Macrophages are giant phagocytes [41], the most numerous family of leucocytes in the colon, divided into two groups: proinflammatory (M1, tumoricidal) and anti-inflammatory (M2, protumorigenic) [42]. As an important part of the tumor microenvironment [42,43], tumor-associated macrophages (TAM) were mostly present in the anti-inflammatory group. ...
Background and Objectives: Nowadays colorectal carcinoma (CRC) is one of the most common causes of death in patients with malignant neoplasms worldwide. Our work aimed to determine the possible involvement of glutathione peroxidases 4 and 8 (GPx4 and GPx8) in this specific tumor process. Materials and Methods: The expression of GPx4 and GPx8 in 58 specimens of human colorectal cancer tissues and normal tissues was detected by the indirect immunohistochemical method under a light microscope. Statistical analysis was done by Chi-squared test. Histological findings were compared with data such as gender, age, tumor grade, histotype and lymph nodes alteration. Results: In all specimens of healthy tissue the presence of both, GPx4 and GPx8, was detected in the cytoplasm of epithelial cells. On the other hand, a positive immunohistochemical reaction against GPx4 only in 41.4% and against GPx8 only in 29.3% of human colorectal adenocarcinoma specimens were observed. Any significant difference between the presence of GPx and the age, the gender of the patient, tumor grade, histotype of cancer and the lesion of regional lymph nodes has not been detected. Conclusions: Our foundation could mean, that GPx4 and GPx8 have no important role in CRC pathogenesis, but the loss of these enzymes probably indicates a serious pathological process ongoing in the large intestine. To our knowledge, this is the first paper describing GPx8 presence in human colorectal carcinoma.
... The main target organs were the heart and intestines. Shigella could induce apoptosis of macrophages, which were not only used for immune protection but also participated in the development and formation of early embryonic tissues and organs (Ovchinnikov, 2008;Robert and Ohta, 2009). Smith and Mohun (2011) found that the development of Xenopus hearts was determined by the presence and activity of macrophages. ...
Shigella sp. is a highly infectious intestinal pathogen worthy of serious attention that is widely present in aquaculture water and some other polluted water types and might inhibit embryonic development as a biological pollutant. In this study, acute toxicity tests in which Xenopus tropical embryos were exposed to Shigella flexneri at subpathogenic concentrations (10⁶, 10⁷, and 10⁸ CFU·mL⁻¹) for 96 h were carried out to evaluate toxicity indicators such as mortality, hatching rate, malformation rate and enzyme activity. Meanwhile, the expression of related genes was also studied to reveal the toxicity and mechanism of S. flexneri involved in embryonic development. Under S. flexneri exposure, embryo mortality, heart rate and malformation rate increased, but the hatching rate decreased and even led to embryonic gene misexpression, oxidative stress and immune responses. The results showed that S. flexneri might affect the growth and development of embryos by causing differences in the expression of genes related to embryonic development, oxidative stress and immune disorders. Its target organs are the intestine and heart, whose toxic effects are positively correlated with exposure concentration. This result provides a certain theoretical reference for rational evaluation of the influence of Shigella on the early embryos of amphibians.
... we document in Trichoplax fiber cells-motility, phagocytosis of cell debris and pathogens, participation in wound healing-are characteristic of macrophage-like cells that reside in different tissues in vertebrates 85 and invertebrates 62 . Mammalian macrophages can self-renew in homeostasis and in response to challenges such as injury or inflammation 86 . ...
Placozoa is a phylum of non-bilaterian marine animals. These small, flat organisms adhere to the substrate via their densely ciliated ventral epithelium, which mediates mucociliary locomotion and nutrient uptake. They have only six morphological cell types, including one, fiber cells, for which functional data is lacking. Fiber cells are non-epithelial cells with multiple processes. We used electron and light microscopic approaches to unravel the roles of fiber cells in Trichoplax adhaerens , a representative member of the phylum. Three-dimensional reconstructions of serial sections of Trichoplax showed that each fiber cell is in contact with several other cells. Examination of fiber cells in thin sections and observations of live dissociated fiber cells demonstrated that they phagocytose cell debris and bacteria. In situ hybridization confirmed that fiber cells express genes involved in phagocytic activity. Fiber cells also are involved in wound healing as evidenced from microsurgery experiments. Based on these observations we conclude that fiber cells are multi-purpose macrophage-like cells. Macrophage-like cells have been described in Porifera, Ctenophora, and Cnidaria and are widespread among Bilateria, but our study is the first to show that Placozoa possesses this cell type. The phylogenetic distribution of macrophage-like cells suggests that they appeared early in metazoan evolution.
... Macrophages are the early targets for HIV and are productively infected [5,6]. Unlike CD4+ T cells which are characterized by a fast and irreversible depletion [7], infected macrophages survive active viral replication with a half-life ranging from months to years, respond poorly to ART [8,9], develop resistance to apoptosis and HIV cytopathic effects, and harbour unintegrated and integrated viral DNA in a state of latency [10,11]. In patients undergoing effective ART, infected macrophages shield HIV viruses against a spectrum of host anti-viral responses [12,13]. ...
Background
Macrophages, besides resting latently infected CD4+ T cells, constitute the predominant stable, major non-T cell HIV reservoirs. Therefore, it is essential to eliminate both latently infected CD4+ T cells and tissue macrophages to completely eradicate HIV in patients. Until now, most of the research focus is directed towards eliminating latently infected CD4+ T cells. However, few approaches have been directed at killing of HIV-infected macrophages either in vitro or in vivo. HIV infection dysregulates the expression of many host genes essential for the survival of infected cells. We postulated that exploiting this alteration may yield novel targets for the selective killing of infected macrophages.
Methods
We applied a pooled shRNA-based genome-wide approach by employing a lentivirus-based library of shRNAs to screen novel gene targets whose inhibition should selectively induce apoptosis in HIV-infected macrophages. Primary human MDMs were infected with HIV-eGFP and HIV-HSA viruses. Infected MDMs were transfected with siRNAs specific for the promising genes followed by analysis of apoptosis by flow cytometry using labelled Annexin-V in HIV-infected, HIV-exposed but uninfected bystander MDMs and uninfected MDMs. The results were analyzed using student’s t-test from at least four independent experiments.
Results
We validated 28 top hits in two independent HIV infection models. This culminated in the identification of four target genes, Cox7a2, Znf484, Cstf2t, and Cdk2, whose loss-of-function induced apoptosis preferentially in HIV-infected macrophages. Silencing these single genes killed significantly higher number of HIV-HSA-infected MDMs compared to the HIV-HSA-exposed, uninfected bystander macrophages, indicating the specificity in the killing of HIV-infected macrophages. The mechanism governing Cox7a2-mediated apoptosis of HIV-infected macrophages revealed that targeting respiratory chain complex II and IV genes also selectively induced apoptosis of HIV-infected macrophages possibly through enhanced ROS production.
Conclusions
We have identified above-mentioned novel genes and specifically the respiratory chain complex II and IV genes whose silencing may cause selective elimination of HIV-infected macrophages and eventually the HIV-macrophage reservoirs. The results highlight the potential of the identified genes as targets for eliminating HIV-infected macrophages in physiological environment as part of an HIV cure strategy.
... Traditionally, macrophages are the large phagocytes that pose various forms in tissues throughout the body (e.g., Kupffer cells in the liver, alveolar macrophages in the lungs, microglia in the cerebrum) and typically play an important role in homeostatic and immune responses during the disease process (4,5). Moreover, macrophages are highly plastic and can modify their properties subsequently according to the microenvironment (6). ...
Macrophages exist in most tissues of the body, where they perform various functions at the same time equilibrating with other cells to maintain immune responses in numerous diseases including cancer. Recently, emerging investigations revealed that metabolism profiles control macrophage phenotypes and functions, and in turn, polarization can trigger metabolic shifts in macrophages. Those findings implicate a special role of metabolism in tumor-associated macrophages (TAMs) because of the sophisticated microenvironment in cancer. Glucose is the major energy source of cells, especially for TAMs. However, the complicated association between TAMs and their glucose metabolism is still unclearly illustrated. Here, we review the recent advances in macrophage and glucose metabolism within the tumor microenvironment, and the significant transformations that occur in TAMs during the tumor progression. Additionally, we have also outlined the potential implications for macrophage-based therapies in cancer targeting TAMs.
... As secretory cells, macrophages produce various chemical substances, including NO, enzymes, complement proteins and regulatory factors [40]. NO is an important inflammatory mediator involved in regulating apoptosis and host defences against microorganisms and tumour cells [41]. ...
Four neutral polysaccharides (ESBP1-1, ESBP1-2, ESBP2-1 and ESBP3-1) were successfully purified from the water extracted crude polysaccharides of Erythronium sibiricum bulbs through the combination of DEAE Sepharose CL-6B and Sephadex G-100 chromatography; their average molecular weights were 1.3 × 104, 1.7 × 104, 9.4 × 105 and 4.1 × 105 Da, respectively. Monosaccharide component analysis indicated that ESBP1-1 and ESBP1-2 were mainly composed of glucose (Glc). ESBP2-1 was composed of Glc, galactose (Gal) and arabinose, with a molar ratio of 24.3:1.1:1, whereas ESBP3-1 comprised Glc and Gal at a molar ratio of 14.8:1. In-vitro study showed that all of the four polysaccharides were able to considerably promote the proliferation and neutral red phagocytosis of RAW 264.7 macrophage cell. They could also stimulate the production of the cell lines’ secretory molecules [nitric oxide, tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)] in a dose-dependent manner. However, ESBP1-2 was not included in IL-1β. Overall, these results suggested that polysaccharides from E. sibiricum bulbs can be developed as immunomodulatory ingredients for complementary medicines or functional foods. However, further animal or clinical studies are required.
... Generally, macrophages act as scavengers of foreign particles and are able to sense intruders as well as tissue dysfunction (Williams et al., 2010). Macrophages are found in all human tissues, with different types of macrophages in each tissue displaying a high degree of heterogeneity in morphology, phenotype and life span (Ovchinnikov, 2008). This heterogeneity is due to the stimulation from nearby cells and components of the extracellular matrix (Gordon and Martinez-Pomares, 2017). ...
Colonisation and chronic lung infection by the opportunistic pathogen Pseudomonas aeruginosa (PA) is the leading cause of morbidity and mortality in cystic fibrosis patients. A critical key determinant of PA pathogenicity is the switch from planktonic to the biofilm mode of growth, which facilitates chronic infections and makes PA eradication extremely difficult. Biofilms are aggregates of microorganisms in which the cells are enclosed in an extracellular polymeric substance (EPS) that contains proteins, extracellular DNA (eDNA) and exopolysaccharides. Psl and Pel are two important exopolysaccharides utilised by PA to construct biofilms. While Psl is composed of D-mannose, D-glucose, and L-rhamnose, Pel contains N-acetylgalactosamine (GalNAc) and N-acetylglucosamine (GlcNAc). C-type lectins receptors (CLRs) are pattern recognition receptors (PRRs) that recognise carbohydrate motifs and are expressed by innate immune cells, including dendritic cells (DCs), macrophages and neutrophils. The overarching aim of this thesis is to investigate the interplay between PA and innate immune cells and how it is affected by biofilm formation. We hypothesise that engagement of CLRs through recognition of carbohydrate structures within PA biofilms could modulate the immune response and interfere with innate immune cells function, hence facilitating the persistence of infection. Previously, our lab demonstrated that PA biofilms and biofilm-associated carbohydrates purified from the Pel-deficient mutant ΔwspF Δpel, engage two CLRs, Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN, CD209) and Mannose receptor (MR, CD206). In this study, we show that Dectin-2 (CLEC6A) is another CLRs that binds PA biofilms and purified biofilm carbohydrates; Dectin-2 binds to biofilms formed by PA strains with different EPS composition as well as biofilms formed by PA wound isolates. Similarly to MR and DC-SIGN, Dectin-2 also recognised purified biofilm-associated carbohydrates. High and low molecular fractions of purified biofilm carbohydrates were tested in this study and Dectin-2, together with DC-SIGN and MR preferentially bound to the HMW preparations. Biofilm-associated HMW carbohydrates did not induce Dectin-2 signalling on huDectin-2 reporter cells or HEK-Blue™ mDectin-2 cells but showed antagonistic activity blocking the response of muDectin-2 reporter cells to the Dectin-2 ligand zymosan. To microscopically examine the distribution of CLRs ligands within the biofilms and to study the interaction of immune cells with biofilm, we optimised biofilm generation in substrates suitable for microscopic examination. Confocal analysis shows DC-SIGN, Dectin-2 and, weakly, MR ligands within PAO1 biofilms concentrated into discrete clusters with additional DC-SIGN ligands dispersed among bacteria aggregates. Monocyte-derived DCs (moDCs) (DC-SIGN+ and MR+) cultured with biofilms formed by strains that overexpress Psl (ΔwspF and ΔwspF Δpel) tend to display round morphology and similar findings were noted when moDCs were incubated with purified biofilm carbohydrates. In a different set of experiments cytokine production by human moDCs in response to biofilms was tested and no differences were seen among biofilms with different carbohydrate compositions or after addition of purified biofilm carbohydrates. Taken together, these data indicate that DC-SIGN, MR and Dectin-2 are receptors for PA biofilms and biofilm-associated carbohydrates. The results of this research support the idea that CLRs engagements upon biofilm recognition by innate immune cells might modulate immune cells function. As the first responder cells of the innate immune system, neutrophils possess a unique set of migration features. Several studies found that neutrophils were not able to eradicate infection caused by biofilm-forming PA, which might indicate that biofilm formation was hindering neutrophil’s activity. Here, we describe an in vitro assay that allows us to examine neutrophil behaviour, using live and confocal microscopy, following their interaction with PA, as a planktonic or biofilm cultures. Using live microscopy analysis, we observed that (1) biofilms reduced neutrophil velocity, net distance covered and the mean square displacement. Using confocal microscopy analysis, we observed that (2) neutrophils appeared unable to release granules when incubated with biofilms. Finally, (3) preliminary observations indicated that cells exhibit higher circularity when incubated with biofilm formed by strains expressing Psl or Psl-deficient biofilms in the presence of purified biofilm carbohydrates. The findings from this study have gone some way towards enhancing our understanding of the potential impact of biofilm formation on innate immune cells which might open new avenues for therapeutic approaches.
... Thus, MΦs numbers and their state of activation haveshown to be correlated to both kidney damage and fibrosis. This shows why it is important to thoroughly understand the mechanisms and pathways in order to further develop specific treatment options for patients with kidney diseases[50][51][52][53][54][55][56][57][58][59]. ...
Background With a global prevalence of around 15%, chronic kidney disease is a significant challenge for affected patients and the health care systems worldwide. In order to further develop new therapeutic approaches and to counteract the continuously increasing prevalence, a better understanding of the underlaying pathophysiology is needed. One well known component in the pathophysiology of chronic kidney disease is the persistent inflammation. Patients with end-stage renal disease and on hemodialysis, regardless of their individual pathological background, tend to exhibit highly elevated plasma oxalate levels, ranging around 30-60 µmol/l. In comparison, healthy individuals exhibit levels around 1-3 µmol/l. The resulting supersaturation of oxalate that occurs when the plasma concentration is above 30 µmol/l, leads to crystal deposition in various organs. Oxalate crystals have been shown to activate the NOD-Like Receptor Protein 3 Inflammasome, resulting in the release of proinflammatory cytokines and with that in systemic inflammation. The presented work deals with the hypothesis that elevated plasma oxalate, even without precipitation to crystals, contributes to systemic inflammation. Whether or not the elevated plasma oxalate, in concentrations as measured in dialysis patients’ plasma has an effect on the immune system, remains unknown and shall be clarified in this work. Methods The hypothesis has been tested with use of in vitro cell-stimulations. Murine as well as human cells were isolated and stimulated with various concentrations of calcium oxalate and sodium oxalate. Oxalate concentrations were set in the range of the plasma oxalate concentrations of patients with chronic kidney disease in order to mimic their hyperoxalemic setting. Supernatant was taken at different time points. Interleukin-1 alpha and Interleukin-1 beta concentrations in the supernatant were measured using an Enzyme-linked Immunosorbent Assay. Subsequent to that, cofactors of stimulation were tested in order to further simulate the uremic conditions. In a consecutive series of experiments, the SLC26A6 oxalate transporter was examined for expression in human dendritic cells. Next, cytokine secretion of cells from both wild-type and Slc26a6-/- mice were compared after stimulation with oxalate. Finally, mortality of immune cells from wild-type and Slc26a6-/- mice after stimulation with oxalate was compared by use of a cell viability assay. Results Using Enzyme-linked Immunosorbent Assay measurements we were able to measure Interleukin-1 alpha and Interleukin-1 beta in the supernatants of murine and human cells after stimulation with oxalate. As part of these measurements, a dose- as well as a time-dependent secretion of Interleukin-1 alpha and Interleukin-1 beta could be detected. Yet, we were not able to show cytokine release after stimulation of oxalate in a concentration of around 45 µmol/l, as seen in patients with CKD. Through the comparison of prestimulation with the Toll like Receptor 4 ligand Lipopolysaccharid and Toll like Receptor 3 ligand Polyinosinic:polycytidylic acid, we were able to demonstrate both cofactors as potent prestimuli of oxalate-dependent secretion of Interleukin-1 alpha. In a next series of experiments, the expression of oxalate transporter SLC26A6 in human dendritic cells was detected. A comparison of the mortality between cells from wild-type and Slc26a6-/- mice after stimulation with oxalate, was able to demonstrate less cell viability of the cells from the Slc26a6-/- mice. Conclusion This work confirmed the hypothesis that soluble oxalate has a pro-inflammatory effect on murine as well as human cells. It further characterizes the cytokine release of these cells by revealing a dose- and time dependent course of the release in reaction to stimulation with oxalate. Thus, the results presented in this work point out the potential impact of elevated plasma oxalate concentrations on the progression of systemic inflammation in patients with chronic kidney disease. Yet, further investigation is needed to illustrate the proinflammatory activity of slightly elevated oxalate concentration as measured in the plasma of patients with chronic kidney disease. Furthermore, this work shows a potential physiological role of the Slc26a6 transporter in macrophages. The comparison of the viability of macrophages from wild-type- and Slc26a6-/- mice after stimulation with soluble oxalate, was found to cause significantly greater loss of viability of the macrophages from Slc26a6-/- mice. This may lead to the insight that the transporter is able to protect macrophages from the overload of soluble oxalate in an hyperoxalemic setting. The results presented in this work calls for further research on the pro-inflammatory effect of oxalate. A better understanding of the underlying pathophysiology could then lead to an improved patient management as well as to new anti-inflammatory therapeutic approaches.
... In addition to stimulating the immune system, macrophages exert an immune modulatory impact by secreting various cytokines and activating the complement system, which may lead to inflammation. Macrophages are also involved in the resolution of inflammation [92,93], normal tissue development [94], and tissue repair responses to biomaterials [24]. Monocytes are recruited from the circulation into normal healthy tissues or at sites of injury, inflammation, infection, or malignancy where they then differentiate into tissue macrophages. ...
Exosomes-like nanoparticles can be released by a variety of plants and vegetables. The relevance of plant-derived nanovesicles (PDNVs) in interspecies communication is derived from their content in biomolecules (lipids, proteins, and miRNAs), absence of toxicity, easy internalization by mammalian cells, as well as for their anti-inflammatory, immunomodulatory, and regenerative properties. Due to these interesting features, we review here their potential application in the treatment of inflammatory bowel disease (IBD), liver diseases, and cancer as well as their potentiality as drug carriers. Current evidence indicate that PDNVs can improve the disease state at the level of intestine in IBD mouse models by affecting inflammation and promoting prohealing effects. While few reports suggest that anticancer effects can be derived from antiproliferative and immunomodulatory properties of PDNVs, other studies have shown that PDNVs can be used as effective delivery systems for small molecule agents and nucleic acids with therapeutic effects (siRNAs, miRNAs, and DNAs). Finally, since PDNVs are characterized by a proven stability in the gastrointestinal tract, they have been considered as promising delivery systems for natural products contained therein and drugs (including nucleic acids) via the oral route.
... Macrophages, in a process known as phagocytosis, ingest microbes, cancer cells, foreign substances, cellular debris, and anything else not having the type of proteins specific to normal body cells on its surface. 12 Macrophages are originated from monocyte cells and located in various body tissues. 13 During the course of atherosclerosis, macrophages located under the endothelium vessels take up ox-LDL, and cholesterol derived from ox-LDL is accumulated in these cells. ...
Cardiovascular disease is the leading cause of death globally. Coronary artery disease (CAD) is a chronic inflammatory disease usually caused by atheroscle-rosis, in which the coronary arteries become narrowed by atheromatous plaque. Plaques in atherosclerosis are formed through the accumulation of lipids and various immune cells. Both adaptive and innate immune systems are involved in the pathogenesis of atherosclerosis and facilitate plaque formation and disease progression. Almost all immune system cells, including neu
... Macrophages engulf and digest cellular debris, cancer cells, foreign substances, and bacteria by phagocytosis. Macrophages play a critical role in nonspecific defense (innate immunity) and are important as antigen presenters to T cells [3]. Macrophages also play important pro-inflammatory and anti-inflammatory roles depending on the specific conditions and modulate immune reactions through cytokine release [4]. ...
Co-enzyme nicotinamide adenine dinucleotide (NAD(H)) redox plays a key role in macrophage function. Surfactant protein (SP-) A modulates the functions of alveolar macrophages (AM) and ozone (O 3) exposure in the presence or absence of SPA and reduces mouse survival in a sex-dependent manner. It is unclear whether and how NAD(H) redox status plays a role in the innate immune response in a sex-dependent manner. We investigated the NAD(H) redox status of AM from SP-A2 and SPA knockout (KO) mice in response to O 3 or filtered air (control) exposure using optical redox imaging technique. We found: (i) In SP-A2 mice, the redox alteration of AM in response to O 3 showed sex-dependence with AM from males being significantly more oxidized and having a higher level of mitochondrial reactive oxygen species than females; (ii) AM from KO mice were more oxidized after O 3 exposure and showed no sex differences; (iii) AM from female KO mice were more oxidized than female SP-A2 mice; and (iv) Two distinct subpopulations characterized by size and redox status were observed in a mouse AM sample. In conclusions, the NAD(H) redox balance in AM responds to O 3 in a sex-dependent manner and the innate immune molecule, SP-A2, contributes to this observed sex-specific redox response. Keywords: optical redox imaging; nicotinamide adenine dinucleotide (NAD(H)); oxidized flavoprotein containing flavin adenine dinucleotide (FAD); redox ratio; surfactant protein A2 (SP-A2); surfactant protein A; macrophage activation; ozone; redox heterogeneity; innate immunity; lung
... Macrophages mature and reside in virtually every tissue throughout the body, including commons sites of C. albicans infections such as the kidneys and the liver (56)(57)(58)(59). Macrophages are a versatile cell type, responsible for clearing local pathogens, producing complement proteins, and signaling to the adaptive immune system by serving as an antigen presenting cell and producing appropriate cytokines. ...
Candida albicans is a polymorphic unicellular fungus that has evolved to proficiently colonize and infect mammals. A common constituent of the microbiome in the GI tract, mouth, vagina, and skin, C. albicans is also an opportunistic pathogen capable of causing a variety of mucosal infections and the life-threatening disseminated candidiasis. Systemic C. albicans infections are a serious and growing issue; the fungus is the fourth most common cause of nosocomial bloodstream infections which has a mortality rate reaching 50%. As antifungal resistance continues to rise, it is critical that I understand the molecular basis of disseminated fungal infections. The phagocytes of the immune system are especially important for preventing disseminated infection. Macrophages are employed to clear pathogens in the harsh environment of a phagosome, but C. albicans, as an adaptable opportunist, is capable of surviving macrophage attack to continue dissemination. The Lorenz Lab and other leading labs in the field have identified that C. albicans rapidly adapts to the macrophage phagosome by upregulating alternative carbon utilization processes. The utilization of three alternative carbon sources particularly contribute to C. albicans pathogenesis: carboxylic acids, amino acids, and N-acetylglucosamine. Studied individually, utilization of each carbon source appears to equally contribute to pathogenesis, although mutants defective in any one carbon utilization pathway display only modest attenuation.
... The effects of PCPW, PCPS1 and PCPS2 on NO production and phagocytosis Macrophages are the predominant immune cells, triggering the removal of cell fragments and pathogens by phagocyting them and further digestion. Several chemical substances such as enzymes, nitric oxide (NO), complement proteins and cytokines are produced by macrophages, serving as secretary cells [33]. As shown in Fig. 7A, among the three of Potentilla chinensis polysaccharides, only PCPW could significantly facilitate the phagocytosis of macrophages compared with the control (≥100 μg/mL, p<0.01). ...
Three novel polysaccharides (PCPW, PCPS1 and PCPS2) were isolated from Potentilla chinensis and subjected to structural analysis by using spectral and physicochemical methods. The molecular weights of PCPW, PCPS1 and PCPS2 were calculated to be 4.45 × 103 Da, 1.18 × 104 Da and 4.23 × 104 Da, respectively. Analysis of monosaccharides composition confirmed that PCPW was composed of mannose, rhamnose, glucose, galactose and arabinose, while the two acidic polysaccharides PCPS1 and PCPS2 were consisted of six monosaccharides, including mannose, rhamnose, galacturonic acid, glucose, galactose and arabinose respectively. In addition, the main linkages of glycosidic bonds of PCPS2 were 1, 4-linked-rha, 1, 4-linked-man,1, 4-linked-galA and 1, 6-linked-man. Immunological tests indicated that both PCPW and PCPS2 could increase NO production of RAW264.7 cells, and promote splenocyte proliferation. All three polysaccharides proved to be activators of NF-κB. Overall, three polysaccharides showed a good immunological activity and pose great potential as a novel food or drug additive.
... MacroPAHges are a type of immune cell that engulfs and digests debris, foreign substances, and microbes [32] . They are patrol guards in the microenvironment of all tissues, which are transformed into active PAHgocytes by morphology and function and react quickly to various kinds of tissue damage. ...
AIM: To assess the biosafety of a poly(acrylamide-co-sodium acrylate) hydrogel as a 3D-printed intraocular lens (IOL) material.
METHODS: The biosafety of the poly(acrylamide-co-sodium acrylate) hydrogel was first analyzed in vitro using human lens epithelial cells (LECs) and the ARPE19 cell line, and a CCK-8 assay was performed to investigate alterations in cell proliferation. A thin film of a poly(acrylamide-co-sodium acrylate) hydrogel and a conventional IOL were intraocularly implanted into the eyes of New Zealand white rabbits respectively, and a sham surgery served as control group. The anterior segment photographs, intraocular pressure (IOP), blood parameters and electroretinograms were recorded. Inflammatory cytokines in the aqueous humor, such as TNF and IL-8, were examined by ELISA. Cell apoptosis of the retina was investigated by TUNEL assay, and macrophage activation was detected by immunostaining.
RESULTS: The poly(acrylamide-co-sodium acrylate) hydrogel did not slow cell proliferation when cocultured with human LECs or ARPE19 cells. The implantation of a thin film of a 3D-printed IOL composed of the poly(acrylamide-co-sodium acrylate) hydrogel did not affect the IOP, blood parameters, electroretinogram or optical structure in any of the three experimental groups (n=3 for each group). Both TNF and IL-8 in the aqueous humor of the hydrogel group were transiently elevated 1 week post-operation and recovered to normal levels at 1 and 3 months post-operation. Iba1+ macrophages in the anterior chamber angle of the hydrogel group were increased markedly compared to those of the control group; however, there was no significant difference compared to those in the IOL group.
CONCLUSION: The poly(acrylamide-co-sodium acrylate) hydrogel is a safe material for 3D printing of personal IOLs that hold great potential for future clinical applications.
... Macrophages participate in host defense [1][2][3][4] by providing an immediate response to invading pathogens while also contributing to the activation of the adaptive immune system [5][6][7]. When lipopolysaccharide (LPS), a component of the outer membrane of gram negative ...
Macrophage cells form part of our first line defense against pathogens. Macrophages become activated by microbial products such as lipopolysaccharide (LPS) to produce inflammatory mediators, such as TNFα and other cytokines, which orchestrate the host defense against the pathogen. Once the pathogen has been eradicated, the activated macrophage must be appropriately deactivated or inflammatory diseases result. Interleukin-10 (IL10) is a key anti-inflammatory cytokine which deactivates the activated macrophage. The IL10 receptor (IL10R) signals through the Jak1/Tyk2 tyrosine kinases, STAT3 transcription factor and the SHIP1 inositol phosphatase. However, IL10 has also been described to induce the activation of the cyclic adenosine monophosphate (cAMP) regulated protein kinase A (PKA). We now report that IL10R signalling leads to STAT3/SHIP1 dependent expression of the EP4 receptor for prostaglandin E2 (PGE2). In macrophages, EP4 is a Gαs-protein coupled receptor that stimulates adenylate cyclase (AC) production of cAMP, leading to downstream activation of protein kinase A (PKA) and phosphorylation of the CREB transcription factor. IL10 induction of phospho-CREB and inhibition of LPS-induced phosphorylation of p85 PI3K and p70 S6 kinase required the presence of EP4. These data suggest that IL10R activation of STAT3/SHIP1 enhances EP4 expression, and that it is EP4 which activates cAMP-dependent signalling. The coordination between IL10R and EP4 signalling also provides an explanation for why cAMP elevating agents synergize with IL10 to elicit anti-inflammatory responses.
... As such, the application of 2PM benefits HCM identification without relying solely on melanocyte-specific immunolabeling visualized with fluorescence or red chromogen-based immunohistochemistry 13,23,37 . Furthermore, 2PM imaging of HCMs visualizes cytoplasmic melanosomes, an important distinguishing feature for differentiating between HCMs and melanin-filled choroidal macrophages in situ, as macrophages do not have melanosome organelles 61,62 . ...
Choroidal melanocytes (HCMs) are melanin-producing cells in the vascular uvea of the human eye (iris, ciliary body and choroid). These cranial neural crest-derived cells migrate to populate a mesodermal microenvironment, and display cellular functions and extracellular interactions that are biologically distinct to skin melanocytes. HCMs (and melanins) are important in normal human eye physiology with roles including photoprotection, regulation of oxidative damage and immune responses. To extend knowledge of cytoplasmic melanins and melanosomes in label-free HCMs, a non-invasive ‘fit-free’ approach, combining 2-photon excitation fluorescence lifetimes and emission spectral imaging with phasor plot segmentation was applied. Intracellular melanin-mapped FLIM phasors showed a linear distribution indicating that HCM melanins are a ratio of two fluorophores, eumelanin and pheomelanin. A quantitative histogram of HCM melanins was generated by identifying the image pixel fraction contributed by phasor clusters mapped to varying eumelanin/pheomelanin ratio. Eumelanin-enriched dark HCM regions mapped to phasors with shorter lifetimes and longer spectral emission (580–625 nm) and pheomelanin-enriched lighter pigmented HCM regions mapped to phasors with longer lifetimes and shorter spectral emission (550–585 nm). Overall, we demonstrated that these methods can identify and quantitatively profile the heterogeneous eumelanins/pheomelanins within in situ HCMs, and visualize melanosome spatial distributions, not previously reported for these cells.
... Macrophages are essential for homeostasis in most of organ systems for tissue repair and development; additionally, these cells provide defense against pathogens, cancer, and chronic inflammation [95]. The involvement of macrophages in a diverse array of cellular functions gives these cells plasticity to adapt well to their microenvironment [96]. In many organs after tissue injury, macrophages establish a tissue repair program, and the associated Wnt ligands are essential players in tissue regeneration and fibrosis [97]. ...
Wnt signaling is one of the important pathways to play a major role in various biological processes, such as embryonic stem-cell development, tissue regeneration, cell differentiation, and immune cell regulation. Recent studies suggest that Wnt signaling performs an essential function in immune cell modulation and counteracts various disorders. Nonetheless, the emerging role and mechanism of action of this signaling cascade in immune cell regulation, as well as its involvement in various cancers, remain debatable. The Wnt signaling in immune cells is very diverse, e.g., the tolerogenic role of dendritic cells, the development of natural killer cells, thymopoiesis of T cells, B-cell-driven initiation of T-cells, and macrophage actions in tissue repair, regeneration, and fibrosis. The purpose of this review is to highlight the current therapeutic targets in (and the prospects of) Wnt signaling, as well as the potential suitability of available modulators for the development of cancer immunotherapies. Although there are several Wnt inhibitors relevant to cancer, it would be worthwhile to extend this approach to immune cells.
... Macrophages are essential for homeostasis in most of organ systems for tissue repair and development; additionally, these cells provide defense against pathogens, cancer, and chronic inflammation [95]. The involvement of macrophages in a diverse array of cellular functions gives these cells plasticity to adapt well to their microenvironment [96]. In many organs after tissue injury, macrophages establish a tissue repair program, and the associated Wnt ligands are essential players in tissue regeneration and fibrosis [97]. ...
Wnt signaling is one of the important pathways to play a major role in various biological processes, such as embryonic stem-cell development, tissue regeneration, cell differentiation, and immune cell regulation. Recent studies suggest that Wnt signaling performs an essential function in immune cell modulation and counteracts various disorders. Nonetheless, the emerging role and mechanism of action of this signaling cascade in immune cell regulation, as well as its involvement in various cancers, remain debatable. The Wnt signaling in immune cells is very diverse, e.g., the tolerogenic role of dendritic cells, the development of natural killer cells, thymopoiesis of T cells, B-cell-driven initiation of T-cells, and macrophage actions in tissue repair, regeneration, and fibrosis. The purpose of this review is to highlight the current therapeutic targets in (and the prospects of) Wnt signaling, as well as the potential suitability of available modulators for the development of cancer immunotherapies. Although there are several Wnt inhibitors relevant to cancer, it would be worthwhile to extend this approach to immune cells.
... Macrophages are essentially present in all tissues, and they are crucial effectors of wound healing, homeostasis, cancer, and immune responses [1,8]. Most macrophages derive from hematopoietic stem cells (HSCs). ...
The tumor microenvironment (TME) is the primary arena where tumor cells and the host immune system interact. Bidirectional communication between tumor cells and the associated stromal cell types within the TME influences disease initiation and progression, as well as tumor immunity. Macrophages and natural killer (NK) cells are crucial components of the stromal compartment and display either pro- or anti-tumor properties, depending on the expression of key regulators. MicroRNAs (miRNAs) are emerging as such regulators. They affect several immune cell functions closely related to tumor evasion of the immune system. This review discusses the role of miRNAs in the differentiation, maturation, and activation of immune cells as well as tumor immunity, focusing particularly on macrophages and NK cells.
... Macrophages are a type of white blood cell of the immune system that are found in all tissues to engulf and digest cellular debris, as well as anything else that does not have the type of proteins specific to healthy body cells (Ovchinnikov, 2008). Prior to investigation of the immunomodulatory activity of AGs and DAGs, their toxic effects on RAW264.7 cells were first evaluated using CCK-8 assay. ...
... Macrophages are a type of white blood cell, of the immune system, that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the type of specific antigen to healthy body cells on its surface in a process called phagocytosis (Ovchinnikov, 2008). Hence macrophage is an important index of tissue damage and inflammation. ...
Mitochondrial dynamics and mitophagy are important aspects of mitochondrial quality control, and are linked to neurodegenerative diseases and muscular diseases. Fis1, a protein on the mitochondrial outer membrane, is thought to mediate mitochondrial fission. However, Fis1 null worms and mammalian cells only display mild fission defects but show aberrant mitophagy. To assess Fis1 function in vivo, we generated conditional knock-out Fis1 mice to allow for specific Fis1 deletion in adult skeletal muscle. In the absence of Fis1 in Type I muscle, mitochondrial hyperfusion, respiratory chain deficiency, and increased mitophagy were found. Moreover, abnormal mitophagy was aggravated by endurance exhaustive exercise stress (EEE), suggesting that Fis1 is involved in maintaining normal mitophagy in mitochondria-rich Type I muscle during exercise. Additionally, Fis1 loss induced delayed onset muscle ultrastructure change (DOMUC) in Type I muscle and strong inflammation in response to acute exhaustive exercise (EE). Thus, we identify a role for Fis1 in maintaining normal mitochondrial structure and function at rest and under exercise stress.
... In addition to the traditional host defense, inflammation, and scavenging functions, macrophages have broader functions, including vital roles in tissue repair and organ development (34)(35)(36). Animal studies have demonstrated that neonatal hyperoxia exposure increases macrophage infiltration into alveolar airspaces (37,38). In this study, we used immunohistochemistry to detect the macrophage infiltration on the lung tissue sections. ...
Hyperoxia therapy is often required to treat newborns with respiratory disorders. Prolonged hyperoxia exposure increases oxidative stress and arrests alveolar development in newborn rats. Tn antigen is N-acetylgalactosamine residue that is one of the most remarkable tumor-associated carbohydrate antigens. Tn immunization increases the serum anti-Tn antibody titers and attenuates hyperoxia-induced lung injury in adult mice. We hypothesized that maternal Tn immunizations would attenuate hyperoxia-induced lung injury through the suppression of oxidative stress in neonatal rats. Female Sprague–Dawley rats (6 weeks old) were intraperitoneally immunized five times with Tn (50 μg/dose) or carrier protein at biweekly intervals on 8, 6, 4, 2, and 0 weeks before the day of delivery. The pups were reared in room air (RA) or 2 weeks of 85% O2, creating the four study groups: carrier protein + RA, Tn vaccine + RA, carrier protein + O2, and Tn vaccine + O2. The lungs were excised for oxidative stress, cytokine, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) expression, and histological analysis on postnatal day 14. Blood was withdrawn from dams and rat pups to check anti-Tn antibody using western blot. We observed that neonatal hyperoxia exposure reduced the body weight, increased 8-hydroxy-2-deoxyguanosine (8-OHdG) expression and lung cytokine (interleukin-4), increased mean linear intercept (MLI) values, and decreased vascular density and VEGF and PDGF-B expressions. By contrast, Tn immunization increased maternal and neonatal serum anti-Tn antibody titers on postnatal day 14, reduced MLI, and increased vascular density and VEGF and PDGF-B expressions to normoxic levels. Furthermore, the alleviation of lung injury was accompanied by a reduction in lung cytokine and 8-OHdG expression. Therefore, we propose that maternal Tn immunization attenuates hyperoxia-induced lung injury in neonatal rats through the suppression of oxidative stress and inflammation.
Creating cellular homeostasis within a defined tissue typically relates to the processes of apoptosis and efferocytosis. A great example here is cell debris that must be removed to prevent unwanted inflammatory responses and then reduce autoimmunity. In view of that, defective efferocytosis is often assumed to be responsible for the improper clearance of apoptotic cells (ACs). This predicament triggers off inflammation and even results in disease development. Any disruption of phagocytic receptors, molecules as bridging groups, or signaling routes can also inhibit macrophage efferocytosis and lead to the impaired clearance of the apoptotic body. In this line, macrophages as professional phagocytic cells take the lead in the efferocytosis process. As well, insufficiency in macrophage efferocytosis facilitates the spread of a wide variety of diseases, including neurodegenerative diseases, kidney problems, types of cancer, asthma, and the like. Establishing the functions of macrophages in this respect can be thus useful in the treatment of many diseases. Against this background, this review aimed to recapitulate the knowledge about the mechanisms related to macrophage polarization under physiological or pathological conditions, and shed light on its interaction with efferocytosis.
The immune response of macrophages plays an important role in defending against viral infection, tumor deterioration and repairing of contused tissue. Macrophage functional differentiation induced by nanodrugs is the leading edge of current research, but nanodrugs have toxic side effects, and the influence of their physical properties on macrophages is not clear. Here we create an alternative way to modulate macrophage function through PLGA-PEG fibers' Young's modulus. Previously, we revealed that by controlling the Young's modulus of the fibers from kPa to MPa, all the fibers entered murine macrophage cells (RWA 264.7) in a similar manner, and based on that, we found that macrophages' mechanical properties were affected by the fibers' Young's modulus, that is, hard fibers with a Young's modulus of ∼1 MPa increased the cell average Young's modulus, but did not affect the cell shape, while soft fibers with a Young's modulus of ∼100 kPa decreased the cell average Young's modulus and modulated the cell shape to a more spherical one. On the other hand, only the soft fibers induced proinflammatory cytokine secretion, indicating an M1 macrophage functional modulation by low Young's modulus fibers. This study explored the mechanical properties of the interactions between PLGA-PEG fibers and cells, in particular, when guiding the direction of the modulation of macrophage function, which is of great significance for the applications of material biology in the biomedical field.
Studies have shown that the trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine (DCVC) inhibits cytokine secretion in pathogen stimulated fetal membrane tissue but little is known about the mechanism for these effects, including which cell types or transcriptomic pathways are impacted. Macrophages play a critical role in fetal membrane immune responses during infection. We tested the hypothesis that DCVC inhibits lipopolysaccharide (LPS) stimulated inflammation pathways in macrophage-like THP-1 cells. We treated THP-1 cells for 24 h then treated with 1, 5, or 10 μM DCVC for 24 h. After a 4 h incubation with lipopolysaccharide (LPS), we collected RNA and cell media. We performed transcriptomic analysis using RNA sequencing for 5 μM DCVC treatments and quantified cytokine release (IL-1β, IL-6, and TNF-α) for 1, 5 and 10 μM DCVC treatments. RNA sequencing analysis revealed 1399 differentially expressed genes (FDR < 0.05 and log 2 fold change magnitude>2.5) in cells co-treated with DCVC and LPS compared to LPS alone. For example, TNF had a log2(fold-change) = −3.5 with the addition of DCVC. Pathways downregulated (adjusted p-value<0.05) in DCVC+LPS treatments versus LPS-only treatments included: “acute inflammatory response”, “production of molecular mediator of immune response” and “phagocytosis”. LPS increased IL-1β, IL-6, and TNF-α levels in culture media (p < 0.001), but this was inhibited by co-treatment with DCVC (p < 0.001 for LPS vs. LPS + DCVC treatments). Our results demonstrate that DCVC suppresses inflammatory responses in macrophages.
Modern approach towards biodegradable biomaterials involves significant capability of magnesium (Mg) alloys. Being a major constituent of the human body, Mg has extraordinary potential to facilitate as temporary orthopaedic implants. Despite many benefits within Mg and its alloys; such as excellent biocompatibility, biodegradability, satisfactory mechanical qualities, its use is still very limited. Rapid corrosion and hydrogen evolution are threats to its limited use. To estimate the mechanism and causes of corrosion in living environments for Mg-alloys accurately, in vitro study is necessary. The present review focuses on factors influencing corrosion rates (bio-corrosion) of Mg-alloys in vivo and in vitro studies. To understand the corrosion behaviour, factors like organic compounds, inorganic ions and some experimental process parameters taken into considerations and are analyzed. It is concluded that some of these factors affect the mechanism of corrosion greatly and their effective management is required to control their corrosion rates. Experimental conditions are most significant because they affect corrosion rates the most and can be helpful to stabilize it. The effects of these factors are summarized at the end of this review.
Macrophages, an important part of human immune system, possess a high plasticity and heterogeneity (macrophage polarization) as classically activated macrophages (M1) and alternatively activated macrophages (M2), which exert pro-inflammatory/anti-tumor and anti-inflammatory/pro-tumor effects, respectively. Thus, drug development in induction of macrophage polarization could be used to treat different human diseases. This review summarizes the recent advancement on modulation of macrophage polarization and its related molecular mechanisms induced by a number of agents. Research on the anti-inflammatory drugs to regulate the macrophage polarization accounts for a large proportion in the field and types of diseases investigated could include atherosclerosis, enteritis, nephritis, and the nervous system and skeletal diseases, while study of the anti-tumor agents to modify macrophage polarization is a novel area of research. Future study of the molecular mechanisms by which the different agents regulate the macrophage polarization could lead to an effective control of various human diseases, including inflammation and cancers.
The surge in vehicular activity in densely populated areas has led to an increased concentration of airborne palladium nanoparticles (PdNPs) in the environment. Recent toxicity data have indicated that PdNPs exhibit adverse effects in in vitro and in vivo models, however, their effect on the immune system is not fully understood. Therefore, in the present study, we aimed to evaluate possible toxic effects of bio-engineered palladium nanoparticles on the murine macrophage cell line (J774). Here we prepared palladium nanoparticles using aqueous leaf extract of Parthenium hysterophorus and characterized them by UV-Vis spectroscopy, XRD, FT-IR spectroscopy, HR-TEM, EDX, SEM and zeta potential. Toxicity parameters such as cell viability, cell membrane integrity, induction of apoptosis and ROS production were assessed on J774 cell lines. Spherical palladium nanoparticles of mean size ∼4 nm, when subjected to time and dose-dependent cytotoxicity assay, showed cell viability was >95% at lower doses (25, 200 μg mL⁻¹) and <50% at higher doses of palladium nanoparticles (400, 500 μg mL⁻¹) after 24 hours of incubation. We also observed cell membrane injury at higher doses by lactate dehydrogenase assay. The induction of apoptosis observed was moderate. H2DCFDA assay revealed visible cell damage which could be due to modest levels of ROS generation. The detection of Pd in the road-dust samples of New Delhi using inductively coupled plasma-mass spectroscopy (ICP-MS) technique was also investigated.
Macrophages are notable immune cells that are recruited to the injury sites after peripheral nerve injury. Following peripheral nerve injury, increasing numbers of macrophages engulf debris and promote nerve regeneration. However, changes of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages, two types of macrophages with dissimilar biological functions, have not been discovered. In the current study, the expression profiles of M1 and M2 macrophage marker genes in the sciatic nerve stumps and dorsal root ganglions (DRGs) after rat sciatic nerve injury were determined using RNA sequencing. Robust up-regulation of macrophage marker genes was observed in the injured sciatic nerve stumps as compared with in the DRGs. Measurement of the dynamic expression levels of M1 macrophage specific marker genes CD38 and Gpr18 as well as M2 macrophage specific marker genes Egr2 and Myc suggested that M1 macrophages were highly involved at all tested time points after peripheral nerve injury while M2 macrophage might be more involved in the later phase after nerve injury. Dynamic changes of M1 macrophage-inducing miRNAs showed that miR-18a, miR-19b, miR-21, miR-29a, and miR-29b were elevated in the injured nerve stump. These up-regulated miRNAs might mediate macrophage polarization by targeting multiple genes, such as Pten. Collectively, our study explored the unique temporal patterns of pro-inflammatory and anti-inflammatory macrophages after peripheral nerve injury for genetic aspects and provided a deeper understanding of the cellular and molecular basis of microenvironment reconstruction after peripheral nerve injury.
Immunity plays a key role in disease susceptibility. Immunomodulators are agents which specifically modulate immune system regulating immunity and disease resistance. In poultry it is specifically important as the growth, disease resistance, FCR, body weight gain production output mainly depends on the health and immunity of the chickens. Different types of immunomodulators are prebiotics, probiotics, vitamins, adjuvants, polysaccharides, herbs etc. Immunology has great potentials in prevention and treatment of various range of disorders for instance the various inflammatory diseases of skin, respiratory tract, gut, central organs and joints. The preliminary objective of immunomodulation is to improve host resistance to external and internal attacks by the microbes or other infectious agents. Immunomodulators can substitute many agents like antibiotics, antimicrobials etc. for the improvement of the immune system. They also enhance the qualities of feed and immune molecules enhancing all possibilities to fight diseases and maintain health homeostasis. Since, they are not popular and not included in the poultry feed on routine basis, more efforts should be made to popularize it.
Macrophages play an important role in the body's immune defense process. Phenotype imbalance between M1 and M2 macrophages induced by inflammation‐related disorders and tumor can also be reversibly converted to treat these diseases. As exogenous substances, a large part of gold‐based nanomaterials interact with macrophages once they enter the body, which provides gold nanomaterials a huge advantage to act as imaging contrasts, active substance carriers, and therapeutic agents for macrophage modulation. By cutting off macrophage recruitment, inhibiting macrophage activities, and modulating M1/M2 polarization, gold nanomaterial engineering exerts therapeutic effects on inflammation‐related diseases at target sites. In this review, biological functions of macrophages in inflammation‐related diseases are introduced, the effect of physicochemical factors of gold nanomaterials including size, shape, and surface chemistry is focused on the interaction between macrophages and gold nanomaterials, and the applications of gold nanomaterials are elaborated for tracking and treating these diseases by macrophages. The rational and smart engineering of gold nanomaterials allows a promising platform for macrophage‐mediated inflammation and tumor imaging and treatment.
Vibrio vulnificus is a food-borne marine pathogen that causes both life-threatening primary septicemia and necrotizing wound infections which accompany severe inflammation. Cytolysin is a very powerful virulence factor of V. vulnificus and is one of the likely candidates in the pathogenesis of V. vulnificus infections. However, the pathogenetic roles of cytolysin in V. vulnificus-induced inflammation are not well understood. In this study, we used the recombinant protein Vibrio vulnificus cytolysin (VVC) to demonstrate that VVC can induce inflammatory responses in RAW264.7 macrophages. Low dose (<5 μg/ml) VVC had no impact on cell viability and induced pro-inflammatory cytokines production in RAW264.7 macrophages such as IL-6 and TNF-α. Moreover, VVC induced p65, p38, ERK1/2, and AKT phosphorylation in RAW264.7 macrophages. We further demonstrated that BAPTA, a specific intracellular calcium chelator, inhibited VVC-induced inflammatory response including pro-inflammatory cytokines production and inflammatory signaling activation in RAW264.7 macrophages. In addition, VVC primed rather than actived NLRP3 inflammasome in RAW264.7 macrophages. To determine whether VVC have a direct inflammatory effect on the host, we examined the effects of VVC injected into the skin of mice. VVC stimulated a significant induction of mRNAs for the pro-inflammatory cytokine IL-6 and inflammatory chemokines such as MCP-1 and IP-10. Histology data also showed that VVC caused inflammatory responses in the skin of mice. Collectively, our findings indicated that VVC induced inflammatory responses in RAW264.7 macrophages and in vivo and suggested the possibility of targeting VVC as a strategy for the clinical management of V. vulnificus-induced inflammatory responses.
Nowadays, melatonin, previously considered only as a pharmaceutical product for rhythm regulation and sleep aiding, has shown its potential as a co‐adjuvant treatment in intestinal diseases, however, its mechanism is still not very clear. A firm connection between melatonin at a physiologically relevant concentration and the gut microbiota and inflammation has recently established. Herein, we summarize their crosstalk and focus on four novelties. First, how melatonin is synthesized and degraded in the gut and exerts potentially diverse phenotypic effects through its diverse metabolites. Second, how melatonin mediates the activation and proliferation of intestinal mucosal immune cells with paracrine and autocrine properties. By modulating T/B cells, mast cells, macrophages and dendritic cells, melatonin immunomodulatory involved in regulating T‐cell differentiation, intervening T/B cell interaction and attenuating the production of pro‐inflammatory factors, achieving its antioxidant action via specific receptors. Third, how melatonin exerts antimicrobial action and modulates microbial components, such as lipopolysaccharide, amyloid‐β peptides via nuclear factor κ‐light‐chain‐enhancer of activated B cells (NF‐κB) or signal transducers and activators of transcription (STAT1) pathway to modulate intestinal immune function in immune‐pineal axis. The last, how melatonin mediates the effect of intestinal bacterial activity signals on the body rhythm system through the NF‐κB pathway and influences the mucosal epithelium oscillation via clock gene expression. These processes are achieved at mitochondrial and nuclear levels to control the host immune cell development. Considering unclear mechanisms and undiscovered actions of melatonin in gut‐microbiome‐immune axis, it's time to reveal them and provide new insight for the outlook of melatonin as a potential therapeutic target in the treatment and management of intestinal diseases.
Objective:
To investigate the effect of sulfur dioxide (SO2) on the apoptosis of alveolar macrophage (AM) in lung protection of limb ischemia/reperfusion (I/R) induced acute lung injury (ALI), and to find a new target for the control of inflammatory response.
Methods:
Twenty pathogen-free, adult male Sprague-Dawley (SD) rats (180-230 g) were used in this study. Five rats were to be used for limb ischemia/reperfusion, then plasma was extracted as ischemia/reperfusion serum stimulation. Fifteen rats were to be used for extracting AM by bronchoalveolar lavage. The AM was isolated and cultured, then the cell count was adjusted to 1×106/mL, and randomly divided into the following 4 groups (n=6): control group, I/R group, SO2 group, and I/R+SO2 group. The I/R group was given ischemia/reperfusion serum (500 μg/L) to stimulate 6 h; the SO2 group was given an SO2 donor, Na2SO3/NaHSO3 [(0.54 mmol/kg) / (0.18 mmol/kg)]; and the I/R+SO2 group was given the same ischemia/reperfusion serum and Na2SO3/NaHSO3 at the same time. The level of mitochondrial membrane potential, the state of mitochondrial permeability transition pore (mPTP), the rate of AM apoptosis, the expression of Bcl-2 and Caspase-3 proteins were detected by flow cytometry, microplate reader and Western blotting.
Results:
Compared with the control group, in the I/R group, the ratio of red to green fluorescence and the absorbance decreased significantly, the percentage of apoptotic cells increased obviously, the apoptotic rate was 43.81%±2.40%, Caspase-3 protein expression increased, Bcl-2 protein expression decreased. While compared with the I/R group, in the I/R+SO2 group, the ratio of red to green fluorescence and the absorbance increased significantly; the apoptotic rate decreased to 37.01%±1.93%, Caspase-3 protein expression decreased, Bcl-2 protein expression increased.
Conclusion:
Exogenous SO2 has the effect of accelerating AM apoptosis by stimulating mPTP to open and mitochondrial membrane potential to decrease; besides, exogenous SO2 could stimulate AM to secrete more anti-inflammatory cytokines and less inflammatory cytokines. In conclusion, exogenous SO2 can reduce macrophage apoptosis by inhibiting mitochondrial pathways.
Macrophages (MPs) are important for skeletal muscle regeneration in vivo and may exert beneficial effects on myogenic cell growth through mitogenic and antiapoptotic activities in vitro. However, MPs are highly versatile and may exert various, and even opposite, functions depending on their activation state. We studied monocyte (MO)/MP phenotypes and functions during skeletal muscle repair. Selective labeling of circulating MOs by latex beads in CX3CR1(GFP/+) mice showed that injured muscle recruited only CX3CR1(lo)/Ly-6C(+) MOs from blood that exhibited a nondividing, F4/80(lo), proinflammatory profile. Then, within muscle, these cells switched their phenotype to become proliferating antiinflammatory CX3CR1(hi)/Ly-6C(-) cells that further differentiated into F4/80(hi) MPs. In vitro, phagocytosis of muscle cell debris induced a switch of proinflammatory MPs toward an antiinflammatory phenotype releasing transforming growth factor beta1. In co-cultures, inflammatory MPs stimulated myogenic cell proliferation, whereas antiinflammatory MPs exhibited differentiating activity, assessed by both myogenin expression and fusion into myotubes. Finally, depletion of circulating MOs in CD11b-diphtheria toxin receptor mice at the time of injury totally prevented muscle regeneration, whereas depletion of intramuscular F4/80(hi) MPs at later stages reduced the diameter of regenerating fibers. In conclusion, injured skeletal muscle recruits MOs exhibiting inflammatory profiles that operate phagocytosis and rapidly convert to antiinflammatory MPs that stimulate myogenesis and fiber growth.
The seven-transmembrane receptor CX3CR1 is a specific receptor for the novel CX3C chemokine fractalkine (FKN) (neurotactin). In vitro data suggest that membrane anchoring of FKN, and the existence of a
shed, soluble FKN isoform allow for both adhesive and chemoattractive properties. Expression on activated endothelium and
neurons defines FKN as a potential target for therapeutic intervention in inflammatory conditions, particularly central nervous
system diseases. To investigate the physiological function of CX3CR1-FKN interactions, we generated a mouse strain in which the CX3CR1 gene was replaced by a green fluorescent protein (GFP) reporter gene. In addition to the creation of a mutant CX3CR1 locus, this approach enabled us to assign murine CX3CR1 expression to monocytes, subsets of NK and dendritic cells, and the brain microglia. Analysis of CX3CR1-deficient mice indicates that CX3CR1 is the only murine FKN receptor. Yet, defying anticipated FKN functions, absence of CX3CR1 interferes neither with monocyte extravasation in a peritonitis model nor with DC migration and differentiation in response
to microbial antigens or contact sensitizers. Furthermore, a prominent response of CX3CR1-deficient microglia to peripheral nerve injury indicates unimpaired neuronal-glial cross talk in the absence of CX3CR1.
ATP-binding-cassette transporter 1 (ABC1) has been implicated in processes related to membrane-lipid turnover. Here, using in vivo loss-of-function and in vitro gain-of-function models, we show that ABC1 promotes Ca2+-induced exposure of phosphatidylserine at the membrane, as determined by a prothrombinase assay, membrane microvesiculation and measurement of transbilayer redistribution of spin-labelled phospholipids. That ABC1 promotes engulfment of dead cells is shown by the impaired ability of ABC1-deficient macrophages to engulf apoptotic preys and by the acquisition of phagocytic behaviour by ABC1 transfectants. Release of membrane phospholipids and cholesterol to apo-AI, the protein core of the cholesterol-shuttling high-density lipoprotein (HDL) particle, is also ABC1-dependent. We propose that both the efficiency of apoptotic-cell engulfment and the efflux of cellular lipids depend on ABC1-induced perturbation of membrane phosphatidylserine turnover. Transient local exposure of anionic phospholipids in the outer membrane leaflet may be sufficient to alter the general properties of the membrane and thus influence discrete physiological functions.
Apoptotic cell death and the efficient clearance of dying cells are essential mechanisms to control tissue homeostasis and to eliminate potential autoantigens. Numerous alterations on the surfaces of dying cells define a highly characteristic membrane signature and enable an unequivocal distinction from vital cells. This way, phagocytosis is initiated and signalling events induced which minimize inflammatory reactions. Therefore, the use of proteins interfering with the clearance process may open up new vistas to improve immunization strategies and may help to understand the mechanisms of autoimmune diseases.
S100A8 (also known as CP10 or MRP8) was the first member of the S100 family of calcium-binding proteins shown to be chemotactic for myeloid cells. The gene is expressed together with its dimerization partner S100A9 during myelopoiesis in the fetal liver and in adult bone marrow as well as in mature granulocytes. In this paper we show that S100A8 mRNA is expressed without S100A9 mRNA between 6.5 and 8.5 days postcoitum within fetal cells infiltrating the deciduum in the vicinity of the ectoplacental cone. Targeted disruption of the S100A8 gene caused rapid and synchronous embryo resorption by day 9.5 of development in 100% of homozygous null embryos. Until this point there was no evidence of developmental delay in S100A8-/- embryos and decidualization was normal. The results of PCR genotyping around 7.5-8.5 days postcoitum suggest that the null embryos are infiltrated with maternal cells before overt signs of resorption. This work is the first evidence for nonredundant function of a member of the S100 gene family and implies a role in prevention of maternal rejection of the implanting embryo. The S100A8 null provides a new model for studying fetal-maternal interactions during implantation.
In human breast carcinomas, overexpression of the macrophage colony–stimulating factor (CSF-1) and its receptor (CSF-1R) correlates with poor prognosis. To establish if there is a causal relationship between CSF-1 and breast cancer progression, we crossed a transgenic mouse susceptible to mammary cancer with mice containing a recessive null mutation in the CSF-1 gene (Csf1op) and followed tumor progression in wild-type and null mutant mice. The absence of CSF-1 affects neither the incidence nor the growth of the primary tumors but delayed their development to invasive, metastatic carcinomas. Transgenic expression of CSF-1 in the mammary epithelium of both Csf1op/Csf1op and wild-type tumor-prone mice led to an acceleration to the late stages of carcinoma and to a significant increase in pulmonary metastasis. This was associated with an enhanced infiltration of macrophages into the primary tumor. These studies demonstrate that the growth of mammary tumors and the development to malignancy are separate processes and that CSF-1 selectively promotes the latter process. CSF-1 may promote metastatic potential by regulating the infiltration and function of tumor-associated macrophages as, at the tumor site, CSF-1R expression was restricted to macrophages. Our data suggest that agents directed at CSF-1/CSF-1R activity could have important therapeutic effects.
The origin and turnover of efferent populations of mouse mononuclear phagocytes has been described. Mononuclear phagocytes were defined as mononuclear cells which are able to adhere to glass and phagocytize.
In vitro labeling studies with thymidine-3H showed that monocytes in the peripheral blood and peritoneal macrophages do not multiply and can be considered end cells in a normal, steady state situation. However, the mononuclear phagocytes of the bone marrow appear to be rapidly dividing cells.
This conclusion was supported by in vivo labeling experiments. A peak of labeled mononuclear phagocytes of the bone marrow was found 24 hr after a pulse of thymidine-3H. This was followed, 24 hr later, by a peak of labeled monocytes in the peripheral blood. From these experiments it was concluded that the rapidly dividing mononuclear phagocytes of the bone marrow, called promonocytes, are the progenitor cells of the monocytes. Labeling studies after splenectomy and after X-irradiation excluded other organs as a major source of the monocytes.
Peak labeling of both the blood monocyte and peritoneal macrophages occurred at the same time. A rapid entry of monocytes from the blood into the peritoneal cavity was observed, after a sterile inflammation was evoked by an injection of newborn calf serum. These data have led to the conclusion that monocytes give rise to peritoneal macrophages.
No indications have been obtained that mononuclear phagocytes originate from lymphocytes.
In the normal steady state the monocytes leave the circulation by a random process, with a half-time of 22 hr. The average blood transit time of the monocytes has been calculated to be 32 hr. The turnover rate of peritoneal macrophages was low and estimated at about 0.1% per hour.
On the basis of these studies the life history of mouse mononuclear phagocytes was formulated to be: promonocytes in the bone marrow, → monocytes in the peripheral blood, → macrophages in the tissue.
Macrophages have been identified in mouse kidney by immunohistochemical localization of the macrophage-specific antigen F4/80. They constitute the majority of the renal medullary interstitial cell population and are also found in contact with cortical distal and proximal tubules and Bowman's capsule. They are a physical component of the juxtaglomerular complex.
We have studied the embryonic development of Drosophila hemocytes and their conversion into macrophages. Hemocytes derive exclusively from the mesoderm of the head and disperse along several invariant migratory paths throughout the embryo. The origin of hemocytes from the head mesoderm is further supported by the finding that in Bicaudal D, a mutation that lacks all head structures, and in twist snail double mutants, where no mesoderm develops, hemocytes do not form. All embryonic hemocytes behave like a homogenous population with respect to their potential for phagocytosis. Thus, in the wild type, about 80-90% of hemocytes become macrophages during late development.
In mutations with an increased amount of cell death (knirps; stardust; fork head), this figure approaches 100%. In contrast, in these mutations, the absolute number of hemocytes does not differ from that in wild type, indicating that cell death does not ‘induce’ the formation of hemocytes. Finally, we show that, in the Drosophila embryo, apoptosis can occur independently of macrophages, since mutations lacking macrophages (Bicaudal D; twist snail double mutants; torso4021) show Abundant cell death.
The study of colony stimulating factor 1 (CSF-1), a homodimeric serum growth factor that regulates mononuclear phagocytes and is involved in maternal-fetal interactions during pregnancy, was dramatically enhanced by the observation that the recessive mutation osteopetrosis, op, is an inactivating mutation in the CSF-1-encoding gene. Homozygous mutant (op/op) mice completely lack CSF-1, are osteopetrotic consequent to a deficiency in osteoclasts, have severely reduced numbers of macrophages, and have reduced fertility evident at the pre- and postimplantation stages of pregnancy. We show here that op/op females have a lactational defect, and consequently, although some are able to produce offspring, few nurture any pups and none feeds a full litter. This lactational defect is due to incomplete mammary gland ductal growth during pregnancy, a precocious development of the lobulo-alveolar system, and despite expression of milk proteins, a failure to switch to a lactational state. These data show that CSF-1 has a role in the development of the mammary gland during pregnancy.
Colony stimulating factor-1 (CSF-1) regulates the survival, proliferation and differentiation of mononuclear phagocytes. The osteopetrotic (op/op) mutant mouse is devoid of CSF-1 due to an inactivating mutation in the CSF-1 gene and is deficient in several mononuclear phagocyte subpopulations. To analyze more fully the requirement for CSF-1 in the establishment and maintenance of mononuclear phagocytes, the postnatal development of cells bearing the macrophage marker antigens F4/80 and MOMA-1, in op/op mice and their normal (+/op or +/+) littermates, were studied during the first three months of life. In normal mice, maximum expression of tissue F4/80+ cells was generally correlated with the period of maximum organogenesis and/or cell turnover. Depending on the tissue, the F4/80+ cell density either decreased, transiently increased or gradually increased with age. In op/op mice, tissues that normally contain F4/80+ cells could be classified into those in which F4/80+ cells were absent and those in which the F4/80+ cell densities were either reduced, normal or initially normal then subsequently reduced. To assess which F4/80+ populations were regulated by circulating CSF-1 in normal mice, op/op mice in which the circulating CSF-1 concentration was restored to above normal levels by daily subcutaneous injection of human recombinant CSF-1 from day 3 were analyzed. These studies suggest that circulating CSF-1 exclusively regulates both the F4/80+ cells in the liver, spleen and kidney and the MOMA-1+ metallophilic macrophages in the spleen. Macrophages of the dermis, bladder, bone marrow and salivary gland, together with a subpopulation in the gut, were partially restored by circulating CSF-1, whereas macrophages of the muscle, tendon, periosteum, synovial membrane, adrenals and the macrophages intimately associated with the epithelia of the digestive tract, were not corrected by restoration of circulating CSF-1, suggesting that they are exclusively locally regulated by this growth factor. Langerhans cells, bone marrow monocytes and macrophages of the thymus and lymph nodes were not significantly affected by circulating CSF-1 nor decreased in op/op mice, consistent with their regulation by other growth factors. These results indicate that important differences exist among mononuclear phagocytes in their dependency on CSF-1 and the way in which CSF-1 is presented to them. They also suggest that the prevalent role of CSF-1 is to influence organogenesis and tissue turnover by stimulating the production of tissue macrophages with local trophic and/or scavenger (physiological) functions. Macrophages involved in inflammatory and immune (pathological) responses appear to be dependent on other factors for their ontogenesis and function.(ABSTRACT TRUNCATED AT 400 WORDS)
Although microglia-mediated cytotoxicity has been extensively investigated, little is known about the potential microglial role in neuronal and glial support. Characterization of trophin elaboration by microglia and identification of responsive populations may define novel functions. We now report that microglia/brain macrophages express neurotrophins of the nerve growth factor (NGF) gene family in vitro and in vivo, suggesting that these cells promote development and normal function of neurons and glia. Moreover, neurotrophins promote microglial proliferation and phagocytic activity in vitro. We found that microglia express neurotrophins in a region-specific manner and that within any region only subpopulations elaborate trophins. Using an antiserum specific for neurotrophin-3 (NT-3) with the microglial/macrophage marker OX-42 on postnatal day 10 in vivo, double-labeled cells were identified in the cerebral cortex, globus pallidus, and medulla; NT-3 was undetectable in OX-42-positive cells in the ependyma, the external capsule, choroid plexus, and meninges. In contrast, ramified microglia in the adult brain did not exhibit NT-3 immunoreactivity, suggesting developmental regulation of microglial NT-3 expression. In situ hybridization studies on purified microglial cultures confirmed that only subpopulations express the NGF and NT-3 genes, substantiating the existence of microglial heterogeneity. We tentatively conclude that microglial subtypes serve trophic roles in the normal brain, in addition to exerting well documented deleterious actions in illness and injury. Microglia were also responsive to neurotrophins: brain-derived neurotrophic factor (BDNF) and NT-3 increased [3H]thymidine incorporation in vitro, and NT-3 promoted proliferation. Moreover, NT-3 induced phagocytic activity, suggesting that the factor plays a role in processes associated with cellular activation.
Colony stimulating factor-1 (CSF-1) was initially identified as a growth factor for mononuclear phagocytes. This study examines the role of CSF-1 in the development of the central nervous system (CNS). CSF-1 treatment of neurons cultured from embryonic brain promoted survival and process outgrowth in a dose-dependent manner. By contrast, CSF-1 treatment of neurons cultured from the osteopetrotic (op/op) mouse, a null mutant for CSF-1, promoted significantly less process outgrowth, suggesting that there are neural abnormalities in op/op animals. Nuclease protection assays were used to determine whether CSF-1 and its receptor are expressed at times appropriate to regulate neural development. Both CSF-1 and its receptor are expressed in developing mouse brain, with a unique pattern of CSF-1 mRNA splice variant expression encoding secreted, and not membrane-bound, growth factor. To determine whether brain function is altered by null mutation of CSF-1, op/op mice were examined using electrophysiologic assays. Brainstem auditory and visual evoked potentials were both abnormal in op/op mice. Further, intracortical recordings revealed aberrant neuronal function within visual cortex and alterations in the cortical circuitry that balances excitation and inhibition. Daily CSF-1 injection of postnatal op/op mice largely rescued the abnormal neural phenotype, confirming that the absence of CSF-1 during development is responsible for the abnormalities. The effects of CSF-1 on cultured embryonic neural cells, the developmentally appropriate expression of CSF-1 and its receptor, and the neurological abnormalities in op/op mice suggest a role for CSF-1 in brain development.
Previous studies have shown that the mononuclear phagocyte growth factor, colony-stimulating factor-1 (CSF-1), has an important role in female reproduction. Mating experiments with osteopetrotic (csfmop/csfmop) mice, which possess an inactivating mutation in the CSF-1 gene, suggested that there are male, as well as female, reproductive defects. In the present study, we have shown that male csfmop/csfmop mice have a sevenfold lower concentration of circulating testosterone (T) and a significantly lower intratesticular T concentration than wild-type mice. These lowered T concentrations were associated with a reduction in mating capability and a reduction in the number of viable sperm. Reconstitution of male csfmop/csfmop mice with either circulating T in the adult or circulating CSF-1 throughout the postnatal period completely restored viable sperm numbers and significantly restored sexual behavior. These observations, coupled with the close association of Leydig cells with testicular macrophages and the proposed function of these macrophages in the regulation of Leydig cell steroidogenesis, suggest that CSF-1-regulated testicular macrophages play an important role in male reproduction.
This fascinating intellectual history is the first critical study of the work of Elie Metchnikoff, the founding father of modern immunology. Metchnikoff authored and championed the theory that phagocytic cells actively defend the host body against pathogens and diseased cells. His program developed from comparative embryological studies that sought to establish genealogical relations between species at the dawn of the Darwinian revolution. In this scientific biography, Tauber and Chernyak explore ore Metchnikoff’s development as an embryologist, showing how it prepared him to propose his theory of host-pathogen interaction. They discuss the profound impact of Darwin’s theory of evolution on Metchnikoff’s progress, and the influence of 19th century debates on vitalism, teleology, and mechanism. As a case study of scientific discovery, this work offers lucid insight into the process of creative science and its dependence on cultural and philosophic sources. Immunologists and historians of science and medicine will find it an absorbing and accessible account of a remarkable individual.
During normal tissue remodeling, macrophages remove unwanted cells, including those that have undergone programmed cell death, or apoptosis. This widespread process extends to the deletion of thymocytes (negative selection), in which cells expressing inappropriate Ag receptors undergo apoptosis, and are phagocytosed by thymic macrophages. Although phagocytosis of effete leukocytes by macrophages has been known since the time of Metchnikoff, only recently has it been recognized that apoptosis leads to surface changes that allow recognition and removal of these cells before they are lysed. Our data suggest that macrophages specifically recognize phosphatidylserine that is exposed on the surface of lymphocytes during the development of apoptosis. Macrophage phagocytosis of apoptotic lymphocytes was inhibited, in a dose-dependent manner, by liposomes containing phosphatidyl-L-serine, but not by liposomes containing other anionic phospholipids, including phosphatidyl-D-serine. Phagocytosis of apoptotic lymphocytes was also inhibited by the L isoforms of compounds structurally related to phosphatidylserine, including glycerophosphorylserine and phosphoserine. The membranes of apoptotic lymphocytes bound increased amounts of merocyanine 540 dye relative to those of normal cells, indicating that their membrane lipids were more loosely packed, consistent with a loss of membrane phospholipid asymmetry. Apoptotic lymphocytes were shown to express phosphatidylserine (PS) externally, because PS on their surfaces was accessible to derivatization by fluorescamine, and because apoptotic cells expressed procoagulant activity. These observations suggest that apoptotic lymphocytes lose membrane phospholipid asymmetry and expose phosphatidylserine on the outer leaflet of the plasma membrane. Macrophages then phagocytose apoptotic lymphocytes after specific recognition of the exposed PS.
Recent studies have suggested that bone marrow cells possess a broad differentiation potential, being able to form new liver cells, cardiomyocytes and neurons. Several groups have attributed this apparent plasticity to ‘transdifferentiation’. Others, however, have suggested that cell fusion could explain these results. Using a simple method based on Cre/lox recombination to detect cell fusion events, we demonstrate that bone-marrow-derived cells (BMDCs) fuse spontaneously with neural progenitors in vitro. Furthermore, bone marrow transplantation demonstrates that BMDCs fuse in vivo with hepatocytes in liver, Purkinje neurons in the brain and cardiac muscle in the heart, resulting in the formation of multinucleated cells. No evidence of transdifferentiation without fusion was observed in these tissues. These observations provide the first in vivo evidence for cell fusion of BMDCs with neurons and cardiomyocytes, raising the possibility that cell fusion may contribute to the development or maintenance of these key cell types.
Ingestion of apoptotic cells in vitro by macrophages induces TGF-β1 secretion, resulting in an anti-inflammatory effect and suppression of proinflammatory mediators. Here, we show in vivo that direct instillation of apoptotic cells enhanced the resolution of acute inflammation. This enhancement appeared to require phosphatidylserine (PS) on the apoptotic cells and local induction of TGF-β1. Working with thioglycollate-stimulated peritonea or LPS-stimulated lungs, we examined the effect of apoptotic cell uptake on TGF-β1 induction. Viable or opsonized apoptotic human Jurkat T cells, or apoptotic PLB-985 cells, human monomyelocytes that do not express PS during apoptosis, failed to induce TGF-β1. PS liposomes, or PS directly transferred onto the PLB-985 surface membranes, restored the TGF-β1 induction. Apoptotic cell instillation into LPS-stimulated lungs reduced proinflammatory chemokine levels in the bronchoalveolar lavage fluid (BALF). Additionally, total inflammatory cell counts in the BALF were markedly reduced 1–5 days after apoptotic cell instillation, an effect that could be reversed by opsonization or coinstillation of TGF-β1 neutralizing antibody. This reduction resulted from early decrease in neutrophils and later decreases in lymphocytes and macrophages. In conclusion, apoptotic cell recognition and clearance, via exposure of PS and ligation of its receptor, induce TGF-β1 secretion, resulting in accelerated resolution of inflammation.
Apoptosis is fundamental to the development and maintenance of animal tissues and the immune system. Rapid clearance of apoptotic cells by macrophages is important to inhibit inflammation and autoimmune responses against intracellular antigens. Here we report a new function for Mer, a member of the Axl/Mer/ Tyro3 receptor tyrosine kinase family, merkd mice with a cytoplasmic truncation of Mer had macrophages deficient in the clearance of apoptotic thymocytes. This was corrected in chimaeric mice reconstituted with bone marrow from wild-type animals. Primary macrophages isolated from merkd mice showed that the phagocytic deficiency was restricted to apoptotic cells and was independent of Fc receptor-mediated phagocytosis or ingestion of other particles. The inability to clear apoptotic cells adequately may be linked to an increased number of nuclear autoantibodies in merkd mice. Thus, the Mer receptor tyrosine kinase seems to be critical for the engulfment and efficient clearance of apoptotic cells. This has implications for inflammation and autoimmune diseases such as systemic lupus erythematosus.
Macrophage Distribution in Adult MiceResident macrophages in bone marrow stromaMacrophage Ontogeny and Role in fetal haemopoiesisThe Phenotype of Tissue Macrophages from Adult MiceConclusions
ReferencesDiscussionReferences
Testicular macrophages of aging mice were studied by TEM. Testicular macrophages retained with Leydig cells the close morphological relationships observed in the adult young animals, but digitations were not found. Lipofuscin granules like those of the Leydig cells from aging mice were observed in the cytoplasm. These organelles were generally absent in the testicular macrophages of young adult mice. Testicular macrophages did not display phagocytosis of the lipofuscin granules. In addition, the latter were not found in the intercellular spaces. These observations indicated that lipofuscin granules were formed, at least in a great part, within testicular macrophages as a consequence of metabolic changes occurring with age. Fine lamellar organization was seen in the lipofuscin granules of both Leydig cells and testicular macrophages. Frequently, lipofuscin granules originated from secondary lysosomes containing lipidic vacuoles only. Together with accumulation of the lipofuscin granules, changes of testicular macrophage fine morphology were observed. Endoplasmic reticulum and Golgi apparatus became poorly developed, and coated vesicles were rarely found. Fewer mitochondria were encountered, but their ultrastructure was not altered. These results suggest that in testicular macrophages lipofuscin accumulation is associated with a functional involution.
The macrophage cell lineage continually arises from hematopoietic stem cells during embryonic, fetal, and adult life. Previous theories proposed that macrophages are the recent progeny of bone marrow-derived monocytes and that they function primarily in phagocytosis. More recently, however, observations have shown that the ontogeny of macrophages in early mouse and human embryos is different from that occurring during adult development, and that the embryonic macrophages do not follow the monocyte pathway. Fetal macrophages are thought to differentiate from yolk sac-derived primitive macrophages before the development of adult monocytes. Further support for a separate lineage of fetal macrophages has come from studies of several species, including chicken, zebrafish, Xenopus, Drosophila, and C. elegans. The presence of fetal macrophages in PU.1-null mice indicates their independence from monocyte precursors and their existence as an alternative macrophage lineage.
Subtitle on facsimile title page: delivered at the Pasteur Institute in 1891. Translation of Leçons sur la pathologie comparée de l'inflammation. Facsimile reprint. Originally published: London : Kegan Paul, Trench, Trub̈ner & Co., 1893.
The mononuclear phagocytes comprise the bone marrow promonocyte, the blood monocyte, and the tissue macrophages: the histiocyte, Kupffer cells, the macrophages of lungs, lymph nodes, bone marrow, serous cavities, nervous system (microglia) and possibly bone (osteoclasts?). Histiocytes are the same cells as macrophages. Excluded from the mononuclear phagocyte line are the reticular cells, the endothelial cells, and the fibroblasts. Phagocytes are the main cells in chronic inflammation and essential in wound healing and tissue repair. They also represent a key cell in immunity, especially as regards the lymphocyte macrophage interactions. Lymphocytes call forth the phagocytes by a chemotactic substance which can be found in cultures of activated lymphocytes. The uptake of antigens is carried out in part by structures on their surfaces which interact witn the Fc piece of some immunoglobulins or with C3. A third property of the phagocyte is their phagocytosis (activated macrophages). It is the T lymphocyte which activates these macrophages. The main point made in this review, is that the phagocytes may participate in inflammation and immunity as a result of the release of chemical mediators. The products secreted by phagocytes are: enzymes (lysosomal enzymes, lysozyme, plasminogen activators, collagenase and elastase); products affecting cells in culture (lymphostimulatory factor, colony stimulating factor, inhibitors of DNA synthesis and toxins); and, finally, the complement proteins (interferons and pyrogen). There appear to be several patterns of modulation of the secretory process. For many products, a stimulus is the phagocytosis of a particle: plasminogen activator, collagenase, elastase and for the C protein. In contrast, secretion of lysozyme is not triggered by a phagocytic challenge, but the nature of the phagocytized particles appears important. The secretory function gives the phagocytes a regulatory influence in inflammation and tissue repair, in infection, perhaps in the control of hemopoiesis, and in critical steps in immunity; they are also prominent cells in various processes of collagen resorption: the tadpole tail during metamorphosis, the postpartum uterus at the time of collagen resorption and in granulomas. In many of these examples, there was some phagocytosis of collagen fibers. When there is intense macrophage infiltration produced by stimulants which are phagocytized and which activate the macrophage, one can predict that there will be an intense release of the products mentioned above. Injection of streptococcal cell wall preparations produces, granulomatous persistent inflammation, with distortion and alteration of connective tissues. Speculation has arisen with regard to secretion of elastase by inflammatory cells and the destruction of the alveolar wall in emphysema: the activated alveolar macrophage is known to secrete elastase. The importance and implications of the secretory process and phagocytes is obvious. (112 references are cited).
The role of the monocyte/macrophage in wound repair has been investigated by studying the healing process in wounds depleted of this cell and/or its phagocytic activity. Hydrocortisone acetate (0.6 mg/g body weight) administered as a subcutaneous depot was used to induce a prolonged monocytopenia in guinea pigs, and antimacrophage serum (AMS) was used for local elimination of tissue macrophages. In vitro, the presence of complement, macrophages are rapidly lysed and used killed by AMS. In the absence of complement, AMS is not cytotoxic but potently inhibits adherence to and phagocytosis of opsonized erythrocytes by macrophages. AMS titers were obtained by observation of adherence and phagocytosis of opsonized erythrocytes in serial dilutions of AMS. Six groups of animals were studied: a) untreated animals, b)animals receiving daily subcutaneous injections of normal rabbit serum (NRS) around each wound, c)animals receiving daily subcutaneous AMS around each wound, d)animals receiving systemic hydrocortisone, e)animals receiving systemic hydrocortisone and daily injections of NRS around each wound, and f)animals receiving systemic hydrocortisone and daily AMS around each wound. Wounds consisted of a series of six linear incisions in the dorsal skin. Subcutaneous AMS alone has no effect on the number of circulating monocytes, nor was there any observable effect on the number or the phagocytic ability of wound macrophages. Fibrosis in these wounds was unaffected. Systemic hydrocortisone induced a prolonged monocytopenia. The macrophage level in the wounds of these monocytopenic animals was reduced to approximately one-third that of controls; the phagocytic activity of the monocytes/macrophages that did appear in these wounds was, however, similar to that of controls. Some inhibition of wound debridement was observed in these wounds, but fibrosis was virtually unaffected. Collagen synthesis, as judged morphometrically, was similar to that of control wounds at all stages of repair. Conjoint systemic hydrocortisone and subcutaneous AMS around each wound resulted in the almost complete disappearance of macrophages from the wounds. Wound fibrin levels were elevated, and clearance of fibrin, neutrophils, erythrocytes and other miscellaneous debris from these wounds was delayed. Fibroblasts, which in control wounds first appear by 3 days postwounding and reach maximal levels by day 5, did not appear in these wounds until day 5, and their subsequent rate of proliferation was slower than that of controls. Continued.
It is currently accepted that stem cells of the definitive blood cell lines originate from the yolk-sac blood islands. Experiments were devised to examine the validity of this theory in the avian embryo. These involved grafting two-day-old quail embryos on to chick yolk-sacs of comparable developmental stages, i.e. before or shortly after the establishment of vascularization.The conclusions of the experiments are based on the possibility of distinguishing chick cell nuclei from those of the quail.
In the developing haemopoietic organs (spleen and thymus) of quail embryos grafted on to the chick and subsequently incubated for 6–11 days, all cells, whether belonging to the granulopoietic, erythropoietic or lymphopoietic series, are of quail type. Thus these organs have not been colonized by chick stem cells.
On the other hand, coelomic graft experiments show that the development of these organs is indeed dependent on an extrinsic colonization by haemopoietic cells; quail spleen or thymus rudiment, developing in the coelom of a chick, is populated by chick cells. Thus no incompatibility which would prevent heterospecific colonization exists in this system.
It is concluded that haemopoietic stem cells of the definitive blood cell series originate from some source other than the yolk-sac, and that this source must be intra-embryonic.
During normal tissue remodeling, macrophages remove unwanted cells, including those that have undergone programmed cell death, or apoptosis. This widespread process extends to the deletion of thymocytes (negative selection), in which cells expressing inappropriate Ag receptors undergo apoptosis, and are phagocytosed by thymic macrophages. Although phagocytosis of effete leukocytes by macrophages has been known since the time of Metchnikoff, only recently has it been recognized that apoptosis leads to surface changes that allow recognition and removal of these cells before they are lysed. Our data suggest that macrophages specifically recognize phosphatidylserine that is exposed on the surface of lymphocytes during the development of apoptosis. Macrophage phagocytosis of apoptotic lymphocytes was inhibited, in a dose-dependent manner, by liposomes containing phosphatidyl-L-serine, but not by liposomes containing other anionic phospholipids, including phosphatidyl-D-serine. Phagocytosis of apoptotic lymphocytes was also inhibited by the L isoforms of compounds structurally related to phosphatidylserine, including glycerophosphorylserine and phosphoserine. The membranes of apoptotic lymphocytes bound increased amounts of merocyanine 540 dye relative to those of normal cells, indicating that their membrane lipids were more loosely packed, consistent with a loss of membrane phospholipid asymmetry. Apoptotic lymphocytes were shown to express phosphatidylserine (PS) externally, because PS on their surfaces was accessible to derivatization by fluorescamine, and because apoptotic cells expressed procoagulant activity. These observations suggest that apoptotic lymphocytes lose membrane phospholipid asymmetry and expose phosphatidylserine on the outer leaflet of the plasma membrane. Macrophages then phagocytose apoptotic lymphocytes after specific recognition of the exposed PS.
Testicular macrophages and Leydig cells from adult animals are known to be functionally coupled. For example, secreted products from macrophages stimulate testosterone secretion by Leydig cells. In adult rat testes, structural coupling also exists between these cells. This coupling consists of cytoplasmic projections from Leydig cells located within cytoplasmic invaginations of macrophages. Although macrophages are known to exist in the testis in immature animals, it is not known when these digitations develop. The purpose of the present study was to determine whether the time of their development coincides with known maturational events that occur in Leydig cells, particularly during the peripubertal period. Testes from rats at 20, 30 and 40-days-of-age as well as testes from mature rats weighing more than 500 gm were prepared for ultrastructural analysis. It was found that digitations form between 20 and 30-days-of-age. These structures varied from simple tubular projections to complicated branched structures, suggesting that digitations are more than simple invaginations of microvilli into coated vesicles as previously described. Subplasmalemmal linear densities were also observed within macrophages juxtaposed to Leydig cells. Collagen was commonly observed between macrophages and Leydig cells in animals 20 days old. These studies demonstrate that although macrophages are present in the testis in maximal numbers at 20 days-of-age, they do not form junctions with Leydig cells until day 30. This is just prior to the major increase in secretory activity of rat Leydig cells that occurs during puberty.
Macrophages are widely distributed in lymphohaemo-poietic and other tissues of the normal and diseased adult, where they play an important role in host defence and repair. Although the development of haemopoiesis has been well studied in several species, the ontogeny of the mononuclear phagocyte system remains poorly understood. We have used a highly specific mAh, F4/80, to examine the distribution of mature macrophages in the developing mouse, with special reference to their presence in the haemopoietic microenvironment. Monocytes and macrophages were first seen in embryos on day 10 in the yolk sac and liver as well as in mesenchyme. In liver, spleen and bone marrow, there was expansion of this population associated with the initiation of haemopoietic on days 11,15 and 17, respectively. Macrophages in these sites formed part of the haemopoietic stroma and their extensively spread plasma membrane processes could be seen making intimate contacts with clusters of differentiating haemopoietic cells. F4/80+ cells were widely dispersed in undifferentiated mesenchymal tissue in organs such as lung, kidney and gut.
Numbers of F4/80-labefled cells increased concomitantly with organ growth and local mitoses were evident, as well as actively phagocytic macrophages. Our studies establish that macrophages are among the earliest haemopoietic cells to be produced during development and that they are relatively abundant in fetal tissues in the absence of overt inflammatory stimuli. Their distribution is correlated with the sequential migration of haemopoiesis and they constitute a prominent component of the stroma in fetal liver, spleen red pulp and bone marrow. Apart from a role in haemopoietic cellular interactions, their highly developed endocytic and biosynthetic activities suggest that macrophages contribute major undefined functions during growth, turnover and modelling of fetal tissues.
Abbreviations: Ab, antibody; ag, antigen; mAb, monoclonal antibody; MΦ, macrophage.
After programmed cell death, a cell corpse is engulfed and quickly degraded by a neighboring cell. For degradation to occur, engulfing cells must recognize, phagocytose and digest the corpses of dying cells. Previously, three genes were known to be involved in eliminating cell corpses in the nematode Caenorhabditis elegans: ced-1, ced-2 and nuc-1. We have identified five new genes that play a role in this process: ced-5, ced-6, ced-7, ced-8 and ced-10. Electron microscopic studies reveal that mutations in each of these genes prevent engulfment, indicating that these genes are needed either for the recognition of corpses by other cells or for the initiation of phagocytosis. Based upon our study of double mutants, these genes can be divided into two sets. Animals with mutations in only one of these sets of genes have relatively few unengulfed cell corpses. By contrast, animals with mutations in both sets of genes have many unengulfed corpses. These observations suggest that these two sets of genes are involved in distinct and partially redundant processes that act in the engulfment of cell corpses.
Macrophages were identified in the intertubular tissue of the rat testis by loading animals with a particulate vital dye (trypan blue or India ink) and by localizing immunocytochemically a macrophage membrane antigen (MRC W3/25). Leydig cells were identified by the histochemical staining reaction for 3 beta-hydroxysteroid dehydrogenase activity and by a monoclonal antibody. Macrophages were scattered in the interstitial tissue closely attached to and mixed with the Leydig cells. They were never found in the seminiferous tubules. The macrophages comprised about 25% of all the cells in the interstitium. Double staining with a vital dye and a marker antibody showed that all the phagocytosing cells were macrophages and that the Leydig cells did not take up vital dyes. Double staining for the demonstration of the 3 beta-hydroxysteroid dehydrogenase activity and the macrophage antigen likewise revealed two distinctly different cell populations. Crude Leydig cell preparations obtained by collagenase treatment of the testis contained macrophages (12-14%). Macrophages were present throughout the postnatal prepuberal development of the testis. Their density was increased in the cryptorchid and irradiated testis.
We generated and characterized greater than 500 Drosophila strains that carry single copies of a novel P-element enhancer detector. In the majority of the strains, the beta-galactosidase reporter gene in the P-transposon responds to nearby transcriptional regulatory sequences in the genome. A remarkable diversity of spatially and temporally regulated staining patterns is observed in embryos carrying different insertions. We selected numerous strains as markers for different embryonic organs, tissues, and cells. Many of these strains should allow the study of complex developmental processes, such as nervous system development, which have not been convenient to analyze previously. Also, we present genetic evidence that some of the detected regulatory elements control nearby Drosophila genes. In light of our results, we discuss the diversity and complexity of cis-acting regulatory elements in the genome and the general applications of the enhancer detector method for the study of Drosophila development.
The regional ability of central neurons and glial cells to produce nerve growth factor (NGF) was studied in vitro. NGF secretion was compared in cultures of perinatal astrocytes or embryonic neurons that were derived from various mouse brain structures. No regional differences were detected among cultures of post-natal day 2 glial cells of hippocampal, cortical, striatal, or mesencephalic origin. In all cases, levels of NGF released by the cells were very similar. They were closely correlated to the growth rate as shown by the fact that exponentially growing cells produced relatively more factor than did confluent cells, a finding in agreement with previous observations. Unlike growth-phase cells, primary astrocytes immediately plated at high cell density did not secrete any assayable factor before the 7th day of culture. Levels of NGF found during the following days remained low. In contrast, striking differences were observed among cultures of embryonic neurons. NGF was found in relatively large amounts in cultures of embryonic day 17 or 19 striatal neurons, whereas media conditioned by neurons from the mesencephalon, cortex, or septum contained much less factor. Amounts of NGF assayed in cultures of hippocampal neurons varied with the time of sampling of this brain structure. Levels of factor were significantly higher in media conditioned by embryonic day 19 neurons than in media of embryonic day 17 neurons. However, amounts of NGF found in supernatants of hippocampal neurons remained smaller than those present in cultures of striatal nerve cells. Altogether, the results suggest that, in addition to astrocytes, central neurons may also synthesize and secrete NGF in vitro and that this phenomenum is dependent on both the origin and the developmental stage of the neuronal population.
Amoeboid microglial cells purified from primary cultures of embryonic rat brains and stimulated with bacterial lipopolysaccharides released high amounts of nerve growth factor. This finding suggests that brain macrophages play a major neurotrophic role during development, in adulthood, and in the regenerative events that follow localized lesions.
The phosphoprotein plastin was originally identified as an abundant transformation-induced polypeptide of chemically transformed
neoplastic human fibroblasts. This abundant protein is normally expressed only in leukocytes, suggesting that it may play
a role in hemopoietic cell differentiation. Protein microsequencing of plastin purified from leukemic T lymphocytes by high-resolution
two-dimensional gel electrophoresis produced eight internal oligopeptide sequences. An oligodeoxynucleotide probe corresponding
to one of the oligopeptides was used to clone cDNAs from transformed human fibroblasts that encoded the seven other oligopeptides
predicted for human plastin. Sequencing and characterization of two cloned cDNAs revealed the existence of two distinct, but
closely related, isoforms of plastin--l-plastin, which is expressed in leukocytes and transformed fibroblasts, and t-plastin,
which is expressed in normal cells of solid tissues and transformed fibroblasts. The leukocyte isoform l-plastin is expressed
in a diverse variety of human tumor cell lines, suggesting that it may be involved in the neoplastic process of some solid
human tumors.
The rat monoclonal antibody F4/80 defines a plasma membrane glycoprotein of about 160 kilodaltons that is expressed by mature mouse macrophages. The antigen has been used to define macrophage distribution within the mouse (normal adult, embryo, infection models) by cytochemistry and quantitative immunochemical analysis. Macrophages migrate into fetal and adult haemopoietic and other tissues in an ordered sequence. The surface properties of 'fixed' macrophages isolated from various organs (bone marrow, liver, spleen) are distinct from those of circulating monocytes or free cells (peritoneal and pleural cavities, alveolar) and may play a role in local adhesion and trophic interactions with other cells.
The c-fms protoncogene which encodes the receptor for macrophage colony-stimulating factor (CSF-1) was localized in the developing mouse embryo by whole in situ hybridization. c-fms was expressed first in placental trophoblasts. Around 9.5 dpc, isolated c-fms-positive cells became detectable in the yolk sac and by 10.5 dpc large numbers were detectable throughout the embryo. The localization of c-fms expression was consistent with its restriction to macrophages, and with the location of those macrophages in sites of tissue turnover and extensive cell death.
In the present study we analyzed expression and biochemical properties of the two recently cloned calcium-binding proteins MRP8 and MRP14, both members of the S-100 family, in murine myelomonocytic cells. Expression of MRPs was found to be restricted to granulocytes and distinct stages of macrophage differentiation when compared to the expression of other markers (Mac-1, F4/80) in transformed macrophage cell lines (M1, RMB.TG, WEHI.TG, J774A, P388D) and resident and exudate peritoneal and tissue macrophages. Similarly, mRNA and protein levels of MRP8/MRP14 in murine bone marrow cells decreased during culture in L cell-conditioned medium. Applying a cross-linking technique, the formation of noncovalently associated heteromeric MRP8/MRP14 complexes of 25, 35, and 48 kd was demonstrated. Our data suggest that MRP8/MRP14 expression and complexation are characteristic for granulocytes and distinct stages of macrophage differentiation in mice. Analysis of the MRP8/MRP14+ phenotype of macrophages may provide further insights into the mechanisms underlying macrophage differentiation.
Many of the neurons which migrate to the cortex die at an early stage of development. In certain animals many cells die when their task is done; a phenomenon known as programmed cell death, or apoptosis. In humans a far commoner cause is the competition hypothesis: if the axon of the cell does not make contact with the dendrites of the cell in its target area it will die. Then the complexity and number of these synapses is more essential to the function of the brain than the actual number of neurons. Examples are given of the effect of sensory deprivation on the survival of neurons. The withdrawal of neuronal growth factor, and subsequent loss of the axon or cell can be a factor in the fine tuning of neural circuits, and therefore in an improvement in learning and the development of skills. However, it may also account for the diminished plasticity of the nervous system, and its ability to adapt to injury. It has been postulated that these changes contribute to the development of personality. Factors which may be involved include differences in brain development between the sexes; temperamental traits which may have a genetic or prenatal origin; and the effects of sensory perception, including language. Surely there can be no doubt that the results of experience represent the fundamental mechanisms by which the organism adapts to its environment.
We demonstrated that a 65-kDa cytosolic protein (pp65) was most heavily phosphorylated in murine macrophages in response to bacterial lipopolysaccharide (J. Immunol. 146:3617, 1991). The pp65 phosphorylation closely correlated with cellular responses in the macrophages. We have thus performed amino acid sequence analysis of the two pp65-derived peptide fragments in order to elucidate its structure and function. The results indicated that pp65 is a novel protein existing almost exclusively in hemopoitetic cells and has the strong homology with human L-plastin, a substrate which has recently been identified as a novel protein transformation-dependently expressed in neoplastic human cells. Our pp65 is apparently the first purified protein whose phosphorylation has been augmented by stimulation with bacterial lipopolysaccharide and whose primary structure has been clarified. Because L-plastin possesses the unique functional domains, detailed investigation of the pp65 phosphorylation should lead to progress in our understanding of the mechanisms of macrophage activation.
We used a panel of monoclonal antibodies and immunocytochemistry to identify macrophages and dendritic cells in mice that are deficient in macrophage colony stimulating factor (M-CSF or CSF-1) because of the recessive osteopetrotic (op/op) mutation. Prior work had shown that osteopetrosis is associated with a lack of osteoclasts, phagocytic cells required for remodelling in bone. Additional macrophage populations proved to be very M-CSF dependent. op/op mice had few and sometimes no peritoneal cavity phagocytes, splenic marginal zone metallophils, and lymph node subcapsular sinus macrophages. Other populations, however, reached substantial levels in the absence of M-CSF, including phagocytes in the thymic cortex, splenic red pulp, lymph node medulla, intestinal lamina propria, liver (Kupffer cells), lung (alveolar macrophages) and brain (microglia). Dendritic cells, which are specialized accessory cells for T-dependent immune responses and tolerance, were readily identified in skin and in the T-dependent regions of spleen, lymph node and Peyer's patch. The identification of dendritic cells utilized antibodies to MHC class II products and four different antigens that are primarily expressed by these accessory cells. Our findings indicate that only a few macrophage populations are critically dependent upon M-CSF in vivo. With respect to dendritic cells, the data are consistent with prior in vitro work where it was noted that GM-CSF but not M-CSF supported dendritic cell viability, function and growth.
The ovulatory process has been compared with inflammation because several classical inflammatory mediators appear to participate in this process. One component of the inflammatory reaction is the migration of leukocytes to the site of inflammation and the subsequent activation of these cells. We have reported recently that perfusion of leukocytes into the rat ovary in vitro enhances the number of LH-induced ovulations, which suggests an active role of leukocytes in ovulation. In the present study we characterize immunohistochemically the distribution of macrophages, T lymphocytes, and granulocytes in the ovaries of untreated immature rats and of eCG-hCG-primed rats killed prior to hCG injection, at ovulation, and at 33-36 h post-ovulation. Macrophages, identified with monoclonal antibodies ED1 and ED2, were the major leukocyte population and were found primarily in the medullary region surrounding the blood vessels. The density of the cells in this region increased continuously during development to sexual maturity and until after ovulation. Macrophages were also present in the thecal layer of the preovulatory follicles, and the numbers of these cells increased about 5-fold in this area in ovulating follicles (12 h after hCG) compared to preovulatory follicles (before hCG). A portion of macrophages in both areas expressed major histocompatibility complex (MHC) class II antigens (OX6+); these cells were present mostly in the medullary region, with no apparent change in density during the periovulatory period. Neutrophilic granulocytes comprised a lesser proportion of the total leukocyte population in the medullary region but were abundant in the thecal layer. The density of neutrophils increased 3-fold in the medullary region and 8-fold in the thecal region in ovulatory compared to preovulatory follicles. T lymphocytes (OX52+) were evenly distributed at relatively low density in the medulla and the stroma of the cortex. Most T lymphocytes expressed the CD8 antigen (OX8+) and hence were of the MHC class I-restricted phenotype. Few T lymphocytes were present in the thecal layer. In summary, macrophages, neutrophilic granulocytes, and T lymphocytes are present in the ovary at ovulation. There is a selective increase in the numbers of macrophages and neutrophilic granulocytes in the medullary region and in the thecal layer as the ovulatory period progresses, indicating that these cells may actively be involved in the tissue remodeling occurring at ovulation.
ATP binding cassette (ABC) transporters define a family of proteins with strong structural similarities conserved across evolution and devoted to the translocation of a variety of substrates across cell membranes. A few members of the family are known in mammals, but although all of them are medically relevant proteins, knowledge of their molecular function remains scanty. We report here a morphological and functional study of the recently identified mammalian ABC transporter, ABC1. Its expression during embryonic development correlates spatially and temporally with the areas of programmed cell death. More specifically, ABC1 is expressed in macrophages engaged in the engulfment and clearance of dead cells. Moreover, ABC1 transporter is required for engulfment since the ability of macrophages to ingest apoptotic bodies is severely impaired after antibody-mediated steric blockade of ABC1. A structural homologue of ABC1 has been identified in the Caenorhabditis elegans genome and maps close to the ced-7 locus. Since ced-7 phenotype is precisely defined by an imparied engulfment of cell corpses, it is tempting to surmise that ABC1 might be a mammalian homologue of ced-7.
Programmed cell death is first observed at stage 11 of embryogenesis in Drosophila. The systematic removal of apoptotic cells is mediated by cells that are derived from the procephalic mesoderm and differentiate into macrophages. We describe a macrophage receptor for apoptotic cells. This receptor, croquemort (catcher of death), is a member of the CD36 superfamily. Croquemort-mediated phagocytosis represents the concept that phagocytosis evolved primarily as a cellular process for the removal of effete cells. Our findings support the idea that the primordial function of macrophages may have been in tissue modeling and that their adapted role is in host defense.
Emergence of hemopoietic stem cells in the mammalian embryo has yet to be definitively allocated. Previously, we detected multipotent hemopoietic precursors in the region surrounding the dorsal aorta (paraaortic splanchnopleura) beginning at 8.5 days postcoitum (dpc). However, as circulation is already established, it remained unclear whether hemopoietic precursors arise in situ or are blood-delivered. By adding an organotypic step to our former culture system, we now detect lymphocyte and multipotent myeloid precursors from the intraembryonic splanchnopleura as early as 7.5 dpc. Under identical conditions, yolk sacs from the same embryos are unable to generate lymphoid progeny and have a reduced potential for myeloid differentiation and maintenance. Thus, if isolated before circulation, the yolk sac does not produce multipotent precursors and therefore does not contribute to definitive hemopoiesis in the mouse.
The adult hematopoietic system of mammals is a dynamic hierarchy of cells with the hematopoietic stem cell at its foundation. During embryonic development, the source and expansion potential of this cell remain unclear. Two sites of hematopoietic activity, the yolk sac and aorta-gonad-mesonephros (AGM) region, function in mouse ontogeny at the pre-liver stage of hematopoiesis. However, cellular interchange between these tissues obscures the embryonic site of hematopoietic stem cell generation. Here we present the results of a novel in vitro organ culture system demonstrating that, at day 10 in gestation, hematopoietic stem cells initiate autonomously and exclusively within the AGM region. Furthermore, we provide evidence for the in vitro expansion of hematopoietic stem cells within the AGM region. These results strongly suggest that the AGM region is the source of the definitive adult hematopoietic system, which subsequently colonizes the liver.