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The JAK-STAT signaling pathway in Drosophila melanogaster. (A) Activation of JAK-STAT signaling. Binding of either cytokine, unpaired (upd1, 2, and 3), to the type i cytokine receptor Domeless activates trans-phosphorylation of the JAK kinase Hopscotch (Hop) and Dome phosphorylation, creating a docking site for STAT (Stat92e). Hop-phosphorylated STAT forms dimers which translocate into the nucleus and activate target genes via binding to TTcN (3-4)GAA sites. The green box in Dome corresponds to the cytokine binding domain (cBM), the blue box to a conserved region between Lat/et and Dome (LDHR), the fibronectin iii (Fn iii) motifs are in red, the signal peptide in yellow and the intra-cytoplasmic region in gray. (B) Negative regulation of JAK-STAT signaling. Lat/et acts as a dominant negative Dome co-receptor. Suppressor of cytokine signaling (SocS) (Socs36e, Socs44A) prevents Stat92e recruitment onto the receptor. protein inhibitors of activated STAT (piAS) and pTp61F inhibit Stat92e function. Sumoylation of Stat92e has a repressive role in the regulation of the JAK-STAT pathway in Drosophila. BcL6 (Ken and Barbie, marked Ken) and NuRF compete with Stat92e for binding to DNA.
Source publication
Genetic alterations affecting the JAK-STAT signaling pathway are linked to several malignancies and hematological disorders in humans. Despite being one of the most extensively studied pathways, there remain many gaps to fill. JAK-STAT components are widely conserved during evolution. Here, we review the known roles of the JAK-STAT pathway in Droso...
Contexts in source publication
Context 1
... and STATs mediate intracellular signaling in response to secreted type I cytokines. JAK tyrosine kinases are associated with the intracellular part of single pass transmembrane pro- teins that form homo-or heteromeric receptors. Ligand binding induces a conformational change that triggers pathway activa- tion, via trans-phosphorylation of JAK molecules associated with the intracellular part of the receptor. Phosphorylated (activated) JAKs then phosphorylate the receptor, creating docking sites for members of the STAT family of transcription factors, which in turn become phosphorylated. Phosphorylated (activated) STATs homo-or heterodimerize prior to nuclear translocation and tran- scriptional activation of target genes (Fig. 1). Four JAKs, seven STATs, and more than 30 different cytokines and growth fac- tors have been identified in mammals. 6 In contrast, in Drosophila there is only one active type I cytokine receptor (Domeless, Dome), one JAK (Hopscotch/Hop), one STAT (Stat92E/ Marelle), and three cytokines called Unpaired (Upd, Upd2, and Upd3). 2 Negative regulators of the pathway have been identified, including three suppressors of cytokine signaling (SOCS), one PIAS (dPIAS/Su [var]2-10), the nucleosome remodeling factor NURF, 7 one BCL-6 homolog Ken and Barbie, the nuclear STAT phosphatase PTP61, and the sumoylation of STAT 92E. 8 One short form of the cytokine receptor encoded by CG14225, called Eye Transformer (Et) or Latran (Lat), was recently shown to act as a tissue-specific dominant negative receptor ( Fig. 1 insect-specific reaction that contributes to wound healing; lam- ellocytes, corresponding to a cryptic, stress-induced cell fate, encapsulate foreign bodies too large to be phagocytosed, such as eggs laid in Drosophila larvae by parasitoid wasps. Drosophila hematopoiesis occurs in two waves during development. First, a population of precursor cells for plasmatocytes and crystal cells is specified from the embryonic head mesoderm. Some of these cells differentiate before dispersing in the embryo, while others divide and differentiate later in circulation at the larval stage. A fraction of the embryonic hemocytes attach to the inner surface of the larval cuticle. 19 Whether these "sessile" hemocytes, which can be mobilized upon immune challenge, perform specific functions remains unclear. 19,20 A second population of plasmatocytes and crystal cells is released at the onset of metamorphosis, from a spe- cific larval hematopoietic organ called the lymph gland (LG). 21,22 Lamellocytes rarely differentiate under normal conditions but massively differentiate in the LG in response to wasp parasitism. and 10). Beside the canonical JAK-STAT pathway, recent reports suggest that the association of STAT92E/HP1 complexes to heterochromatin, in the absence of JAK signaling, represents an alternative mechanism by which STAT could regulate transcrip- tion in Drosophila. 11,12 Finally, recent data obtained for vertebrate STAT proteins indicate non canonical functions as they can be involved in chromatin organization, mitochondrial respiration and the regulation of tubulin dynamics. ...
Context 2
... and STATs mediate intracellular signaling in response to secreted type I cytokines. JAK tyrosine kinases are associated with the intracellular part of single pass transmembrane pro- teins that form homo-or heteromeric receptors. Ligand binding induces a conformational change that triggers pathway activa- tion, via trans-phosphorylation of JAK molecules associated with the intracellular part of the receptor. Phosphorylated (activated) JAKs then phosphorylate the receptor, creating docking sites for members of the STAT family of transcription factors, which in turn become phosphorylated. Phosphorylated (activated) STATs homo-or heterodimerize prior to nuclear translocation and tran- scriptional activation of target genes (Fig. 1). Four JAKs, seven STATs, and more than 30 different cytokines and growth fac- tors have been identified in mammals. 6 In contrast, in Drosophila there is only one active type I cytokine receptor (Domeless, Dome), one JAK (Hopscotch/Hop), one STAT (Stat92E/ Marelle), and three cytokines called Unpaired (Upd, Upd2, and Upd3). 2 Negative regulators of the pathway have been identified, including three suppressors of cytokine signaling (SOCS), one PIAS (dPIAS/Su [var]2-10), the nucleosome remodeling factor NURF, 7 one BCL-6 homolog Ken and Barbie, the nuclear STAT phosphatase PTP61, and the sumoylation of STAT 92E. 8 One short form of the cytokine receptor encoded by CG14225, called Eye Transformer (Et) or Latran (Lat), was recently shown to act as a tissue-specific dominant negative receptor ( Fig. 1 insect-specific reaction that contributes to wound healing; lam- ellocytes, corresponding to a cryptic, stress-induced cell fate, encapsulate foreign bodies too large to be phagocytosed, such as eggs laid in Drosophila larvae by parasitoid wasps. Drosophila hematopoiesis occurs in two waves during development. First, a population of precursor cells for plasmatocytes and crystal cells is specified from the embryonic head mesoderm. Some of these cells differentiate before dispersing in the embryo, while others divide and differentiate later in circulation at the larval stage. A fraction of the embryonic hemocytes attach to the inner surface of the larval cuticle. 19 Whether these "sessile" hemocytes, which can be mobilized upon immune challenge, perform specific functions remains unclear. 19,20 A second population of plasmatocytes and crystal cells is released at the onset of metamorphosis, from a spe- cific larval hematopoietic organ called the lymph gland (LG). 21,22 Lamellocytes rarely differentiate under normal conditions but massively differentiate in the LG in response to wasp parasitism. and 10). Beside the canonical JAK-STAT pathway, recent reports suggest that the association of STAT92E/HP1 complexes to heterochromatin, in the absence of JAK signaling, represents an alternative mechanism by which STAT could regulate transcrip- tion in Drosophila. 11,12 Finally, recent data obtained for vertebrate STAT proteins indicate non canonical functions as they can be involved in chromatin organization, mitochondrial respiration and the regulation of tubulin dynamics. ...
Citations
... Unpaired cytokines are responsible for the initiation of JAK/STAT signaling by binding to the domeless receptor [18]. Loss of upd2 or upd3 leads to impaired lamellocyte production and therefore an inadequate immune response to wasp infection [10] (Fig. 2A). ...
Background
The metabolically demanding nature of immune response requires nutrients to be preferentially directed towards the immune system at the expense of peripheral tissues. We study the mechanisms by which this metabolic reprograming occurs using the parasitoid infection of Drosophila larvae. To overcome such an immune challenge hemocytes differentiate into lamellocytes, which encapsulate and melanize the parasitoid egg. Hemocytes acquire the energy for this process by expressing JAK/STAT ligands upd2 and upd3, which activates JAK/STAT signaling in muscles and redirects carbohydrates away from muscles in favor of immune cells.
Methods
Immune response of Drosophila larvae was induced by parasitoid wasp infestation. Carbohydrate levels, larval locomotion and gene expression of key proteins were compared between control and infected animals. Efficacy of lamellocyte production and resistance to wasp infection was observed for RNAi and mutant animals.
Results
Absence of upd/JAK/STAT signaling leads to an impaired immune response and increased mortality. We demonstrate how JAK/STAT signaling in muscles leads to suppression of insulin signaling through activation of ImpL2, the inhibitor of Drosophila insulin like peptides.
Conclusions
Our findings reveal cross-talk between immune cells and muscles mediates a metabolic shift, redirecting carbohydrates towards immune cells. We emphasize the crucial function of muscles during immune response and show the benefits of insulin resistance as an adaptive mechanism that is necessary for survival.
... The JAK-STAT signaling pathway has been highly conserved throughout evolution, as it is involved in the regulation of immune responses in mammals (46) and also controls different steps of hematopoiesis and the response to immune challenge in D. melanogaster (47). We previously found that gene orthologs encoding elements of this pathway were not enriched in MGHs of D. ananassae (12). ...
Background
Insects have specialized cell types that participate in the elimination of parasites, for instance, the lamellocytes of the broadly studied species Drosophila melanogaster. Other drosophilids, such as Drosophila ananassae and the invasive Zaprionus indianus, have multinucleated giant hemocytes, a syncytium of blood cells that participate in the encapsulation of the eggs or larvae of parasitoid wasps. These cells can be formed by the fusion of hemocytes in circulation or originate from the lymph gland. Their ultrastructure highly resembles that of the mammalian megakaryocytes.
Methods
Morphological, protein expressional, and functional features of blood cells were revealed using epifluorescence and confocal microscopy. The respective hemocyte subpopulations were identified using monoclonal antibodies in indirect immunofluorescence assays. Fluorescein isothiocyanate (FITC)-labeled Escherichia coli bacteria were used in phagocytosis tests. Gene expression analysis was performed following mRNA sequencing of blood cells.
Results
D. ananassae and Z. indianus encapsulate foreign particles with the involvement of multinucleated giant hemocytes and mount a highly efficient immune response against parasitoid wasps. Morphological, protein expressional, and functional assays of Z. indianus blood cells suggested that these cells could be derived from large plasmatocytes, a unique cell type developing specifically after parasitoid wasp infection. Transcriptomic analysis of blood cells, isolated from naïve and wasp-infected Z. indianus larvae, revealed several differentially expressed genes involved in signal transduction, cell movements, encapsulation of foreign targets, energy production, and melanization, suggesting their role in the anti-parasitoid response. A large number of genes that encode proteins associated with coagulation and wound healing, such as phenoloxidase activity factor-like proteins, fibrinogen-related proteins, lectins, and proteins involved in the differentiation and function of platelets, were constitutively expressed. The remarkable ultrastructural similarities between giant hemocytes and mammalian megakaryocytes, and presence of platelets, and giant cell-derived anucleated fragments at wound sites hint at the involvement of this cell subpopulation in wound healing processes, in addition to participation in the encapsulation reaction.
Conclusion
Our observations provide insights into the broad repertoire of blood cell functions required for efficient defense reactions to maintain the homeostasis of the organism. The analysis of the differentiation and function of multinucleated giant hemocytes gives an insight into the diversification of the immune mechanisms.
... ROS is also known to stimulate cytokine production in Drosophila, activating the JAK-STAT and JNK signaling pathways (Morin-Poulard et al. 2013). These ROS molecules trigger systemic production of nitric oxide by activating inducible NO synthase (iNOS). ...
Leishmaniasis transmission cycles are maintained and sustained in nature by the complex crosstalk of the Leishmania parasite, sandfly vector, and the mammalian hosts (human, as well as zoonotic reservoirs). Regardless of the vast research on human host-parasite interaction, there persists a substantial knowledge gap on the parasite’s development and modulation in the vector component. This review focuses on some of the intriguing aspects of the Leishmania-sandfly interface, beginning with the uptake of the intracellular amastigotes from an infected host to the development of the parasite within the sandfly’s alimentary canal, followed by the transmission of infective metacyclic stages to another potential host. Upon ingestion of the parasite, the sandfly hosts an intricate repertoire of immune barriers, either to evade the parasite or to ensure its homeostatic coexistence with the vector gut microbiome. Sandfly salivary polypeptides and Leishmania exosomes are co-egested with the parasite inoculum during the infected vector bite. This has been attributed to the modulation of the parasite infection and subsequent clinical manifestation in the host. While human host–based studies strive to develop effective therapeutics, a greater understanding of the vector-parasite-microbiome and human host interactions could help us to identify the targets and to develop strategies for effectively preventing the transmission of leishmaniasis.
... Results revealed a possible overcome of the natural immunity pathways by L. pseudomesenteroides, by blocking the production of antimicrobial peptides (AMPs) and leading to an increase of gut tissue damage (Hiebert et al. 2020a). However, this study only focused on the JAK/STAT pathway, which is linked to cell proliferation, and response to tissue damage and external stress (Morin-Poulard et al. 2013). Garriga et al. (2020) conducted another study on the humoral and cellular immune response of D. suzukii upon infection with a nematode-bacterial complex, describing the capacity of the bacteria to hinder the production and activity of AMPs and other defence mechanisms, such as the prophenoloxidase system and phagocytosis (Garriga et al. 2020). ...
... A series of 3 SNPs with a lower threshold (5.0 × 10 -08 ) were associated with IGF-II mRNA-binding protein (Imp) (Toledano, D'Alterio, Czech, Levine, & Jones, 2012), which plays a role in the positive regulation of receptor signalling pathway via JAK-STAT. JAK-STAT is a conserved innate immunity pathway in many invertebrates (Dostert et al., 2005;Morin-Poulard, Vincent, & Crozatier, 2013), and with homolog genes in vertebrates (Müller, Pugazhendhi, & Zeidler, 2012). ...
... The Drosophila immune response against bacteria and fungus has been more characterized thanks to extensive work on JAK-STAT (Dostert et al., 2005;Morin-Poulard et al., 2013), IMD, and Toll pathways, and RNA interference (De Gregorio et al., 2002;Prakash et al., 2021;Tanji et al., 2007;Tanji & Ip, 2005;X. H. Wang et al., 2006), however little is known about the immune response towards viral pathogens. ...
Parasites impose high selection pressure on host fitness and are thought to be a major selective factor that promotes the evolution of resistance in host populations. Much of the resistance is determined by genetic factors, however, it is unclear what genetic factors promote resistance to parasites. In this thesis, I used Drosophila melanogaster as a model system to study the genetic basis of resistance against RNA viruses. To understand the genetic basis of infection between different viral and Drosophila genotypes, I investigated two classic models, gene-for-gene and matching-allele models. These models consider that the outcome of the infection depends on the specific compatibility between host and parasite genotypes. Here, I demonstrate that the genetic background of flies explained substantially the resistance against the viral pathogen, which represents an exception to the genotype-by-genotype interaction models. Additionally, I developed an accessible and reproducible protocol to isolate and characterize RNA viruses from wild population of Drosophila. As a result of the protocol, two novel positive-stranded RNA viruses were isolated, La Jolla virus (Iflaviriade) and Newfield virus (Permutotetraviridae). Using RNA sequencing and a customised bioinformatics pipeline, I recovered partial viral genomes which were used to reconstructed their phylogeny. Then, I experimentally explored the impact of the newly isolated viruses on Drosophila infected with Wolbachia, a mutualistic endosymbiotic bacterium that protects the flies against RNA viruses. Furthermore, I determined the host range of these viruses infecting several Drosophila species of the Sophora group. In particular, I evaluated the potential of the novel viruses as biological control agents on the invasive species D. suzukii, one of the most important invasive pests of ripening fruits and wine production worldwide. Finally, I performed a genome-wide association analysis to investigate the genetic variation of resistance to the novel viruses using the Drosophila Genetic Reference Panel. The genome-wide analysis revealed a substantial genetic variation in resistance to the virus isolates, providing new insights into the natural genetic variation in resistance to viruses in Drosophila, and antiviral response in insects.
... Humoral immune responses of insects include the production of antimicrobial peptides (AMPs) [10][11][12], reactive intermediates of oxygen or nitrogen [13,14], and the enzymatic cascades that regulate the melanotic encapsulation of parasites and pathogens [15,16]. Initially, it was reported that the Toll signalling pathway responded to Gr+ bacteria and fungi, the immune deficiency (IMD) pathway to Gr-bacteria, and the JAK-STAT and RNAi pathways to viruses [17][18][19][20]. More recent studies have demonstrated that there is plasticity and cross-talk among and between immune pathways that allow strong multifaceted responses to pathogens and parasites [21][22][23][24]. ...
Common bed bugs, Cimex lectularius, can carry, but do not transmit, pathogens to the vertebrate hosts on which they feed. Some components of the innate immune system of bed bugs, such as antimicrobial peptides (AMPs), eliminate the pathogens. Here, we determined the molecular characteristics, structural properties, and phylogenetic relatedness of two new defensins (CL-defensin1 (XP_024085718.1), CL-defensin2 (XP_014240919.1)), and two new defensin isoforms (CL-defensin3a (XP_014240918.1), CL-defensin3b (XP_024083729.1)). The complete amino acid sequences of CL-defensin1, CL-defensin2, CL-defensin3a, and CL-defensin3b are strongly conserved, with only minor differences in their signal and pro-peptide regions. We used a combination of comparative transcriptomics and real-time quantitative PCR to evaluate the expression of these defensins in the midguts and the rest of the body of insects that had been injected with bacteria or had ingested blood containing the Gram-positive (Gr+) bacterium Bacillus subtilis and the Gram-negative (Gr–) bacterium Escherichia coli. We demonstrate, for the first time, sex-specific and immunization mode-specific upregulation of bed bug defensins in response to injection or ingestion of Gr+ or Gr– bacteria. Understanding the components, such as these defensins, of the bed bugs’ innate immune systems in response to pathogens may help unravel why bed bugs do not transmit pathogens to vertebrates.
... This effector gene is strongly induced by DCV infection, but interestingly not bacteria or fungi, indicating this pathway is virus-specific [107]. Null mutant Hop Drosophila challenged by DCV have reduced expression of vir-1, correlating with a shorter lifespan and a higher viral load [108]. Moreover, this pathway is primarily initiated by viral infection-induced cell damage, not by PAMP recognition [106]. ...
The study of human neurological infection faces many technical and ethical challenges. While not as common as mammalian models, the use of Drosophila (fruit fly) in the investigation of virus–host dynamics is a powerful research tool. In this review, we focus on the benefits and caveats of using Drosophila as a model for neurological infections and neuroimmunity. Through the examination of in vitro, in vivo and transgenic systems, we highlight select examples to illustrate the use of flies for the study of exogenous and endogenous viruses associated with neurological disease. In each case, phenotypes in Drosophila are compared to those in human conditions. In addition, we discuss antiviral drug screening in flies and how investigating virus–host interactions may lead to novel antiviral drug targets. Together, we highlight standardized and reproducible readouts of fly behaviour, motor function and neurodegeneration that permit an accurate assessment of neurological outcomes for the study of viral infection in fly models. Adoption of Drosophila as a valuable model system for neurological infections has and will continue to guide the discovery of many novel virus–host interactions.
... The STAT protein is then phosphorylated and activated, which is translocated as a dimer into the nucleus to regulate target gene transcription (4). In vertebrates, more than 50 cytokines and growth factors are implicated in activating the JAK/STAT pathway through the membrane-located type I cytokine receptors, four intracellular JAKs JAKs (Jak1, Jak2, Jak3, and Tyk2) and seven STATs (STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, and STAT6) have been reported (5,6). In invertebrates, the components of the JAK/STAT pathway are conserved in several arthropod species, but they are simplified-for example, the complete components of the JAK/STAT pathway in Drosophila were identified, with only one JAK (encoded by hopscotch gene, hop), one STAT (encoded by stat92E gene or Marelle), three ligands (encoded by unpaired gene-Upd1, Upd2, and Upd3), one receptor (encoded by Domeless gene, Dome), and a short receptor (encoded by CG14225/latran) (7)(8)(9)(10)(11). ...
The JAK/STAT pathway plays an important role in the development and immune responses of animals. In vertebrates, families of cytokines or growth factors act as activators of the JAK/STAT pathway; however, the activators for the JAK/STAT signaling pathway in arthropods are largely unknown. Herein we report a new ligand, peroxiredoxin 4 (Prx4), for the Domeless in the JAK/STAT pathway of shrimp Marsupenaeus japonicus. Prx4 was induced to secrete into the extracellular surroundings upon Vibrio challenge, which then facilitated the anti-Vibrio activity of shrimp by activating the phosphorylation and nuclear translocation of STAT and the expression of STAT-responsive antimicrobial peptides. Blocking the expression of Prx4 in vivo abrogated the activation of the JAK/STAT pathway by Vibrio infection, while injection of Prx4 protein activated the pathway. The interaction between Prx4 and Domeless was proved by immuno-precipitation and protein pull-down assays. Moreover, two cysteine residues in Prx4 that are critical for the interaction and Prx4’s anti-Vibrio role were identified, and the binding site in Domeless for Prx4 was proved to be the cytokine-binding homology module fragment. Taken together, our study revealed a new function for Prx4 enzyme and established a new enzyme-type ligand for the activation of the JAK/STAT pathway in an aquatic arthropod.
... In addition, the protein inhibitor of activated STATs (PIAS) inactivates STAT through direct binding [reviewed in (10)(11)(12)]. Graphical representations of the Jak-STAT pathway in insects can be found in several reviews (10,13,14). ...
Phlebotomine sand flies (Diptera, Psychodidae) belonging to the Lutzomyia genus transmit zoonoses in the New World. Lutzomyia longipalpis is the main vector of Leishmania infantum , which is the causative agent of visceral leishmaniasis in Brazil. To identify key molecular aspects involved in the interaction between vector and pathogens and contribute to developing disease transmission controls, we investigated the sand fly innate immunity mediated by the Janus kinase/signal transducer and activator of transcription (Jak-STAT) pathway in response to L. infantum infection. We used two study models: L. longipalpis LL5 embryonic cells co-cultured with L. infantum and sand fly females artificially infected with the parasite. We used qPCR to follow the L. longipalpis gene expression of molecules involved in the Jak-STAT pathway. Also, we modulated the Jak-STAT mediated immune response to understand its role in Leishmania parasite infection. For that, we used RNAi to silence the pathway regulators, protein inhibitor of activated STATs (PIAS) in LL5 cells, and STAT in adult females. In addition, the pathway suppression effect on parasite development within the vector was assessed by light microscopy in late-phase infection. The silencing of the repressor PIAS in LL5 cells led to a moderate increase in a protein tyrosine phosphatase 61F (PTP61F) expression. It suggests a compensatory regulation between these two repressors. L. infantum co-culture with LL5 cells upregulated repressors PIAS, suppressor of cytokine signaling (SOCS), and PTP61F. It also downmodulated virus-induced RNA-1 (VIR-1), a pathway effector, indicating that the parasite could repress the Jak-STAT pathway in LL5 cells. In Leishmania -infected L. longipalpis females, STAT and the antimicrobial peptide attacin were downregulated on the third day post-infection, suggesting a correlation that favors the parasite survival at the end of blood digestion in the sand fly. The antibiotic treatment of infected females showed that the reduction of gut bacteria had little effect on the Jak-STAT pathway regulation. STAT gene silencing mediated by RNAi reduced the expression of inducible nitric oxide synthase (iNOS) and favored Leishmania growth in sand flies on the first day post-infection. These results indicate that STAT participated in the iNOS regulation with subsequent effect on parasite survival.
... The JAK-STAT signal transduction pathway controls haemocyte proliferation in Drosophila larvae, together with the Toll signalling pathway [91,109,110]. For example, the lamellocyte-active enhancer located within the misshapen (encodes a protein kinase within the Jun Nterminal kinase signalling pathway that functions to form an active AP-1 complex) likely serves as a transcriptional target within an activated JNK auto-regulatory circuit that functions to continuously promote the differentiation of lamellocytes from a progenitor haemocyte population [111]. ...
... Changes in expression of JAK-STAT and Toll genes have been observed post parasitization by Leptopilina parasitoids. Also, overproliferation and differentiation of haemocytes following parasitization were observed [109]. Mutations in different genes in these pathways lead to over proliferation of lamellocytes and the development of tumor [112]. ...
The host defense of insects includes a combination of cellular and humoral responses. The cellular arm of the insect innate immune system includes mechanisms which are directly mediated by hemocytes (e.g., phagocytosis, nodulation, and encapsulation). In addition, melanization accompanying coagulation, clot formation, and wound healing, nodulation, and encapsulation processes lead to the formation of cytotoxic redox‐cycling melanin precursors and reactive oxygen and nitrogen species. However, demarcation between cellular and humoral immune reactions as two distinct categories is not straightforward. This is because many humoral factors affect hemocyte functions and hemocytes themselves are an important source of many humoral molecules. There is also a considerable overlap between cellular and humoral immune functions that span from recognition of foreign intruders to clot formation. Here we review these immune reactions starting with the cellular mechanisms that limit hemolymph loss and participate in wound healing and clot formation and advancing to cellular functions that are critical in restricting pathogen movement and replication. This information is important because it highlights that insect cellular immunity is controlled by a multilayered system, different components of which are activated by different pathogens or during the different stages of the infection.
