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The course of Plasmodium chabaudi chabaudi infections in interferon-γ receptor deficient mice
Abstract
Interferon-gamma receptor (IFN-gamma R) deficient mice parasitized with blood-stage Plasmodium chabaudi chabaudi were used to assess the anti-malarial activity of interferon-gamma (IFN-gamma). There was no significant difference in the parasitaemia between the two types of mice during the first peak of parasitaemia. However, IFN-gamma R deficient mice displayed an increased leucocytosis and a high mortality rate, whereas all of the wild type mice survived. IFN-gamma R deficient mice, unlike wild type mice, developed a pronounced second parasitaemia peak, 9 to 11 days after the first one, with a parasitaemia of up to 65% associated with mortality. Furthermore, increased serum levels of nitric oxide (NO) were only found in wild type mice at the peak of parasitaemia, whereas it remained at background levels in IFN-gamma R deficient mice. Parasite-specific antibody production was not significantly different in IFN-gamma R deficient mice, as compared to wild type mice. In addition, both wild type and IFN-gamma R deficient mice were equally protected upon reinfection. These results indicate a delayed development of protective immunity and imply a crucial function for the IFN-gamma R in the control of blood stage malaria during the initial three weeks of infection.
... However, its role is still controversial. Some researchers claim that cerebral malaria is probably an unfortunate consequence of high amounts of NO production to promote the death of the parasites [26,27] while others support the idea that cerebral malaria results from a low bioavailability of this compound [28]. ...
... They have reached this conclusion by comparing serum nitric oxide levels in Plasmodium infected mice and humans against control levels in mice and human individuals. These studies conclude that nitrite and nitrate levels (NN-stable metabolites of NO) in infected individuals do not differ from control levels, and even with an increased NN serum concentration during the blood-stage of malaria, parasitemia is not different compared to control values [26,35,[81][82][83][84][85][86][87]. ...
... Studies indicate that NO produced by iNOS activation plays an important role in killing several pathogens, including Plasmodium [96]. However, recent studies in animal models have shown that NOS deficiency or inhibition is not enough for protection against P. berghei [26,82,86,97] but hemozoin induces NO formation via iNOS [20] and the increase in monocyte count may be associated with high levels of mRNA of this enzyme [65]. ...
Several studies have evaluated the oxidant and antioxidant status of thalassemia patients but most focused mainly on the severe and intermediate states of the disease. Moreover, the oxidative status has not been evaluated for the different beta-thalassemia mutations.
To evaluate lipid peroxidation and Trolox equivalent antioxidant capacity in relation to serum iron and ferritin in beta thalassemia resulting from two different mutations (CD39 and IVS-I-110) compared to individuals without beta-thalassemia.
One hundred and thirty subjects were studied, including 49 who were heterozygous for beta-thalassemia and 81 controls. Blood samples were subjected to screening tests for hemoglobin. Allele-specific polymerase chain reaction was used to confirm mutations for beta-thalassemia, an analysis of thiobarbituric acid reactive species was used to determine lipid peroxidation, and Trolox equivalent antioxidant capacity evaluations were performed. The heterozygous beta-thalassemia group was also evaluated for serum iron and ferritin status.
Thiobarbituric acid reactive species (486.24 ± 119.64 ng/mL) and Trolox equivalent antioxidant capacity values (2.23 ± 0.11 mM/L) were higher in beta-thalassemia heterozygotes compared to controls (260.86 ± 92.40 ng/mL and 2.12 ± 0.10 mM/L, respectively; p-value < 0.01). Increased thiobarbituric acid reactive species values were observed in subjects with the CD39 mutation compared with those with the IVS-I-110 mutation (529.94 ± 115.60 ng/mL and 453.39 ± 121.10 ng/mL, respectively; p-value = 0.04). However, average Trolox equivalent antioxidant capacity values were similar for both mutations (2.20 ± 0.08 mM/L and 2.23 ± 0.12 mM/L, respectively; p-value = 0.39). There was no influence of serum iron and ferritin levels on thiobarbituric acid reactive species and Trolox equivalent antioxidant capacity values.
This study shows an increase of oxidative stress and antioxidant capacity in beta-thalassemia heterozygotes, mainly in carriers of the CD39 mutation.
... However, its role is still controversial. Some researchers claim that cerebral malaria is probably an unfortunate consequence of high amounts of NO production to promote the death of the parasites [26,27] while others support the idea that cerebral malaria results from a low bioavailability of this compound [28]. Additionally, host-parasite interactions are quite complex and promote constant changes in the delicate balance between pro-oxidant and antioxidant molecules since the host and parasite are capable of producing both. ...
... They have reached this conclusion by comparing serum nitric oxide levels in Plasmodium infected mice and humans against control levels in mice and human individuals. These studies conclude that nitrite and nitrate levels (NN—stable metabolites of NO) in infected individuals do not differ from control levels, and even with an increased NN serum concentration during the blood-stage of malaria, parasitemia is not different compared to control values [26,35,81828384858687. Sobolewski et al. [35] also questioned the role of NO in the progression of malaria parasitemia, stating that intraerythrocytic Plasmodia are protected from reactive oxygen species by hemoglobin, occurring naturally in high concentrations within red blood cells (RBC), requiring levels of reactive oxygen species that surpass hemoglobin protection. ...
... Studies indicate that NO produced by iNOS activation plays an important role in killing several pathogens, including Plasmodium [96]. However, recent studies in animal models have shown that NOS deficiency or inhibition is not enough for protection against P. berghei [26,82,86,97] but hemozoin induces NO formation via iNOS [20] and the increase in monocyte count may be associated with high levels of mRNA of this enzyme [65]. In contrast, NO produced by endothelial NOS on all tissues acts as blood flow regulator, causing vasodilatation, preventing platelet aggregation and inhibiting adhesion of lymphocytes and monocytes to to endothelium [77,79], which prevents local ischemia. ...
Malaria is a significant public health problem in more than 100 countries and causes an estimated 200 million new infections every year. Despite the significant effort to eradicate this dangerous disease, lack of complete knowledge of its physiopathology compromises the success in this enterprise. In this paper we review oxidative stress mechanisms involved in the disease and discuss the potential benefits of antioxidant supplementation as an adjuvant antimalarial strategy.
... Studies in mice models indicated that treatment of mice infected with blood-stage P. berghei by anti-IFN-γ antibody failed to control the infection parasites 69,70 . Additionally, delayed parasite elimination was found among IFN-γ-deficient [71][72][73] . During Plasmodium infection, γδ T-cells that express CD40 ligand produce IFN-γ in response to infection by enhancement of dendritic cell activation to remove malaria parasites 74 . ...
Interferon (IFN)-γ contributes to the pathogenesis of severe malaria; however, its mechanism remains unclear. Herein, differences in IFN-γ levels between patients with severe and uncomplicated malaria were evaluated using qualitative and quantitative (meta-analysis) approaches. The systematic review protocol was registered at PROSPERO (ID: CRD42022315213). The searches for relevant studies were performed in five databases, including PubMed, Scopus, Embase, MEDLINE and Web of Science, between 1 January and 10 July 2022. A meta-analysis was conducted to pool the mean difference (MD) of IFN-γ levels between patients with severe malaria and those with uncomplicated malaria using a random-effects model (DerSimonian and Laird method). Overall, qualitative synthesis indicated that most studies (14, 58.3%) reported no statistically significant difference in IFN-γ levels between patients with severe malaria and those with uncomplicated malaria. Meanwhile, remaining studies (9, 37.5%) reported that IFN-γ levels were significantly higher in patients with severe malaria than those in patients with uncomplicated malaria. Only one study (4.17%) reported that IFN-γ levels were significantly lower in patients with severe malaria than those in patients with uncomplicated malaria. The meta-analysis results indicated that patients with severe malaria had higher mean IFN-γ levels than those with uncomplicated malaria (p < 0.001, MD: 13.63 pg/mL, 95% confidence interval: 6.98–20.29 pg/mL, I²: 99.02%, 14 studies/15 study sites, 652 severe cases/1096 uncomplicated cases). In summary, patients with severe malaria exhibited higher IFN-γ levels than those with uncomplicated malaria, although the heterogeneity of the outcomes is yet to be elucidated. To confirm whether alteration in IFN-γ levels of patients with malaria may indicate disease severity and/or poor prognosis, further studies are warranted.
... A deficiency of cytokines such as IL-2 and interferon (IFN)gamma exacerbates the parasitemia of P. chabaudi [37,38]. Deleting the IFN-gamma receptor resulted in high parasitemia and mortality of P. chabaudi infection [39]. Increased susceptibility to non-lethal malarial strains in immune deficit models is similar to that observed in Nmnat3 KO mice, suggesting the possibility of decreased immune response in Nmnat3-deficient animals. ...
Malaria is an infectious disease caused by Plasmodium parasites and has high mortality rates, especially among children in African and Southeast Asian countries. Patients with hemolytic anemia are suggested to adapt protective measures against malarial infection. Nicotinamide adenine dinucleotide (NAD⁺) is a crucial cofactor associated with numerous biological processes that maintain homeostasis in all living organisms. In a previous study, we had demonstrated that the deficiency of nicotinamide mononucleotide adenylyltransferase 3 (Nmnat3), an enzyme catalyzing NAD⁺ synthesis, causes hemolytic anemia accompanied by a drastic decline in the NAD⁺ levels in the erythrocytes. It is well known that hemolytic anemia is linked to a reduced risk of malarial infections. In the present study, we investigated whether hemolytic anemia caused by Nmnat3 deficiency is beneficial against malarial infections. We found that Nmnat3 deficiency exacerbated malarial infection and subsequently caused death. Moreover, we demonstrated that the NAD + levels in malaria-infected Nmnat3 red blood cells significantly increased and the glycolytic flow was largely enhanced to support the rapid growth of malarial parasites. Our results revealed that hemolytic anemia induced by the deletion of Nmnat3 was harmful rather than protective against malaria.
... The role of (NO) in the protection against malaria infection remains controversial (Percário et al. 2012). Previous studies suggested that the generation of reactive nitrogen and oxygen species could play a crucial role in the development of the systemic complications caused by severe malaria infection (Favre et al. 1997;Maneerat et al 2000). Cerebral malaria (CM) is an unfavourable outcome of high amounts of (TNF-a)-induced (NO) production (Clark et al. 1991). ...
The complex interaction between the host and the parasite remains a puzzling question. Control of parasitic infections requires an efficient immune response that must be balanced against destructive pathological consequences. Nitric oxide is a nitrogenous free radical which has many molecular targets and serves diverse functions. Apart from being a signaling messenger, nitric oxide is critical for controlling numerous infections. There is still controversy surrounding the exact role of nitric oxide in the immune response against different parasitic species. It proved protective against intracellular protozoa, as well as extracellular helminths. At the same time, it plays a pivotal role in stimulating detrimental pathological changes in the infected hosts. Several reports have discussed the anti-parasitic and immunoregulatory functions of nitric oxide, which could directly influence the control of the infection. Nevertheless, there is scarce literature addressing the harmful cytotoxic impacts of this mediator. Thus, this review provides insights into the most updated concepts and controversies regarding the dual nature and opposing sides of nitric oxide during the course of different parasitic infections.
... In the case of P. falciparum infections, irf1 expression has been associated with control of the parasite (Mangano et al., 2008). In Plasmodium infections of mice initiated with SBP parasites, IFN-dependent and macrophage responses in the spleen are important in controlling acute blood-stage parasitaemia, with IFN signatures, ISG sand type I IFNs upregulated (Araujo et al., 2012;Favre et al., 1997;Gun et al., 2014;Kim et al., 2008Kim et al., , 2012Li et al., 1999;Meding et al., 1990;Su and Stevenson, 2000;Yoneto et al., 1999). Although the numbers of splenic IFNγ-producing NK, NK1.1 + NKT, γδ T cells and αβ T cells observed here in RMT and SBP P. chabaudi infections within the first 7 days of infection were similar, our comparative transcriptome analysis showed small but consistently higher expression levels of a number of irf genes, such as irf1, which mediates signalling of type I/II IFNs, and regulates antigen-presentation, and irf7 which is a master regulator of Type I IFN (Negishi et al., 2018). ...
Natural infection with Plasmodium parasites, the causative agents of malaria, occurs via mosquito vectors. However, most of our knowledge of the immune response to the blood stages of Plasmodium is from infections initiated by injection of serially blood-passaged infected red blood cells, resulting in an incomplete life cycle in the mammalian host. Vector transmission of the rodent malaria parasite, Plasmodium chabaudi chabaudi AS has been shown to give rise to a more attenuated blood-stage infection in C57Bl/6J mice, when compared to infections initiated with serially blood-passaged P. chabaudi-infected red blood cells. In mouse models, the host immune response induced by parasites derived from natural mosquito transmission is likely to more closely resemble the immune responses to Plasmodium infections in humans. It is therefore important to determine how the host response differs between the two types of infections.
As the spleen is considered to be a major contributor to the protective host response to P. chabaudi, we carried out a comparative transcriptomic analysis of the splenic response to recently mosquito-transmitted and serially blood-passaged parasites in C57Bl/6J mice. The attenuated infection arising from recently mosquito-transmitted parasites is characterised by an earlier and stronger myeloid- and IFNγ-related response. Analyses of spleen lysates from the two infections similarly showed stronger or earlier inflammatory cytokine and chemokine production in the recently mosquito-transmitted blood-stage infections. Furthermore, tissue macrophages, including red pulp macrophages, and IFNγ-signalling in myeloid cells, are required for the early control of P. chabaudi recently mosquito-transmitted parasites, thus contributing to the attenuation of mosquito-transmitted infections.
The molecules responsible for this early activation response to recently-transmitted blood-stage parasites in mice would be important to identify, as they may help to elucidate the nature of the initial interactions between blood-stage parasites and the host immune system in naturally transmitted malaria.
... The result showing the delay in IFN-g peak production with LPS preconditioning may be tied to the reduction in parasite burden seen in these mice. However, mice deficient in IFN-g or its receptor were reported to have strongly suppressed protective immunity against infection with nonlethal malaria parasites (21,22). In contrast, these mice have shown significant reductions in cerebral malaria and liver damage caused by infection with lethal malaria parasites (23-25). ...
Malaria remains a grave concern for humans, as effective medical countermeasures for Plasmodium infection have yet to be developed. Phagocytic clearance of parasitized red blood cells (pRBCs) by macrophages is an important front-line innate host defense against Plasmodium infection. We previously showed that repeated injections of low-dose lipopolysaccharide (LPS) prior to bacterial infection, called LPS preconditioning, strongly augmented phagocytic/bactericidal activity in murine macrophages. However, if LPS preconditioning prevents murine Plasmodium infection is unclear. We investigated the protective effects of LPS preconditioning against lethal murine Plasmodium infection, focusing on CD11b high F4/80 low liver macrophages, which are increased by LPS preconditioning. Mice were subjected to LPS preconditioning by intraperitoneal injections of low-dose LPS for 3 consecutive days, and 24 h later, they were intravenously infected with pRBCs of Plasmodium yoelii 17XL. LPS preconditioning markedly increased the murine survival and reduced parasitemia, while it did not reduce TNF secretions, only delaying the peak of plasma IFN-γ after Plasmodium infection in mice. An in vitro phagocytic clearance assay of pRBCs showed that the CD11b high F4/80 low liver macrophages, but not spleen macrophages, in the LPS-preconditioned mice had significantly augmented phagocytic activity against pRBCs. The adoptive transfer of CD11b high F4/80 low liver macrophages from LPS-preconditioned mice to control mice significantly improved the survival after Plasmodium infection. We conclude that LPS preconditioning stimulated CD11b high F4/80 low liver macrophages to augment the phagocytic clearance of pRBCs, which may play a central role in resistance against Plasmodium infection.
... The higher rate of mortality and morbidity in IFN-γ knock-out mice was observed upon challenged with P. Chabaudi. These findings gave valuable insights to the crucial role played by this CMI effecter to control parasitemia and survival of the host during primary infection [70][71][72]. Recent studies, as earlier [73,74], has confirmed the requirement of IFN-γ responses to several pre-erythrocytic and blood-stage P. falciparum vaccine candidates as decrease was seen in the absence of malaria transmission. ...
Transdermal immunization exhibits poor immunogenic responses due to poor permeability of antigens through the skin. Elastic liposomes, the ultradeformable nanoscale lipid vesicles, overcome the permeability issues and prove a versatile nanocarrier for transcutaneous delivery of protein, peptide, and nucleic acid antigens. Elastic liposome-mediated subcutaneous delivery of chimeric fusion protein (PfMSP-Fu24) of Plasmodium falciparum exhibited improved immunogenic responses. Elastic liposomes-mediated immunization of PfMSP-Fu24 conferred immunity to the asexual blood-stage infection. Present study is an attempt to compare the protective immune response mounted by the PfMSP-Fu24 upon administered through transdermal and intramuscular routes. Humoral and cell-mediated immune (CMI) response elicited by topical and intramuscularly administered PfMSP-Fu24-laden elastic liposomes (EL-PfMSP-Fu24) were compared and normalized with the vehicle control. Sizeable immune responses were seen with the transcutaneously immunized EL-PfMSP-Fu24 and compared with those elicited with intramuscularly administered antigen. Our results show significant IgG isotype subclass (IgG1and IgG3) response of specific antibody levels as well as cell-mediated immunity (CMI) activating factor (IFN-γ), a crucial player in conferring resistance to blood-stage malaria in mice receiving EL-PfMSP-Fu24 through transdermal route as compared to the intramuscularly administered formulation. Heightened immune response obtained by the vaccination of EL-PfMSP-Fu24 was complemented by the quantification of the transcript (mRNA) levels cell-mediated (IFN-γ, IL-4), and regulatory immune response (IL-10) in the lymph nodes and spleen. Collectively, elastic liposomes prove their immune-adjuvant property as they evoke sizeable and perdurable immune response against PfMSP-Fu24 and justify its potential for the improved vaccine delivery to inducing both humoral and CM immune response.
... IFN-c, a key cytokine of the systemic immune response produced by both innate and adaptive immune cells, has been implicated in the protective immunity to Pf infection. [34][35][36][37][38][39] In humans, IFN-c concentration is correlated with protection from symptomatic malaria 40 and resistance to Pf reinfection. 41,42 Ex vivo studies have demonstrated that natural killer (NK) cells are the major source of IFN-c during the very early immune response following Pf infection. ...
Objectives
The sickle‐cell trait phenotype is associated with protection from malaria. Multiple molecular mechanisms have been proposed to explain this protection, but the role of the host immune system has been poorly investigated. We hypothesised that cellular immunity to malaria may develop differently in sickle‐cell trait children (HbAS) and children with normal haemoglobin (HbAA) repeatedly exposed to Plasmodium falciparum (Pf).
Methods
Paired samples collected prior to the Pf transmission season and during the first malaria episode of the ensuing transmission season from HbAS and HbAA children were analysed by multiplex bead‐based assay and comprehensive multi‐dimensional flow cytometry profiling.
Results
Cellular immune profiles were enriched in HbAS relative to HbAA children before the start of the Pf transmission season, with a distinct NK subset. These cells were identified as a novel subset of memory‐activated NK cells characterised by reduced expression of the ecto‐enzyme CD38 as well as co‐expression of high levels of HLA‐DR and CD45RO. The frequency of this NK subset before the transmission season was negatively correlated with parasite density quantified during the first malaria episode of the ensuing transmission season. Functional assessment revealed that these CD38dim CD45RO⁺ HLA‐DR⁺ NK cells represent a important source of IFN‐γ.
Conclusion
Our data suggest that this novel memory‐activated NK cell subset may contribute to an accelerated and enhanced IFN‐γ‐mediated immune response and to control of parasite density in individuals with the sickle‐cell trait. This distinct cellular immune profile may contribute to predispose HbAS children to a relative protection from malaria.
... sFGL2 promotes parasite growth through impeding the production of IFN- secreted by NK/NKT cells Next, we sought to determine whether sFGL2 enhances parasite growth by manipulating the innate immune response against bloodstage infection. Given that IFN- plays a central role in the innate immune response against malaria blood-stage infection (25)(26)(27), we compared the serum IFN- levels of parasite-infected WT and FGL2 −/− mice. Consistent with reduced parasitemia, the IFN- level in FGL2 −/− mice was much higher than that in WT mice at 6 days after infection ( Fig. 2A). ...
Malaria parasites suppress host immune responses to facilitate their survival, but the underlying mechanism remains elusive. Here, we found that blood-stage malaria parasites predominantly induced CD4 ⁺ Foxp3 ⁺ CD25 ⁺ regulatory T cells to release soluble fibrinogen-like protein 2 (sFGL2), which substantially enhanced the infection. This was attributed to the capacity of sFGL2 to inhibit macrophages from releasing monocyte chemoattractant protein-1 (MCP-1) and to sequentially reduce the recruitment of natural killer/natural killer T cells to the spleen and the production of interferon-γ. sFGL2 inhibited c-Jun N-terminal kinase phosphorylation in the Toll-like receptor 2 signaling pathway of macrophages dependent on FcγRIIB receptor to release MCP-1. Notably, sFGL2 were markedly elevated in the sera of patients with malaria, and recombinant FGL2 substantially suppressed Plasmodium falciparum from inducing macrophages to release MCP-1. Therefore, we highlight a previously unrecognized immune suppression strategy of malaria parasites and uncover the fundamental mechanism of sFGL2 to suppress host innate immune responses.
... This finding is in line with a study in Poland by Wroczynska et al. (2005), who reported that the mean serum level of IFN-γ was found to be significantly higher in severe and uncomplicated malaria groups compared to the controls. Also, another study done by Favre et al. (1997) reported that these findings are consistent with a requirement for an early production of IFN-γ to mount resistance against infection. Interestingly, in this study, a significant correlation between IL-10 with gender and age was found. ...
... This finding is in line with a study in Poland by Wroczynska et al. (2005), who reported that the mean serum level of IFN-γ was found to be significantly higher in severe and uncomplicated malaria groups compared to the controls. Also, another study done by Favre et al. (1997) reported that these findings are consistent with a requirement for an early production of IFN-γ to mount resistance against infection. Interestingly, in this study, a significant correlation between IL-10 with gender and age was found. ...
... This finding is in line with a study in Poland by Wroczynska et al. (2005), who reported that the mean serum level of IFN-γ was found to be significantly higher in severe and uncomplicated malaria groups compared to the controls. Also, another study done by Favre et al. (1997) reported that these findings are consistent with a requirement for an early production of IFN-γ to mount resistance against infection. Interestingly, in this study, a significant correlation between IL-10 with gender and age was found. ...
Background: The cytokines interferon gamma (IFN-γ), interleukin-10 (IL-10) and tumor necrosis factor-α (TNF- α) play an important role in malaria infection. The aim of this study was to determine the prevalence of malaria and to evaluate cytokine responses to malaria infection in patients from the East Nile locality of Khartoum State.
Methods: This study was carried out from May to July 2018 in the East Nile Locality, Khartoum State. Blood samples were collected from 384 randomly selected patients for blood film analysis. Of these, 39 were selected for cytokine level analysis (10 control and 29 patient samples), determined using enzyme-linked immunosorbent assays.
Results: The malaria prevalence rate among 384 patients was 18.5%. Plasmodiumfalciparum was the most prevalent (13%), while the prevalence of Plasmodiumvivax was 4.6%. The rate of mixed infection was 0.8%. There was a higher prevalence rate (22.7%) in males than females (15.6%). However, we found no significant correlation between cytokine levels and parasitemia in the study group. Nevertheless, our study demonstrated a significant correlation between cytokine levels and recurrent infections.
Conclusions: Together, our data show that malaria remains a public health problem in East Nile locality with a high prevalence. Additionally, cytokine levels were found to be correlated with recurrent malaria infection.
... TCD8 + cells are able to cause the elimination of host-infected cells by redundant mechanisms in which INFy and TNF are identified as cytokines playing an important role during malaria infection [11]. This resistance in mice is dependent on signals related to the early production of INFy, IL-12, and TNFα [12,13] in humans. ...
... Another important cytokine implicated in the early inflammatory response and essential for controlling the initial wave of parasitaemia in mice is IFN-γ release by NK cells and γδ + T cell that strongly expanded during the early phases of malaria infection ( Fig. 9) (Hensmann and Kwiatkowski, 2001;Inoue et al., 2013;Stevenson and Riley, 2004), and enhances phagocyte activity, resulting in the elimination of extracellular parasites. Indeed, IFN-γ deletion during P. chabaudi infection led to impaired cytokine responses, uncontrolled parasitemia and increased mortality (Favre et al., 1997;Su and Stevenson, 2000). Additionally, IL-12p40 subunit deficiency in resistant mice reduced IFN-γ induction and increased mortality (Su and Stevenson, 2002), while administration of recombinant IL-12 to susceptible mice enhanced IFN-γ production, parasite control, and survival (Stevenson et al., 1995). ...
Recent findings have raised the hypothesis that clinical susceptibility to malaria may be related to allergy-type response. In human infection with P. falciparum, as well as in murine models of malaria, increased levels of histamine have been shown to be associated with disease severity. Histamine releasing factor (HRF), shown to be implicated in the release of pro-inflammatory histamine during late-phase allergy, was demonstrated to be produced by the parasite during mild and severe malaria infections suggesting that Plasmodium HRF may affect host immune responses and contributes to the pathogenesis. The objectives of this work were to evaluate the role of Plasmodium HRF in the development of the immune response and to determine whether its expression is associated with the severity of malaria disease by studying two HRF-deficient (hrfΔ) murine parasites (PbANKA and PbNK65). Infection with PbANKA-hrfΔ sporozoites showed a decrease in the frequency of ECM due to the impairment of the development of the mutant parasites in liver stages as a consequence of the up-regulation of IL-6. Infection with PbNK65-hrfΔ parasites confirmed the importance of HRF in enhancing the virulence of the parasite. Indeed, PbNK65-hrfΔ infection results in parasite clearance leading to a long-lasting protection and immune memory as reflected by an up-regulation of IL-6, a down-regulation of PD-1 expression on T cells and in the enhancement of Ab-mediated phagocytosis. HRF is the first parasite gene which directly modulates the host immune response.
... Nevertheless, strong parasite-specific cellular immune responses were observed, including the production of gamma interferon (IFN-␥) and nitric oxide synthase (26). An association of protection with the production of IFN-␥, tumor necrosis factor (TNF), and interleukin-2 (IL-2) by T cells following parasite stimulation has been noted in various studies (10,27,(29)(30)(31)(32)(33)(34)(35)(36)(37). IFN-␥ and TNF have also been associated with NAI in humans (38)(39)(40)(41); additionally, protective antibody responses to blood-stage parasites are well recognized in NAI (42,43). ...
Naturally acquired immunity to malaria is robust and protective against all strains of the same species of Plasmodium. This develops as a result of repeated natural infection, taking several years to develop. Evidence suggests that apoptosis of immune lymphocytes due to uncontrolled parasite growth contributes to the slow acquisition of immunity. To hasten and augment the development of natural immunity, we studied controlled infection immunization (CII) using low dose exposure to different parasite species (P. chabaudi, P. yoelii or P. falciparum) in two rodent systems (BALB/c and C57BL/6) and in human volunteers, with drug therapy commencing at the time of initiation of infection. CIIs with infected erythrocytes and in conjunction with doxycycline or azithromycin, which are ‘delayed death’ drugs targeting the parasite’s apicoplast, allow extended exposure to parasites at low levels. In turn, this induces strong protection in all immunized mice against homologous challenge. We show that P. chabaudi/P. yoelii infection initiated at the commencement of doxycycline therapy leads to cellular or antibody-mediated protective immune responses in mice, with a broad Th1 cytokine response providing the best correlate of protection against homologous and heterologous species of Plasmodium. P. falciparum CII with doxycycline was additionally tested in a pilot clinical study (n=4) and was found to be well tolerated and immunogenic, with immunological studies primarily detecting increased cellular-associated immune responses. Furthermore, we report that a single dose of the longer-acting drug, azithromycin, given to mice (n=5) as a single subcutaneous treatment at the initiation of infection controlled P. yoelii infection and protected all mice against subsequent challenge.
... Previous studies using a rodent model of malaria showed that CD4 + T-cell-depleted mice fail to control Plasmodium infection, [5][6][7][8] as is the case with interferon-c (IFN-c)-signalling-deficient mice. 2,[9][10][11][12][13] IFN-c-signalling-deficient mice may exhibit decreased dendritic cell activation and T helper type 1 (Th1) responses during infection. 9 Therefore, both cellular and humoral immunities are crucial for protective immunity against Plasmodium infection. ...
It is unclear whether γδ T cells are involved in humoral immunity against Plasmodium infection. Here, we show that B cell‐immunodeficient mice and γδ T cell‐deficient mice were incapable of protecting against Plasmodium berghei XAT parasites. γδ T cell‐deficient mice developed reduced levels of antigen‐specific antibodies during the late phase of infection. The numbers of follicular helper T cells and germinal centre B cells in γδ T cell‐deficient mice were lower than in wild‐type mice during the late phase of infection. Expression profiling of humoral immunity‐related cytokines in γδ T cells showed that IL‐21 and IFN‐γ are increased during the early stage of infection. Furthermore, blockade of IL‐21 and IFN‐γ signalling during the early stage of infection led to reduction in follicular helper T cells and germinal centre B cells. γδ T cell‐production of IL‐21 and IFN‐γ is crucial for the development and maintenance of follicular helper T cells and germinal centre B cells during the late phase of infection. Our data suggest that γδ T cells modulate humoral immunity against Plasmodium infection.
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... Involvement of CD4 T cells, and IFNγ cytokine has been shown to confer protective immunity against various protozoan pathogens during mammalian infection (Favre et al., 1997;Igarashi et al., 1999;Hemmer et al., 2000a;Hoft et al., 2000;Wang et al., 2004;McCall and Sauerwein, 2010). Previous studies showed that although not essential, CD4 T cells and IFNγ also play important roles in protective immunity against B. microti infection in mice (Igarashi et al., 1999;Hemmer et al., 2000a,b;Skariah et al., 2017). ...
Babesia microti is a malaria-like parasite, which infects ∼2000 people annually, such that babesiosis is now a notifiable disease in the United States. Immunocompetent individuals often remain asymptomatic and are tested only after they feel ill. Susceptible C3H/HeJ mice show several human-like disease manifestations and are ideal to study pathogenesis of Babesia species. In this study, we examined parasitemia of B. microti at different time points and assessed its impact on hemoglobin levels in blood, on spleen pathology and overall immune response in C3H/HeJ mice. Peak parasitemia of 42.5% was immediately followed by diminished hemoglobin level. Parasitemia at 21 days of infection was barely detectable by microscopy presented 5.7 × 108 to 5.9 × 109 B. microti DNA copies confirming the sensitivity of our qPCR. We hypothesize that qPCR detects DNA released from recently lysed parasites or from extracellular B. microti in blood, which are not easily detected in blood smears and might result in under-diagnosis of babesiosis in patients. Splenectomized patients have been reported to show increased babesiosis severity and result in high morbidity and mortality. These results emphasize the importance of splenic immunity in resolution of B. microti infection. Splenomegaly in infected mice associated with destruction of marginal zone with lysed erythrocytes and released B. microti life forms in our experiments support this premise. At conclusion of the experiment at 21 days post-infection, significant splenic B and T cells depletion and increase in macrophages levels were observed in B. microti infected mice suggesting a role of macrophage in disease resolution. Infected mice also showed significantly higher plasmatic concentration of CD4 Th1 cells secreted cytokines such as IL-2 and IFN-γ while cytokines such as IL-4, IL-5, and IL-13 secreted by Th2 cells increase was not always significant. Thus, Th1 cells-mediated immunity appears to be important in clearance of this intracellular pathogen. Significant increase in IL-6 that promotes differentiation of Th17 cells was observed but it resulted in only moderate change in IL-17A, IL-17F, IL-21, and IL-22, all secreted by Th17 cells. A similar immune response to Trypanosoma infection has been reported to influence the clearance of this protozoan, and co-infecting pathogen(s).
... IFN-γ produced by activated T cells has been shown to be critical for immune protection in various studies 22,32,[56][57][58][59][60][61] . Mice deficient in IFN-γ signaling have a delayed parasitemia resolution 62,63 , and IFN-γ and IFN-γ-induced chemokines are required for mobilization of myeloid progenitors to the spleen during P. chabaudi infection 49 . Elevated levels of IFN-γ are also correlated with natural resistance to P. falciparum infection in the Malian Fulani population 56 . ...
Malaria is a fatal disease that displays a spectrum of symptoms and severity, which are determined by complex host-parasite interactions. It has been difficult to study the effects of parasite strains on disease severity in human infections, but the mechanisms leading to specific disease phenotypes can be investigated using strains of rodent malaria parasites that cause different disease symptoms in inbred mice. Using a unique mouse malaria model, here we investigated the mechanisms of splenic cell death and their relationship to control of parasitemia and host mortality. C57BL/6 mice infected with Plasmodium yoelii nigeriensis N67C display high levels of pro-inflammatory cytokines and chemokines (IL-6, IFN-γ, TNF-α, CXCL1, and CCL2) and extensive splenic damage with dramatic reduction of splenic cell populations. These disease phenotypes were rescued in RAG2−/−, IFN-γ−/−, or T cell depleted mice, suggesting IFN-γ and T cell mediated disease mechanisms. Additionally, apoptosis was one of the major pathways involved in splenic cell death, which coincides with the peaks of pro-inflammatory cytokines. Our results demonstrate the critical roles of T cells and IFN-γ in mediating splenic cell apoptosis, parasitemia control, and host lethality and thus may provide important insights for preventing/reducing morbidity associated with severe malaria in humans.
... Human hepcidin possesses 25 amino acid residues with 8 cysteines that need to form 4 disulfide bridges [4] . The disulfide bond connectivity is as follows: Cys1-Cys8, Cys3-Cys6, Cys2-Cys4, and Cys5-Cys7 [15] . The refolded hepcidin was purified. ...
The present study was designed to investigate the antimalarial activity of synthetic hepcidin and its effect on cytokine secretion in mice infected with Plasmodium berghei. The mice were infected with P. berghei intravenously and treated with hepcidin according to 4-day suppression test and Rane's test. The serum levels of interleukins (IL-1β, IL-2, IL-6, IL-10, IL-12p70, and IL-17A), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) in the experimental mice were determined using a cytometric bead array (CBA) kit. The survival rate of the infected mice was also registered. Additionally, the serum iron, alanine transaminase (ALT), aspartate transaminase (AST), and total bilirubin (BIL) were detected to evaluate liver functions. Hepcidin exerted direct anti-malarial function in vivo and increased survival rate in a dose-dependent manner. In addition, the secretion of T helper cell type 1 (Th1), Th2, and Th17 cytokines, TNF-α, and IFN-γ were inhibited by hepcidin. In conclusion, our results demonstrated that synthetic hepcidin exerts in vivo antimalarial activity and possesses anti-inflammatory function, which provides a basis for future design of new derivatives with ideal anti-malarial activity.
... Another inflammatory cytokine that has been implicated in parasite clearance and is highly increased during acute malaria is IFN-γ, with the particularity that increased levels of this cytokine during liver-stage infection were correlated with lack of blood-stage development in humans [165] and monkeys [166], suggesting that this cytokine may be important to inhibit progression of the disease, a finding that is specially relevant for vaccines targeting the liver stage. Studies in mice have shown that IFN-γ is key in the elimination of Plasmodium, since infected mice given exogenous IFN-γ showed lower parasitemias and delayed mortality, while mice deficient in the IFN-γ gene or treated with anti-IFN-γ monoclonal antibodies had higher parasitemia and increased mortality [153,155,156,[167][168][169][170][171][172][173][174][175]. ...
The innate immune response to malaria has always attracted the interest of researchers trying to understand the basis for the high fevers observed in malaria patients during blood-stage infection and the lack of an apparent response to the liver-stage infection. Research targeting specific parts of the immune response has contributed to a basic understanding of the concepts that play a role in malaria-induced inflammation. Given the complexity of the immune response in general and to the parasite in particular, some findings have been contradictory. Here we summarize a large body of work including the host innate immune response to a Plasmodium liver and blood-stage infection, focusing on the different parasite- and host-derived molecules that trigger inflammation, the immune cell types involved, and the role of different cytokines in inflammation and pathology of malaria.
... IFN-gamma adalah protein alami yang diproduksi oleh sel dari sistem imun pada sebagian besar vertebrata untuk merespon tantangan benda asing seperti virus atau parasit. Sitokin tersebut dapat berasal baik dari lengan innate atau adaptif dari respon imun (Favre et al., 1997;Stevenson et al., 1995). Adalah penting untuk menentukan kontribusi sitokin tersebut pada imunitas dan patologi infeksi malaria, karena mereka dapat mendukung aspek selama respon pro-inflamasi (Artavanis-Tsakonas & Riley, 2002). ...
Pengembangan vaksin terhadap malaria yang merupakan penyakit yang mematikan tetap menjadi satu prioritas kesehatan masyarakat global, termasuk pemanfaatan parasit iradiasi sebagai bahan vaksin. Imunisasi dengan sporozoit iradiasi mampu memberikan imunitas protektif pada hewan coba dan sukarelawan. Mekanisme sistem kekebalan tubuh ini banyak dipelajari karena merupakan faktor penting dalam pengembangan vaksin, demikian halnya profil dan/atau ekspresi protein pasca iradiasi yang terkait erat dengan keamanan dan aspek lain dari bahan vaksin. Meskipun telah melalui penelitian yang ekstensif, vaksin yang aman dan protektif belum dapat diperoleh karena masih diperlukan pengetahuan yang lebih mendalam mengenai mekanisme imunitas dan protein dalam litbang malaria. Hasil penelitian menunjukkan bahwa sel limfosit T berperan penting dalam pengaturan respon imun dan pembentukan memori imunologik yang mengontrol dan mengeliminasi infeksi. Sitokin proinflamasi seperti interleukin-12 (IL-12), interferon-gamma (IFN-γ), dan tumor necrosis factor alpha (TNF-α) juga merupakan mediator esensial dari imunitas protektif pada malaria eritrositik. Berbagai pendekatan lain terkait respon imun seperti genetika molekuler saat ini sedang dilakukan. Studi juga menunjukkan bahwa profil protein bergantung pada beberapa faktor yang akan dibahas lebih lanjut dalam makalah. The development of vaccine against malaria as the deadly disease remains the global public health priority; and it includes the use of irradiated parasites as vaccine materials. Immunization with irradiated sporozoites could provide protective immunity in animals and volunteers. The mechanism of this body immunity system has been studied widely due to its important role in the development of vaccines and profiles and/or protein expression post-irradiation which are closely related to safety and other aspects of vaccine materials. Even though extensive research has been done, a safe and protective vaccine remains elusive because more deeply knowledge on immunity mechanism and protein in malaria research is still needed. Results showed that T-cell lymphocytes have an important role in the regulation of immune response and in the formation of immunological memory which controls and eliminates the infection. Pro-inflammatory cytokines such as interleukin-12 (IL-12), interferon-gamma (IFN-γ), and alpha tumor necrosis factor (TNF-α) are also essential mediators of protective immunity in erythrocytic malaria. Various other approaches related to immune response such as molecular genetics has been carried out. The study also showed that protein profile is depended on some factors that will be discussed further in the paper.
... IFN-g is a critical cytokine for the innate and adaptive immune response against a wide range of viral and bacterial infections, including Chlamydia. Among its many roles in the host immune response, IFN-g has been associated with protection and immune activation against viral, bacterial, and protozoal infections [52][53][54], activation of macrophages, induction of class ll MHC [53], and involvement in autoimmune diseases [55]. IFN-g also activates the expression of indoleamine 2,3-dioxygenase (IDO). ...
Genital infections with Chlamydia trachomatis continue to be a major health problem worldwide. While some individuals clear their infection (presumed to be the result of an effective Th1/interferon-γ response), others develop chronic infections and some are prone to repeat infections. In females in particular, chronic asymptomatic infections are common and can lead to pelvic inflammatory disease and infertility. Recent studies suggest that the genital tract microbiota could be a significant factor and explain person-to-person variation in C. trachomatis infections. One hypothesis suggests that C. trachomatis can use its trpBA genes to rescue tryptophan from indole, which is a product of anaerobic members of the genital tract microbiota. Women with particular microbiota types, such as seen in bacterial vaginosis, have increased numbers of anaerobes, and this would enable the chlamydia in these individuals to overcome the host's interferon-γ attempts to eliminate it, resulting in more repeat and/or chronic infections.
... A number of PAMPs (pathogen-associated molecular patterns), including GPI (by which merozoite surface proteins are anchored to the membrane) and haemozoin (produced from the parasites' digestion of RBC haemoglobin), are thought to bind to Toll-like receptors (TLRs), and stimulate both CD4 + and CD8 + T-cells to produce pro-inflammatory cytokines [56,93,236]. These cytokines include Interferonγ (IFNγ) and Tumour Necrosis Factor α (TNFα), which are thought to contribute to parasite killing in the early stages of infection [92,231,232]. However, the activation of an inflammatory immune response in malaria has more often been associated with a negative outcome for the host, the over-production of cytokines being considered highly immunopathological [199]. ...
Malaria is a widespread and serious disease which affects billions of people. Protein-protein interactions occurring between host and Plasmodium parasites are critical to the pathogenesis of malaria and thus represent prime targets for greatly-needed novel therapeutics. Identifying these host-pathogen interactions is challenging, but recent advances in our understanding of parasite biology and in high-throughput biomolecular interaction detection methods have paved the way to a number of successes.
In this work I produced a library of recombinant Plasmodium falciparum proteins to screen for interactions with human receptors in a number of high-throughput assays. Using an established ELISA-based protein-protein interaction detection method, I identified an interaction between P. falciparum merozoite protein 7 (PfMSP7) and human P-selectin (SELP). I used surface plasmon resonance and flow cytometry approaches to validate this interaction and, by screening more widely across the MSP7 protein family, identified that SELP-binding is a conserved property of multiple MSP7s in at least three Plasmodium species. The evolutionary conservation indicates that SELP-MSP7 interactions might have an important function in malaria. Isolating the interacting regions of SELP and PfMSP7 to the secreted, flexible N-terminus of PfMSP7 and the known ligand-binding domains of SELP led to a hypothesis that PfMSP7 could prevent the leukocyte recruitment and activation properties of SELP. I used PfMSP7 to block the interactions between SELP and leukocyte ligands in vitro, providing support to this hypothesis. Further evidence will be required to determine whether Plasmodium MSP7 proteins and their interactions with SELP mediate an immunomodulatory mechanism in malaria, and whether the MSP7 proteins represent useful therapeutic targets.
I also developed a biochemical co-purification assay aiming to detect additional interactions between recombinant P. falciparum merozoite extracellular proteins and those present in human serum. This assay was successful in detecting previously-identified interactions but did not identify novel binding partners for 56 P. falciparum ligands. By expanding the screen or by decreasing its stringency this method could facilitate the identification of further receptors for Plasmodium ligands which could in turn, like the interaction between SELP and MSP7s, aid our understanding of how host and pathogen interact to cause disease.
... Recent studies using IFN␥ or its receptor gene KO mice provide conclusive evidence for the pivotal role played by this cytokine in the control of acute parasitemia and survival of the host during primary infection [47][48][49]. Studies in human malaria also show that IFN␥ production is associated with protection [50,51]. ...
As transdermal immunization results in poor immunogenicity, which is attributed to poor permeability of antigens through the skin, we believed ultradeformable lipid vesicles (elastic liposome) might address the challenges encountered during transdermal immunization. The elastic liposome, versatile carrier, proves better vehicle for transcutaneous delivery of protein, peptide and nucleic acid antigens. Our recently published article (1) is suggestive of improved immunogenicity of carboxyl-terminal 19 kDa fragment of merozoite surface protein-1 (PfMSP-119) of Plasmodium falciparum when administered subcutaneously via elastic liposomes ( Fig. 1 ).
... A central role is played by IFN-γ . Among others, IFN-γ induces myelopoiesis in the bone marrow, enhances the respiratory burst and cytokine secretion during the phagocytic process and, later during infection, IFN-γ augments the antigen-presenting capacity of DCs, monocyte/macrophages and B cells resulting in activation and intensification of acquired T-and B-cell immunity (Shear et al. 1989;Kumaratilake et al. 1992;Favre et al. 1997;Schroder et al. 2004;Belyaev et al. 2010). Therefore, Th1-type reactions are crucial to mount efficient anti-malarial immunity. ...
Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.
... In murine malaria models, several reports demonstrate that this cytokine is indispensable for protection against bloodstage infections. Mice genetically deficient in IFN-γ (GKO) or IFN-γ receptor (γRKO) suffer from prolonged malaria infections or even succumb to otherwise non-lethal malaria infections (Favre et al., 1997; Yoneto et al., 1999). Moreover, dosing WT mice with a neutralizing antibody targeting IFN-γ remarkably attenuated their resistance to malaria parasites (Waki et al., 1992). ...
IFN-γ plays both pathological and protective roles during blood-stage malaria. One of its pathological roles is its contribution to anemia by suppressing erythropoiesis. Here, to evaluate the effects of IFN-γ-mediated alterations in erythropoiesis on the course of malaria infection, mice deficient in IFN-γ (GKO) were infected with two strains of the rodent malaria parasite Plasmodium yoelii, 17XL (PyL) and 17XNL (PyNL), whose host cell ranges differ. Regardless of genotype, all mice infected with PyL, which can invade any erythrocyte, developed high parasitemia and died quickly. Although PyNL caused a transient non-lethal infection in wild-type (WT) mice, some GKO mice were unable to control the infection and died. However, GKO mice were resistant to the early phase of infection, showing an impaired increase in parasitemia compared with WT mice. This resistance in the GKO mice was associated with having significantly fewer reticulocytes, which are the preferred host cells for PyNL parasites, than the WT mice. Compared with the amount of reticulocytes in GKO mice during the early stages of infection, there was a significant increase in the amount of these cells at later stages, which coincided with the inability of these mice to control the infection. We found that the growth of PyNL parasites correlated with the amount of reticulocytes. Thus, the reduced number of reticulocytes in mice lacking IFN-γ appears to be responsible for the limited parasite growth. Notably, these differences in GKO mice were at least partially reversed when the mice were injected with exogenous IFN-γ. Additionally, an artificial induction of hemolytic anemia and an increase in reticulocytes by phenylhydrazine treatment in GKO mice completely abolished the lower parasitemia and resistance during early phase infection. These results suggest that IFN-γ may contribute to the early growth of PyNL parasites by increasing the amount of reticulocytes, presumably by enhancing erythropoiesis.
... Recent studies using IFN␥ or its receptor gene KO mice provide conclusive evidence for the pivotal role played by this cytokine in the control of acute parasitemia and survival of the host during primary infection [47][48][49]. Studies in human malaria also show that IFN␥ production is associated with protection [50,51]. ...
... In mice infected with P. chabaudi AS, IFNγ knockout mice experience both significantly higher parasitaemia and more mortality than WT mice (Su and Stevenson, 2000). Furthermore, resistance to P. yoelii and P. chabaudi and disease resolution, as well as protection from experimental cerebral malaria (ECM) after infection with P. berghei, are associated with an early IFNγ response (De Souza et al., 1997;Favre et al., 1997;Mitchell et al., 2005;Rudin et al., 1997;Shear et al., 1989;van der Heyde et al., 1997). Administration of recombinant murine IFNγ can confer protection against P. yoelii in susceptible mice, potentially through enhanced phagocytosis by splenic macrophages (Shear et al., 1989). ...
Rosetting is an adhesion property of malaria parasites whereby infected erythrocytes
bind to two or more uninfected erythrocytes, forming a so-called rosette. Rosetting of
Plasmodium falciparum is associated with disease severity and high parasitaemia in
sub-Saharan Africa, although currently the function of rosetting remains unknown.
An early IFNg response elicited from the innate immune system is associated with
resolution of malaria infection in mice. Published data suggests that optimal IFNg
production may require contact between peripheral blood mononuclear cells and P.
falciparum infected erythrocytes. The first part of this thesis investigates the
hypothesis that rosetting is an immune evasion strategy to hide infected erythrocytes
from detection by innate immune cells. Across five laboratory strains of P.
falciparum rosetting was not associated with differential IFNg production when
parasites were grown in group O blood. Reappraisal of the data with respect to blood
group for one strain found that rosetting significantly reduced the IFNg response to
parasites grown in group A blood (P=0.022, Wilcoxon signed-rank test), where it is
known that rosettes are bigger and stronger. This is consistent with the hypothesis
that rosetting is an immune evasion strategy and the first study to find evidence for a
function of rosetting. Further work is needed in order to generalise this finding.
The cytokine response to P. falciparum varies between people and this variation may
be indicative of disease progression. In mice infected with malaria it is also apparent
that parasite strain can determine the cytokine response of the host. It is unclear
whether P. falciparum strains vary in their ability to induce cytokines. The second
part of this thesis investigates variation in cytokine induction between P. falciparum
strains. Across four laboratory strains of P. falciparum, IFNg production was
significantly dependent on parasite strain (F3,178= 48.49, P
... To examine the global host responses associated with mild malaria, we carried out whole-blood transcriptional profiling and identified up-regulation of nitric oxide, phagocytosis, humoral, and adaptive immune response pathways and the IFN-γ, TNF-α, interleukin 1, and type I IFN cytokine pathways [19][20][21]. There is abundant evidence documenting the importance of IFN-γ, TNF-α, and nitric oxide and the role of antimalarial antibodies in parasite clearance in human and/or animal models [22][23][24][25]. The collective upregulation of cytokine pathways in turn is controlled by regulatory pathways, which we found to be up-regulated (regulation of cytokine secretion and regulation of chemokine production). ...
Plasmodium falciparum infection can result in severe disease which is associated with elevated inflammation and vital organ dysfunction; however malaria endemic residents gain protection from lethal outcomes and manifest only mild symptoms during infection. To characterize host responses associated with this more effective antimalarial response, we characterized whole blood transcriptional profiles in Rwandan adults during a mild malaria episode and compared them to a convalescence sample. We observed transcriptional upregulation in many pathways, including Type-I IFN, IFN-γ, complement activation and nitric oxide during malaria infection, which provide benchmarks of mild disease physiology. Transcripts encoding negative regulators of T cell activation such as programmed death ligand 1 (PD-L1), programmed cell death 1 ligand 2 (PD-L2) and the butyrophilin family member BTNL2 were also increased. To support an important functional role for BTNL2 during malaria infection, we studied chimeric mice reconstituted with BTNL2(-/-) or wild type (WT) hematopoietic cells that were inoculated with P. berghei ANKA, a murine model of cerebral malaria. We found that BTNL2(-/-) chimeric mice had a significant loss of survival than WT counterparts. Collectively these data characterize the immune responses associated with mild malaria and uncovers a novel role for BTNL2 in the host response to malaria.
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... Murine malaria studies have causally implicated innate inflammatory responses, and IFNγ in particular, in control of parasite burden. In the P. chabaudi model, deletion of IFNγ or its receptor in resistant mice led to impaired cytokine responses, uncontrolled parasitemia and increased mortality [83,84]. Deficiency in the IL-12 p40 subunit in resistant mice reduced IFNγ induction and increased mortality [85], while administration of recombinant IL-12 to susceptible mice enhanced IFNγ production, parasite control, and survival [86]. ...
... The dislodgement of a substantial proportion of lineage-restricted myeloid progenitors to the spleen and temporary establishment of myelopoiesis is one element contributing to macrophage hyperplasia in the spleen [9]. Similarly, previous reports have documented a delayed resolution of parasitemia in mice deficient for IFN-c signaling and infected with malaria parasites [37,38]. The presence of lineage-restricted myeloid progenitors in conjunction with the presence of subsequent stages of monocytic progenitors critically coincided with peak parasitemia. ...
Resolution of a variety of acute bacterial and parasitic infections critically relies on the stimulation of myelopoiesis leading in cases to extramedullary hematopoiesis. Here, we report the isolation of the earliest myeloid-restricted progenitors in acute infection with the rodent malaria parasite, Plasmodium chabaudi. The rapid disappearance of these infection-induced myeloid progenitors from the bone marrow (BM) equated with contraction of the functional myeloid potential in that organ. The loss of BM myelopoiesis was not affected by the complete genetic inactivation of toll-like receptor signaling. De-activation of IFN-γ signaling completely abrogated the contraction of BM myeloid progenitors. Radiation chimeras of Ifngr1-null and control BM revealed that IFN-γ signaling in an irradiation-resistant stromal compartment was crucial for the loss of early myeloid progenitors. Systemic IFN-γ triggered the secretion of C-C motif ligand chemokines CCL2 and CCL7 leading to the egress of early, myeloid-committed progenitors from the bone marrow mediated by their common receptor CCR2. The mobilization of myeloid progenitors initiated extramedullary myelopoiesis in the spleen in a CCR2-dependent manner resulting in augmented myelopoiesis during acute malaria. Consistent with the lack of splenic myelopoiesis in the absence of CCR2 we observed a significant persistence of parasitemia in malaria infected CCR2-deficient hosts. Our findings reveal how the activated immune system mobilizes early myeloid progenitors out of the BM thereby transiently establishing myelopoiesis in the spleen in order to contain and resolve the infection locally.
Parasite-specific CD4+ Th1 cell responses are the predominant immune effector for controlling malaria infection; however, the underlying regulatory mechanisms remain largely unknown. This study demonstrated that ATG5 deficiency in myeloid cells can significantly inhibit the growth of rodent blood-stage malarial parasites by selectively enhancing parasite-specific CD4+ Th1 cell responses. This effect was independent of ATG5-mediated canonical and non-canonical autophagy. Mechanistically, ATG5 deficiency suppressed FAS-mediated apoptosis of LY6G- ITGAM/CD11b+ ADGRE1/F4/80- cells and subsequently increased CCL2/MCP-1 production in parasite-infected mice. LY6G- ITGAM+ ADGRE1- cell-derived CCL2 selectively interacted with CCR2 on CD4+ Th1 cells for their optimized responses through the JAK2-STAT4 pathway. The administration of recombinant CCL2 significantly promoted parasite-specific CD4+ Th1 responses and suppressed malaria infection. Conclusively, our study highlights the previously unrecognized role of ATG5 in modulating myeloid cells apoptosis and sequentially affecting CCL2 production, which selectively promotes CD4+ Th1 cell responses. Our findings provide new insights into the development of immune interventions and effective anti-malarial vaccines.Abbreviations: ATG5: autophagy related 5; CBA: cytometric bead array; CCL2/MCP-1: C-C motif chemokine ligand 2; IgG: immunoglobulin G; IL6: interleukin 6; IL10: interleukin 10; IL12: interleukin 12; MFI: mean fluorescence intensity; JAK2: Janus kinase 2; LAP: LC3-associated phagocytosis; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; pRBCs: parasitized red blood cells; RUBCN: RUN domain and cysteine-rich domain containing, Beclin 1-interacting protein; STAT4: signal transducer and activator of transcription 4; Th1: T helper 1 cell; Tfh: follicular helper cell; ULK1: unc-51 like kinase 1.
Production of IFN-γ by CD4 T cells is widely theorized to control Plasmodium parasite burden during blood-stage malaria. Surprisingly, the specific and crucial mechanisms through which this highly pleiotropic cytokine acts to confer protection against malarial disease remain largely untested in vivo. Here we used a CD4 T cell-restricted Cre-Lox IFN-γ excision mouse model to test whether and how CD4 T cell-derived IFN-γ controls blood-stage malaria. Although complete absence of IFN-γ compromised control of the acute and the chronic, recrudescent blood-stage infections with P. c. chabaudi, we identified a specific, albeit modest, role for CD4 T cell-derived IFN-γ in limiting parasite burden only during the chronic stages of P. c. chabaudi malaria. CD4 T cell IFN-γ promoted IgG Ab class switching to the IgG2c isotype during P. c. chabaudi malaria in C57BL/6 mice. Unexpectedly, our data do not support gross defects in phagocytic activity in IFN-γ-deficient hosts infected with blood-stage malaria. Together, our data confirm CD4 T cell-dependent roles for IFN-γ but suggest CD4 T cell-independent roles for IFN-γ in immune responses to blood-stage malaria.
Background: The cytokines interferon gamma (IFN-γ), interleukin-10 (IL-10) and tumor necrosis factor-α (TNF- α) play an important role in malaria infection. The aim of this study was to determine the prevalence of malaria and to evaluate cytokine responses to malaria infection in patients from the East Nile locality of Khartoum State.
Methods: This study was carried out from May to July 2018 in the East Nile Locality, Khartoum State. Blood samples were collected from 384 randomly selected patients for blood film analysis. Of these, 39 were selected for cytokine level analysis (10 control and 29 patient samples), determined using enzyme-linked immunosorbent assays.
Results: The malaria prevalence rate among 384 patients was 18.5%. Plasmodium falciparum was the most prevalent (13%), while the prevalence of Plasmodium vivax was 4.6%. The rate of mixed infection was 0.8%. There was a higher prevalence rate (22.7%) in males than females (15.6%). However, we found no significant correlation between cytokine levels and parasitemia in the study group. Nevertheless, our study demonstrated a significant correlation between cytokine levels and recurrent infections.
Conclusions: Together, our data show that malaria remains a public health problem in East Nile locality with a high prevalence. Additionally, serum levels of IFN- γ and TNF- α were significantly higher in malaria-infected individuals compared to non-infecting individuals and cytokine levels were found to be correlated with recurrent malaria infection.
Many maternal immune cells populate the decidua, which is the mucosal lining of the uterus transformed during pregnancy. Here, abundant natural killer (NK) cells and macrophages help the uterine vasculature adapt to fetal demands for gas and nutrients, thereby supporting fetal growth. Fetal trophoblast cells budding off the forming placenta and invading deep into maternal tissues come into contact with these and other immune cells. Besides their homeostatic functions, decidual NK cells can respond to pathogens during infection, but in doing so, they may become conflicted between destroying the invader and sustaining fetoplacental growth. We review how maternal NK cells balance their double duty both in the local microenvironment of the uterus and systemically, during toxoplasmosis, influenza, cytomegalovirus, malaria and other infections that threat pregnancy. We also discuss recent developments in the understanding of NK-cell responses to SARS-Cov-2 infection and the possible dangers of COVID-19 during pregnancy.
Oxidative stress is a major contributor of disease aetiology, progression and outcomes. Host systems and parasite infectivity play critical roles in the generation and manipulation of oxidative stress in malaria. Host systems involve the immunological and inflammatory responses that generate free radical species as host signalling processes as well as parasite combating and destructive entities. Parasites trigger molecules with inherent free radical generation in the host. Without the ability to synthesize amino acids, the parasite depends on the breakdown of haemoglobin to salvage the same within the food vacuole. This creates a highly oxidative stress environment from the Fenton reaction through the central ferrous moiety. Elimination of host oxidative stress process, from haemoglobin degradation product haeme, has critically evolved to protect parasites from the hostile intracellular compartment where it is an obligatory inhabitant. Parasites produce antioxidant species from both enzymatic and non-enzymatic molecules which cushions the parasites proteins from oxidation. The parasite also converts haeme, through biocrystallization, to haemozoin, a seemingly biologically inert molecule. In the presence of parasite DNA, haemozoin induces oxidative and inflammatory mediators (cytokines, chemokines, inducible nitric oxide synthase, nitric oxide, oxygen free radical, nitrogen free radicals, peroxynitrite etc.) with a high propensity toward oxidative stress able to override host antioxidant defence systems. Other parasite proponents, e.g. glycosylphosphotidylinositol, are instrumental in negatively modulating host oxidative stress. Without intervention, the disease machineries of oxidative stress go into a vicious cycle of self-propagation mode that leads to host debilitation, cachexia and death. Current drugs are mainly antiparasitic and relieve the “disease” aspect of malaria sparingly. Phytotherapeutics and phytochemicals (asiatic acid, maslinic acid, oleanolic acid), which display anti-oxidant and pro-oxidant properties, have shown both “antiparasite” and “anti-disease” effects promising efficacy in combating malaria. These pleiotropic properties are displayed in different environments with potential to buffer malarial disease syndrome.
In the oral cavity, reactive oxygen and nitrogen species are continuously generated by bacterial metabolism and host-mediated cellular factors. These reactive species facilitate a critical function that regulates the outcomes of both oral and systemic diseases, such as dental caries, periodontitis, and the maintenance of blood pressure. As a result, the protective effects of ROS and RNS are being explored for future therapeutic applications.
Malaria is a devastating infectious disease affecting mostly tropical and sub-tropical regions. Owning to the emergence of resistance to the existing chemotherapy, the development of anti-malarial drugs as novel chemotherapeutics remains unavoidable. Malaria parasite, Plasmodium, experiences oxidative stress throughout its life cycle upon infection, and underlying redox metabolism is quite complex. Alterations in the redox homeostasis occur during host-pathogen interactions. Parasite is highly vulnerable to such alterations in redox homeostasis. To circumvent this, the parasites engage in an efficient redox system having protective roles towards the turbulence faced by the parasite. Targeting the redox system of malaria parasite is tempting in developing novel antimalarial drugs. On the other hand, oxidative stress, generated during anti-malarial drug metabolism, acts as a source of inhibition against progression of this outrageous parasite. This review aims to provide updated knowledge on redox networks of parasite and structural insights of redox system enzymes, underpinning the balance between antioxidant and pro-oxidant candidates throughout the host-parasite interactions. Furthermore, it also highlights the importance of reactive oxygen species generation during anti-malarial drug metabolism. This review summarises on the vulnerabilities of the malaria parasite due to oxidative stress and the potential cues towards development of the novel antimalarial drugs.
Sex hormones play an influential role in the control of parasitic infection by their ability to modulate different components of both the innate and adaptive immune responses. The parasites themselves are phylogenetically diverse, target a range of different tissues, and have evolved numerous alternative strategies to evade or inhibit protective immune responses. Consequently, the influence of sex hormones on these infective agents can be complex. For example, while females exhibit greater resistance to infection by parasites including Trypanosoma cruzi, Trypanosoma brucei, Giardia lamblia, Leishmania mexicana, Plasmodium chabaudi, and Trichinella spiralis, their male counterparts are found to be more resistant to infection with Trichomonas vaganalis, Toxoplasma gondii and Schistosoma mansoni. This chapter will discuss: (1) the role of sex hormones in regulating the outcome of parasite infection, (2) mechanisms by which these hormones modulate host immune responses, and (3) the implications of these observations for the pathogenesis of human parasitic disease.
Malaria is a most causative agent for worldwide death. Plasmodium falciperum infected malaria most dangerous than other plasmodium species. It has closely association to compliment receptor type -1 (CD35) gene polymorphism. CD35 (CR1) is a cell surface receptor for plasmodium falciperum containing PfEMP-1 as a legend. Density of CD35 on erythrocyte can be determined by CR1 allele (HH, HL, and LL). HH allele of CR1 gene express high density of CD35 whereas LL in low density. High density of CD35 is more susceptible to falciperum infection. CD35 is also responsible for sever malaria. During plasmodium infection, pro-inflammatory cytokine like TNF-α, IFN-γ levels are increased. The elevated ratio of TNF-α/IL10 indicates falciperum infection. Cell adhesion protein like VCAM, ICAM also mediate the malarial infection.
The host response to infection requires an immune response to be strong enough to control the pathogen but restrained, to minimise immune-mediated pathology. The conflicting pressures of immune activation and immune suppression are particularly apparent in parasite infections, where co-evolution of host and pathogen has selected many different compromises between protection and pathology. Cytokine signals are critical determinants of both protective immunity and immunopathology and, in this review, we outline the key cytokines that are responsible for the protective and pathological immune responses elicited by parasite infections. We focus on the regulatory cytokine IL-10 and its role in protozoan and helminth infections. We discuss the sources and targets of IL-10 during parasite infection, the signals that initiate and reinforce its action, and its impact on the invading parasite, on the host tissue, and on coincident immune responses. This article is protected by copyright. All rights reserved.
Malaria is caused by infection with Plasmodium parasites. Various studies with knockout mice have indicated that IFN-γ plays essential roles in protective immunity against blood-stage Plasmodium infection. However, after Plasmodium infection, increased IFN-γ production by various types of cells is involved not only in protective immunity, but also in immunopathology. Recent reports have shown that IFN-γ acts as a pro-inflammatory cytokine to induce not only the activation of macrophages, but also the generation of uncommon myelolymphoid progenitor cells after Plasmodium infection. However, the effects of IFN-γ on hematopoietic stem cells and progenitor cells are unclear. Therefore, the regulation of hematopoiesis by IFN-γ during Plasmodium infection remains to be clarified. Although there are conflicting reports concerning the significance of γδ T cells in protective immunity against Plasmodium infection, γδ T cells may respond to infection and produce IFN-γ as innate immune cells in the early phase of blood-stage malaria. Our recent studies have shown that γδ T cells express CD40 ligand and produce IFN-γ after Plasmodium infection, resulting in the enhancement of dendritic cell activation as part of the immune response to eliminate Plasmodium parasites. These data suggest that the function of γδ T cells is similar to that of NK cells. Although several reports suggest that γδ T cells have the potential to act as memory cells for various infections, it remains to be determined whether memory γδ T cells are generated by Plasmodium infection and whether memory γδ T cells can contribute to the host defense against re-infection with Plasmodium. Here, we summarize and discuss the effects of IFN-γ and the various functions of γδ T cells in blood-stage Plasmodium infection.
We consider a model incorporating the influence of innate and adaptive immune responses on malaria pathogenesis. By calculating the model reproduction number for a special representation of cytokine interaction, we have shown that the cytokine tumour necrosis factor-α can be administered to inhibit malaria infection. We have also found that if the cytokine F ∗ and a generic drug of efficacy ε are administered as dual therapy then clearance of the parasite can be achieved even for a generic drug of low efficacy. Our study is recommending administration of dual therapy as a strategy to prevent parasites from developing resistance to malaria treatment drugs.
IFN-γ receptor-deficient (IFN-γR(-/-)) mice and control wild-type (WT) mice, with or without chloroquine (CQ) treatment, were infected intraperitoneally with Plasmodium yoelii 17XL (lethal) and P. yoelii 17XNL (nonlethal), and then mouse survival, parasitemia, and antibody production were investigated during the course of infection. Without CQ treatment, both IFN-γR(-/-) and WT mice were susceptible to infection showing 100 % mortality after infection with 1 × 10(5) P. yoelii 17XL-parasitized erythrocytes. The P. yoelii 17XL-infected WT mice could survive by CQ treatment at a dose of 20 mg/kg for 3 days from day 3 postinfection (pi). Malaria parasites in their bloodstream could not be detected in the surviving mice after day 13 pi. CQ treatment, however, could not rescue IFN-γR(-/-) mice infected with P. yoelii 17XL. Next, we examined the production of the parasite-specific antibodies in P. yoelii 17XL-infected, CQ-treated mice. Although the production of malaria-specific IgG1, IgG2a, IgG2b, and IgG3 antibodies was observed on days 14 and 28 pi in WT mouse sera, only IgG1 was detected on day 28 pi in IFN-γR(-/-) mouse sera. On the other hand, in the nonlethal P. yoelii 17XNL infection, WT mice could control a primary infection with 1 × 10(5) parasitized erythrocytes. Although IFN-γR(-/-) mice could not control and died with increasing parasitemia, the mice could survive by CQ treatment. Both WT and IFN-γR(-/-) mice with and without medication, which survived from P. yoelii 17XNL infection, showed the variable levels of malaria-specific IgG1, IgG2a, IgG2b, and IgG3 antibodies during the course of infection. The present data indicate that the IFN-γ receptors are needed to control the infection and parasite-specific IgG2a antibody plays an essential role in recovery from the infection of erythrocytic stages of P. yoelii 17XL or P. yoelii 17XNL parasite.
It has been suggested that phospholipids and antibodies directed against phospholipids are important in the pathology of malaria. We have investigated the influence of imm_unizations with phospholipids on the course of subsequent blood-stage Plasmodium chabaudi chabaudi infections in ICR inbred mice. We observed a significant reduction in the parasitaemia following imm_unization with phosphatidylcholine (PC), but not with phosphatidylethanolamine (PE) imm_unization. At the peak of the infection, PC-imm_unized mice displayed a T-helper 2 (Th2)-type cytokine production pattern, whereas PE-imm_unized or non-treated controls displayed a cytokine production pattern of the T-helper 1 (Th1) type. Serum imm_unoglobulin transfer from PC-imm_unized mice protected naive mice in a similar fashion to PC-imm_unization, demonstrating that the observed reduction of parasitaemia was caused by the presence of PC-specific antibodies.
Adhesion of parasitized erythrocytes to post-capillary venular endothelium or uninfected red cells is strongly implicated in the pathogenesis of severe Plasmodium falciparum malaria. Neoantigens at the infected red-cell surface adhere to a variety of host receptors, demonstrate serological diversity in field isolates and may also be a target of the host-protective immune response. Here we use sequential cloning of P. falciparum by micromanipulation to investigate the ability of a parasite to switch antigenic and cytoadherence phenotypes. Our data show that antigens at the parasitized cell surface undergo clonal variation in vitro in the absence of immune pressure at the rate of 2% per generation with concomitant modulations of the adhesive phenotype. A clone has the potential to switch at high frequency to a variety of antigenic and adhesive phenotypes, including a new type of cytoadherence behaviour, 'auto-agglutination' of infected erythrocytes. This rapid appearance of antigenic and functional heterogeneity has important implications for pathogenesis and acquired immunity.
Interleukin 12 (IL-12) activates natural killer (NK) and T cells with the secondary synthesis and release of interferon-gamma (IFN-gamma) and other cytokines. IL-12-induced organ alterations are reported for mice and the pathogenetic role of IFN-gamma is investigated by the use of mice deficient in the IFN-gamma receptor (IFN-gamma R-/-). IL-12 caused a rapid infiltration of liver and splenic red pulp with activated macrophages; this and increased NK cells resulted in a fivefold increase of splenic weight in wild-type mice. Splenomegaly was associated with myelosuppression and decreasing peripheral leukocyte counts. IL-12-induced changes in wild-type mice were associated with markedly increased IFN-gamma serum levels and up-regulation of major histocompatibility complex (MHC) class I and II expression in various epithelia. IL-12 induced a qualitatively similar macrophage infiltration in IFN-gamma R-/- mice, less marked splenomegaly (to 2 x normal), and no MHC upregulation. Strikingly increased vascular endothelial intercellular adhesion molecule-1 expression was apparent in both IFN-gamma R-/- and IFN-gamma R+/+ mice. Restricted to mutant mice was a severe, invariably lethal, interstitial, and perivascular pulmonary macrophage infiltration with diffuse pulmonary edema. Extensive quantitative reverse transcriptase polymerase chain reaction analysis revealed an increase of only IL-6 and IL-10 pulmonary gene transcripts in IFN-gamma R-/- mice compared with wild-type mice. IL-12-induced myelosuppression is due to IFN-gamma-release from NK cells and T cells, and is associated with macrophage activation and distinct MHC class I and II antigen upregulation. The pulmonary pathology in IFN-gamma R-/- mice, however, reveals a toxic potential for IL-12 and suggests that endogenous IFN-gamma plays a protective role in preventing fatal pulmonary disease in these mice.
Plasmodium falciparum expresses on the host erythrocyte surface clonally variant antigens and ligands that mediate adherence to endothelial receptors. Both are central to pathogenesis, since they allow chronicity of infection and lead to concentration of infected erythrocytes in cerebral vessels. Here we show that expression of variant antigenic determinants is correlated with expression of individual members of a large, multigene family named var. Each var gene contains copies of a motif that has been previously shown to bind diverse host receptors; expression of a specific var gene correlated with binding to ICAM-1. Thus, our findings are consistent with the involvement of var genes in antigenic variation and binding to endothelium.
Interferon-gamma (IFN-gamma) exerts pleiotropic effects, including antiviral activity, stimulation of macrophages and natural
killer cells, and increased expression of major histocompatibility complex antigens. Mice without the IFN-gamma receptor had
no overt anomalies, and their immune system appeared to develop normally. However, mutant mice had a defective natural resistance,
they had increased susceptibility to infection by Listeria monocytogenes and vaccinia virus despite normal cytotoxic and T
helper cell responses. Immunoglobulin isotype analysis revealed that IFN-gamma is necessary for a normal antigen-specific
immunoglobulin G2a response. These mutant mice offer the possibility for the further elucidation of IFN-gamma-mediated functions
by transgenic cell- or tissue-specific reconstitution of a functional receptor.
We investigated whether gamma interferon (IFN-gamma; a Th1 cytokine), tumor necrosis factor alpha (TNF-alpha), and interleukin-4 (IL-4; a Th2 cytokine) modulate nitric oxide (NO) production in vivo during blood stage infection with Plasmodium chabaudi AS. Treatment of resistant C57BL/6 mice, which resolve infection with P. chabaudi AS and produce increased levels of IFN-gamma, TNF-alpha, and NO early during infection, with anti-IFN- gamma plus anti-TNF-alpha monoclonal antibodies (MAbs) resulted in a reduction of both splenic inducible NO synthase mRNA and serum NO3- levels by 50 and 100%, respectively. Treatment with the anti-TNF-alpha MAb alone reduced only serum NO3- levels by 35%, and treatment with the anti-IFN-gamma MAb alone had no effect on NO production by these mice during infection. Susceptible A/J mice, which succumb to infection with P. chabaudi AS and produce increased levels of IL-4 but low levels of IFN-gamma, TNF-alpha, and NO early during infection, were treated with an anti-IL-4 MAb. The latter treatment had no effect on NO production by this mouse strain during infection. In addition, our results also demonstrate that treatment of resistant C57BL/6 mice with anti-IFN-gamma plus anti-TNF-alpha MAbs affects, in addition to NO production, other traits of resistance to P. chabaudi AS malaria such as the peak level of parasitemia and the development of splenomegaly. Furthermore, the change in spleen weight was shown to be an IFN-gamma-independent effect of TNF-alpha. Treatment of susceptible A/J mice during infection with an anti IL-4 MAb had no effect on these markers of resistance. Thus, these results demonstrate that TNF-alpha and IFN-gamma are critical in the regulation of NO production and other traits of resistance during P. chabaudi AS malaria in C57BL/6 mice. These data also indicate that treatment with an anti-IL-4 antibody alone is not able to induce NO production or confer resistance to A/J mice against P. chabaudi AS malaria.
Parasite-derived proteins expressed on the surface of erythrocytes infected with Plasmodium falciparum are important virulence factors, since they mediate binding of infected cells to diverse receptors on vascular endothelium and are targets of a protective immune response. They are difficult to study because they undergo rapid clonal antigenic variation in vitro, which precludes the derivation of phenotypically homogeneous cultures. Here we have utilized sequence-specific proteases to dissect the role of defined antigenic variants in binding to particular receptors. By selection of protease-resistant subpopulations of parasites on defined receptors we (i) confirm the high rate of antigenic variation in vitro; (ii) demonstrate that a single infected erythrocyte can bind to intercellular adhesion molecule 1, CD36, and thrombospondin; (iii) show that binding to intercellular adhesion molecule 1 and CD36 are functions of the variant antigen; and (iv) suggest that binding to thrombospondin may be mediated by other components of the infected erythrocyte surface.
Tumor necrosis factor (TNF) induced by Plasmodium berghei ANKA (PbA) infection was suggested to play an important role in the development of cerebral malaria (CM). We asked whether TNF-alpha/beta double-deficient mice, which have a complete disruption of the TNF-signaling pathways, are protected from CM and what might be the possible mechanisms of protection. PbA infection induces fatal CM in wild-type mice, which die within 5 to 8 days with severe neurological signs. In contrast, TNF-alpha/beta-deficient mice are completely resistant to PbA-induced CM. As PbA-induced up-regulation of endothelial intercellular adhesion molecule (ICAM)-1 expression as well as the systemic release of nitric oxide is found only in wild-type mice, TNF is apparently central for the recruitment of mononuclear cells and microvascular damage. Mononuclear cell adhesion to the endothelium, vascular leak and, perivascular hemorrhage are found only in the brain of wild-type mice. By contrast, the development of parasitemia and anemia is independent of TNF. Resistance to CM in TNF-alpha/beta-deficient mice is associated with reduced interferon-gamma and interleukin-12 expression in the brain, in the absence of increased T helper type 2 cytokines. In conclusion, TNF apparently is required for PbA-induced endothelial ICAM-1 up-regulation and subsequent microvascular pathology resulting in fatal CM. In the absence of TNF, ICAM-1 and nitric oxide up-regulation are reduced, and PbA infection fails to cause fatal CM.
Interferon-gamma (IFN-gamma) exerts pleiotropic effects, including antiviral activity, stimulation of macrophages and natural killer cells, and increased expression of major histocompatibility complex antigens. Mice without the IFN-gamma receptor had no overt anomalies, and their immune system appeared to develop normally. However, mutant mice had a defective natural resistance, they had increased susceptibility to infection by Listeria monocytogenes and vaccinia virus despite normal cytotoxic and T helper cell responses. Immunoglobulin isotype analysis revealed that IFN-gamma is necessary for a normal antigen-specific immunoglobulin G2a response. These mutant mice offer the possibility for the further elucidation of IFN-gamma-mediated functions by transgenic cell- or tissue-specific reconstitution of a functional receptor.
We have tested the hypothesis that nitric oxide may be responsible for the immunosuppression reported during malaria infections. We first showed that reactive nitrogen intermediates, which indicate nitric oxide generation, were increased in the plasma of Plasmodium vinckei-infected mice. We next found that Concanavalin A-induced proliferation of spleen cells from these mice was reduced compared with that observed in uninfected animals. The addition of NG-methyl-L-arginine (L-NMMA) for the duration of the cultures restored the malarial proliferative response to normal. We then tested the effect of oral L-NMMA on the proliferative response of P. chabaudi-infected mice to a human red blood cell lysate. The secondary response to this antigen, measured as spleen cell proliferation in vitro ten days after immunization and when there was no discernible parasitaemia, remained normal in L-NMMA- treated P. chabaudi mice, but was decreased in the untreated infected mice. These results suggest a role for nitric oxide in malarial immunosuppression.
Protective immunity to asexual malaria parasites appears to be mediated predominantly by the CD4+ subset of T lymphocytes. To examine the role of this T-cell population in the immune response to the murine malaria parasite Plasmodium chabaudi, CD4+ clones derived from infected mice were raised and propagated in vitro. Analysis of the reactivity of clones responsive to parasite antigen demonstrated that the CD4+ cell response is heterogeneous and is consistent with the idea of two functionally distinct CD4+ subsets. Those populations derived early during primary infection secreted interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) upon antigenic stimulation in vitro, i.e. they had a cytokine repertoire typical of the delayed-type inflammatory T-helper 1 (Th1) CD4+ subset. In contrast, cells taken after clearance of a secondary infection produced IL-4 and acted as effective helper cells for anti-malarial antibody (Ab) synthesis in vitro, and thereby had the characteristics of Th2 cells. The appearance in vivo of Th1 and then Th2 clones specific for P. chabaudi-parasitized erythrocytes (pRBC) supports the proposal from limiting culture analyses that for this malaria parasite resolution of primary parasitaemia is predominantly through the action of cytokines rather than Ab, and that final clearance requires helper cells and specific immunoglobulin.
The pathophysiology of the anaemia of falciparum malaria is both complex and multifactorial, and results in a condition which is a major cause of mortality and morbidity in patients, especially children and pregnant women, living in malarial endemic areas. The importance of anaemia as a cause of death in malaria may well be underestimated because of difficulty in diagnosis, especially where parasitaemia may be low and the clinical picture may be confused with other causes of anaemia. Two clinical presentations predominate: severe acute malaria in which anaemia supervenes, and severe anaemia in patients in whom there have been repeated attacks of malaria. The major mechanisms are those of red cell destruction and decreased red cell production. Potential causes of haemolysis include loss of infected cells by rupture or phagocytosis, removal of uninfected cells due to antibody sensitization or other physicochemical membrane changes, and increased reticuloendothelial activity, particularly in organs such as the spleen. Decreased production results from marrow hypoplasia seen in acute infections, and dyserythropoiesis, a morphological appearance, which in functional terms results in ineffective erythropoiesis. The role of parvovirus B19 as a possible cause of bone marrow aplasia in a few cases is postulated. Finally, there is now evidence which points to genetic factors, HLA associated, which may protect against the development of malarial anaemia and which has become common in areas endemic for malaria.
A role has been proposed for inflammatory mediators such as gamma interferon (IFN-gamma) and reactive oxygen intermediates in the control of the blood stages of Plasmodium organisms. It was previously shown that IFN-gamma can be detected in the plasma of mice with a primary infection by Plasmodium chabaudi chabaudi (AS). We found that susceptible and other resistant mouse strains produced IFN-gamma, suggesting that susceptibility is not due to a defect in IFN-gamma production. Administration of IFN-gamma to intact C57BL/6 mice slightly decreased and partially delayed parasitemia, whereas in vivo depletion of IFN-gamma through injection of a "cocktail" of monoclonal antibodies against IFN-gamma exacerbated infection. Since CD4+ T cells are essential for the development of a protective immune response to P. chabaudi chabaudi, we tested whether CD4+ T cells are responsible for IFN-gamma production in vivo and whether exogenous IFN-gamma can replace the protective function of the CD4+ T cells. Mice depleted of CD4+ T cells were unable to produce IFN-gamma, but factors in addition to IFN-gamma may be important in parasite clearance.
CD4+ T cells are an essential component of the protective immune response to Plasmodium chabaudi. In order to determine whether the presence of CD4+ T cells is necessary throughout a primary infection for a protective immune response to develop mice were depleted of their CD4+ T cells in vivo by treatment with specific antibodies. Removal of CD4+ T cells during the acute phase of infection renders mice incapable of clearing their infection. In contrast, removal of CD4+ T cells after this time did not affect their ability to control their parasitaemia. The ability to control parasitaemia correlated with appearance of malaria-specific IgG antibodies. Our data, therefore, suggest a mechanism requiring the presence of CD4+ T cells during the acute pre-IgG period. Later, after IgG has been produced, this mechanism is no longer required.
The role of gamma interferon (IFN-gamma), a pluripotent lymphokine capable of activating macrophages, in acquired immunity to blood-stage malaria was investigated. C57BL-derived, lipopolysaccharide-resistant C57BL/10ScN mice, which were found to be resistant to intraperitoneal (i.p.) infection with 10(6) Plasmodium chabaudi AS parasitized erythrocytes, were treated with monoclonal anti-IFN-gamma antibody (MAb). Two MAbs were used: R4-6A2, a rat anti-mouse, neutralizing immunoglobulin G1, which was prepared against natural murine IFN-gamma, and DB-1, a murine anti-rat immunoglobulin G1 prepared against recombinant rat IFN-gamma, which can neutralize the murine molecule as well as the rat molecule. C57BL/10ScNH mice were injected i.p. with 200 micrograms of R4-6A2 1 day before infection and every 3 days through day 21. Control mice were treated with normal rat serum. In separate experiments, DB-1 (1.0 mg per week for 4 weeks) was administered i.p. to C57BL/10ScNH mice beginning on the day of infection; control mice were untreated. Control and MAb-treated mice were infected i.p. with 10(6) P. chabaudi AS parasitized erythrocytes, and the course and outcome of infection were determined. Control mice exhibited a course of infection that was characterized by a peak parasitemia between 30 and 40% parasitized erythrocytes and elimination of the parasite by 4 weeks. MAb-treated mice exhibited a significantly greater parasitemia 1 to 2 days before the peak parasitemia as well as a significantly greater peak parasitemia but also completely cleared the infection by 4 weeks. Thus, these results suggest that treatment with anti-IFN-gamma MAb impairs but does not completely abrogate host resistance to P. chabaudi AS. We also examined the kinetics of IFN-gamma production by spleen cells cultured in vitro with malaria antigen or concanavalin A. Spleen cells were recovered from individual C57BL/6 mice at various times after i.p. infection with 10(6) P. chabaudi AS parasitized erythrocytes. The amount of IFN-gamma produced was quantitated by enzyme-linked immunosorbent assay. In each case, the peak of IFN-gamma production occurred just before the peak parasitemia, followed by a decrease to little or no IFN-gamma production through 42 days postinfection. There was thus a parallel between the kinetics of production of IFN-gamma in vitro by spleen cells from infected animals and the requirement in vivo for the endogenous molecule just before and at the time of peak parasitemia. In conclusion, these results suggest that IFN-gamma-dependent and -independent mechanisms contribute to host resistance to P. chabaudi AS.
An ELISA assay, designed to detect interferon-gamma (IFN-gamma) in the picogram range, was used to study the presence of IFN-gamma in serum and its production by T cells taken from C57BL/6 mice infected with Plasmodium chabaudi chabaudi. IFN-gamma was detectable in mouse plasma for two to three days before the peak of parasitaemia. Similarly, IFN-gamma production by T cells could be detected in vitro. In limiting dilution cultures, the production of IFN-gamma by as few as 1,000 T cells was detectable using this assay. The limiting dilution analysis revealed that a substantial IFN-gamma response by specific T cells occurs very early in a primary infection with P. chabaudi.
To study the cellular mechanisms involved in the ineffective erythropoiesis associated with malaria, an in vitro proliferative assay was used to measure the response to erythropoietin (Epo) of erythroid progenitor cells from malaria-infected mice. In this assay, spleen (SP) cells from phenylhydrazine (PHZ)-treated mice (PHZ-SP), enriched for erythroid progenitor cells, respond to Epo in a dose-dependent manner. Despite a similar degree of anemia, SP and bone marrow (BM) cells from Plasmodium berghei- or P. vinckei-infected mice did not show a significant response to Epo in this assay. When SP or BM cells from malaria-infected mice were added to cultures of SP or BM cells from PHZ-treated mice the response to Epo of these cells was significantly inhibited. Removal of parasitized red blood cells (pRBC) from SP cells of P. berghei-infected mice had no effect on the ability of the cells to inhibit the response to Epo. Adherent SP cells and SP cells positive for the Mac-1 antigen, from malaria-infected mice, were shown to be enriched for cells that could inhibit the response to Epo. Cell-free conditioned media (CM) prepared from SP cells of P. berghei- or P. vinckei-infected mice or from normal SP cells incubated with pRBC were also able to inhibit the response to Epo of SP cells from PHZ-treated mice. These investigations have shown that during the course of malaria infection, cells appear in the SP and BM capable of inhibiting, via soluble mediators, the response to Epo of erythroid progenitor cells. The cells responsible are probably macrophages. The nature of the factor(s) and its mechanism of action are not known. Through the ability to inhibit erythropoiesis, soluble factors may, in part, mediate the anemia associated with malaria.
Cell-mediated immunity to malaria may involve macrophages, the monokines that mediate endotoxicity, and reactive oxygen species. Since interferon-gamma activates macrophages to release reactive oxygen species, and tumor necrosis factor-alpha (TNF-alpha) helps both to mediate endotoxicity and to induce leukocytes to secrete reactive oxygen, we monitored the effects of administering recombinant forms of these cytokines on Plasmodium chabaudi adami infections in mice. We also fed infected mice a diet containing 0.75% butylated hydroxyanisole, a scavenger of free radicals. Infections were suppressed by daily i.p. injections of 5 x 10(4) U of recombinant mouse interferon-gamma from day -1 or by recombinant human TNF released from i.p. osmotic pumps at the rate of 6 x 10(3) U/hr. Degenerate intraerythrocytic parasites (crisis forms) were evident much sooner in the course of the suppressed infections, and parasitemias fell correspondingly earlier. The butylated hydroxyanisole diet, in contrast, enhanced the infections. In these mice crisis forms were seen later, and at higher parasitemias, than they normally occur. These observations are consistent with the concept that T cell-dependent, macrophage-derived mediators are central to the type of malarial immunity that kills parasites inside circulating red cells. They also suggest, but do not prove, that both TNF and reactive oxygen species are involved, and that the role of TNF may be more indirect, although no less important, than that of reactive forms of oxygen.
Inoculation of adult C57/BC mice with 10(6) red cells infected with Plasmodium chabaudi induces an acute primary parasitaemia peaking around the 8th or 9th day and lasting 10-14 days. Concomitantly, the spleen enlarges to reach 6-7 times its normal weight by the 11th day. The major component of this increase is between day 9 and 11, due primarily to an increase in erythropoietic cells in the red pulp. Although initially the white pulp increases in size, by day 11 it shows partial lymphocyte depletion which coincides with the occurrence of massive absolute lymphocytosis in the peripheral blood. 3H-Thymidine labelling in vivo suggests that this lymphocytosis is not due to lymphocytopoiesis. Collectively, these findings suggest a redistribution of lymphocytes. Lymphocyte migration was investigated around peak parasitaemia, using enriched populations of T and B cells labelled with 51Cr. The traffic patterns of these cells were followed over 36 h. These studies show decreased uptake (or decreased retention) of T and B cells by spleens of infected mice. Concomitantly, there is increased retention of T and B cells in the liver and lungs of infected mice, suggesting a complex redistribution of these cells. Lymphocyte migration to lymph nodes was unimpaired in these animals. Similar changes in T and B cell migration do not occur in Babesia microti infections in C57/BL mice. We relate our findings to histological and histochemical changes in the liver and spleen of malarious mice and discuss the significance of these findings to immunosuppression in malaria and to the development of parasiticidal immunity.
IFN-gamma receptor deficient (IFN-gamma R-/-) mice, immunized with different developmental stages of malaria parasites, were used to define the mechanisms of protection against the various stages of this infection. IFN-gamma R-/- mice failed to develop protective immunity against Plasmodium yoelii sporozoites or liver stages, upon immunization with a single dose of irradiated sporozoites, whereas in immunized wild-type mice, parasite development was strongly inhibited. Immunized wild-type mice expressed high levels of inducible nitric oxide synthase (iNOS) mRNA in their liver, upon challenge with viable sporozoites, whereas only background levels of iNOS were detected in immunized IFN-gamma R-/- mice. In contrast, after immunization with multiple doses of irradiated sporozoites, both IFN-gamma R-/- and wild-type mice mounted an immune response, which strongly inhibited the development of liver stage parasites. In both types of mice, protection occurred in the absence of appreciable expression of liver iNOS mRNA. As for the course of the erythrocytic phase of infection by nonlethal malaria species, P. yoelii yoelii and P. chabaudi adami, we observed only a moderately prolonged parasitemia in IFN-gamma R-/- mice compared with wild-type mice, indicating that IFN-gamma may only play a modest role in immunity against erythrocytic stages. These results indicate that IFN-gamma is the main mediator of the protective mechanism that develops first upon immunization with sporozoites. However, the nature of the anti-parasite mechanism(s) changes in the course of immunization, so that multiple immunizing doses elicit additional protective mechanisms, which are independent of IFN-gamma and its receptor.
The production and function of nitric oxide during the early phase of blood-stage infection with Plasmodium chabaudi AS was analyzed using two inbred strains of mice that differ in the level of resistance to this parasite. Northern blot analysis of in vivo expression of inducible nitric oxide synthase (iNOS) revealed that early during infection resistant C57BL/6 mice, which clear the infection by 4 wk, have higher levels of iNOS mRNA in the spleen than susceptible A/J mice. In contrast, susceptible A/J mice have significantly increased levels of iNOS mRNA in the liver later in the course of infection just before death occurs. Splenic macrophages recovered from resistant C57BL/6 mice on day 7 postinfection express iNOS mRNA which is up-regulated following overnight stimulation of the cells with LPS. Furthermore, during the first week postinfection, splenic macrophages recovered from resistant hosts produce significantly higher levels of nitrite (NO2-) in vitro in response to LPS than similarly stimulated macrophages from susceptible A/J mice. Increased levels of nitrate (NO3-) were only detected in serum of resistant C57BL/6 mice at the time of peak parasitemia. Treatment with the iNOS inhibitor, aminoguanidine, reduced NO3- levels in serum of C57BL/6 mice and eliminated resistance of these hosts to P. chabaudi AS malaria without affecting parasitemia. These results demonstrate that the ability to produce high amounts of nitric oxide (NO) early during infection with blood-stage P. chabaudi AS correlates with resistance, but that NO may not be involved in parasite killing. Moreover, the tissue site of NO production, that is, spleen vs liver, appears to be critical and correlates with resistance vs susceptibility to P. chabaudi AS malaria, respectively.
The effects of IL-12 administration on the development of protective immunity to blood-stage Plasmodium chabaudi AS were analyzed. Treatment of susceptible A/J mice on the day of infection and for 5 days postinfection with various doses 0.025-0.3 microgram) of rIL-12 significantly decreased the peak parasitemia level, but only treatment with 0.1 microgram resulted in increased survival. Treatment of resistant B6 mice with 0.1 microgram of rIL-12 using the same regimen also significantly decreased the peak parasitemia level, but 40% of the animals died. Treatment of these mice with anti-IL-12 mAb resulted in a more severe course of infection, but survival was not significantly altered. The mechanism of IL-12-induced resistance was examined in A/J mice during infection. Compared with spleen cells from untreated mice, cells from IL-12-treated mice produced significantly higher levels of IFN-gamma spontaneously as well as in response to Con A or Ag stimulation on day 7 postinfection. Significantly higher levels of INF-gamma and TNF-alpha were found in the sera of IL-12-treated mice, which correlated with high levels of the nitric oxide (NO) metabolite, NO3-. Furthermore, CD4+T cell depletion was found to abrogate IL-12-induced resistance. Administration of neutralizing mAb against IFN-gamma or TNF-alpha to IL-12-treated mice showed that simultaneous depletion of both cytokines resulted in 100% mortality. The role of NO was investigated by administration of aminoguanidine, a selective inhibitor of cytokine-inducible nitric oxide synthase, to IL-12-treated mice. Significantly increased mortality was observed following treatment twice daily with 9 mg of aminoguanidine, but there was no effect on parasitemia. In conclusion, these results demonstrate that IL-12 regulates the development of resistance to P. chabaudi AS via a CD4+ Th1 response, which involves the cytokines IFN-gamma and TNF-alpha, and is in part NO dependent. Therefore, IL-12, given in the appropriate dose, may be useful in the induction of protective immunity to blood-state malaria.
Malaria is a disease caused by repeated cycles of growth of the parasite Plasmodium in the erythrocyte. Various cellular and molecular strategies allow the parasite to evade the human immune response for many cycles of parasite multiplication. Under certain circumstances Plasmodium infection causes severe anemia or cerebral malaria; the expression of disease is influenced by both parasite and host factors, as exemplified by the exacerbation of disease during pregnancy. This article provides an overview of malaria pathogenesis, synthesizing the recent field, laboratory, and epidemiological data that will lead to the development of strategies to reduce mortality and morbidity.
The induction of T helper cell subsets during the course of non-lethal or lethal blood-stage Plasmodium chabaudi AS infection was investigated using inbred strains of mice which differ in the level of resistance to this intraerythrocytic parasite. Resistant C57Bl/6 mice experience a non-lethal course of infection characterized by moderate levels of both parasitaemia and anaemia and resolution of primary acute infection by 4 weeks, while susceptible A/J mice experience lethal infection with fulminant parasitaemia and severe anaemia. T helper subset function was assessed during infection by determining the kinetics of spleen cell production in vitro of the Th1-derived cytokine, interferon-gamma (IFN-gamma), and of the Th2-derived cytokine, IL-5, using sandwich ELISAs. Spleen cells from resistant C57Bl/6 mice were found to produce high levels of IFN-gamma within 1 week of infection in response to both the mitogen concanavalin A (Con A) and malaria antigen. Furthermore, CD4+ T cells were found to be the source of IFN-gamma while both CD4+ and CD8+ T cells were found to produce IL-5. Decreased IFN-gamma production after day 10 was concomitant with significant production of IL-5 between 2 and 3 weeks post infection. In contrast, spleen cells from susceptible A/J mice produced high levels of IL-5 within the first week of infection. In addition, these animals were found to have high serum levels of IL-5. These results, thus, confirm previous observations that resolution of primary blood-stage P. chabaudi infection occurs by sequential activation of Th1 CD4+ T cells followed by activation of the Th2 subset, and in addition, suggest that induction of a strong Th2 response early in infection may lead to a severe and lethal course of malaria.
This review describes the role of cytokines produced by CD4+ T cells and macrophages in response to the erythrocytic stages of P. chabaudi chabaudi and other malaria infections in mice. Since virtually all compartments of the immune system are activated during the response against malaria, the variety of cytokines produced during infection is considerable. There is, however, a clear differential expression of different cytokines during primary infection. Th1-related cytokines are predominantly produced during the acute phase of infection, and lead mainly to the induction of macrophage-derived cytokines. This antibody-independent pathway is probably on the one hand, sufficient for parasite control early in infection via macrophage-associated inflammatory responses, but can, on the other hand, also lead to the pathological consequences of infection. As the infection progresses, the pattern of cytokine production shifts towards a Th2-like response. B cells play a crucial role in this process. A major consequence of this switch to a production of Th2-related cytokines later in infection would be the down-regulation of IFN-gamma-induced macrophage activation and the promotion of antibody production by mature B cells. This suggest that the mechanism of parasite control in the later stages of infection is predominantly antibody-dependent.
The induction of T-helper cell subsets during the course of blood stage Plasmodium chabaudi chabaudi infection was compared in immunologically intact NIH mice and mice that were depleted of B cells from birth by treatment with anti-mu antibodies. For intact mice, in which the acute primary parasitemia peaked 10 days following infection, purified splenic CD4+ T cells recovered during the ascending parasitemia produced high levels in vitro of interleukin 2 (IL-2) (peak levels on day 10) and gamma interferon (IFN-gamma) (peak levels on day 7). Sera collected from these mice at around this time contained relatively high levels of P. c. chabaudi-specific immunoglobulin 2a (peak levels on day 12), and serum nitric oxide activity was significantly elevated at peak parasitemia. During the descending primary parasitemia, production of IFN-gamma and IL-2 decreased, while levels of IL-4 and IL-10 produced by splenic CD4+ T cells were significantly raised from the time at which subpatency was recorded (day 17) and persisted for at least 50 days. This was concomitant with a significant increase in levels of parasite-specific immunoglobulin G1, which peaked at around the time of recrudescence. Thus, in normal mice, sequential appearance of Th1 and Th2 responses was observed. In contrast, in B-cell-depleted mice, recovery from acute primary parasitemia was followed by a persistent patent infection which did not drop below 0.1% for at least 75 days after initiation of infection. These mice were unable to mount a significant Th2 response, manifest as an enduring inability of splenic CD4+ T cells to produce significant levels of IL-4 and IL-10. IL-2 and IFN-gamma levels remained significantly elevated throughout the 50-day observation period, and there was sustained production of nitric oxide. These data show that immune responses mediated by CD4+ T cells of the Th1 subset are capable of limiting infection beyond the initial acute phase, but that they do not eliminate parasitemia. Furthermore, as the progression from a Th1-regulated to a Th2-regulated immune response fails to occur in B-cell-depleted mice, the data suggest that B cells are required for the downregulation of Th1-mediated and/or the generation of Th2-mediated protective immunity to P. c. chabaudi.
Mice treated with anti-IFN-gamma monoclonal antibodies were unable to recover from infection with an attenuated variant of P. berghei (Pb XAT) which causes non-lethal malaria in normal mice. On the other hand, treatment with anti-IL-4 monoclonal antibodies had no effect on the course of infection. IFN-gamma was produced by spleen cells in vitro during the early phase of the infection. Treatment with anti-IFN-gamma suppressed development of an anti-plasmodial IgG2a immunoglobulin isotype in the serum of infected mice whereas anti-IL-4 interfered with the IgG1 response. An IgG2a fraction of immune serum collected from mice that had recovered from Pb XAT transferred immunity to naive mice but the IgG1 fraction did not. When glutaraldehyde fixed parasitized erythrocytes were incubated with immune serum in suspension, specific IgG2a antibodies were detected by fluorescein staining on the membranes of cells infected with mature stages of parasites. These results indicate that IFN-gamma is a key to inducing B cells to produce the protective antiplasmodial IgG2a immunoglobulin isotype. Antibody-dependent cell-mediated parasite killing seems to be involved in the mechanism of recovery from infection with Pb XAT.
In this work, the authors analysed T and B lymphocyte subsets and cytokine production in the spleen of BALB/c mice during polyclonal lymphocyte activation (primary infection) and parasite-specific response to Plasmodium chabaudi chabaudi (secondary infection). The secondary response was evaluated in fully immunoprotected animals, 60 days after a chloroquine-cured infection. The authors observed that in polyclonal lymphocyte activation antibody-secreting cells of all isotypes increased, with predominance of IgG2a and IgG3 classes. At that time, IFN-gamma was largely produced, but IL-4/IL-5 were just slightly enhanced. In mice re-infected after 60 days, the Ig-isotype pattern was restricted to IgG1 and only IL-4/IL-5 were produced. In both responses, however, the levels of IL-2 were greatly reduced, while those of IL-10 were enhanced to similar levels. The different involvement of Th1 and Th2 cells in both responses was confirmed through analysis of CD45RB expression by CD4+ cells. The authors observed that CD45RBhigh cells were the major CD4+ subpopulation in primary infected mice, while CD45RBlow cells predominated in 60 days re-infected animals. Moreover, the great majority of activated (large) CD4+ cells in the primary infection belonged to the CD45RBhigh subset, while after reinfection most of the CD4+ large had a CD45RBlow phenotype.
To investigate the modulatory role of IFN-gamma on the induction and maintenance of Th2 mucosal immunity in vivo, experiments were performed in mice lacking the IFN-gamma R. Aerosol OVA challenge of immunized wild-type mice resulted in an infiltration of eosinophils into the lung, associated with the ex vivo production of Th2 cytokines (IL-4 and IL-5) from purified lung Thy1.2+ cells stimulated via the CD3/TCR complex. However, while immunized IFN-gamma R-deficient mice exhibited elevated levels of IgE, IgG1, and reduced levels of IgG2a compared with wild-type mice, there was no difference in the recruitment of eosinophils into the lung or the production of IL-4 and IL-5 from lung T cells on day 3. In contrast, up to 2 mo after a single Ag challenge, eosinophils were still present in the lungs of IFN-gamma R-deficient, but not wild-type, mice. Likewise, lung-derived T cells from IFN-gamma R-deficient mice produced higher levels of IL-4 and IL-5, both at 1 and 2 mo after OVA challenge compared with T cells from wild-type mice. We conclude that endogenous IFN-gamma regulates the humoral isotype Ab pattern, but does not modulate the commitment of T cells to a Th2 phenotype in vivo or the acute infiltration of eosinophils to the lung. However, in the absence of IFN-gamma-mediated signaling, there is a transition from a spontaneously resolving to a persisting eosinophilic inflammation of the lungs, associated with a sustained capacity of lung T cells to secrete a Th2 cytokine profile.
Mice that have recovered from a primary infection with Plasmodium chabaudi have been shown to resist a secondary infection. In the present study the authors investigated how natural killer (NK) cells were involved in this resistance. Spleen cells from P. chabaudiprimed C57BL/6 mice could transfer protection against P. chabaudi infection into naive syngeneic mice, but spleen cells from unprimed mice could not. T-enriched cells purified from primed spleen cells could also transfer such protection. Transfer of NK cells from primed spleen cells failed to protect against challenge infection. However, depletion of NK cells in host mice by injection of an anti-NK1.1 monoclonal antibody resulted in higher mortality relative to controls. The possible protective roles of NK cells in P. chabaudi infection are discussed.
We have shown previously that at the time of peak primary parasitaemia of P. chabaudi infection in NIH mice, significant levels of nitric oxide are produced, detectable as nitrate in the serum, and that these contribute to the protective immune response to infection. Here, we demonstrate that following reinfection, mice show a markedly diminished ability to produce nitrate. However, if mice are treated with L-NG-monomethyl arginine specifically to block nitric oxide metabolism during the primary infection, and are then reinfected, production of nitrate is restored to levels approaching those attained at peak primary parasitaemia. These experiments, together with others we have reported, indicate that whereas nitric oxide appears to play a significant role in control of the primary parasitaemia of P. chabaudi infection, it performs no such function during subsequent patent parasitaemias. Furthermore, they suggest that factors as yet unknown may regulate nitric oxide activity during malaria infection, such that under normal circumstances its production comes under strict control. This is exemplified by the observation that after the burst of nitric oxide activity that coincides with peak primary parasitaemia, there follows a prolonged period of immunological tolerance during which nitrate levels remain low even at secondary challenge infection. This tolerized state is lifted only several months after initial infection, when the nitric oxide activity at reinfection appears to correlate with the size of the parasite challenge and the presence of a patent parasitaemia. The implications of these findings for protective immunity to malaria, malarial immunosuppression, and immunoregulation in general, are discussed.
A major advance in immunology has been the establishment of a framework for analysing how certain immune responses dominate following exposure to a particular pathogen or antigen. CD4(+) T helper (Th) cells can be separated into two major subsets which mediate qualitatively distinct cell-mediated (Th1) and humoral (Th2) immune responses. Immunity to most pathogens can be broadly categorized into a predominant protective response of either type. A characteristic of murine malarias is that primary infections with asexual erythrocytic parasites (the pathogenic stage of the malaria life cycle) generate a host protective immune response with a broad spectrum of Th1- and Th2-type CD4(+) T-cell involvement and so can be examined as models of the interaction of Th1 and Th2 cells during an immune response to an infectious agent. Andrew Taylor-Robinson here describes recent events in the dissection of the mechanisms responsible for the generation of protective immunity to Plasmodium chabaudi chabaudi and other experimental malarias in mice.
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Course of P. chabaudi chabaudi infections in IFN-gR deficient mice
Course of P. chabaudi chabaudi infections in IFN-gR deficient mice
1997 Blackwell Science Ltd, Parasite Immunology, 19, 375–383