CD8+ T cells and IFN-γ mediate the time-dependent accumulation of infected red blood cells in deep organs during experimental cerebral malaria

Background

Infection with Plasmodium berghei ANKA (PbA) in susceptible mice induces a syndrome called experimental cerebral malaria (ECM) with severe pathologies occurring in various mouse organs. Immune mediators such as T cells or cytokines have been implicated in the pathogenesis of ECM. Red blood cells infected with PbA parasites have been shown to accumulate in the brain and other tissues during infection. This accumulation is thought to be involved in PbA–induced pathologies, which mechanisms are poorly understood.

Methods and Findings

Using transgenic PbA parasites expressing the luciferase protein, we have assessed by real-time in vivo imaging the dynamic and temporal contribution of different immune factors in infected red blood cell (IRBC) accumulation and distribution in different organs during PbA infection. Using deficient mice or depleting antibodies, we observed that CD8⁺ T cells and IFN-γ drive the rapid increase in total parasite biomass and accumulation of IRBC in the brain and in different organs 6–12 days post-infection, at a time when mice develop ECM. Other cells types like CD4⁺ T cells, monocytes or neutrophils or cytokines such as IL-12 and TNF-α did not influence the early increase of total parasite biomass and IRBC accumulation in different organs.

Conclusions

CD8⁺ T cells and IFN-γ are the major immune mediators controlling the time-dependent accumulation of P. berghei-infected red blood cells in tissues.     

Specific Depletion of Ly6Chi Inflammatory Monocytes Prevents Immunopathology in Experimental Cerebral Malaria

Plasmodium berghei ANKA (PbA) infection of C57BL/6 mice leads to experimental cerebral malaria (ECM) that is commonly associated with serious T cell mediated damage. In other parasitic infection models, inflammatory monocytes have been shown to regulate Th1 responses but their role in ECM remains poorly defined, whereas neutrophils are reported to contribute to ECM immune pathology. Making use of the recent development of specific monoclonal antibodies (mAb), we depleted in vivo Ly6C^hi inflammatory monocytes (by anti-CCR2), Ly6G⁺ neutrophils (by anti-Ly6G) or both cell types (by anti-Gr1) during infection with Ovalbumin-transgenic PbA parasites (PbTg). Notably, the application of anti-Gr1 or anti-CCR2 but not anti-Ly6G antibodies into PbTg-infected mice prevented ECM development. In addition, depletion of Ly6C^hi inflammatory monocytes but not neutrophils led to decreased IFNγ levels and IFNγ⁺CD8⁺ T effector cells in the brain. Importantly, anti-CCR2 mAb injection did not prevent the generation of PbTg-specific T cell responses in the periphery, whereas anti-Gr1 mAb injection strongly diminished T cell frequencies and CTL responses. In conclusion, the specific depletion of Ly6C^hi inflammatory monocytes attenuated brain inflammation and immune cell recruitment to the CNS, which prevented ECM following Plasmodium infection, pointing out a substantial role of Ly6C⁺ monocytes in ECM inflammatory processes.     

Identification of a novel antigen cross‐presenting cell type in spleen

Antigen-presenting cells (APC), like dendritic cells (DC), are essential for T-cell activation, leading to immunity or tolerance. Multiple DC subsets each play a unique role in the immune response. Here, a novel splenic dendritic-like APC has been characterized in mice that has immune function and cell surface phenotype distinct from other, described DC subsets. These were identified as a cell type continuously produced in spleen long-term cultures (LTC) and have an in vivo equivalent cell type in mice, namely ‘L-DC’. This study characterizes LTC-DC in terms of marker phenotype and function, and compares them with L-DC and other known splenic DC and myeloid subsets. L-DC display a myeloid dendritic-like phenotype equivalent to LTC-DC as CD11c^loCD11b^hiMHC-II⁻CD8α⁻ cells, distinct by high accessibility and endocytic capacity for blood-borne antigen. Both LTC-DC and L-DC have strong antigen cross-presentation ability leading to strong activation of CD8⁺ T cells, particularly after exposure to lipopolysaccharide. However, they have weak ability to stimulate CD4⁺ T cells in antigen-specific responses. Evidence is presented here for a novel DC type produced by in vitro haematopoiesis which has distinct antigen-presenting potential and reflects a DC subset present also in vivo in spleen.     

Dendritic Cell Cross-Priming Is Essential for Immune Responses to Listeria monocytogenes

Cross-presentation is now recognized as a major mechanism for initiating CD8 T cell responses to virus and tumor antigens in vivo. It provides an elegant mechanism that allows relatively few Dendritic cells (DCs) to initiate primary immune responses while avoiding the consumptive nature of pathogenic infection. CD8 T cells play a major role in anti-bacterial immune responses; however, the contribution of cross-presentation for priming CD8 T cell responses to bacteria, in vivo, is not well established. Listeria monocytogenes (Listeria) is the causative agent of Listeriosis, an opportunistic food-borne bacterial infection that poses a significant public health risk. Here, we employ a transgenic mouse model in which cross-presentation is uniquely inactivated, to investigate cross-priming during primary Listeria infection. We show that cross-priming deficient mice are severely compromised in their ability to generate antigen-specific T cells to stimulate MHC I-restricted CTL responses following Listeria infection. The defect in generation of Listeria-elicited CD8 T cell responses is also apparent in vitro. However, in this setting, the endogenous route of processing Listeria-derived antigens is predominant. This reveals a new experimental dichotomy whereby functional sampling of Listeria-derived antigens in vivo but not in vitro is dependent on cross-presentation of exogenously derived antigen. Thus, under normal physiological circumstances, cross-presentation is demonstrated to play an essential role in priming CD8 T cell responses to bacteria.     

Real-Time Imaging Reveals the Dynamics of Leukocyte Behaviour during Experimental Cerebral Malaria Pathogenesis

During experimental cerebral malaria (ECM) mice develop a lethal neuropathological syndrome associated with microcirculatory dysfunction and intravascular leukocyte sequestration. The precise spatio-temporal context in which the intravascular immune response unfolds is incompletely understood. We developed a 2-photon intravital microscopy (2P-IVM)-based brain-imaging model to monitor the real-time behaviour of leukocytes directly within the brain vasculature during ECM. Ly6C^hi monocytes, but not neutrophils, started to accumulate in the blood vessels of Plasmodium berghei ANKA (PbA)-infected MacGreen mice, in which myeloid cells express GFP, one to two days prior to the onset of the neurological signs (NS). A decrease in the rolling speed of monocytes, a measure of endothelial cell activation, was associated with progressive worsening of clinical symptoms. Adoptive transfer experiments with defined immune cell subsets in recombinase activating gene (RAG)-1-deficient mice showed that these changes were mediated by Plasmodium-specific CD8⁺ T lymphocytes. A critical number of CD8⁺ T effectors was required to induce disease and monocyte adherence to the vasculature. Depletion of monocytes at the onset of disease symptoms resulted in decreased lymphocyte accumulation, suggesting reciprocal effects of monocytes and T cells on their recruitment within the brain. Together, our studies define the real-time kinetics of leukocyte behaviour in the central nervous system during ECM, and reveal a significant role for Plasmodium-specific CD8⁺ T lymphocytes in regulating vascular pathology in this disease.     

Parasite Fate and Involvement of Infected Cells in the Induction of CD4+ and CD8+ T Cell Responses to Toxoplasma gondii

During infection with the intracellular parasite Toxoplasma gondii, the presentation of parasite-derived antigens to CD4⁺ and CD8⁺ T cells is essential for long-term resistance to this pathogen. Fundamental questions remain regarding the roles of phagocytosis and active invasion in the events that lead to the processing and presentation of parasite antigens. To understand the most proximal events in this process, an attenuated non-replicating strain of T. gondii (the cpsII strain) was combined with a cytometry-based approach to distinguish active invasion from phagocytic uptake. In vivo studies revealed that T. gondii disproportionately infected dendritic cells and macrophages, and that infected dendritic cells and macrophages displayed an activated phenotype characterized by enhanced levels of CD86 compared to cells that had phagocytosed the parasite, thus suggesting a role for these cells in priming naïve T cells. Indeed, dendritic cells were required for optimal CD4⁺ and CD8⁺ T cell responses, and the phagocytosis of heat-killed or invasion-blocked parasites was not sufficient to induce T cell responses. Rather, the selective transfer of cpsII-infected dendritic cells or macrophages (but not those that had phagocytosed the parasite) to naïve mice potently induced CD4⁺ and CD8⁺ T cell responses, and conferred protection against challenge with virulent T. gondii. Collectively, these results point toward a critical role for actively infected host cells in initiating T. gondii-specific CD4⁺ and CD8⁺ T cell responses.     

Efficacy of TLR7 agonistic imidazoquinoline as immunochemotherapeutic agent against P. Berghei ANKA infected rodent host

Malaria is a serious disease and is one of the most alarming public health issues. Plasmodium is being resistant to various antimalarials including Chloroquine (CQ) which was the first-line therapy for malaria treatment. WHO recommended several combination therapies but declining efficacy was reported to many of these therapies. Despite a great amount of research, efficient malaria vaccine still seems to be a distant dream. Immunochemotherapy could be an alternate strategy to deal with malaria. Based on the differential activity of various cytokines in the pathogenesis of and protection against malaria, the efficacy of highly active TLR7 agonistic imidazoquinoline (BBIQ) in combination with a suboptimal dose of CQ against P. berghei ANKA (PbA) in vivo was investigated. In mice treated with CQ alone, parasite appeared on Day 17 and all mice of this group died by Day 21. Whereas, mice treated with BBIQ along with CQ exhibited no appearance of parasite till Day 23. Frequencies of T cells (CD3⁺, CD4⁺and CD8⁺) and T regulatory cells (CD4⁺, CD25 ⁺and FoxP3⁺) were found to be lower in brain of BBIQ?+?CQ treated mice as compared to BBIQ alone and CQ alone treated mice on Day 10. Inhibition of infiltration of inflammatory T cells and activation of T helper and T cytotoxic cells against the parasite was observed in the mice treated with this combination therapy. Serum levels of IFN-γ and IL-12 were found to be higher on same day in mice treated with BBIQ?+?CQ which revealed the generation of strong Th1 immune response in mice against the infection. Overall, TLR7 agonist acted as an efficient partner when combined with potent antimalarial drug.     

Endothelial Cell Stimulation Overcomes Restriction and Promotes Productive and Latent HIV-1 Infection of Resting CD4+ T Cells

Highly active antiretroviral therapy (HAART) is able to suppress human immunodeficiency virus type 1 (HIV-1) to undetectable levels in the majority of patients, but eradication has not been achieved because latent viral reservoirs persist, particularly in resting CD4⁺ T lymphocytes. It is generally understood that HIV-1 does not efficiently infect resting CD4⁺ T cells, and latent infection in those cells may arise when infected CD4⁺ T lymphoblasts return to resting state. In this study, we found that stimulation by endothelial cells can render resting CD4⁺ T cells permissible for direct HIV infection, including both productive and latent infection. These stimulated T cells remain largely phenotypically unactivated and show a lower death rate than activated T cells, which promotes the survival of infected cells. The stimulation by endothelial cells does not involve interleukin 7 (IL-7), IL-15, CCL19, or CCL21. Endothelial cells line the lymphatic vessels in the lymphoid tissues and have frequent interactions with T cells in vivo. Our study proposes a new mechanism for infection of resting CD4⁺ T cells in vivo and a new mechanism for latent infection in resting CD4⁺ T cells.     

Experimental Cerebral Malaria Pathogenesis—Hemodynamics at the Blood Brain Barrier

Cerebral malaria claims the lives of over 600,000 African children every year. To better understand the pathogenesis of this devastating disease, we compared the cellular dynamics in the cortical microvasculature between two infection models, Plasmodium berghei ANKA (PbA) infected CBA/CaJ mice, which develop experimental cerebral malaria (ECM), and P. yoelii 17XL (PyXL) infected mice, which succumb to malarial hyperparasitemia without neurological impairment. Using a combination of intravital imaging and flow cytometry, we show that significantly more CD8+ T cells, neutrophils, and macrophages are recruited to postcapillary venules during ECM compared to hyperparasitemia. ECM correlated with ICAM-1 upregulation on macrophages, while vascular endothelia upregulated ICAM-1 during ECM and hyperparasitemia. The arrest of large numbers of leukocytes in postcapillary and larger venules caused microrheological alterations that significantly restricted the venous blood flow. Treatment with FTY720, which inhibits vascular leakage, neurological signs, and death from ECM, prevented the recruitment of a subpopulation of CD45^hi CD8+ T cells, ICAM-1+ macrophages, and neutrophils to postcapillary venules. FTY720 had no effect on the ECM-associated expression of the pattern recognition receptor CD14 in postcapillary venules suggesting that endothelial activation is insufficient to cause vascular pathology. Expression of the endothelial tight junction proteins claudin-5, occludin, and ZO-1 in the cerebral cortex and cerebellum of PbA-infected mice with ECM was unaltered compared to FTY720-treated PbA-infected mice or PyXL-infected mice with hyperparasitemia. Thus, blood brain barrier opening does not involve endothelial injury and is likely reversible, consistent with the rapid recovery of many patients with CM. We conclude that the ECM-associated recruitment of large numbers of activated leukocytes, in particular CD8+ T cells and ICAM+ macrophages, causes a severe restriction in the venous blood efflux from the brain, which exacerbates the vasogenic edema and increases the intracranial pressure. Thus, death from ECM could potentially occur as a consequence of intracranial hypertension.     

Chemokine Transfer by Liver Sinusoidal Endothelial Cells Contributes to the Recruitment of CD4+ T Cells into the Murine Liver

Leukocyte adhesion and transmigration are central features governing immune surveillance and inflammatory reactions in body tissues. Within the liver sinusoids, chemokines initiate the first crucial step of T-cell migration into the hepatic tissue. We studied molecular mechanisms involved in endothelial chemokine supply during hepatic immune surveillance and liver inflammation and their impact on the recruitment of CD4⁺ T cells into the liver. In the murine model of Concanavalin A-induced T cell-mediated hepatitis, we showed that hepatic expression of the inflammatory CXC chemokine ligands (CXCL)9 and CXCL10 strongly increased whereas homeostatic CXCL12 significantly decreased. Consistently, CD4⁺ T cells expressing the CXC chemokine receptor (CXCR)3 accumulated within the inflamed liver tissue. In histology, CXCL9 was associated with liver sinusoidal endothelial cells (LSEC) which represent the first contact site for T-cell immigration into the liver. LSEC actively transferred basolaterally internalized CXCL12, CXCL9 and CXCL10 via clathrin-coated vesicles to CD4⁺ T cells leading to enhanced transmigration of CXCR4⁺ total CD4⁺ T cells and CXCR3⁺ effector/memory CD4⁺ T cells, respectively in vitro. LSEC-expressed CXCR4 mediated CXCL12 transport and blockage of endothelial CXCR4 inhibited CXCL12-dependent CD4⁺ T-cell transmigration. In contrast, CXCR3 was not involved in the endothelial transport of its ligands CXCL9 and CXCL10. The clathrin-specific inhibitor chlorpromazine blocked endothelial chemokine internalization and CD4⁺ T-cell transmigration in vitro as well as migration of CD4⁺ T cells into the inflamed liver in vivo. Moreover, hepatic accumulation of CXCR3⁺ CD4⁺ T cells during T cell-mediated hepatitis was strongly reduced after administration of chlorpromazine. These data demonstrate that LSEC actively provide perivascularly expressed homeostatic and inflammatory chemokines by CXCR4- and clathrin-dependent intracellular transport mechanisms thereby contributing to the hepatic recruitment of CD4⁺ T-cell populations during immune surveillance and liver inflammation.     

Adoptive Transfer of EBV Specific CD8+ T Cell Clones Can Transiently Control EBV Infection in Humanized Mice

Epstein Barr virus (EBV) infection expands CD8⁺ T cells specific for lytic antigens to high frequencies during symptomatic primary infection, and maintains these at significant numbers during persistence. Despite this, the protective function of these lytic EBV antigen-specific cytotoxic CD8⁺ T cells remains unclear. Here we demonstrate that lytic EBV replication does not significantly contribute to virus-induced B cell proliferation in vitro and in vivo in a mouse model with reconstituted human immune system components (huNSG mice). However, we report a trend to reduction of EBV-induced lymphoproliferation outside of lymphoid organs upon diminished lytic replication. Moreover, we could demonstrate that CD8⁺ T cells against the lytic EBV antigen BMLF1 can eliminate lytically replicating EBV-transformed B cells from lymphoblastoid cell lines (LCLs) and in vivo, thereby transiently controlling high viremia after adoptive transfer into EBV infected huNSG mice. These findings suggest a protective function for lytic EBV antigen-specific CD8⁺ T cells against EBV infection and against virus-associated tumors in extra-lymphoid organs. These specificities should be explored for EBV-specific vaccine development.     

HTLV-1 bZIP Factor Impairs Anti-viral Immunity by Inducing Co-inhibitory Molecule,T Cell Immunoglobulin and ITIM Domain (TIGIT)

Human T-cell leukemia virus type 1 (HTLV-1) infects CD4⁺ T cells and induces proliferation of infected cells in vivo, which leads to the onset of adult T-cell leukemia (ATL) in some infected individuals. The HTLV-1 bZIP factor (HBZ) gene, which is encoded in the minus strand of HTLV-1, plays critical roles in pathogenesis. In this study, RNA-seq and ChIP-seq analyses using HBZ transduced T cells revealed that HBZ upregulates the expression and promoter acetylation levels of a co-inhibitory molecule, T cell immunoglobulin and ITIM domain (TIGIT), in addition to those of regulatory T cells related genes, Foxp3 and Ccr4. TIGIT was expressed on CD4⁺ T cells from HBZ-transgenic (HBZ-Tg) mice, and on ATL cells and HTLV-1 infected CD4⁺ T cells of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in vivo. Expression of Blimp1 and IL-10 was upregulated in TIGIT⁺CD4⁺ cells of HBZ-Tg mice compared with TIGIT^-CD4⁺ T cells, suggesting the correlation between TIGIT expression and IL-10 production. When CD4⁺ T cells from HBZ-Tg mice were stimulated with TIGIT’s ligand, CD155, their production of the inhibitory cytokine IL-10 was enhanced. Furthermore, dendritic cells from HBZ-Tg mice produced high levels of IL-10 after stimulation. These data suggest that HBZ alters immune system to suppressive state via TIGIT and IL-10. Importantly, TIGIT suppressed T-cell responses to another HTLV-1 virus protein, Tax, in vitro. Blocking of TIGIT and PD-1 slightly increased anti-Tax T-cell activity in some HAM/TSP patients. These results suggest that HBZ-induced TIGIT on HTLV-1 infected cells impairs T-cell responses to viral antigens. This study shows that HBZ-induced TIGIT plays a pivotal role in attenuating host immune responses and shaping a microenvironment favorable to HTLV-1.     

Coxsackievirus B3 Inhibits Antigen Presentation In Vivo,Exerting a Profound and Selective Effect on the MHC Class I Pathway

Many viruses encode proteins whose major function is to evade or disable the host T cell response. Nevertheless, most viruses are readily detected by host T cells, and induce relatively strong T cell responses. Herein, we employ transgenic CD4⁺ and CD8⁺ T cells as sensors to evaluate in vitro and in vivo antigen presentation by coxsackievirus B3 (CVB3), and we show that this virus almost completely inhibits antigen presentation via the MHC class I pathway, thereby evading CD8⁺ T cell immunity. In contrast, the presentation of CVB3-encoded MHC class II epitopes is relatively unencumbered, and CVB3 induces in vivo CD4⁺ T cell responses that are, by several criteria, phenotypically normal. The cells display an effector phenotype and mature into multi-functional CVB3-specific memory CD4⁺ T cells that expand dramatically following challenge infection and rapidly differentiate into secondary effector cells capable of secreting multiple cytokines. Our findings have implications for the efficiency of antigen cross-presentation during coxsackievirus infection.     

Phosphatidylinositol 3-Kinase γ Is Required for the Development of Experimental Cerebral Malaria

Experimental cerebral malaria (ECM) is characterized by a strong immune response, with leukocyte recruitment, blood-brain barrier breakdown and hemorrhage in the central nervous system. Phosphatidylinositol 3-kinase γ (PI3Kγ) is central in signaling diverse cellular functions. Using PI3Kγ-deficient mice (PI3Kγ^-/-) and a specific PI3Kγ inhibitor, we investigated the relevance of PI3Kγ for the outcome and the neuroinflammatory process triggered by Plasmodium berghei ANKA (PbA) infection. Infected PI3Kγ^-/- mice had greater survival despite similar parasitemia levels in comparison with infected wild type mice. Histopathological analysis demonstrated reduced hemorrhage, leukocyte accumulation and vascular obstruction in the brain of infected PI3Kγ^-/- mice. PI3Kγ deficiency also presented lower microglial activation (Iba-1+ reactive microglia) and T cell cytotoxicity (Granzyme B expression) in the brain. Additionally, on day 6 post-infection, CD3⁺CD8⁺ T cells were significantly reduced in the brain of infected PI3Kγ^-/- mice when compared to infected wild type mice. Furthermore, expression of CD44 in CD8+ T cell population in the brain tissue and levels of phospho-IkB-α in the whole brain were also markedly lower in infected PI3Kγ^-/- mice when compared with infected wild type mice. Finally, AS605240, a specific PI3Kγ inhibitor, significantly delayed lethality in infected wild type mice. In brief, our results indicate a pivotal role for PI3Kγ in the pathogenesis of ECM.     

The immune system utilizes two distinct effector mechanisms of T cells depending on two different life cycle stages of a single pathogen,Toxoplasma gondii,to control its cerebral infection

Toxoplasma gondii takes two different life cycle stages within intermediate hosts including humans. Tachyzoites proliferate during the acute stage, and they transform into cysts to establish a chronic infection preferentially in the brain. IFN-γ production by infiltrated CD4⁺ and CD8⁺ T cells is required for the prevention of cerebral tachyzoite growth. IFN-γ production by brain-resident cells, most likely microglia, plays a key first line defense role to facilitate both innate and T cell-mediated protective immunity to control the tachyzoite growth. IFN-γ produced by brain-resident cells activates cerebral expression of IFN-dependent effector molecules to suppress tachyzoite growth during the early stage of infection. Their IFN-γ production also induces an expression of CXCL9 and CXCL10 chemokines to recruit immune T cells into the brain, and upregulates cerebral expression of MHC class I and II molecules for antigen presentation to the recruited T cells to activate their IFN-γ production. CD8⁺ T cells also have the activity to remove T. gondii cysts from the brains of infected hosts. Of interest, the anti-cyst activity of CD8⁺ T cells does not require their IFN-γ but does require perforin. Notably, we discovered that CD8⁺ cytotoxic T cells penetrate in the cysts in a perforin-mediated manner, which induces morphological deterioration and destruction of the cysts and an accumulation of microglia and macrophages for their elimination. Thus, the immune system employs two distinct effector mechanisms mediated by IFN-γ or perforin depending on two different life cycle stages of a single pathogen, T. gondii, to control its cerebral infection.     

Regulatory CD8 T cells induced by exposure to all-trans retinoic acid and TGF-β suppress autoimmune diabetes

Antigen-specific regulatory CD4⁺ T cells have been described but there are few reports on regulatory CD8⁺ T cells. We generated islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific regulatory CD8⁺ T cells from 8.3-NOD transgenic mice. CD8⁺ T cells from 8.3-NOD splenocytes were cultured with IGRP, splenic dendritic cells (SpDCs), TGF-β, and all-trans retinoic acid (ATRA) for 5 days. CD8⁺ T cells cultured with either IGRP alone or IGRP and SpDCs in the absence of TGF-β and ATRA had low Foxp3⁺ expression (1.7 ± 0.9% and 3.2 ± 4.5%, respectively). In contrast, CD8⁺ T cells induced by exposure to IGRP, SpDCs, TGF-β, and ATRA showed the highest expression of Foxp3⁺ in IGRP-reactive CD8⁺ T cells (36.1 ± 10.6%), which was approximately 40-fold increase compared with that before induction culture. CD25 expression on CD8⁺ T cells cultured with IGRP, SpDCs, TGF-β, and ATRA was only 7.42%, whereas CD103 expression was greater than 90%. These CD8⁺ T cells suppressed the proliferation of diabetogenic CD8⁺ T cells from 8.3-NOD splenocytes in vitro and completely prevented diabetes onset in NOD-scid mice in cotransfer experiments with diabetogenic splenocytes from NOD mice in vivo. Here we show that exposure to ATRA and TGF-β induces CD8⁺Foxp3⁺ T cells ex vivo, which suppress diabetogenic T cells in vitro and in vivo.     

Heat Shock Protein 60 in Eggs Specifically Induces Tregs and Reduces Liver Immunopathology in Mice with Schistosomiasis Japonica

Background

Parasitic helminths need to suppress the host immune system to establish chronic infections. Paradoxically, immunosuppression induced by the worm also benefits the host by limiting excessive inflammation and tissue damage, which remains the major cause leading to serious morbidity and mortality. Regulatory T cells (Tregs) are key immune regulators of this mutualism. The successive rise in Tregs during schistosome infection plays a critical role in immunoregulation. We and others previously showed that Schistosoma japonicum (S. japonicum) egg antigens (SEA) induce Tregs both in vitro and in vivo. In addition, we identified that SjHSP60 derived from SEA significantly induces Tregs in vivo and in vitro. However, the contribution of SjHSP60 in SEA to Treg induction and the related mechanisms of the Treg induction have not yet been identified.

Methodology/Principal Findings

In this study, we showed that S. japonicum stress protein HSP60 (SjHSP60) was constitutively and extensively expressed in eggs of S. japonicum. SjHSP60 specially induced Tregs in vivo and in vitro without inducing other CD4⁺ T sub-populations including Th1, Th2 and Th17 cells. Furthermore, we showed that the SjHSP60-depleted SEA almost lost the ability in vitro and displayed a significant impaired ability to induce Tregs in vivo. Finally, our study illustrated that the mechanisms of SjHSP60-mediated induction of Tregs are through both conversion of CD4⁺CD25^- T cells into CD4⁺CD25⁺Foxp3⁺ Tregs and expansion of preexisting CD4⁺CD25⁺Foxp3⁺ Tregs in a TLR4-dependent manner.

Conclusions/Significance

Collectively, our findings identify SjHSP60 as a major parasitic contributor of Treg induction in S. japonicum egg antigens, which not only contributes to the better understanding of the mechanism of immunoregulation during helminth infection, but also suggests its potential as a therapeutic target for control of immunopathology, allergic and autoimmune diseases.     

Semen CD4+ T Cells and Macrophages Are Productively Infected at All Stages of SIV infection in Macaques

The mucosal events of HIV transmission have been extensively studied, but the role of infected cells present in the genital and rectal secretions, and in the semen, in particular, remains a matter of debate. As a prerequisite to a thorough in vivo investigation of the early transmission events through infected cells, we characterized in detail by multi-parameter flow cytometry the changes in macaque seminal leukocytes during SIVmac251 infection, focusing on T cells, macrophages and dendritic cells. Using immunocytofluorescence targeting SIV proteins and real-time quantitative PCR targeting SIV DNA, we investigated the nature of the infected cells on sorted semen leukocytes from macaques at different stages of infection. Finally, we cocultured semen CD4⁺ T cells and macrophages with a cell line permissive to SIV infection to assess their infectivity in vitro. We found that primary infection induced strong local inflammation, which was associated with an increase in the number of leukocytes in semen, both factors having the potential to favor cell-associated virus transmission. Semen CD4⁺ T cells and macrophages were productively infected at all stages of infection and were infectious in vitro. Lymphocytes had a mucosal phenotype and expressed activation (CD69 & HLA-DR) and migration (CCR5, CXCR4, LFA-1) markers. CD69 expression was increased in semen T cells by SIV infection, at all stages of infection. Macrophages predominated at all stages and expressed CD4, CCR5, MAC-1 and LFA-1. Altogether, we demonstrated that semen contains the two major SIV-target cells (CD4+ T cells and macrophages). Both cell types can be productively infected at all stages of SIV infection and are endowed with markers that may facilitate transmission of infection during sexual exposure.     

Iron Prevents the Development of Experimental Cerebral Malaria by Attenuating CXCR3-Mediated T Cell Chemotaxis

Cerebral malaria is a severe neurological complication of Plasmodium falciparum infection. Previous studies have suggested that iron overload can suppress the generation of a cytotoxic immune response; however, the effect of iron on experimental cerebral malaria (ECM) is yet unknown. Here we determined that the incidence of ECM was markedly reduced in mice treated with iron dextran. Protection was concomitant with a significant decrease in the sequestration of CD4⁺ and CD8⁺ T cells within the brain. CD4⁺ T cells demonstrated markedly decreased CXCR3 expression and had reduced IFNγ-responsiveness, as indicated by mitigated expression of IFNγR2 and T-bet. Additional analysis of the splenic cell populations indicated that parenteral iron supplementation was also associated with a decrease in NK cells and increase in regulatory T cells. Altogether, these results suggest that iron is able to inhibit ECM pathology by attenuating the capacity of T cells to migrate to the brain.