Harmful Effects of Granulocytic Myeloid-Derived Suppressor Cells on Tuberculosis Caused by Hypervirulent Mycobacteria.

BACKGROUND: The role of myeloid-derived suppressor cells (MDSCs) in patients with severe tuberculosis who suffer from uncontrolled pulmonary inflammation caused by hypervirulent mycobacterial infection remains unclear. METHODS: This issue was addressed using C57BL/6 mice infected with highly virulent Mycobacterium bovis strain MP287/03. RESULTS: CD11b+GR1int population increased in the bone marrow, blood and lungs during advanced disease. Pulmonary CD11b+GR1int (Ly6GintLy6Cint) cells showed granularity similar to neutrophils and expressed immature myeloid cell markers. These immature neutrophils harbored intracellular bacilli and were preferentially located in the alveoli. T-cell suppression occurred concomitantly with CD11b+GR1int cell accumulation in the lungs. Furthermore, lung and bone marrow GR1+ cells suppressed both T-cell proliferation and interferon γ production in vitro. Anti-GR1 therapy given when MDSCs infiltrated the lungs prevented expansion and fusion of primary pulmonary lesions and the development of intragranulomatous caseous necrosis, along with increased mouse survival and partial recovery of T-cell function. Lung bacterial load was reduced by anti-GR1 treatment, but mycobacteria released from the depleted cells proliferated extracellularly in the alveoli, forming cords and clumps. CONCLUSIONS: Granulocytic MDSCs massively infiltrate the lungs during infection with hypervirulent mycobacteria, promoting bacterial growth and the development of inflammatory and necrotic lesions, and are promising targets for host-directed therapies.

Inhibiting Adenosine Receptor Signaling Promotes Accumulation of Effector CD4+ T Cells in the Lung Parenchyma During Severe Tuberculosis.

BACKGROUND: Tuberculous pneumonia, necrotic granulomatous lesions, and bacterial dissemination characterize severe forms of mycobacterial infection. METHODS: To evaluate the pulmonary CD4+ T-cell response during severe tuberculosis, C57BL/6 mice were infected with approximately 100 bacilli of 3 hypervirulent mycobacterial isolates (Mycobacterium tuberculosis strain Beijing 1471 and Mycobacterium bovis strains B2 and MP287/03) or the H37Rv M tuberculosis strain as reference for mycobacterial virulence. Because high expression of both CD39 and CD73 ectonucleotidases was detected on parenchymal CD4+ T cells, we investigated whether CD4+ T-cell suppression in the context of severe disease was due to the extracellular adenosine accumulation that resulted from tissue damage. RESULTS: Lowest expression of CD69, which is an activation marker implicated in maintaining cells in tissues, was observed in lungs from mice displaying the most severe pulmonary pathology. Reduced interferon (IFN)γ-producing CD4+ T cells were also found in the lung of these mice. Intranasal administration of the adenosine receptor antagonist caffeine substantially enhanced the frequency and number of parenchymal CD4+ T cells as well as both CD69 expression and IFNγ production. CONCLUSIONS: These results indicate that adenosine, which may be generated by extracellular adenosine triphosphate degradation, impairs the parenchymal CD4+ T-cell response and contributes to the development of severe tuberculosis.

P2X7 receptor drives Th1 cell differentiation and controls the follicular helper T cell population to protect against Plasmodium chabaudi malaria.

A complete understanding of the mechanisms underlying the acquisition of protective immunity is crucial to improve vaccine strategies to eradicate malaria. However, it is still unclear whether recognition of damage signals influences the immune response to Plasmodium infection. Adenosine triphosphate (ATP) accumulates in infected erythrocytes and is released into the extracellular milieu through ion channels in the erythrocyte membrane or upon erythrocyte rupture. The P2X7 receptor senses extracellular ATP and induces CD4 T cell activation and death. Here we show that P2X7 receptor promotes T helper 1 (Th1) cell differentiation to the detriment of follicular T helper (Tfh) cells during blood-stage Plasmodium chabaudi malaria. The P2X7 receptor was activated in CD4 T cells following the rupture of infected erythrocytes and these cells became highly responsive to ATP during acute infection. Moreover, mice lacking the P2X7 receptor had increased susceptibility to infection, which correlated with impaired Th1 cell differentiation. Accordingly, IL-2 and IFNγ secretion, as well as T-bet expression, critically depended on P2X7 signaling in CD4 T cells. Additionally, P2X7 receptor controlled the splenic Tfh cell population in infected mice by promoting apoptotic-like cell death. Finally, the P2X7 receptor was required to generate a balanced Th1/Tfh cell population with an improved ability to transfer parasite protection to CD4-deficient mice. This study provides a new insight into malaria immunology by showing the importance of P2X7 receptor in controlling the fine-tuning between Th1 and Tfh cell differentiation during P. chabaudi infection and thus in disease outcome.

In vivo approaches reveal a key role for DCs in CD4+ T cell activation and parasite clearance during the acute phase of experimental blood-stage malaria.

Dendritic cells (DCs) are phagocytes that are highly specialized for antigen presentation. Heterogeneous populations of macrophages and DCs form a phagocyte network inside the red pulp (RP) of the spleen, which is a major site for the control of blood-borne infections such as malaria. However, the dynamics of splenic DCs during Plasmodium infections are poorly understood, limiting our knowledge regarding their protective role in malaria. Here, we used in vivo experimental approaches that enabled us to deplete or visualize DCs in order to clarify these issues. To elucidate the roles of DCs and marginal zone macrophages in the protection against blood-stage malaria, we infected DTx (diphtheria toxin)-treated C57BL/6.CD11c-DTR mice, as well as C57BL/6 mice treated with low doses of clodronate liposomes (ClLip), with Plasmodium chabaudi AS (Pc) parasites. The first evidence suggesting that DCs could contribute directly to parasite clearance was an early effect of the DTx treatment, but not of the ClLip treatment, in parasitemia control. DCs were also required for CD4+ T cell responses during infection. The phagocytosis of infected red blood cells (iRBCs) by splenic DCs was analyzed by confocal intravital microscopy, as well as by flow cytometry and immunofluorescence, at three distinct phases of Pc malaria: at the first encounter, at pre-crisis concomitant with parasitemia growth and at crisis when the parasitemia decline coincides with spleen closure. In vivo and ex vivo imaging of the spleen revealed that DCs actively phagocytize iRBCs and interact with CD4+ T cells both in T cell-rich areas and in the RP. Subcapsular RP DCs were highly efficient in the recognition and capture of iRBCs during pre-crisis, while complete DC maturation was only achieved during crisis. These findings indicate that, beyond their classical role in antigen presentation, DCs also contribute to the direct elimination of iRBCs during acute Plasmodium infection.

Quantitative trait loci analysis of melon (Cucumis melo L.) domestication-related traits.

KEY MESSAGE: Loci on LGIV, VI, and VIII of melon genome are involved in the control of fruit domestication-related traits and they are candidate to have played a role in the domestication of the crop. The fruit of wild melons is very small (20-50 g) without edible pulp, contrasting with the large size and high pulp content of cultivated melon fruits. An analysis of quantitative trait loci (QTL) controlling fruit morphology domestication-related traits was carried out using an in vitro maintained F2 population from the cross between the Indian wild melon "Trigonus" and the western elite cultivar 'Piel de Sapo'. Twenty-seven QTL were identified in at least two out of the three field trials. Six of them were also being detected in BC1 and BC3 populations derived from the same cross. Ten of them were related to fruit morphological traits, 12 to fruit size characters, and 5 to pulp content. The Trigonus alleles decreased the value of the characters, except for the QTL at andromonoecious gene at linkage group (LG) II, and the QTL for pulp content at LGV. QTL genotypes accounted for a considerable degree of the total phenotypic variation, reaching up to 46%. Around 66% of the QTL showed additive gene action, 19% exhibited dominance, and 25% consisted of overdominance. The regions on LGIV, VI, and VIII included the QTL with more consistent and strong effects on domestication-related traits. QTLs on those regions were validated in BC2S1, BC2S2, and BC3 families, with "Trigonus" allele decreasing the fruit morphological traits in all cases. The validated QTL could represent loci involved in melon domestication, although further experiments as genomic variation studies across wild and cultivated genotypes would be necessary to confirm this hypothesis.

IFN-γ-induced priming maintains long-term strain-transcending immunity against blood-stage Plasmodium chabaudi malaria.

The mechanism by which protective immunity to Plasmodium is lost in the absence of continued exposure to this parasite has yet to be fully elucidated. It has been recently shown that IFN-γ produced during human and murine acute malaria primes the immune response to TLR agonists. In this study, we investigated whether IFN-γ-induced priming is important to maintain long-term protective immunity against Plasmodium chabaudi AS malaria. On day 60 postinfection, C57BL/6 mice still had chronic parasitemia and efficiently controlled homologous and heterologous (AJ strain) challenge. The spleens of chronic mice showed augmented numbers of effector/effector memory (TEM) CD4(+) cells, which is associated with increased levels of IFN-γ-induced priming (i.e., high expression of IFN-inducible genes and TLR hyperresponsiveness). After parasite elimination, IFN-γ-induced priming was no longer detected and protective immunity to heterologous challenge was mostly lost with >70% mortality. Spontaneously cured mice had high serum levels of parasite-specific IgG, but effector T/TEM cell numbers, parasite-driven CD4(+) T cell proliferation, and IFN-γ production were similar to noninfected controls. Remarkably, the priming of cured mice with low doses of IFN-γ rescued TLR hyperresponsiveness and the capacity to control heterologous challenge, increasing the TEM cell population and restoring the CD4(+) T cell responses to parasites. Contribution of TLR signaling to the CD4(+) T cell responses in chronic mice was supported by data obtained in mice lacking the MyD88 adaptor. These results indicate that IFN-γ-induced priming is required to maintain protective immunity against P. chabaudi and aid in establishing the molecular basis of strain-transcending immunity in human malaria.

MyD88 signaling is directly involved in the development of murine placental malaria.

Malaria is a widespread infectious disease caused by the parasite Plasmodium. During pregnancy, malaria infection leads to a range of complications that can affect both the mother and fetus, including stillbirth, infant mortality, and low birth weight. In this study, we utilized a mouse model of placental malaria (PM) infection to determine the importance of the protein MyD88 in the host immune response to Plasmodium during pregnancy. Initially, we demonstrated that Plasmodium berghei NK65GFP adhered to placental tissue via chondroitin sulfate A and induced PM in mice with a C57BL/6 genetic background. To evaluate the involvement of MyD88 in the pathology of PM, we performed a histopathological analysis of placentas obtained from MyD88(-/-) and wild-type (WT) mice following infection on the 19th gestational day. Our data demonstrated that the detrimental placental alterations observed in the infected mice were correlated with the expression of MyD88. Moreover, in the absence of this protein, production of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) was significantly reduced in the infected mice. More importantly, in contrast to fetuses from infected WT mice, which exhibited a reduction in body weight, the fetuses from infected MyD88(-/-) mice did not display significant weight loss compared to their noninfected littermates. In addition, we observed a decrement of maternal care associated with malaria infection, which was attenuated in the MyD88-deficient mice. Collectively, the results of this study illustrate the pivotal importance of the MyD88 signaling pathway in the pathogenesis of placental malaria, thus presenting new possibilities for targeting MyD88 in therapeutic interventions.

P2RX7 signaling drives the differentiation of Th1 cells through metabolic reprogramming for aerobic glycolysis.

Introduction: This study provides evidence of how Th1 cell metabolism is modulated by the purinergic receptor P2X7 (P2RX7), a cation cannel activated by high extracellular concentrations of adenosine triphosphate (ATP). Methods: In vivo analysis was performed in the Plasmodium chabaudi model of malaria in view of the great relevance of this infectious disease for human health, as well as the availability of data concerning Th1/Tfh differentiation. Results: We show that P2RX7 induces T-bet expression and aerobic glycolysis in splenic CD4+ T cells that respond to malaria, at a time prior to Th1/Tfh polarization. Cell-intrinsic P2RX7 signaling sustains the glycolytic pathway and causes bioenergetic mitochondrial stress in activated CD4+ T cells. We also show in vitro the phenotypic similarities of Th1-conditioned CD4+ T cells that do not express P2RX7 and those in which the glycolytic pathway is pharmacologically inhibited. In addition, in vitro ATP synthase blockade and the consequent inhibition of oxidative phosphorylation, which drives cellular metabolism for aerobic glycolysis, is sufficient to promote rapid CD4+ T cell proliferation and polarization to the Th1 profile in the absence of P2RX7. Conclusion: These data demonstrate that P2RX7-mediated metabolic reprograming for aerobic glycolysis is a key event for Th1 differentiation and suggest that ATP synthase inhibition is a downstream effect of P2RX7 signaling that potentiates the Th1 response.

T cell-specific P2RX7 favors lung parenchymal CD4+ T cell accumulation in response to severe lung infections.

CD4+ T cells are key components of the immune response during lung infections and can mediate protection against tuberculosis (TB) or influenza. However, CD4+ T cells can also promote lung pathology during these infections, making it unclear how these cells control such discrepant effects. Using mouse models of hypervirulent TB and influenza, we observe that exaggerated accumulation of parenchymal CD4+ T cells promotes lung damage. Low numbers of lung CD4+ T cells, in contrast, are sufficient to protect against hypervirulent TB. In both situations, lung CD4+ T cell accumulation is mediated by CD4+ T cell-specific expression of the extracellular ATP (eATP) receptor P2RX7. P2RX7 upregulation in lung CD4+ T cells promotes expression of the chemokine receptor CXCR3, favoring parenchymal CD4+ T cell accumulation. Our findings suggest that direct sensing of lung eATP by CD4+ T cells is critical to induce tissue CD4+ T cell accumulation and pathology during lung infections.

Absence of Bim sensitizes mice to experimental Trypanosoma cruzi infection.

Chagas disease is a life-threatening disorder caused by the protozoan parasite Trypanosoma cruzi. Parasite-specific antibodies, CD8+ T cells, as well as IFN-γ and nitric oxide (NO) are key elements of the adaptive and innate immunity against the extracellular and intracellular forms of the parasite. Bim is a potent pro-apoptotic member of the Bcl-2 family implicated in different aspects of the immune regulation, such as negative selection of self-reactive thymocytes and elimination of antigen-specific T cells at the end of an immune response. Interestingly, the role of Bim during infections remains largely unidentified. To explore the role of Bim in Chagas disease, we infected WT, Bim+/-, Bim-/- mice with trypomastigotes forms of the Y strain of T. cruzi. Strikingly, our data revealed that Bim-/- mice exhibit a delay in the development of parasitemia followed by a deficiency in the control of parasite load in the bloodstream and a decreased survival compared to WT and Bim+/- mice. At the peak of parasitemia, peritoneal macrophages of Bim-/- mice exhibit decreased NO production, which correlated with a decrease in the pro-inflammatory Small Peritoneal Macrophage (SPM) subset. A similar reduction in NO secretion, as well as in the pro-inflammatory cytokines IFN-γ and IL-6, was also observed in Bim-/- splenocytes. Moreover, an impaired anti-T. cruzi CD8+ T-cell response was found in Bim-/- mice at this time point. Taken together, our results suggest that these alterations may contribute to the establishment of a delayed yet enlarged parasitic load observed at day 9 after infection of Bim-/- mice and place Bim as an important protein in the control of T. cruzi infections.

P2x7 Receptor Signaling Blockade Reduces Lung Inflammation and Necrosis During Severe Experimental Tuberculosis.

The risk of developing severe forms of tuberculosis has increased by the acquired immunodeficiency syndrome (AIDS) epidemic, lack of effective drugs to eliminate latent infection and the emergence of drug-resistant mycobacterial strains. Excessive inflammatory response and tissue damage associated with severe tuberculosis contribute to poor outcome of the disease. Our previous studies using mice deficient in the ATP-gated ionotropic P2X7 receptor suggested this molecule as a promising target for host-directed therapy in severe pulmonary tuberculosis. In this study, we assessed the effects of P2X7 pharmacological blockade on disease severity. First, we observed an increase in P2RX7 gene expression in the peripheral blood of tuberculosis patients compared to healthy donors. Lung leukocytes of mice infected with hypervirulent mycobacteria also showed increased expression of the P2X7 receptor. P2X7 blockade in mice with advanced tuberculosis recapitulated in many aspects the disease in P2X7-deficient mice. P2X7-directed therapy reduced body weight loss and the development of inflammatory and necrotic lung lesions, as well as delayed mycobacterial growth. Lower TNF-α production by lung cells and a substantial reduction in the lung GR-1+ myeloid cell population were observed after P2X7 inhibition. The effector CD4+ T cell population also decreased, but IFN-γ production by lung cells increased. The presence of a large population with characteristics of myeloid dendritic cells, as well as the increase in IL-6 production by lung cells, also indicate a qualitative improvement in the pulmonary immune response due to P2X7 inhibition. These findings support the use of drugs that target the P2X7 receptor as a therapeutic strategy to improve the outcome of pulmonary tuberculosis.

Shaping melons: agronomic and genetic characterization of QTLs that modify melon fruit morphology.

The consistency of quantitative trait locus (QTL) effects among genetic backgrounds is a key factor for introgressing QTLs from initial mapping experiments into applied breeding programs. We have selected four QTLs (fs6.4, fw4.3, fw4.4 and fw8.1) involved in melon fruit morphology that had previously been detected in a collection of introgression lines derived from the cross between a Spanish cultivar, "Piel de Sapo," and the Korean accession PI161375 (Songwan Charmi). Introgression lines harboring these QTLs were crossed with an array of melon inbred lines representative of the most important cultivar types. Hybrids of the introgression and inbred lines, with the appropriate controls, were evaluated in replicated agronomic trials. The effects of the QTLs were consistent among the different genetic backgrounds, demonstrating the utility of these QTLs for applied breeding programs in modifying melon fruit morphology. Three QTLs, fw4.4, fs6.4 and fs12.1 were subjected to further study in order to map them more accurately by substitution mapping using a new set of introgression lines with recombination events within the QTL chromosome region. The position of the QTLs was narrowed down to 36-5 cM, depending on the QTL. The results presented in the current study set the basis for the use of these QTLs in applied breeding programs and for the molecular characterization of the genes underlying them.

Neurodegeneration and increased production of nitrotyrosine, nitric oxide synthase, IFN-gamma and S100beta protein in the spinal cord of IL-12p40-deficient mice infected with Trypanosoma cruzi.

BACKGROUND/AIM: Chagas' disease is caused by Trypanosoma cruzi and occurs in most Latin American countries. The protozoan may colonize the central nervous system (CNS) of immune-compromised human hosts, thus causing neuronal disorders. Systemic control of the intracellular forms of the parasite greatly depends on the establishment of a TH1 response and subsequent nitric oxide (NO) release. At the CNS, it is known that low concentrations of NO promote neuronal survival and growth, while high concentrations exert toxic effects and neuron death. Accounting for NO production by astrocytes is the glia-derived factor S100beta, which is overproduced in some neurodegenerative diseases. In the current work, we studied the expression of NO, interferon (IFN)-gamma and S100beta in the spinal cord tissue of IL-12p40KO mice infected with T. cruzi, a model of neurodegenerative process. METHODS: IL-12p40KO and wild-type (WT) female mice infected with T. cruzi Sylvio X10/4 (10(5) trypomastigotes, intraperitoneally) were euthanized when IL-12p40KO individuals presented limb paralysis. Spinal cord sections were submitted to immunohistochemical procedures for localization of neurofilament, laminin, nitrotyrosine, NO synthases (NOS), IFN-gamma and S100beta. The total number of neurons was estimated by stereological analysis and the area and intensity of immunoreactivities were assessed by microdensitometric/morphometric image analysis. RESULTS: No lesion was found in the spinal cord sections of WT mice, while morphological disarrangements, many inflammatory foci, enlarged vessels, amastigote nests and dying neurons were seen at various levels of IL-12p40KO spinal cord. Compared to WT mice, IL-12p40KO mice presented a decrement on total number of neurons (46.4%, p < 0.05) and showed increased values of immunoreactive area for nitrotyrosine (239%, p < 0.01) and NOS (544%, p < 0.001). Moreover, the intensity of nitrotyrosine (16%, p < 0.01), NOS (38%, p < 0.05) and S100beta (21%, p < 0.001) immunoreactivities were also augmented. No IFN-gamma-labeled cells were seen in WT spinal cord tissue, contrary to IL-12p40KO tissue that displayed inflammatory infiltrating cells and also some parenchymal cells positively labeled. CONCLUSION: We suggest that overproduction of NO may account for neuronal death at the spinal cord of T. cruzi-infected IL-12p40KO mice and that IFN-gamma and S100beta may contribute to NOS activation in the absence of IL-12.

Gradual decline in malaria-specific memory T cell responses leads to failure to maintain long-term protective immunity to Plasmodium chabaudi AS despite persistence of B cell memory and circulating antibody.

The mechanisms responsible for the generation and maintenance of immunological memory to Plasmodium are poorly understood and the reasons why protective immunity in humans is so difficult to achieve and rapidly lost remain a matter for debate. A possible explanation for the difficulty in building up an efficient immune response against this parasite is the massive T cell apoptosis resulting from exposure to high-dose parasite Ag. To determine the immunological mechanisms required for long-term protection against P. chabaudi malaria and the consequences of high and low acute phase parasite loads for acquisition of protective immunity, we performed a detailed analysis of T and B cell compartments over a period of 200 days following untreated and drug-treated infections in female C57BL/6 mice. By comparing several immunological parameters with the capacity to control a secondary parasite challenge, we concluded that loss of full protective immunity is not determined by acute phase parasite load nor by serum levels of specific IgG2a and IgG1 Abs, but appears to be a consequence of the progressive decline in memory T cell response to parasites, which occurs similarly in untreated and drug-treated mice with time after infection. Furthermore, by analyzing adoptive transfer experiments, we confirmed the major role of CD4(+) T cells for guaranteeing long-term full protection against P. chabaudi malaria.

Correction: CD28 deficiency leads to accumulation of germinal-center independent IgM+ experienced B cells and to production of protective IgM during experimental malaria.

[This corrects the article DOI: 10.1371/journal.pone.0202522.].

Enantioselective Synthesis and Activity of All Diastereoisomers of ( E)-Phytal, a Pheromone Component of the Moroccan Locust, Dociostaurus maroccanus.

The Moroccan locust, Dociostaurus maroccanus (Thunberg, 1815) (Orthoptera: Acrididae), is a polyphagous pest capable of inflicting large losses in agriculture under favorable environmental and climatic conditions. Currently, control of the pest relies solely on the application of conventional insecticides that have negative effects on the environment and human safety. In the search for a more rational, environmentally acceptable approach for locust control, we have previously reported that ( Z/ E)-phytal (1) is a male-produced candidate sex pheromone of this acridid. This molecule, with two stereogenic centers at C-7 and C-11, has four different diastereomers along with the Z/ E stereochemistry of the double bond at C-2. In this paper, we present for the first time the enantioselective synthesis of the four diastereomers of ( E)-phytal and their electrophysiological and behavioral activity on males and females. Our results demonstrate that the ( R, R)-phytal is the most active diastereomer in both assays, significantly attracting females in a double-choice Y olfactometer, and confirming the previous chromatographic assignment as component of the sex pheromone of the Moroccan locust.

IL-1α promotes liver inflammation and necrosis during blood-stage Plasmodium chabaudi malaria.

Malaria causes hepatic inflammation and damage, which contribute to disease severity. The pro-inflammatory cytokine interleukin (IL)-1α is released by non-hematopoietic or hematopoietic cells during liver injury. This study established the role of IL-1α in the liver pathology caused by blood-stage P. chabaudi malaria. During acute infection, hepatic inflammation and necrosis were accompanied by NLRP3 inflammasome-independent IL-1α production. Systemically, IL-1α deficiency attenuated weight loss and hypothermia but had minor effects on parasitemia control. In the liver, the absence of IL-1α reduced the number of TUNEL+ cells and necrotic lesions. This finding was associated with a lower inflammatory response, including TNF-α production. The main source of IL-1α in the liver of infected mice was inflammatory cells, particularly neutrophils. The implication of IL-1α in liver inflammation and necrosis caused by P. chabaudi infection, as well as in weight loss and hypothermia, opens up new perspectives for improving malaria outcomes by inhibiting IL-1 signaling.

CD28 deficiency leads to accumulation of germinal-center independent IgM+ experienced B cells and to production of protective IgM during experimental malaria.

Protective immunity to blood-stage malaria is attributed to Plasmodium-specific IgG and effector-memory T helper 1 (Th1) cells. However, mice lacking the costimulatory receptor CD28 (CD28KO) maintain chronic parasitemia at low levels and do not succumb to infection, suggesting that other immune responses contribute to parasite control. We report here that CD28KO mice develop long-lasting non-sterile immunity and survive lethal parasite challenge. This protection correlated with a progressive increase of anti-parasite IgM serum levels during chronic infection. Serum IgM from chronically infected CD28KO mice recognize erythrocytes infected with mature parasites, and effectively control Plasmodium infection by promoting parasite lysis and uptake. These antibodies also recognize autoantigens and antigens from other pathogens. Chronically infected CD28KO mice have high numbers of IgM+ plasmocytes and experienced B cells, exhibiting a germinal-center independent Fas+GL7-CD38+CD73- phenotype. These cells are also present in chronically infected C57BL/6 mice although in lower numbers. Finally, IgM+ experienced B cells from cured C57BL/6 and CD28KO mice proliferate and produce anti-parasite IgM in response to infected erythrocytes. This study demonstrates that CD28 deficiency results in the generation of germinal-center independent IgM+ experienced B cells and the production of protective IgM during experimental malaria, providing evidence for an additional mechanism by which the immune system controls Plasmodium infection.

Programmed Cell Death Protein 1-PDL1 Interaction Prevents Heart Damage in Chronic Trypanosoma cruzi Infection.

Chagas disease is a neglected parasitic infection that affects around six to seven million people, mainly in Latin America. About 30-35% of infected people present chronic Chagas cardiomyopathy (CCC), which eventually leads to death. This condition is characterized by local parasite persistence and leukocyte infiltration. In a murine model of CCC, we observed that among infiltrating leukocytes, CD4+ and CD8+ T cells were in higher frequency in the heart of chronically infected mice, although elevated expression of the regulatory molecules programmed cell death protein 1 (PD1) and PDL1 suggested these cells could be inhibited. To investigate if PD1-PDL1 interaction in the heart of chronically infected mice negatively impacts on the local immune response, facilitating parasite persistence, and progression to CCC, we attempted to recover the local immune response by treating chronically infected mice with anti-PD1 and anti-PDL1-blocking antibodies together with irradiated Trypanosoma cruzi, which provides immune response boosting. Irradiated parasites promote expression of costimulatory molecules in dendritic cells and provide specific parasite antigen, which should aid T cell reactivation upon checkpoint blockade. Following treatment, there was an increased frequency of heart-infiltrating CD4+ and CD8+ T cells with an effector memory phenotype, an increased histopathology score and decreased heart rate, supporting our previous hypothesis of local immunosuppression induced by this pathway during CCC. In addition, blood parasitemia was reduced, which was associated with increased T. cruzi-specific immunoglobulin G 1 antibodies. However, no difference was observed in cytokine production or T. cruzi burden in the hearts of treated mice. Taken together, our results suggest PD1-PDL1 interaction protects the heart from excessive immune response.

Publisher Correction: TLR4-Mediated Placental Pathology and Pregnancy Outcome in Experimental Malaria.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.