ovalbumin and Leishmaniasis--Visceral

Vaccination is the most effective tool against infectious diseases. Subunit vaccines are safer compared to live-attenuated vaccines but are less immunogenic and need to be delivered with an adjuvant. Adjuvants are essential for enhancing vaccine potency by improving humoral and cell-mediated immune responses. Only a limited number of adjuvants are licensed for human vaccines, and their mode of action is still not clear.

Topics: Adjuvants, Immunologic; Animals; B7-1 Antigen; B7-2 Antigen; Cell Line; Disease Models, Animal; Eukaryotic Initiation Factors; Female; Humans; Inflammation; Interleukin-1beta; Leishmania infantum; Leishmaniasis, Visceral; Macrophages; Mice; Mice, Inbred BALB C; Neutrophil Infiltration; Ovalbumin; Protozoan Proteins; Tumor Necrosis Factor-alpha

Experimental visceral leishmaniasis (VL) represents an exquisite model to study CD8(+) T cell responses in a context of chronic inflammation and antigen persistence, since it is characterized by chronic infection in the spleen and CD8(+) T cells are required for the development of protective immunity. However, antigen-specific CD8(+) T cell responses in VL have so far not been studied, due to the absence of any defined Leishmania-specific CD8(+) T cell epitopes. In this study, transgenic Leishmania donovani parasites expressing ovalbumin were used to characterize the development, function, and fate of Leishmania-specific CD8(+) T cell responses. Here we show that L. donovani parasites evade CD8(+) T cell responses by limiting their expansion and inducing functional exhaustion and cell death. Dysfunctional CD8(+) T cells could be partially rescued by in vivo B7-H1 blockade, which increased CD8(+) T cell survival but failed to restore cytokine production. Nevertheless, B7-H1 blockade significantly reduced the splenic parasite burden. These findings could be exploited for the design of new strategies for immunotherapeutic interventions against VL.

Topics: Animals; Animals, Genetically Modified; Antigens, CD; B7-1 Antigen; B7-H1 Antigen; CD8-Positive T-Lymphocytes; Cell Proliferation; Cloning, Molecular; Dendritic Cells; Disease Models, Animal; Leishmania donovani; Leishmaniasis, Visceral; Lymphocyte Activation; Membrane Glycoproteins; Mice; Ovalbumin; Peptide Fragments; Peptides; Spleen; Superinfection; Vaccinia virus

CD8+ T cells have a protective role in experimental visceral leishmaniasis. However, the observation that inflammatory cytokines induce bystander activation of CD8+ T cells questions the need for antigen-dependent effector function. Here, we demonstrate that successful adoptive immunotherapy with CD8+ T cells is strictly dependent upon the presence of cognate antigen.

Topics: Animals; Antigens, Protozoan; CD8-Positive T-Lymphocytes; Immunotherapy, Adoptive; Leishmania donovani; Leishmaniasis, Visceral; Mice; Mice, Transgenic; Ovalbumin

Little is currently understood about the consequences of chronic parasitic infection for the fate of memory CD4+ T cells that recognize heterologous antigens, e.g. resulting from prior infections or vaccination. Here, we address how Leishmania donovani infection affected the fate of non-cross-reactive (OVA)-specific memory CD4+ T cells. DO11 cells were adoptively transferred into naive recipient mice, which were then immunized to generate memory DO11 cells. After 6 weeks, mice were infected with L. donovani and the fate of DO11 cells was determined. L. donovani infection stimulated an approximately threefold expansion in the total number of CD4+ T cells and DO11 cells, compared to that observed in uninfected mice. DO11 T cells were more actively dividing in infected mice, as judged by 5-bromo-2' deoxyuridine labeling, whereas their rate of apoptosis in control and infected mice was identical. Both CD45RBhiCD44lo naive T cells and to a greater extent CD45RBloCD44hi memory DO11 cells increased in number in the spleens of infected mice, whereas no changes occurred to DO11 cell number or phenotype in the draining lymph nodes. These data indicate that heterologous CD4+ T cells may actively divide during chronic infectious diseases, with important implications for how chronic infection may impact on heterologous immunity.

Topics: Animals; Apoptosis; CD4-Positive T-Lymphocytes; Female; Immunologic Memory; Leishmania donovani; Leishmaniasis, Visceral; Male; Mice; Mice, Inbred BALB C; Mice, SCID; Ovalbumin; Splenomegaly

The activation of CD8+ T cell responses is commonplace during infection with a number of nonviral pathogens. Consequently, there has been much interest in the pathways of presentation of such exogenous antigens for major histocompatibility complex class I-restricted recognition. We had previously shown that Leishmania promastigotes transfected with the ovalbumin (OVA) gene could efficiently target OVA to the parasitophorous vacuole (PV), with subsequent recognition by class II-restricted T cells. We now report the results of studies aimed at evaluating the PV as a route of entry into the exogenous class I pathway. Bone marrow-derived macrophages can present soluble OVA (albeit at high concentrations) to the OVA(257-264)-specific T cell hybridoma 13.13. In contrast, infection with OVA-transfected Leishmania promastigotes failed to result in the stimulation of this hybridoma. This appeared unrelated to variables such as antigen concentration, parasite survival, and macrophage activation status. These results prompted an analysis of the effects of promastigotes on class I peptide binding using RMA-S cells and OVA(257-264). Our data indicate that the major surface protease of Leishmania, gp63, inhibits this interaction by virtue of its endopeptidase activity against the OVA(257-264) peptide. The data suggest that this activity, if maintained within the PV, would result in loss of the OVA(257-264) epitope. Although we can therefore draw no conclusions from these studies regarding the efficiency of the PV as a site of entry of antigen into the exogenous class I pathway, we have identified a further means by which parasites may manipulate the immune repertoire of their host.

Topics: Animals; Antigen Presentation; CD8-Positive T-Lymphocytes; Cricetinae; Endopeptidases; Endosomes; Epitopes; H-2 Antigens; Hydrogen-Ion Concentration; Leishmania donovani; Leishmaniasis, Visceral; Lymphocyte Activation; Mesocricetus; Metalloendopeptidases; Mice; Mice, Inbred C57BL; Ovalbumin; Protozoan Proteins; Subcellular Fractions; Transfection

Novel lipopeptides 84/201 and 86/450 synthesized in this laboratory stimulated antibody and delayed type hypersensitivity (DTH) response to ovalbumin in guinea pigs. Lipopeptide 86/450 also stimulated antibody and DTH responses in albino mice and enhanced nonspecifically macrophage migration index (MMI), phagocytic activity and incorporation of [14C] glucosamine in peritoneal macrophages of the treated animals. Proliferative response of splenocytes from lipopeptide 86/450 treated animals was significantly higher than that from untreated controls. Peritoneal macrophages from lipopeptide 86/450 treated mice were less susceptible to Leishmania donovani promastigote invasion when co-cultured in vitro. The treated animals on challenge with L. donovani promastigote/amastigote showed 80 to 90% lower intake of infection than the control animals.

Topics: Adjuvants, Immunologic; Amino Acid Sequence; Animals; Antibody Formation; Cell Movement; Cricetinae; Female; Guinea Pigs; Hypersensitivity, Delayed; In Vitro Techniques; Leishmania donovani; Leishmaniasis, Visceral; Lipopeptides; Lipoproteins; Lymphocyte Activation; Macrophages, Peritoneal; Male; Mesocricetus; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Ovalbumin; Phagocytosis