Antigen Requirements for Efficient Priming of CD8+ T Cells by Leishmania major-Infected Dendritic Cells

Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Infection and Immunity (Impact Factor: 3.73). 11/2005; 73(10):6620-8. DOI: 10.1128/IAI.73.10.6620-6628.2005
Source: PubMed


CD4+ and CD8+ T-cell responses have been shown to be critical for the development and maintenance of acquired resistance to infections
with the protozoan parasite Leishmania major. Monitoring the development of immunodominant or clonally restricted T-cell subsets in response to infection has been difficult,
however, due to the paucity of known epitopes. We have analyzed the potential of L. major transgenic parasites, expressing the model antigen ovalbumin (OVA), to be presented by antigen-presenting cells to OVA-specific
OT-II CD4+ or OT-I CD8+ T cells. Truncated OVA was expressed in L. major as part of a secreted or nonsecreted chimeric protein with L. donovani 3′ nucleotidase (NT-OVA). Dendritic cells (DC) but not macrophages infected with L. major that secreted NT-OVA could prime OT-I T cells to proliferate and release gamma interferon. A diminished T-cell response was
observed when DC were infected with parasites expressing nonsecreted NT-OVA or with heat-killed parasites. Inoculation of
mice with transgenic parasites elicited the proliferation of adoptively transferred OT-I T cells and their recruitment to
the site of infection in the skin. Together, these results demonstrate the possibility of targeting heterologous antigens
to specific cellular compartments in L. major and suggest that proteins secreted or released by L. major in infected DC are a major source of peptides for the generation of parasite-specific CD8+ T cells. The ability of L. major transgenic parasites to activate OT-I CD8+ T cells in vivo will permit the analysis of parasite-driven T-cell expansion, differentiation, and recruitment at the clonal

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    • "Proteins secreted via the classical route or located on the surface of the parasite are more efficiently presented to stimulate CD4 and CD8 T cells (40, 42, 43). "
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    ABSTRACT: Visceral leishmaniasis is a neglected infectious disease caused primarily by Leishmania donovani and Leishmania infantum protozoan parasites. A significant number of infections take a fatal course. Drug therapy is available but still costly and parasites resistant to first line drugs are observed. Despite many years of trial no commercial vaccine is available to date. However, development of a cost effective, needle-independent vaccine remains a high priority. Reverse vaccinology has attracted much attention since the term has been coined and the approach tested by Rappuoli and colleagues. This in silico selection of antigens from genomic and proteomic data sets was also adapted to aim at developing an anti-Leishmania vaccine. Here, an analysis of the efforts is attempted and the challenges to be overcome by these endeavors are discussed. Strategies that led to successful identification of antigens will be illustrated. Furthermore, these efforts are viewed in the context of anticipated modes of action of effective anti-Leishmania immune responses to highlight possible advantages and shortcomings.
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    • "In addition to the killing of the parasite, the processing of Leishmania proteins for antigen presentation on both MHC class II molecules and MHC class I molecules during crosspresentation is a highly regulated process that requires molecular properties acquired during phagolysosome biogenesis (Jutras and Desjardins, 2005). Although the precise molecular mechanisms involved in the processing of Leishmania proteins for cross-presentation are still poorly understood, it is assumed that parasite proteins are proteolytically cleaved in maturing phagosomes, generating peptides that can either be directly loaded on MHC class I molecules in phagosomes or translocated to the cytoplasm for further processing by the proteasome (Bertholet et al., 2005, 2006). Hence, trafficking events involved in phagolysosome biogenesis are likely to play key roles in cross-presentation during Leishmania infection. "
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    ABSTRACT: During phagocytosis, microorganisms are taken up by immune cells into phagosomes. Through membrane-trafficking events mediated by SNARE proteins, phagosomes fuse with lysosomes, generating degradative phagolysosomes. Phagolysosomes contribute to host immunity by linking microbial killing within these organelles with antigen processing for presentation on MHC class I or II molecules to T cells. We show that the intracellular parasite Leishmania evades immune recognition by inhibiting phagolysosome biogenesis. The Leishmania cell surface metalloprotease GP63 cleaves a subset of SNAREs, including VAMP8. GP63-mediated VAMP8 inactivation or Vamp8 disruption prevents the NADPH oxidase complex from assembling on phagosomes, thus altering their pH and degradative properties. Consequently, the presentation of exogenous Leishmania antigens on MHC class I molecules, also known as cross-presentation, is inhibited, resulting in reduced T cell activation. These findings indicate that Leishmania subverts immune recognition by altering phagosome function and highlight the importance of VAMP8 in phagosome biogenesis and antigen cross-presentation.
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    • "Beside cytokine production, CD8+ T cells are also thought to participate in controlling the infection through cytotoxic mechanisms, but the exact route of CD8+ T cell activation in leishmaniasis is still not known. Since the parasites reside in a parasitophorous vacuole inside the host macrophages it is not entirely clear how these cells present antigen through MHC I [55], [56]. The most likely mechanism is cross-presentation, which has been well documented for macrophages and DCs [57], [58], but to date has not been demonstrated in Leishmania infection. "
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