Type I interferon signalling suppresses anti-parasitic CD4+ T cell responses during visceral leishmaniasis

Many pathogens, including viruses, bacteria, and protozoan parasites, suppress cell mediated immune responses through activation of type I Interferon (IFN-1) signalling. However the role of IFN-1 during Leishmania donovani infection causing visceral leishmaniasis (VL) is not well known. Here we report that IFN-1 play an important role in the pathogenesis of VL by impairing parasite clearance and suppressing pro-inflammatory cytokine production. Mice lacking type-1 IFN signalling (B6.IFNαR1 −/− mice) had enhanced pro-inflammatory cytokine production and better control of parasite burden in liver as well as spleen compared to wild type C57BL/6 mice. IFN-1 signalling suppressed the CD4+ derived IFN-γ production and prevented Th1 response from controlling parasite replication. Experiment using bone marrow chimeric mice revealed that IFN-1 did not suppress CD4+ T via directly acting to this cell type. Using conventional dendritic cell (cDC) specific IFN-1 deficient mice (CD11c Cre-IFNAR fl/fl ), we observed that IFN-1 hampered CD4+ T cells response acting via dendritic cells. Studies in VL patients supported these findings and showed enhanced accumulation of mRNA encoding type I IFN signature genes in peripheral blood mononuclear cells (PBMCs) that were reduced following successful drug therapy. Critically, we also showed, using a whole blood assay, that blockade of type-1 IFN signalling enhanced antigen specific IFN-γ production, and that this response was HLA-II restricted. Together, these results identify the type-1 IFN signalling pathways as a potential therapeutic target to treat VL by stimulating anti-parasitic CD4 + T cell responses.