We investigated the properties of leishmania exosomes with respect to influencing innate and adaptive immune responses. Exosomes from Leishmania donovani modulated human monocyte cytokine responses to IFN-γ in a bimodal fashion by promoting IL-10 production and inhibiting that of TNF-α. Moreover, these vesicles were inhibitory with respect to cytokine responses (IL-12p70, TNF-α, and IL-10) by human monocyte-derived dendritic cells. Exosomes from wild-type (WT) L. donovani failed to prime monocyte-derived dendritic cells to drive the differentiation of naive CD4 T cells into IFN-γ–producing Th1 cells. In contrast, vesicles from heat shock protein (HSP)100−/− L. donovani showed a gain-of-function and proinflammatory phenotype and promoted the differentiation of naive CD4 lymphocytes into Th1 cells. Proteomic analysis showed that exosomes from WT and HSP100−/− leishmania had distinct protein cargo, suggesting that packaging of proteins into exosomes is dependent in part on HSP100. Treatment of C57BL/6 mice with WT L. donovani exosomes prior to challenge with WT organisms exacerbated infection and promoted IL-10 production in the spleen. In contrast, HSP100−/− exosomes promoted spleen cell production of IFN-γ and did not adversely affect hepatic parasite burdens. Furthermore, the proparasitic properties of WT exosomes were not species specific because BALB/c mice exposed to Leishmania major exosomes showed increased Th2 polarization and exacerbation of disease in response to infection with L. major. These findings demonstrate that leishmania exosomes are predominantly immunosuppressive. Moreover, to our knowledge, this is the first evidence to suggest that changes in the protein cargo of exosomes may influence the impact of these vesicles on myeloid cell function.

No abstract

Mcl-1 protein expression was found to be up-regulated during infection with virulent Mycobacterium tuberculosis strain H37Rv. Mcl-1 induction in THP-1 cells was optimal at a multiplicity of infection of 0.8–1.2 bacilli per macrophage and was independent of opsonin coating of the bacteria. Mcl-1 expression was elevated as early as 4 h, peaked at 5.8-fold above control cells at 24 h, and remained elevated at 48 h after infection. In THP-1 cells, mMcl-1 mRNA was induced by infection with live H37Rv but not with attenuated M. tuberculosis strain H37Ra, heat-killed H37Rv, or latex beads. In THP-1 cells and monocyte-derived macrophages (MDMs), Mcl-1 protein was induced by infection with live H37Rv but not with attenuated M. tuberculosis strain H37Ra, heat-killed H37Rv, or latex beads. Treatment of uninfected, H37Ra-infected, and H37Rv-infected THP-1 cells and MDMs with antisense oligonucleotides to mcl-1 reduced Mcl-1 expression by >84%. This resulted in an increase in apoptosis of both MDMs and THP-1 cells that were infected with H37Rv, but not cells that were uninfected or infected with H37Ra. Increased apoptosis correlated with a decrease in M. tuberculosis CFUs recovered from antisense-treated, H37Rv-infected cells at 4 and 7 days after infection. In contrast, CFU recoveries from sense-treated, H37Rv-infected cells or from antisense- or sense-treated, H37Ra-infected cells were unchanged from controls. Thus, the antiapoptotic effect of the induction of Mcl-1 expression in H37Rv-infected macrophages promotes the survival of virulent M. tuberculosis.