Leishmania Specific CD4 T Cells Release IFNc That Limits Parasite Replication in Patients with Visceral

Visceral leishmaniasis (VL) is associated with increased circulating levels of multiple pro-inflammatory cytokines and chemokines, including IL-12, IFNc, and TNFa, and elevated expression of IFNc mRNA in lesional tissue such as the spleen and bone marrow. However, an immunological feature of VL patients is that their peripheral blood mononuclear cells (PBMCs) typically fail to respond to stimulation with leishmanial antigen. Unexpectedly, it was recently shown that Leishmania specific IFNc, can readily be detected when a whole blood stimulation assay (WBA) is used. We sought to define the conditions that permit whole blood cells to respond to antigen stimulation, and clarify the biological role of the IFNc found to be released by cells from VL patients. CD4+ T cells were found to be crucial for and the main source of the IFNc production in Leishmania stimulated whole blood (WB) cultures. Complement, antibodies and red blood cells present in whole blood do not play a significant role in the IFNc response. The IFNc production was reduced by blockade of human leukocyte antigen (HLA)-DR, indicating that the response to leishmanial antigens observed in WB of active VL patients is a classical HLA- T cell receptor (TCR) driven reaction. Most importantly, blockade of IFNc in ex-vivo splenic aspirate cultures demonstrated that despite the progressive nature of their disease, the endogenous IFNc produced in patients with activ