Leishmania donovani infection of a susceptible host results in CD4⁺ T- cell apoptosis and decreased Th1 cytokine production

The disease visceral leishmaniasis is caused by a protozoan parasite, Leishmania donovani and is characterized by depressed cell-mediated immunity (CMI) and unhindered parasite growth in a susceptible host. The opposite trend is observed in a resistant host. However, the mechanism of this loss of CMI during the progressive disease is unknown as yet. In this report, we demonstrate that more than 40% of CD4⁺ T cells from a susceptible host undergo apoptosis resulting in a significant decrease in interleukin (IL)-2 and interferon (IFN)-γ secretion, leaving IL-4 secretion unaffected. These changes are not apparent in the case of CD4⁺ T cells derived from a resistant host. The data reported here suggest that experimental Leishmania donovani infection leads to selective deletion of the IL-2 and IFN-γ- secreting cells but not Th2-like cells in a susceptible but not a resistant host.