Leishmania donovani parasites interact with γ/δ⁺ human periphera blood T cells and induce susceptibility to NK cell-mediated lysis

We recently reported that Leishmania donovani infect the human T-cell line in vitro. To examine whether primary human T cells could be infected by this parasite, a direct interaction of the peripheral blood T cells with L. donovani was examined. The percentage of γ/δ⁺ T cells was markedly increased when in vitro generated normal human T-cell blasts were cultured with L. donovani amastigotes. About 30% of the γ/δ⁺ T cells in the parasite exposed T-cell blasts expressed parasite antigens intracellularly without detectable intracellular parasites. Parasite exposed T-cell blasts had a reduced surface expression of HLA-DR and were lysed by the sorted CD56⁺ cells. In contrast, neither L. donovani amastigotes nor T-cell blasts exposed to heat killed amastigotes and/or were sensitive to the NK cell- mediated lysis. Of interest is that about 10% CD3⁺ peripheral blood T cells in two out of three Indian Kala-azar patients tested expressed intracellular L. donovani antigens.