Leishmania donovani mediated higher expression of CCL4 induces differential accumulation of CD4CD56NKT and CD8CD56NKT cells at infection site.

Sterile cure from visceralized Leishmania donovani (L. donovani) needs Th1 cell support along with the assistance from innate immune cells, NK cells and NKT cells. NKT cells play as a connecting link between innate and adaptive immune cell and support T helper cell function. Earlier, a categorical function of CD56 positive CD4 or CD8 NKT cells was reported in visceral leishmaniasis (VL). It was observed in in vitro that CD4CD56NKT cells, but not CD8CD56NKT cells, were accumulated at the L. donovani infection site. Therefore, in vitro experiments have been carried out to decipher the mechanism behind preferential accumulation of CD4CD56NKT cells at infection site. In this study, 1.89 fold higher expression of CCL4/MIP-1β was noticed in infected macrophages. The higher expression of CCL4 was correlated with preferential accumulation of CCR5CD4CD56NKT cells and apoptosis of CD8CD56NKT cells at in vitro infection site. The CD4CD56NKT cells were also observed expressing TGF-β dominantly. Interaction of CCL4 chemotaxis was interrupted by blocking, which led to drift back the TGF-β producing CD4CD56NKT cells and promoted CD8CD56NKT cells recruitment in in vitro infection site. CCR5 blockade also reduced CD25 and FoxP3 positive CD4CD56NKT cells in in vitro infection site. Therefore, it was concluded that Leishmania promotes strategic expression of CCL4, which alternately attracts CCR5 cells, mostly expressing regulatory cytokines, at infection site. This reduces the CD8CD56NKT cells at infection site through Smad4 mediated TGF-β expression and activation of caspases. Data indicates that L. donovani induces higher expression of CCL4 in host cell to attract CCR5 cells under its strategic plan to downregulate host immune response.