Immature human dendritic cells infected with Leishmania infantum are resistant to NK-mediated cytolysis but are efficiently recognized by NKT cells.

Dendritic cells (DC) play an important role in innate and adaptive immunity, interacting with T cells, NK, and NKT cells. A critical step in the interaction of the parasitic protozoa Leishmania with their host is the evasion of both innate and adaptive immunity, producing a long-lasting chronic infection. There is growing evidence that these parasites can modify the Ag-presenting and immunoregulatory functions of DCs. The cells and mechanisms involved in innate immune response against Leishmania are still poorly understood. In this study, we investigated how Leishmania infantum infection affects DC interactions with NK and invariant NKT (iNKTs) cells in humans. We found that infected immature DCs (iDCs) do not up-regulate HLA class I molecules. Despite this, iDCs become resistant to killing mediated by autologous NK cells due to the up-regulation of HLA-E expression, which protects target cells from NK-mediated lysis through interaction with the inhibitory receptor CD94/NKG2A. Furthermore, iDCs infected with L. infantum up-regulate CD1d cell surface expression and consequently can be efficiently recognized and killed by iNKT cells that produce IFN-gamma. These data suggest that L. infantum could be able to evade NK recognition; in contrast, iNKTs may play an important role in the immune response against Leishmania.