TNF and leishmaniasis: Multiple studies suggest dendritic cells provide the principal source of IL-12 early in leishmaniasis, triggering NK cell activation.[65, 66] Direct stimulation of the TLR-2 on NK cells by an L. major lipophosphoglycan (LPG) leads to up-regulation of TLR-2 and increased production of IFN-γ and TNF-α,[67] suggesting the existence of an additional, accessory cell-independent route of NK cell activation in leishmaniasis.