Fig. 1.

Invariant natural killer T (iNKT) cells can become activated through a number of directly or indirect pathways. The ‘direct’ pathway acts through the recognition of synthetic or microbial ligands presented in the context of CD1d. In contrast, the ‘indirect’ pathways relies upon the release of cytokines from antigen-presenting cells (APC) that have been activated through Toll-like receptor (TLR) ligation in the presence or absence of recognition of CD1d–self-glycolipid complexes. In addition, iNKT cell–APC interactions can be influenced by ligation of a number of co-stimulatory molecules; for example, CD28, CD40L, OX40, GITR, ICOS, 41BB (CD137).