Unlike classical T cells, NKT cells are activated by CD1d and not MHCs. While classical T cells recognize MHC-presented peptides, NKT cells recognize lipids/glycolipids. One of the most famous NKT ligands is called α-galactosylceramide (αGalCer). Originally derived from sea sponges, this compound was found to effectively activate NKT cells. αGalCer also shares structural similarities with components in bacterial cell walls. As such, NKT cells can be potent fighters against bacterial infection.
NKT cells will reciprocally activate its antigen presenting cell upon lipid/glycolipid presentation. Once mature, NKT cells produce massive amounts of IFN-γ. Unique among lymphocytes, they are also capable of explosively releasing IL-4 and IL-13 (Th2-related cytokines). NKT cells burn up fast, downregulating their TCR following activation, and undergoing massive apoptosis once the threat has passed. NKT cell numbers remain deflated until new NKT cells emigrate from the thymus. Because of its ability to promote Th2 cells, NKTs been implicated in Type 1 Diabetes and Asthma.
Structure for αGalCer , a popular ligand of NKT cells.
Bendelac, A. et al. 2007. Ann. Rev. Immunol. 25:336.