NKT-cell subsets: promoters and protectors in inflammatory liver disease.

Natural killer T cells (NKT) are innate-like cells which are abundant in liver sinusoids and express the cell surface receptors of NK cells (e.g., NK1.1 (mouse) or CD161+/CD56+(human)) as well as an antigen receptor (TCR) characteristic of conventional T cells. NKT cells recognize lipid antigens in the context of CD1d, a non-polymorphic MHC class I-like molecule. Activation of NKT cells has a profound influence on the immune response against tumors and infectious organisms and in autoimmune diseases. NKT cells can be categorized into at least two distinct subsets: iNKT or type I use a semi-invariant TCR, whereas type II NKT TCRs are more diverse. Recent evidence suggests that NKT-cell subsets can play opposing roles early in non-microbial liver inflammation in that type I NKT are proinflammatory whereas type II NKT cells inhibit type I NKT-mediated liver injury.