Highly conserved antigen-presenting function of CD1d molecules

The lack of polymorphism of nonclassical antigen-presenting molecules has l ed to the proposal that they may carry out some conserved and essential ant igen-presenting function. Although this is a plausible hypothesis, the majo r histocompatibility complex has undergone dramatic expansions and contract ions through evolution, and there is surprisingly little evidence for inter species conservation of nonclassical class I molecules. The CD1d molecule, by contrast, shows an extremely high degree of functional conservation betw een mice and humans, with regard to its interaction with the relatively inv ariant TCRs that are expressed by NK T cells. This conservation for CD1d re cognition is observed either in the absence of exogenous Ag or together wit h a lipoglycan antigen. The close functional and phenotypic conservation of NK T cells, in mammalian species separated by approximately 50 million yea rs, suggests an essential. role in the immune system for CD1d recognition b y NK T cells.