CD1d1 is a 48 kDa transmembrane glycoprotein in the CD1 family of glycolipid antigen-presenting MHC-like molecules. Complexes of CD1d1 with beta 2-microglobulin and endogenous glycolipids are constitutively expressed on antigen presenting cells, cortical thymocytes, liver sinusoidal endothelial cells, Kupffer cells, and hepatocytes. CD1d1-presented glycolipids are recognized by canonical NKT cells that utilize an invariant mouse V alpha 14-J alpha 18 chain in their T cell receptor (V alpha 24-J alpha 18 in human). The interaction with glycolipid-loaded CD1d1 is critical for NKT cell development and induces their rapid secretion of both Th1 and Th2 type cytokines. In humans, infection with HSV-1 suppresses NKT cell activation by blocking the intracellular cycling of CD1d1 in antigen presenting cells.