CD1d is a non-polymorphic, MHC class I-like molecule encoded by the CD1D gene, which is a member of the CD1 family of glycoproteins expressed on the surface of various human antigen-presenting cells. It presents lipid antigens, including phospholipids and glycosphingolipids, to a subset of T cells known as invariant natural killer T （iNKT） cells. When activated by CD1d-presented antigens, iNKT cells rapidly produce Th1 and Th2 cytokines, such as interferon-gamma and interleukin-4. CD1d is also involved in the selection and regulation of iNKT cells. Some known ligands for CD1d include α-galactosylceramide （α-GalCer）, a compound derived from a marine sponge, and various microbial and self-antigens.