CD1D(CD1d molecule) also known as R3G1, Antigen-presenting glycoprotein CD1d, R3G1, CD1D, is the sole group-2 member of the CD1 family of major histocompatibility (MHC)-like glycoproteins. Expressed on the surface of various human antigen-presenting cells. They are related to the class I MHC molecules, and are involved in the presentation of lipid antigens to T cells. It is the only member of the group 2 CD1 molecules. CD1d presented lipid antigens activate a special class of T cells, known as Natural Killer T (NKT) cells. When activated, NKT cells rapidly produce Th1 and Th2 cytokines, typically represented by interferon-gamma and IL-4 production. Jayawardena-Wolf et al. described 2 different pathways of Cd1d trafficking to endosomal compartments in mouse cells. A tyrosine-based motif governs recycling between the plasma membrane and the endosome, while Cd1d associates, like major histocompatibility complex class II antigens, with the invariant chain, or Ii, in the endoplasmic reticulum. Both pathways enhance antigen presentation to Cd1d-restricted natural killer T cells.