CD1a is a 49 kDa transmembrane glycoprotein in the CD1 family of glycolipid antigen-presenting MHC-like molecules. CD1a contains one Ig-like domain in its extracellular region. It is expressed by most nonhuman mammals but not by mice or rats. Complexes of CD1a with beta 2-microglobulin and endogenous glycolipids are constitutively expressed on antigen presenting cells, cortical thymocytes, and Langerhans cells. CD1a is a target of autoreactive Th22 helper T cells in the skin.