CD1a: ProductsCluster of Differentiation 1a (CD1a) is a transmembrane glycoprotein in the CD1 family of MHC-like molecules. It is expressed by most mammals but not by mice or rats. Human CD1a is a 311 amino acid protein with a predicted molecular mass of 49 kDa. It binds to lipid and glycolipid antigens and presents them to T cells. Antigen-presenting cells, Langerhans cells, and thymocytes express CD1a, where it traffics between endosomes and plasma membrane lipid rafts. Heterodimerization with beta-2-Microglobulin is required for CD1a membrane trafficking, and CD1a binding to exogenous lipids results in CD1a protein stability. The activation of thymus-localized T cells during the development of Gravesâ disease and Hashimotoâs thyroiditis may be initiated by CD1a expressed by CD83+ dendritic cells.