CD1 (or Cluster of Differentiation 1) is related to class I MHC molecules. CD1 is expressed on the surface of antigen presenting cells and presents lipid antigens to T cells. There are 3 groups of CD1 differing in their lipid anchoring. Group 1 contains CD1a, CD1b and CD1c. Group 2 contains CD1d. Group 3 contains CD1e. CD1 structure is comprised of a heavy chain with a1, a2 and a3 domains which is non-covalently associated with β-microglobulin. CD1 contains a larger and deeper antigen binding groove than class I MHC molecules.
