{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"CD1 proteins have been demonstrated to restrict T-cell response to non-peptide lipid and glycolipid antigens. At least five CD1 genes (CD1a, b, c, d, and e) have been identified. CD1a is a protein of 43-49 kDa, belonging to a family of glycoproteins expressed on the surface of various human antigen-presenting cells such as dendritic cells and cortical thymocytes. Langerhans cells in the skin and some epithelia also express CD1a."}]}]}