CD1 is a family of 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.CD1 glycoproteins can be classified primarily into two groups which differ in their lipid anchoring: Group 1 (CD1a, CD1b and CD1c) is expressed on cells specialized for antigen presentation; Group 2 (CD1d) is expressed on a wider variety of cells; CD1e is a outlier,expressed intracellularly with unknown function.CD1 proteins play important role in CD1-restricted T cells functions in antimicrobial responses, antitumor immunity, and in regulating the balance between tolerance and autoimmunity.