CD1 (cluster of differentiation 1) is a family of glycoproteins expressed on the surface of various human antigen-presenting cells. CD1 glycoproteins are structurally related to the class I MHC molecules, however, in contrast to MHC class 1 proteins, they present lipids, glycolipids and small molecules antigens, from both endogenous and pathogenic proteins, to T cells and activate an immune response.
T cells recognise CD1 using TCR αβ, γδ, or CD36 family members. T cells that are activated by CD1-antigen complexes are called CD1-restricted T cells. 10% of all αβ T lymphocytes in human peripheral blood are Cd1-restricted, out of which, the most abundant are the T cells specific for CD1c.
The human CD1 gene cluster is located on chromosome 1. Genes of the CD1 family were first cloned in 1986, by Franco Calabi and C. Milstein, whereas the first known lipid antigen for CD1 was discovered in 1994, during studies of Mycobacterium tuberculosis. The first antigen that was discovered to be able to bind CD1 and then be recognised by TCR is C80 mycolic acid. Even though their precise function is unknown, The CD1 system of lipid antigen recognition by TCR offers the prospect of discovering new approaches to therapy and developing immunomodulatory agents.