CD1-Restricted T Cells: T Cells with a Unique Immunological Niche

Until recently, antigen presentation to T cells was defined only by proteins encoded within the MHC locus. That definition has now been expanded to include proteins encoded outside the MHC locus, most notably the CD1 family of proteins. The pathway of CD1-presented antigens diverges from that of MHC processing, indicating that the CD1 antigen-processing pathway may be complementary to the MHC pathways. The most surprising finding of the CD1 antigen-presenting system is that the antigens presented by CD1 are not peptides, but rather lipid and glycolipid in nature. The most compelling evidence for the role of CD1-restricted T cells in immune homeostasis stems from studies of mycobacterial infection and autoimmunity. These studies suggest that CD1-restricted T cells promote cell-mediated immune responses to intracellular infection and protect against anti-self responses.