UNUSUAL MHC-LIKE MOLECULES - CD1, FC RECEPTOR, THE HEMOCHROMATOSIS GENE-PRODUCT, AND VIRAL HOMOLOGS

The MHC fold, with its well-characterized peptide-binding groove, can perform other functions in addition to presentation of antigenic pepti des to T cells. Homologs of MHC molecules have diverse roles that incl ude presentation of lipid antigens (by CD1), transport of immunoglobul ins (by the neonatal Fc receptor), regulation of iron metabolism (by t he hemochromatosis gene product, HFE), and deception of the host immun e system (by viral homologs). Recent crystal structures of two of thes e non-standard MHC-like molecules have allowed comparison of the recog nition properties of classical MHC molecules with those of their unusu al homologs.