Major Histocompatibility Complex Class I Related Gene Protein (MR1)

MAIT cells are selected and/or restricted by MR1, a monomorphic major histocompatibility complex class I-related molecule that is markedly conserved in diverse mammalian species. MAIT cells are not present in germ-free mice, indicating that commensal flora are required for their expansion in the gut lamina propria. The localization of MR1 on chromosome 1 was also supported by the results of PCR amplification of the MR1 fragment from somatic cell hybrid DNAs. In contrast to other known human divergent class I genes, MR1 encodes peptide-binding domains similar to those encoded by HLA class I genes on chromosome 6 and by nonmammalian classical MHC class I genes. Identification of a homolog of MR1 in the mouse genome implied that the ancestor of MR1 was present in the primordial mammalian species.