Typing Alleles of HLA-DM

Human leukocyte antigen DM (HLA-DM) is a major histocompatibility complex (MHC) class II-like molecule that facilitates antigen processing by catalyzing the exchange of invariant chain-derived peptides (CLIP) from class II molecules for antigenic peptides. The genes encoding HLA-DM, HLA-DMA and -DMB , are located in tandem in the class II region of the MHC, between HLA-DP and HLA-DQ loci (1 ). HLA-DMA and -DMB products co-localize with HLA-DR in the specialized acidic MHC class II compartment (MIIC) of antigen presenting cells, but no expression of these molecules is detectable at the cell surface. The interaction of DM with class II also aids in the subsequent rapid loading of high-affinity antigen-derived peptides into the MHC class II groove. There is now accumulating evidence that HLA-DM functions as a peptide editor that removes low-stability ligands and skews the class II peptide repertoire toward high-stability ligands (2 –4 ). Because of their role in antigen processing and their location within the class II region of the MHC, these genes have attracted attention as possible disease susceptibility loci.