HLA-DR is a αβ heterodimer cell surface receptor in the HLA system. The subunits are coded by the genes: HLA-DRA, HLA-DRB1, HLA-DRB3, HLA-DRB4, HLA-DRB5. DRA is functionally preserved, and the variation comes from the 4 β-chain loci. There are only 2 distinct α peptides, but 100s of B1 variants and 10s from B3-B5. The combinations determine the DR serotype: DR1-DR18, and DR51-53 from DRB3-DRB5.
DR type is associated with many autoimmune conditions and other diseases.