 The HLA-DRB3 locus encodes the HLA-DR52 specificity, is moderately variable and is variably associated with certain HLA-DRB1 types.The HLA-DRB4 locus encodes the HLA-DR53 specificity, has some variation, and is associated with certain HLA-DRB1 types.The HLA-DRB5 locus encodes the HLA-DR51 specificity, which is typically invariable, and is linked to the HLA-DR2 types.