HLA-DRB1 and rheumatoid arthritis: Conditional haplotype analyses demonstrated that B*08/Asp-9 and/or HLA-DPB1/Phe-9 alleles increase the RA risk on specific HLA-DRB1 backgrounds such as *09:01 and *15:02, with position 11 in HLA-DRB1 being determinant to this effect: while Val-11 and Leu-11 confer high risk, Ser-11 is highly protective for the disease.