HLA-DRB1 and rheumatoid arthritis: HLA-DRB1*11:01 was the most frequent PR allele among HC, followed by *16:02 and *13:01 (15.2%, 8.2%, and 7.7% of all HC, respectively), while in RA patients the most frequent PR allele was *16:02, followed by *11:01 and *13:02 (9.8%, 6.8%, and 4.1% of all patients, respectively) (Figure 2, Table 2).