HLA-DRB1 and rheumatoid arthritis: Interestingly, while IgG anti-KAc-His2B was not associated with HLA-DRB1 SE in the RA cohort with or without subdividing based on CCP2 we could observe a negative association with HLA-DRB1*03 among CCP2+ patients that was to some extent dependent on IgG anti-CCP2 levels.