HLA-DRB1 and rheumatoid arthritis: Also in these samples, HLA-DRB1 is significantly higher expressed in HLA-DRB1 SE-positive RA patients (carrying at least one HLA-DRB1*04 allele) compared to HLA-DRB1 SE-negative RA patients (carrying no HLA-DRB1*04 alleles) (Figure 6A).