HLA-DRB1 and rheumatoid arthritis: However, when considering the single alleles (DRB1*01 or DRB1*04), UPIA and RA patients carrying HLA DRB1*04 allele showed a higher positivity for Pg DNA in the synovial tissue compared to patients negative for the allele (57.1% vs. 16.7%, P = 0.04).