HLA-DRB1 and rheumatoid arthritis: Moreover, Saal et al. showed that SE-positive individuals with EBV DNA detected in the synovial membrane had a higher risk of developing RA than individuals who were negative for one or both of these variables [19], and Chen et al. demonstrated synergistic effects between HLA-DRB1*04 and parvovirus B19 infection in RA susceptibility [12].