HLA antigens and rheumatoid arthritis. Association between HLA-DRw4 positivity and IgM rheumatoid factor production.

Serologic HLA typing was carried out on 33 seropositive and 15 seronegative patients with rheumatoid arthritis (RA). Association with the DRw4 antigen was found only in seropositive RA (61%, compared with 27% in normal controls; P less than 0.05, Fisher's exact test), whereas the antigen had a normal frequency in seronegative RA patients (27%). The serum concentrations of IgM and IgE immunoglobulins were significantly higher in seropositive than in seronegative RA patients (p less than 0.01, Mann-Whitney test), whereas the concentrations of the other immunoglobulin classes and of the complement factors C3 and C4 did not show any significant differences.