Class-specific rheumatoid factors, DR antigens, and amyloidosis in patients with rheumatoid arthritis.

Class-specific rheumatoid factors (RFs) were measured by enzyme immunoassay in 59 patients with rheumatoid arthritis complicated by systemic amyloidosis (RA+A), 47 patients with rheumatoid arthritis without amyloid (RA), 106 patients with other rheumatic diseases (juvenile rheumatoid arthritis, systemic lupus erythematosus, Sjögren's syndrome), and 55 blood donors. The patients with RA+A were characterised by a high prevalence of RF negativity; the IgM RF concentration was raised in only 18 of the 59 patients (31%, p less than 0.001 v RA), the IgG RF concentration in 20 of 59 (34%, p less than 0.001 v RA), and the IgA RF concentration in 24 of 59 (41%, p less than 0.001 v RA). A higher prevalence of HLA-DR4 (p less than 0.001) and a lower prevalence of DR2 (p less than 0.05) were found among 48 tested patients with RA+A when compared with a control panel consisting of 500 blood donors. No significant differences in the prevalence of DR1-DR7 or B27 antigens were observed, however, between patients with RA with or without amyloid.