To compare IgG subclass distribution of autoantibodies to native type II collagen in patients with rheumatoid arthritis (RA) and in other rheumatic and inflammatory diseases including systemic lupus erythematosus (SLE).
The IgG subclass of antibodies to native type II collagen were measured by modified ELISA using chemiluminescent detection and subclass-specific monoclonal antibodies in sera that contained IgG antibodies to collagen using conventional ELISA.
Antibodies to native type II collagen were present in sera of 20% of 323 patients with RA. 9% of 211 patients with SLE, 12% of 50 patients with osteoarthritis, and 13% of 75 patients with other chronic inflammatory diseases, but the highest levels occurred in patients with RA. The IgG subclass distribution of these antibodies differed markedly according to disease. In RA the predominant subclasses were IgG1 (58%) and IgG3 (47%), whereas in SLE the predominant subclass was IgG4 (69%). IgG2 was represented across all disease groups. Overall the frequency of IgG1 and/or IgG3 antibodies to type II collagen (84%) was significantly greater in RA than in other disease groups combined (20%) (p < 0.0001).
Antibodies to native collagen in RA were predominantly of the complement fixing and potentially damaging subclasses IgG1 and IgG3, but in SLE were of the non-complement fixing subclass IgG4; in other diseases, where present, antibodies were mostly IgG2 and of low level. These observations support the importance of autoimmunity to collagen in the pathogenesis of RA.