The immunologic and clinical associations of the split products of C3 in plasma in juvenile rheumatoid arthritis.

A qualitative counterimmunoelectrophoretic assay for the complement activation products C3c and C3d was used to study plasma from children with juvenile rheumatoid arthritis (JRA) and other rheumatic diseases. Positive tests for C3c,d were found in all patients with active systemic lupus erythematosus (SLE), 7 of 10 patients with active systemic JRA, 16 of 29 with active polyarticular JRA, 7 of 20 with active pauciarticular JRA, and in only 2 of 20 with inactive joint disease. The incidence of positive assays for C3c,d in JRA was increased in the presence of positive latex fixation tests, antinuclear antibody tests, or elevated values for antiglobulins as determined by affinity chromatography, but these associations were not statistically significant. Three joint fluids from children with pauciarticular JRA were negative for C3c,d. These studies show that the subgroups of JRA defined by clinical criteria are heterogeneous by current laboratory parameters and that evidence implicating antigen-antibody complexes in the pathogenesis of JRA is lacking in many patients.