TERMINAL COMPLEMENT COMPLEXES AND C1/C1 INHIBITOR COMPLEXES IN RHEUMATOID-ARTHRITIS AND OTHER ARTHRITIC CONDITIONS

Terminal complement complex (TCC) and Clr-Cls-Cl inhibitor complex (Cl/Cl INH) concentrations were measured in plasma and synovial fluid from patients with arthritis and related to other measures of disease activity. Both TCC and Cl/Cl INH concentrations were significantly increased in patients with rheumatoid arthritis (RA) compared with patients with osteoarthritis (plasma and synovial fluid, P < 0.05) and normal subjects (plasma only, P < 0.001). In the patients with RA, there was no correlation between plasma or synovial fluid TCC concentrations and IgM rheumatoid factor, immune complex or Cl/Cl INH levels. However, in 10 patients with seronegative RA, Cl/Cl INH and immune complex levels correlated significantly in synovial fluid (r = 0.69, P < 0.05) although not in plasma (r = 0.52). Plasma and synovial fluid TCC and Cl/Cl INH concentrations did not differ in rheumatoid patients with severe compared with mild joint disease (categorized by the Ritchie score). These results confirm a role for complement activation in RA but suggest that several mechanisms are involved in its pathogenesis.