Elevated C3 anaphylatoxin levels in synovial fluids from patients with rheumatoid arthritis.

Because cleavage products of the third component of complement augment inflammation and may contribute to arthritis, we used a competitive inhibition radioimmunoassay to measure levels of the low molecular weight cleavage products of the third component of complement, C3a and C3adesArg, in 72 synovial fluid samples. Mean levels of C3a/C3adesArg were more than sevenfold higher in 41 patients who had rheumatoid arthritis than in 15 patients who had degenerative joint disease or 5 patients who had traumatic arthritis. Striking elevations were also present in 2 patients who had acute gouty arthritis. A calculation of the fraction of intraarticular C3 cleaved showed that the patients with rheumatoid arthritis had a mean C3 cleavage of 11.6 +/- 11.0%, which was significantly higher than values of less than 1.5% for patients with degenerative joint disease or traumatic arthritis. In rheumatoid arthritis and gouty arthritis, specific immunoassay identified substantial quantities of the initial C3 cleavage fragments.