Elevated plasma C3 anaphylatoxin levels in rheumatoid arthritis patients

Because synovial fluid levels of the C3 anaphylatoxins, C3a and C3a desArg, are more than 7 times higher in patients with rheumatoid arthritis (RA) than in patients with degenerative joint disease or traumatic arthritis, we conducted a prospective study of plasma levels of C3 and C5 anaphylatoxins in 11 RA patients. The mean level of C3 anaphylatoxin in 37 RA plasma specimens was twice as high as that in samples obtained from 9 normal volunteers (272.9 +/- 106.1 ng/ml versus 133.9 +/- 19.4 ng/ml) (P less than 0.05). We found that the joint index and the disease activity index were correlated with the plasma C3 anaphylatoxin level, and that the correlation values were similar to those for serum C-reactive protein level and for the Westergren erythrocyte sedimentation rate. In correlations of the joint index and disease activity index with combinations of laboratory test results, the plasma C3a level, the serum C-reactive protein level, and the erythrocyte sedimentation rate, we found that almost any pair of laboratory tests correlated more strongly than did any one test.