Correlation between levels of breakdown products of C3, C4, and properdin factor B in synovial fluids from patients with rheumatoid arthritis.

Synovial fluids from 31 patients with seropositive rheumatoid arthritis (RA) and 23 patients with seronegative RA had significantly increased levels of breakdown products to C3, C4, and properdin factor B when compared to patients with osteoarthritis (OA) (P less than 0.01). The same patients exhibited a considerable overlap of native C3, C4, and properdin factor B levels when their results were compared with those of OA patients. The parallel increase of C3d, C4d, and Ba levels in patients with RA suggests an activation of the complement system rather than a nonspecific enzymatic breakdown in synovial fluids.