Terminal complement pathway activation and low lysis inhibitors in rheumatoid arthritis synovial fluid.

Abstract

To investigate terminal complement activation and lysis inhibitors in rheumatoid arthritis (RA). C5a, vitronectin and clusterin were quantitated by enzyme immunoassays in plasma and synovial fluid (SF) in RA (n = 30) and osteoarthritis (OA) (n = 11). In RA the concentration of C5a was 3-fold increased in plasma (21.9 vs 7.2 micrograms/l) and 5-fold increased in SF (7.8 vs 1.7 micrograms/l) compared to OA. The SF/plasma ratios for C5a, vitronectin and clusterin were 0.35, 0.36 and 0.23, respectively, not significantly different in the 2 diseases. SF terminal pathway activation in RA combined with low local levels of lysis inhibitors might allow lytic or sublytic attacks on local cells, resulting in inflammation and cell damage.