Protease inhibitors in rheumatoid synovial fluid. Analyses of electrophoretic homogeneity and protease inhibitory capacity.

Paired plasma and synovial fluids from 17 patients with seropositive rheumatoid arthritis were examined for electrophoretic homogeneity/heterogeneity and enzymic inhibitory capacity of the protease inhibitors. The high degree of saturation (approximately 90%) of the polyvalent protease inhibitor alpha 2-macroglobulin in the rheumatoid synovial fluid contrasts sharply with the low saturation of alpha 1-anti-trypsin. The inhibitory reactivity of the non-complexed fraction of both of these dominating antiproteases was retained (approximately 85-90%). Thus, a selective inactivation of synovial alpha 1-antitrypsin could not be demonstrated. alpha 1-Anti-chymotrypsin revealed electrophoretic homogeneity in all synovial fluids. Electrophoretic heterogeneity of the plasmin inhibitor antiplasmin was detected in the majority of synovial fluids indicating plasmin activation. The existence of a protease-antiprotease imbalance in the rheumatoid joint was indicated by the high degree of saturation of alpha 2-macroglobulin and a cleavage of C3 in rheumatoid synovial fluids.