Protease inhibitors in rheumatoid synovial fluid

Abstract

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 (∼90%) of the polyvalent protease inhibitor α₂-macroglobulin in the rheumatoid synovial fluid contrasts sharply with the low saturation of α₁-antitrypsin. The inhibitory reactivity of the non-complexed fraction of both of these dominating antiproteases was retained (∼85–90%). Thus, a selective inactivation of synovial α₁-antitrypsin could not be demonstrated. α₁-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 α₂-macroglobulin and a cleavage of C3 in rheumatoid synovial fluids.