Elimination of protease-inhibitor complexes from the arthritic joint.

In the rheumatic joint, destructive proteolytic enzymes are released and counteracted by complexation to the predominant inhibitors alpha 2-macroglobulin and alpha 1-antitrypsin. The articular elimination of these complexes is thought to be of decisive importance in the protease-inhibitor interplay influencing the inhibitory capacity of the synovial fluid. Protease-alpha 2-macroglobulin complexes showed an intraarticular half-life shorter than 2 hours in arthritis and were eliminated by various routes including phagocytosis in cells of the synovial membrane and in regional lymph nodes, in addition to haematogenous resorption and uptake in the liver. The phagocytosed complexes were degraded to low-molecular-weight metabolites excretable in the urine. The articular elimination of elastase-alpha 1-antitrypsin complexes seemed to be an equivalent process, but an additional intrasynovial dissociation of the complexes was also indicated. Thus the intraarticularly released elastase seemed to be bound and eliminated in complex with alpha 2-macroglobulin.