Protease inhibitors in rheumatoid synovial fluid: a quantitative analysis.

The concentrations of the main endogenous inhibitors of granulocyte proteases (anti-leukoprotease, alpha 1-antitrypsin, alpha 1-antichymotrypsin, and alpha 2-macroglobulin) were estimated in paired samples of synovial fluid and serum/plasma from seropositive rheumatoid arthritics and controls. Rheumatoid synovial fluid contained significantly higher levels of all inhibitors except antileukoprotease. The influence of the synovial membrane on these concentrations was taken into account by comparing the ratio between the observed concentration and that predicted from a certain regression curve fitted to a set of non-inhibitory reference proteins of extra-articular origin (orosomucoid, albumin, and ceruloplasmin). Divergences were interpreted as the net result of intra-articular production or consumption of the inhibitor in question. The results suggested a consumption of antileukoprotease and alpha 1-antitrypsin in the rheumatoid joint, while the increased levels of alpha 1-antichymotrypsin and alpha 2-macroglobulin probably reflected the altered trans-synovial membrane protein flux with some reservation for alpha 2-macroglobulin.