The fibrinolytic activity (FA) has been studied on the synovial membrane obtained from 16 patients with osteoarthritis (OA), 20 patients with rheumatoid arthritis (RA) and 11 control subjects. Todd's autohistographic method, modified by Lotti, was used to investigate the FA and the monoclonal antibodies against u-PA and t-PA were used to identify the main plasminogen activator.

Our results show that the FA is increased in the synovial membrane of patients with OA in comparison with the synovial FA of control subjects. In the synovial membranes from patients with RA, the FA shows different results: in some specimens FA is increased, and in others it is diminished or similar, compared with FA of samples from healthy controls. Thus, our data on synovial FA in OA confirm the previous reports, performed in vitro, on the activation of the plasmin system in this degenerative disease. The activity of the fibrinolytic system seems to participate in the cartilage degeneration and, via the activation of collagenase, to perpetuate the cartilage damage.