Fibrin dissolution in synovial fluid.

Fibrinogen, fibrinogen-fibrin breakdown products (b.d.p.), fibrin stabilizing factor (FSF), plasminogen, alpha-2 macroglobulin and alpha-1 antitrypsin concentrations were estimated immunologically in normal and in pathological synovial fluids from patients with RA, gout, monoarthritis, rheumatic fever, osteoarthritis and traumatic arthritis. The fibrinolytic activity was determined by the fibrinplate method. Normal synovial fluid contained no fibrinogen, b.d.p., FSF or alpha-2 macroglobulin, but traces of plasminogen and alpha-1 antitrypsin. By increasing inflammatory reactions increasing amounts of the various factors were demonstrable. No distinct, specific, patterns were found. Spontaneous fibrinolytic activity was demonstrable in the most exsudative cases, and in these high concentrations of fibrin breakdown products were present. These were also demonstrable in most pathological synovial fluids proving a recent proteolytic activity. It is suggested, that the fibrin breakdown products in pathological synovial fluids are partly resistent to proteolytic activity.