Demonstration of urokinase-related fibrinolytic activity in human plasma

Various preparations of anti-urokinase antibodies were found to quench a part of the plasma fibrinolytic activity. This part was also inhibited by a specific, urokinase inhibitor isolated from placenta. These observations indicate that plasma contains a urokinase-related immuno-reactivity. This activity was found to belong to the factor XII-independent proactivator system.