Factor XII-induced fibrinolysis. Diminished proactivator activity and drastic reduction of activator activity in...

Fibrinolytic studies in gamma G fractions of three Fletcher factor-deficient plasmas (functionally deficient in prekallikrein) revealed weak or no factor XII-independent activator activity. Two of the three Fletcher trait patients showed no plasminogen activator activity in clot lysis, fibrin plate, and amidolytic assays. The third patient showed no activator activity as determined by clot lysis and amidolytic assays but gave 10% of the activator activity detected in normal undiluted gamma G fraction in absence of HFf when determined by fibrin plate assay. Normal plasma gamma G fractions showed detectable and significant plasminogen activator activity. These fractions did not contain kallikrein or activated factor XI activities, thus indicating that the activator activity could not be attributed to the presence in these fractions or trace of these activated factors. Furthermore, factor XI-deficient plasma gamma G fraction, which was shown to contain no activated prekallikrein, showed normal plasminogen activator activity. Finally, specific antibodies to prekallikrein were shown not to quench the activity of plasminogen activator present in normal plasma gamma fraction. A double genetic deficiency to explain the absence in Fletcher factor-deficient plasma gamma G fractions of both prekallikrein proactivator and activator activities is not likely. Thus plasma prekallikrein, besides being a known plasminogen proactivator, appears to be required for the expression of a plasminogen activator activity.