Plasminogen activator in acute myeloid leukaemic marrows: u‐PA in contrast to t‐PA in normal marrow

Leukaemic and normal bone marrow samples were compared in terms of their content of the fibrinolytic agents, tissue plasminogen activator (t‐PA) and urokinase‐type plasminogen activator (u‐PA) and their inhibitors, plasminogen activator inhibitors 1 and 2 (PAI‐1 and PAI‐2). Normal marrow contained t‐PA as the principal plasminogen activator, whereas in leukaemic marrow samples u‐PA was the predominant activator. Both normal and leukaemic marrows contained PAI‐1 in similar amounts, but whereas normal marrow contained significant amounts of PAI‐2 the leukaemic marrows contained very little. Plasminogen activators were present in uncomplexed, active forms and plasmin–α2‐antiplasmin complexes were generated locally more prominently in leukaemic marrows. u‐PA associated with blast cells may contribute to the severe forms of haemorrhage sometimes occurring in myeloid types of leukaemia.