Studies of the Procoagulant and Fibrinolytic Activity of Promyelocytes in Acute Promyelocytic Leukaemia

Abstract

S ummary . Malignant cells from four patients with acute promyelocytic leukaemia (APL) were analysed for coagulant and fibrinolytic activity. For comparison polymorphonuclear leucocytes from normal donors and myeloblasts from patients with acute myelogenous leukaemia (AML) were also tested. The APL cells compared to the other cells consistently shortened the recalcification time and partial thromboplastin time of normal, factor VIII deficient and factor IX deficient plasma, but had no effect on factor X deficient or factor VII‐X deficient plasma. APL cells demonstrated increased (250–1500%) tissue factor activity when tested in a two‐stage assay in which tissue factor is the rate limiting component. The increased tissue factor activity was primarily found in the granular fraction of APL cells. Fibrinolytic and proteolytic activity of the APL cells was variable. Cells from three of the APL patients demonstrated a slight increase (150–400%), while the cells from one APL patient had markedly diminished proteolytic activity. The increased fibrinolytic activity was associated primarily with the granular fraction. Although the fibrinolytic activity is increased, it does not parallel the increase in tissue factor activity. This imbalance of coagulation and fibrinolysis in the cellular composition of promyelocytes could explain the high incidence of clinical thrombo‐haemorrhagic disorders related to intravascular coagulation in APL.