Abundant urokinase activity on the surface of mononuclear cells from blood and bone marrow of acute leukemia patients.

We have examined the mononuclear cell fraction from 35 individuals, 18 with hematologic malignancies and 17 healthy controls for the presence of cell surface-associated plasminogen activator (PA) activity. PA activity was found on the cell surface of 10 out of 12 samples from patients with acute leukemia. In addition to active urokinase (uPA) found on the cell surface in four out of five acute myeloid leukemia patients, tissue-type PA activity was detected in the same samples (3 of 5). Two out of four samples from acute lymphoid leukemia displayed only uPA activity and three out of three samples from biphenotypic leukemia were also clearly uPA-positive. Plasmin activity was not detected in any of the samples. PA activity was not found on the surface of mononuclear cells from either patients with chronic lymphoid leukemia or healthy controls and, in this respect, the cell surface-bound uPA activity behaved as a marker for acute leukemia. The finding of PA activity on the cell surface in acute leukemia suggests that there may be continuous generation of plasmin with consequent consumption of plasma plasmin inhibitors.