Generation of Procoagulant Activity ( PCA ) by Phorbol - Esters - Induced Macrophages Derived From a Leukemic Promyelocytic Cell

Normal human monocytes and macrophages. as well as leukemic promyelocytes. generate potent procoagulant activity (PCA) resembling thromboplastin. In the present study only mild PCA was detected in a leukemic promyelocytic cell line (HL-60) and in promyelocytic cells induced to differentiate into neutrophils by dimethylsulfoxide (DMSO). After exposure to 1 2-O-tetradecanoylphorbol1 3-acetate (TPA). the leukemic promyelocytic cells assume characteristics specific to monocytes and macrophages. This differentiation was associated with potent PCA generation. No PCA was found in lymphoblasts and several lymphoid cell lines after exposure to TPA. The PCA in TPA-induced HL-60 cells resembles tissue thromboplastin and normal monocyte PCA in several aspects: (A) All three accelerate clotting through the extrinsic coagulation pathway; (B) all three are inhibited by concanavalin-A and protected by methyl-a-D-mannopyranoside. suggesting that the PCA contains carbohydrate moieties; (C) the PCA is located in the cell membrane. However. the mechanism of PCA generation in normal monocytes and in TPAinduced HL-60 cells differs in several aspects: (A) Endotoxin and phytohemagglutinin. which are potent stimuli of PCA generation in normal monocytes. have no effect on TPA-induced HL-60 cells; (B) HL-60 cells treated with TPA develop PCA before acquiring any other specific characteristic of monocyte or macrophages; (C) the development of PCA in TPA-induced macrophages is not dependent on cell adhesion or the presence of T cells. In spite of these differences. the production of PCA is additional evidence of the similarity between TPA-induced macrophages and normal human monocytes and macrophages. The HL-60 cells may provide a unique model for studying PCA generation in mononuclear cells.