Tissue Factor-Like Activity Of The Human Monocytic Tumor Cell Line U937

Abstract

Cells of the human monocytic cell line U937, derived from a patient with histiocytic lymphoma (Sundstrom and Nilsson, Int. J. Cancer 17:565, 1976) have procoagulant activity similar to that of activated peripheral blood monocytes, although about 10-fold more U937 cells than monocytes are required for equivalent activity. Procoagulant activity of the cells is Ca2+ dependent and is not demonstrable in factor VII deficient or factor X deficient plasma. Culture with E. coli 0127:B8 1ipopolysaccharide increases the procoagulant activity of washed U937 cells two-fold. Exposure of U937 cells to lymphokines from normal lymphocytes does not induce further coagulant activity. The slope of the log/log plot of cells vs. clotting time parallels that of human brain thromboplastin. Other cell lines of myeloid or lymphoid origin, e.g., K562 cells, WI-L2 cells, do not have procoagulant activity. Thus, U937 cells have constitutive factor VII-dependent coagulant activity similar to the tissue factor activity induced by activation of normal monocytes.In further experiments, U937 cells were incubated with purified human factor VII in the presence or absence of Ca2+ and then repeatedly washed. When subsamples of the cells were then added to recalcified factor VII deficient plasma in the absence of added tissue factor, the following clotting times were obtained: for cells incubated with factor VII in the presence of Ca2+,45"; for cells incubated with factor VII in the absence of Ca2+, 150". These data suggest that U937 cells can bind factor VII in a reaction requiring Ca2+, which then enables the cells to express their tissue factor-like activity in factor VII deficient plasma.