Tissue factor-like activity of the human monocytic tumor cell line U937

Undisrupted cells of the human monocytic tumor cell line U937 have procoagulant activity that is Ca2+ dependent and is not demonstrable in Factor VII or Factor X deficient plasma. Furthermore, U937 cells when incubated with purified human Factor VII in the presence of Ca2+ and then repeatedly washed promoted coagulation of Factor VII deficient plasma in the absence of added tissue factor. Culture with endotoxin increased the procoagulant activity of U937 cells approximately 5-fold. In separate experiments, exposure to lymphokines obtained from phytohemagglutinin-stimulated lymphocytes enhanced the procoagulant activity of U937 cells 4 to 110-fold. Other cell lines (of myeloid and lymphoid origin) tested lacked the procoagulant activity found in U937 cells. These results indicate that the constitutive tissue factor-like activity of U937 cells resembles that of normal activated human monocytes.