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The procoagulant activity of mononuclear cells (MNCs) may play an important role in the disseminated intravascular coagulation seen in septic shock. This study compares the capacity of Escherichia coli (E. coli) and recombinant human TNF-α (rhTNF-α) to induce procoagulant activity by baboon MNCs. In vivo studies showed that MNC procoagulant activity was significantly increased at T + 120 min after LD100 E. coli infusion into baboons. Most of this procoagulant activity was attributable to tissue factor. In contrast, a bolus infusion of rhTNF-α (150 μg/kg) and a monoclonal antibody to activated protein C (2 mg/kg) did not induce any increase of MNC procoagulant activity at T + 120 min even though the plasma TNF-a level was 10 times higher than that seen following infusion of E. coli. In vitro studies showed that E. coli at concentrations comparable to that observed in the in vivo study and LPS at a concentration of 2.5 ng/mL induced more intense tissue factor expression by both human and baboon monocytes than rhTNF-α in the concentrations ranging from 10 to 1,000 ng/mL. These results suggest that TNF-α alone is not sufficient to induce noticeable MNC procoagulant activity, at least, in the early stage of this septic shock model.