Human atheromatous plaque extracts induce tissue factor activity (TFa) in monocytes and also express constitutive TFa

Tissue factor activity (TFa) is a major activator of the coagulation cascad e and may play a role in atheroma-induced thrombosis. Monocyte-macrophages (MO-MF) generate considerable quantities of TFa when stimulated by a variet y of inducers. To test the hypothesis that MO could be induced by atheromat ous plaque to generate TFa, plaque extracts obtained from patients with obs tructive atheromatous disease were used. These extracts were also assayed f or constitutive TFa. The constitutive activity was variable from extract to extract but could be very high, up to 250 U TFa. The TFa induced in MO cou ld be also very high. up to 200 U (i.e, 1/5 of the TFa of full strength rab bit brain thromboplastin). These findings point to a major role for MO-MF T Fa in the induction or thrombosis by atheromatous plaque.