Tissue factor is a major stimulus for vegetation formation in enterococcal endocarditis in rabbits.

We examined the possible mechanisms of local initiation of coagulation in vegetation formation in enterococcal endocarditis by using a rabbit model. Contact activation and tissue factor expression by freshly excised aortic valves were assessed using assays developed for use with cultured cells. Bacteria alone lacked procoagulant activity and contact activation of plasma by excised valves did not occur. 4-d infected but not control valves expressed significant tissue factor activity (231 +/- 17 mU vs. 51 +/- 7 SE), which did not correlate with numbers of bacteria in vegetations. Tissue factor activity was also present in valves from rabbits infected for 1 and 2 d, as well as those from granulocytopenic and monocytopenic animals. Our findings suggest that tissue factor, expressed by host cells in response to infection, is a major stimulus for fibrin deposition in vegetation development.