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Blood, 15 August 2004, Vol. 104, No. 4, pp. 1034-1041. Prepublished online as a Blood First Edition Paper on April 6, 2004; DOI 10.1182/blood-2003-12-4293.
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Fibrin-incorporated vitronectin is involved in platelet adhesion and thrombus formation through homotypic interactions with platelet-associated vitronectinFrom the Departments of Haematology, Medical Oncology, and Immunology, University Medical Centre, Utrecht, the Netherlands; and Department of Nephrology, Leiden University Medical Centre, the Netherlands.
When a blood clot is formed, vitronectin (VN) is incorporated. Here we studied the consequence of VN incorporation for platelet interactions under flow. Perfusion of whole blood over a fibrin network, formed from purified fibrinogen, resulted in approximately 20% surface coverage with blood platelets. Incorporation of purified multimeric VN into the fibrin network resulted in a 2-fold increase in surface coverage with platelets and in enhancement of platelet aggregate formation. A human monoclonal antibody (huMab VN18), directed against the multimeric form of VN, inhibited platelet adhesion to the combined fibrin/VN matrix to the level of adhesion on fibrin alone. This inhibition was also shown when whole blood was perfused over a plasma-derived clot. Surprisingly, the inhibitory action of the antibody was not directed toward VN incorporated into the fibrin network but toward VN released from the platelets. We conclude that VN-potentiated platelet-clot interaction requires VN in the clot and multimeric VN bound to the platelet surface. Our results provide evidence that homotypic VN interactions contribute to platelet adhesion and aggregation to a blood clot. This report demonstrates for the first time that self-assembly of VN may provide a physiologically relevant contribution to platelet aggregation on a blood clot.
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