Platelet tissue factor pathway inhibitor modulates intravascular coagulation.

Tissue factor pathway inhibitor (TFPI) is produced by megakaryocytes and is found internally within quiescent platelets but is not in α-granules. It is released in soluble form and expressed on the surface of platelets that are dual activated with thrombin plus collagen. Platelet TFPI is exclusively TFPIα, the most evolutionarily conserved TFPI isoform. It appears to be physiologically active as an inhibitor of tissue factor (TF) initiated FXa generation in vitro, and acts locally to dampen clot growth in a murine vascular injury model. These data suggest that platelet TFPI plays an important role in modulating TF activity within a growing clot thereby preventing formation of an occlusive clot.