Tissue factor pathway inhibitor (TFPI) is a trivalent Kunitz type protease inhibitor. Its function is to regulate the tissue factor pathway of coagulation via inhibition of the tissue factor/activated factor VII complex and activated factor X. Studies performed in animal models and on human plasma samples have shown that it is the major regulator of tissue factor induced coagulation in vivo and in vitro. Previous studies performed in our laboratory have investigated the levels and distribution of TFPI in plasma. However, because the majority of TFPI is produced and stored in endothelial cells in vivo, it is important that further studies are performed in an endothelial cell model. The initial aim of this study is to validate and optimise a routinely used method to isolate and culture endothelial cells from umbilical cords. Using this model, the expression and regulation of tissue factor and TFPI in response to a number of stimulants will be determined. These include: heparin, known to release large quantities of TFPI from the cell surface; lipoproteins, to which TFPI is bound in plasma; and anti-TFPI antibodies, recently discovered in the plasma of patients with the anti-phospholipid syndrome. This project will provide a greater understanding about the role of TFPI in haemostasis. It will present new information on cell culture conditions used in TFPI studies, and the effect(s) of a number of important stimulants on TFPI expression and/or release.