Systemic activation of coagulation and thrombus formation in the microvasculature accompanies organ dysfunction and excess mortality in severe sepsis.
1 Tissue factor (thromboplastin) is a major initiator of the blood coagulation process.
2 Tissue factor is a transmembrane cell surface receptor for plasma clotting factor VII and exhibits homology with the cytokine-receptor family.
3 Tissue factor pathway inhibitor (TFPI) is an endogenous serine protease inhibitor, synthesized and secreted by endothelial cells, which inhibits factor Xa directly and the factor VIIa/tissue factor catalytic complex in a Xa dependent fashion.
4,5 A significant portion of endogenous TFPI is bound to the microvasculature through low-affinity binding to glycosaminoglycans. This pool of TFPI is releasable into the circulation by exposure to heparin. A small pool of TFPI is stored in platelets and secreted on activation and degranulation. The majority of circulating TFPI is bound to lipoproteins.
5 The circulating concentrations of TFPI vary widely in healthy volunteers and in patients with sepsis.
6 A study by Shimura et al
7 suggested that full-length TFPI was consumed in predisseminated intravascular coagulation conditions and that the truncated form of TFPI-antigen increased in patients with disseminated intravascular coagulation. The functional properties of circulating TFPI are not well delineated.