GewebeFaktorVIIaKomplex

GewebeFaktorVI is not a standard term in modern coagulation biology. The correct and widely used term is tissue factor, often called Gewebefaktor in German, and it is designated Factor III in the coagulation cascade. There is no current Factor VI in the established nomenclature; historically a Factor VI label appeared briefly but it was removed or reassigned, with its functions integrated into other factors.

Tissue factor is a transmembrane glycoprotein encoded by the F3 gene (CD142) and is expressed by subendothelial cells, fibroblasts, and some leukocytes in response to injury or inflammation. Upon vascular injury, tissue factor comes into contact with circulating Factor VIIa, forming the tissue factor–Factor VIIa complex. This complex initiates the extrinsic coagulation pathway by activating Factor X to Xa and, to a lesser extent, Factor IX to IXa, leading to thrombin generation and fibrin formation. The extrinsic pathway works in concert with the intrinsic pathway to establish a stable clot.

Regulation of tissue factor activity involves tissue factor pathway inhibitor (TFPI), which limits TF–VIIa activity and helps prevent excessive coagulation. TF can also be carried by circulating microparticles from various cells, including cancer cells, contributing to a prothrombotic state in certain conditions.

Clinically, the activity of the tissue factor pathway is reflected in the prothrombin time (PT) test, which assesses the integrity of the TF-initiated extrinsic pathway. Aberrant TF expression or regulation is associated with bleeding disorders when deficient, or thrombosis in states of TF overexpression, such as during inflammation or malignancy.