TFVIIakompleksi

TFVIIakompleksi, also called the tissue factor–factor VIIa complex, is a proteolytically active enzyme formed when tissue factor (TF) on cell surfaces binds circulating factor VIIa. It serves as the principal initiator of the extrinsic pathway of blood coagulation.

Formation occurs when TF is exposed to blood after vascular injury. In the presence of calcium ions and a phospholipid surface, the TF–VIIa complex proteolytically activates Factor X to Xa and Factor IX to IXa. Through these reactions, a small amount of thrombin is generated, which then drives the conversion of fibrinogen to fibrin and the propagation of clot formation. The complex can also activate Factor VII to VIIa, providing a positive feedback loop that amplifies coagulation.

Regulation and clinical relevance: The activity of the TF–VIIa complex is tightly controlled by tissue factor pathway inhibitor (TFPI), which inhibits TF–VIIa and Factor Xa on the membrane surface. Abnormal TF expression, such as during inflammation or cancer, can promote thrombosis, while deficiency can predispose to bleeding. Clinically, the extrinsic pathway is assessed by the prothrombin time (PT), which reflects TF–VIIa–dependent clotting.

Notes on biology: TF is a transmembrane glycoprotein that presents the protease VIIa to substrate proteins on the cell surface, enabling rapid initiation of coagulation upon injury. The TF–VIIa complex thus links vascular injury to thrombin generation and fibrin formation, integrating inflammatory signals with hemostasis.