Factor iii

Factor III, or tissue factor, is a non-enzymatic cofactor that activates factor VII. Factor III is a protein that is located extra- and intracellularly. Its mass is 29kD. Factor III consists of three domains. One domain is located on the cell membrane and binds factor VII in the presence of calcium and phospholipids, and another domain is located intracellularly and performs signalling functions. Together with calcium and the negatively charged phospholipids, the membrane domain increases the protein binding between factor VII and factor X.

Factor III is assigned to cytokine receptor class II, which activates leukocytes. The complex of tissue factor and factor VII plays an important role in angionesis and the inhibition of apoptosis. Factor III is not detectable in serum or plasma if no clotting process is taking place. It can be isolated from almost all tissues. It is released in the event of injury, where it activates the F-VII after contact with it and increases its activity approximately a thousand fold. Endothelial cells produce the tissue factor after contact with the tumor necrosis factor alpha. Monocytes produce the tissue factor after contact with inflammation-activating molecules. Due to the heterogeneity of the complexes with phospholipids, the molecular weight in plasma is between 53,000 and 425,000 D. The most active forms of factor III can be detected in the lungs, brain and placenta.

In 1832 de Blainville made the observation that the injection of brain tissue in animal experiments leads to immediate clotting and thus to the death of the animal. Tackrah confirmed this observation by finding that injured tissue releases an activity that leads to clotting. Buchanan later systematically investigated this property. In 1892 Alexander Schmidt postulated a zymoplastic substance that converts prothrombin into thrombin. Further investigations by Fuld and Morawitz were finally able to separate the tissue-activating properties from the direct property of thrombikinase. Howell referred to the tissue property that is able to activate the extrinsic coagulation pathway as the "tissue factor". Hammarsten proved that the effect of the tissue factor is dependent on calcium ions.

1. HA Neumann (2014) The coagulation system. ABW-Wissenschaftsverlag GmbH Berlin S. 55f.