WHO/BS/2023.2457 WHO 1st International Standard TAFI, Plasma

TAFI (thrombin activatable fibrinolysis inhibitor), also known as procarboxypeptidase U or CPB2 gene product, is a protein that plays a crucial role in regulating blood clotting and fibrinolysis. It is synthesized and secreted by endothelial cells and circulates in the bloodstream as an inactive zymogen. TAFI can be activated to form TAFIa (carboxypeptidase U) by the enzymes thrombin (enhanced by thrombomodulin) and plasmin. Once activated, TAFI inhibits fibrinolysis by removing C-terminal lysine residues generated by plasmin in partially degraded fibrin, a process that reduces the binding of plasminogen to fibrin and inhibits the catalytic conversion to plasmin by tPA.