AssayPro—Human Factor XI(FXI)

Introduction
Human coagulation factor XI (FXI), also called plasma thromboplastin antecedent, is a serine protease important for initiating the contact activation or intrinsic pathway of blood coagulation. FXI is present in plasma as a homodimer zymogen consisting of two identical polypeptide chains of 607 amino acids and 80 kDa each. FXI circulates in normal plasma at a concentration of 5 μg/ml. It is activated to form FXIa not only by factor XIIa through the contact pathway, but also by thrombin through feedback activation linking to tissue factor or extrinsic pathway. FXIa in turn cleaves factor IX and triggers a cascade event converting fibrinogen to a stable cross-linked fibrin clot formation (1 - 3). FXI also plays a role in the prevention of clot lysis from fibrinolysis (4). Congenital FXI deficiency is accompanied by mild and injury-related bleeding. Severe FXI deficiency is linked to low occurrence of ischemic stroke or venous thrombosis (5). In contrast, elevated FXI activity is a risk factor for stroke, venous thrombosis and coronary artery disease (6 - 8). FXI is a new target for the treatment and prevention of thromboembolism.

Principle of the Assay
The AssayMax Human Factor XI (FXI) ELISA kit is designed for detection of human factor XI in plasma, serum, and cell culture supernatants. This assay employs a quantitative sandwich enzyme immunoassay technique that measures FXI in less than 4 hours. A polyclonal antibody specific for FXI has been pre-coated onto a 96-well microplate with removable strips. FXI in standards and samples is sandwiched by the immobilized antibody and the biotinylated polyclonal antibody specific for FXI, which is recognized by a streptavidin-peroxidase conjugate. All unbound material is then washed away and a peroxidase enzyme substrate is added. The color development is stopped and the intensity of the color is measured.