Factor IX (FIX) antibody, also known as Christmas Factor due to its pioneering patient Stephen Christmas, is a single-chain protein found in plasma (Mr 55,000) and contains the vitamin K-dependent amino acid γ-carboxyglutamic acid. Activation of factor IX antibody by factor XIa removes a 35 amino acid activation peptide to give a two-chain structure consisting of a light chain disulfide-bonded to a heavy chain. In the presence of calcium, the serine protease activated Factor IX (FIXa) complexes with Factor VIIIa on phospholipid surfaces to create the tenase complex, which converts Factor X to its activated form. Factor IX antibody is also inhibited by antithrombin. FIX plays an essential role in the coagulation cascade leading to thrombus formation. Its presence increases with age in humans and mice. Absent or defective FIX antibody is the cause of the X-linked recessive bleeding disorder hemophilia B. Recombinant factor IX is one current treatment, but Factor IX has also been an active target of gene therapy studies, and a number of pharmaceutical companies are currently engaged in clinical trials to find a gene therapy solution to hemophilia B. Extensive studies have determined that FIX functionality can be affected by changes in individual amino acids, such as the R338L Padua variant, and the naturally occurring Thr 148 variant. Green Mountain Antibodies has internally developed nine mouse monoclonal antibodies to Factor IX. The antibodies, their species specificities by ELISA, and their applications are listed in the following table. The antibodies have been tested in western blot, inhibition in APTT assay, ELISAs, and BLI. GMA-101 has been used in immunohistochemistry. A number of pairs have been identified, such as GMA-102 and biotinylated GMA-184, which can be used in a sandwich ELISA format to detect low levels of human FIX in plasma. Antibodies to Factor IX are produced via in vitro production methods, under serum-free conditions, and purified by Protein G affinity chromatography. They show to be > 98 % pure by SDS-PAGE. Custom conjugation is available. Products typically ship within 24 hours after receiving the purchase order.