Human Coagulation Factor XI Heavy Chain Antibody

Coagulation factors XI and XIa refer to the pro and active forms of the same protease, respectively (1). Factor XI is synthesized in the liver and circulates in the plasma as a disulfide bond-linked dimer complexed with high molecular weight kininogen. Factor XI is converted into XIa via either the contact phase of blood coagulation or thrombin-mediated activation on the platelet surface. The resulting XIa converts factor IX into IXa, which subsequently activates factor X into Xa. Factor Xa in turn activates factor II/thrombin to complete the coagulation cascade. Patients with factor XI deficiency are prone to excessive bleeding after hemostatic challenge. There are two alternative splicing forms. Isoform 1 corresponds to the circulating plasma factor XI and isoform 2 is produced by platelets and megakaryocytes but absent from other blood cells (2). The 625 amino acid precursor of isoform 1 consists of a signal peptide (aa 1‑18) and the mature chain (aa 19‑625). The mature chain (XI) can be further processed into the heavy chain (aa 19‑387) and the light chain (aa 388‑625) (XIa).