Fibrinogen is a plasma clotting factor composed of three different polypeptide chains (, and ). Under chronic inflammatory conditions, fibrinogen can be acted upon by the enzyme peptidylarginine deiminase 4 (PAD4), converting specific arginine residues to citrulline. Patients with rheumatoid arthritis (RA) produce antibodies that bind citrullinated human fibrinogen.1 The citrullinated fibrinogen and rEActive antibodies form immune complexes in RA patients, and these immune complexes can stimulate macrophages.2,3 Recently, it has been discovered that immunizing certain strains of mice with citrullinated human fibrinogen can induce the production of anti-citrullinated human fibrinogen antibodies and the development of arthritis that shares many pathophysiological fEAtures of the human disEAse.4,5Technical InformationSynonymscFBGcFGPurityHomogeneous by SDS-PAGE. Clottable proteins: 95%SourceFibrinogen, purified from human plasma, that has been shown by certified tests to be negative for HBsAg and for antibodies to HIV and HCV. Citrullinated with human recombinant PAD4MWUncitrullinated fibrinogen: chain isoform 1 (95 kDa), chain isoform 2 (69.8 kDa), chain (55.9 kDa) and isoform -B chain (51.5 kDa)FormulationFrozen solution with 50 mM Tris-HCl, pH 7.4, 150 mM sodium chloride