Complement factor C9 is a 71-kDa single-chain ellipsoid a-globular molecule of 558 amino acids including a leader sequence of 20 amino acids. C9 bind the C5b8 comple, Xenopus/Amphibian, on membranes and have an unique property in forming tubular structures containing between 12 and 18 monomers, closely resembling the membrane attack comple, Xenopus/Amphibian, (MAC). Primary site of synthesis is hepatocytes, secondary sites are monocytes, fibroblasts and glial cells. The normal level of C9 in plasma is 60 ug/mL, and up regulated from hepatocytes by IFN-g. This antibody is specific for complement factor C9.