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 complex on membranes and have an unique property in forming tubular structures containing between 12 and 18 monomers, closely resembling the membrane attack complex (MAC). Primary site of synthesis is hepatocytes, secondary sites are monocytes, fibroblasts and glial cells. The normal level of C9 in plasma is 60 g/mL, and up regulated from hepatocytes by IFN-g. This antibody is specific for complement factor C9.