Fast migrating protein, immunochemically related to human factor VIII, studied by crossed immunoelectrophoresis in agarose

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Abstract
Summary. A fast migrating protein (FMP) was detected by agarose radio‐crossed immunoelectrophoresis, in addition to factor VIII antigen (VII:RAg), using antiserum to human factor VIII (FVIII). FMP had partial immunochemical identity with FVIII, migrated as an α‐protein, and was distinct from α‐2 macroglobulin, fibronectin or IgM. FMP was precipitated by concanavalin A and was separable from the bulk of VII:RAg by ammonium sulphate fractionation. A significant amount of FMP was seen in normal serum (n= 12), plasma from patients with: (a) disseminated intravascular coagulation (n= 12) and (b) severe haemophilia A (n= 6). Trace amounts of FMP were observed in plasma from normal donors (n= 12), but neither VIII: RAg nor FMP was detectable in the plasma or serum from patients with severe von Willebrand's disease (n= 3). Freshly prepared cryoprecipitate contained trace amounts of FMP, similar to normal plasma, but increased levels were observed in antihaemophilic factor concentrates prepared for patient use. Significant levels of FMP were also seen in cryoprecipitate after storage at 4°C for 7 d and this generation of FMP was diminished by the addition of protease inhibitors. The presence of significant levels of FMP in situations where proteolytic enzymes may be activated and inhibition of its generation by protease inhibitors, suggest that this protein is produced by proteolytic action of enzyme(s) on the FVIII molecule.