VIII:C was purified from intermediate-purity concentrate by adsorption on polyelectrolyte E5 and affinity chromatography on Sepharose/anti-VIIIR:Ag. The highly purified VIII:C preparation (sp. act. 1598 U/mg) was used to immunize Balb-C mice. Spleen cells from a mouse with a serum antibody titer of 963 U/ml were fused with P3 NSI mouse myeloma cells. Hybrid clones were screened by a coagulation inhibition assay and by a four-layer antibody adsorption procedure. Nine monoclonal antibodies specific to VIII:C were produced. Five of these antibodies have been cloned and grown in mouse ascitic fluid. Antibody titers from ascitic fluid ranged from 35 to 82,000 BU/ml. The antibodies, when radiolabeled, form a high-molecular-weight complex with antigens present in normal plasma and factor VIII concentrate, but not when incubated with CRM-negative hemophilic plasma. A two-site assay using a combination of monoclonal antibodies is able to detect VIII:CAg in normal plasma and in factor VIII concentrate. Sensitive two-site immunoradiometric assays using monoclonal antibodies as the solid phase have been set up.
