Immunological evidence that human factor VIII is composed of two linked moieties

The relationship between the three measurable components of the factor VIII complex, procoagulant activity (VIII:C), Ristocetin cofactor (VIIIR:WF) and factor VIII related antigen (VIIR:AG), has been investigated using a solid phase immunoadsorption system in which homologous antibodies specific for VIII:C are insolubilized onto Sepharose beads. The VIII:C component of partially purified factor VIII can be completely separated from the Willebrand factor (VIIIR:WF/VIIIR:AG) by this technique. The loss of VIII:C has no detectable effect on the molecular size, antigenicity or electrophoretic mobility of the original molecule. The Willebrand factor (WF) recovered from these immunoadsorption columns was used to absorb heterologous antisera to factor VIII. A specific heterologous antiserum to VIII:C, which no longer neutralized VIIIR:WF nor precipitated VIIIR:AG, was obtained. Heterologous antisera to WF were prepared which potently neutralized VIIR:WF and precipitated with VIIIR:AG, but also weakly neutralized VIII:C (titre I u/ml). This study is compatible with the theory that VIII:C and VIIIR:WF/VIIIR:AG are two different but linked entities.