Synthesis of procoagulant antihaemophilic factor in vitro

The cells which produce the procoagulant part of antihaemophilic factor (factor VIII-C) in normal people have remained unknown. Normal blood leucocytes cultured in vitro with phytohaemagglutinin synthesised a procoagulant with the properties of factor VIII-C. The procoagulant was inhibited by human VIII-C inhibitor and itself absorbed human VIII-C inhibitor--properties which are regarded as specific for factor VIII-C. Unexpectedly, cultured leucocytes from haemophiliacs also synthesised the procoagulant in similar amounts. Possible explanations and implications of these findings are briefly considered.