The mechanism of factor VIII inactivation by human antibodies. II. The effect of factor VIII R: antigen on the rate of interaction

Factor VIII R:Ag by binding to the procoagulant component (VIII:C) inhibits the extent and rate of interaction of human antifactor VIII antibodies with VIII:C. When this reaction is examined under ionic strength conditions (0.24M CaCl) which dissociate the two factor VIII components, the extent of the reaction is increased approximately two fold and the initial rate of interaction is increased three to four fold for both intact IgG antibody and its Fab' derivative. With isolated procoagulant component, increased ionic strength conditions only influence the rate of interaction. These studies further explain the peculiar time-dependence of this interaction.