Neutralization of inhibitor activity by recombinant factor VIII fragments. Neutralization of the inhibitory activity by factor VIII light chain (•) and factor VIII C2 domain (○). The patient's plasma was diluted to 2 BU/mL and incubated for 2 hours at 37°C with the indicated concentrations of recombinant factor VIII light chain or C2 domain. The residual factor VIII activity in the incubation mixture was determined relative to a control sample that was incubated in the absence of inhibitor plasma. Each datapoint represents the mean (±SD) of three experiments.