Affinity of FVIII-specific antibodies reveals major differences between neutralizing and nonneutralizing antibodies in humans.

Recently, we reported that distinct immunoglobulin (Ig) isotypes and IgG subclasses of factor VIII (FVIII)-specific antibodies are found in different cohorts of patients with hemophilia A and in healthy individuals. Prompted by these findings, we further investigated the distinguishing properties among the different populations of FVIII-specific antibodies. We hypothesized that the affinity of antibodies would discriminate between the neutralizing and nonneutralizing antibodies found in different study cohorts.