ELISA titers for biotinylated mAb in the presence of human inhibitor plasmas. ELISA titers for the binding of biotinylated mAbs ESH4 (A), 1B5 (B), and ESH8 (C) in the presence of test or control (noninhibitor hemophilia A) plasma were determined as described in “Methods.” The normal range for control plasma is shown as the gray band. A test-to-control ELISA titer ratio less than 2 SDs from the mean of the control plasma was considered significant. Plasmas represented by ● were run 2 or 3 times; error bars represent SDs. SDs are not reported for plasmas whose ELISA titers were lower than lowest dilution in the titration curve. ○ represent plasmas that were only run once because of limited amounts of plasma. (D) Venn diagram representing the overall distribution of C2 antibodies in the 26 patient plasmas.