Comparison of titers and apparent affinities for FVIII-binding IgG1 antibodies in patients in subgroups (SG) 2 and 4. Medians and IQRs for titers and apparent affinity constants of FVIII-binding IgG1 antibodies, as detected in patients of subgroup 2, who did not develop FVIII inhibitors, and patients in subgroup 4, who developed persistent FVIII inhibitors. Median IQRs for titers and apparent affinity constants include all antibody data for each patient in the respective subgroup at each time point analyzed. There is a significant difference in both titers and apparent affinity constants between patients of subgroups 2 and 4. ****P < .0001.