MZ B-cell depletion prevents FVIII inhibitor development when administered with PIC. Mice with hemophilia A received either MZ B-cell–depleting antibodies (MZ B cell depl), saline, or isotype control (Iso Cont) antibodies, followed by injection of PIC and 4 weekly doses of 2 μg of FVIII. Control mice that received saline followed by FVIII without PIC are included for comparison. Plasma was collected and evaluated for anti-FVIII IgG by ELISA (A). Plasma was also evaluated for anti-FVIII IgG by ELISA after an additional “boost” dose of 4 μg of FVIII (B). Plasma was evaluated for inhibitor titer by Bethesda assay both before (C) and after (D) the “boost” dose of FVIII. Error bars indicate SD. Horizontal lines represent mean of each group. **P < .003, ***P < .0002, ****P < .0001, 1-way ANOVA, post hoc Tukey test. ns, not significant.