CD4 T-cell–specific CXCR5 deficiency impairs anti-FVIII inhibitor induction. (A) Schematic diagram for generating mixed BM chimeras. Mixed BM chimera in irradiated CD4^−/− mice reconstituted with 80% BM from CD4^−/− mice plus 20% from WT mice or 80% from CD4^−/− mice plus 20% from CXCR5^−/− mice. (B) Flow cytometry analysis of CD4 and CD8 T-cell reconstitution in blood at 10 weeks after BM transplantation. Mixed-BM chimeric mice were immunized with rhF8, as shown in the experimental schematic in panel C. (D) One week after the fourth injection with rhF8, plasma samples were collected for a Bethesda assay to determine the FVIII inhibitor titers. The data shown are for 6 mice per group. **P < .01.