CpG ODNs accelerate GVHD by TLR9 ligation of host but not donor APCs. CpG ODNs were given intraperitoneally to cohorts of mice on d0, d7, d14, d21, and d28 (100 μg/dose). Recipients were lethally irradiated on d−1. (A) B6 TLR9^−/− mice were given wild-type BALB/c BM and splenocytes (15 × 10⁶). n = 8 per group, P = .085. (B) Wild-type B6 mice were given BALB/c wild-type BM and BALB/c TLR9^−/− splenocytes (15 × 10⁶). n = 8 per group, P = .012. (C) B6 MyD88^−/− mice were given wild-type BALB/c BM and splenocytes (5 × 10⁶). n = 7 to 8 per group, P = .432.