Neither spleen nor inhibitory Fcγ receptor is required for IVIG amelioration of ITP in BALB/c mice. (A) Nonsplenectomized wild-type BALB/c mice respond to IVIG (1.0 g/kg) treatment; n = 8 per group. *P ≤ .0001, compared with untreated group. (B) Splenectomized wild-type BALB/c mice respond to IVIG (1.0 g/kg) treatment; n = 6 per group. P values are indicated. (C) FcγRIIB^−/− KO BALB/c mice (BALB/c KO) respond to IVIG (1.0 g/kg); n = 9 per group. *P ≤ .0001, compared with untreated group.