IVIg treatment is effective against antibody-mediated ITP but not cell-mediated ITP. Platelet counts in irradiated SCID mice transferred with (A) 5 × 10⁴ nondepleted immune splenocytes from CD61 KO mice immunized against BALB/c platelets (n = 15; ○) or 5 × 10⁴ immune splenocytes depleted of either (B) CD8⁺ T cells (n = 18; ○) or (C) CD19⁺ B cells (n = 14; ○). Platelet counts in the SCID mice depletion groups treated with 2 g/kg IVIg (□) are also shown. Data are expressed as in Figure 1. The numbers above the data points are the P values calculated for the IVIg treatment groups as in Figure 1. NS indicates not significant. Kaplan-Meier survival plots for each group in panels A through C are shown in panels D through F. (D) The survival plot for control SCID mice that received human serum albumin (2 g/kg; *) is also shown.