Effect of IVIG treatment using different mice, IVIG preparations, and antibodies. (A) C57BL/6 mice were treated with 2 g/kg Gamimune IVIG. Results were similar to those seen with BALB/c mice in Figure 1B-C. n = 3; *P < .05. (B) Results in BALB/c mice pretreated with 2 g/kg of another preparation of IVIG (Gamunex) were also comparable to those treated with Gamimune IVIG in Figure 1B-C. n = 3; *P < .05. (C) Two additional anti-GPIbα monoclonal antibodies were tested in BALB/c mice. Mice were pretreated with 2 g/kg Gamimune IVIG on day 1, and given 7 μg of either p0p9 or p0p11 antibody on day 2. IVIG pretreatment was ineffective at attenuating thrombocytopenia caused by these 2 antibodies; n = 3. (D) No anti-idiotype effect of Gamimune IVIG on these monoclonal antibodies was found. Incubation of IVIG with each mAb did not affect their ability to bind to platelets in vitro. Also, no IVIG was detected bound to platelets, or bound to platelets preincubated with JON or p0p antibody (data not shown); n = 3. In the control group, sheep anti–rat IgG-Fab fragment antiserum significantly decreased the ability of JON1 to bind to platelets. n = 3; *P < .005.