Injection of anti-GPIbα antibody induces thrombocytopenia. Mice were injected with PBS, IgG negative control, or 1.0, 1.5, 2.0, 3.0, 4.0, or 5.0 µg anti-GPIbα antibody, and platelet counts were determined after 12 hours. Untreated mice (-) are shown as a control.