IVIg and anti-CD44 antibody inhibit thrombocytopenia in FcRn- and β₂M-deficient mice. (A) C57BL/6 or FcRn-deficient mice were pretreated with nothing (“Nil,” “anti-PLT”) or with 50 mg IVIg or 50 μg anti-CD44 antibody KM114. Thirty minutes later, all mice except Nil received antiplatelet antibody. Twenty-four hours later, all mice were bled and platelets enumerated. The x-axis indicates treatment groups; and y-axis, platelet count. n = 10 mice per group from 5 independent experiments. Data are mean ± SEM. (B) C57BL/6 or β₂M-deficient mice were treated as in panel A. n = 6 mice per group from 3 independent experiments. Data are mean ± SEM. (C) C57BL/6 or human FcRn transgenic mice were treated as in panel A, except that 1 μL of a rabbit polyclonal antiplatelet antibody was used to induce thrombocytopenia. Twenty-four hours later, all mice were bled and platelets enumerated. n = 4 mice per group from 2 independent experiments. Data are mean ± SEM.