FCGR2B and autoimmune thrombocytopenic purpura: Similar to IVIg in treating murine ITP, we have found that CD44 antibodies function independent of FcRn expression [36] and do not function in FcγRIIB deficient mice on the B6; 129S background [32]; dissimilar to IVIg [6], CD44 antibodies do not require the Fc portion to function therapeutically in murine ITP [32].