Patients with thrombocytopenia after vaccination respond favorably to immunotherapy with intravenous steroids and immunoglobulins [169], whose possible benefits include blocking Fcγ receptor IIa (FcRγIIA), neutralizing anti-platelet factor-4 (PF4) antibodies by anti-idiotype antibodies, facilitating the catabolism of anti-PF4 antibodies, and modulating the immune cell compartment, including B cells that produce anti-PF4 [185]. The gene discussed is PF4; the disease is Thrombocytopenia.