Evidence for immunosuppression by high-dose gammaglobulin.

High-dose immunoglobulin therapy, which is useful for the treatment of idiopathic thrombocytopenic purpura, autoimmune neutropenia, childhood epilepsy, and Kawasaki disease is postulated here to act by immunosuppressing the patients. Evidence provided here shows that the immunoglobulin inhibits phytohemagglutinin (PHA) stimulation, mixed lymphocyte culture (MLC) response, natural killer assay, antibody-dependent cell-mediated cytotoxicity, and cell-mediated lympholysis. These assays were all inhibited by IgG concentrations that exceeded normal levels by 1.5-2 times. It is also shown that Fc fragments were 100-1000 times more effective than intact IgG in inhibiting the PHA and MLC responses. Thus, it is likely that the Fc portion of immunoglobulin functions as an inhibitor of cellular immunity.