In vitro synthesis of human IgE is suppressed by human IgG

Recently it has been shown that intravenous immunoglobulin (IVIG) preparations suppress the in vitro synthesis of IgG, IgA, and IgM. In this paper we demonstrate that IVIG and IgG purified from a single donor's serum also suppress the in vitro synthesis of IgE. We had noticed this effect when we added human serum (HS) to in vitro cultures for IgE synthesis. The interleukin-4 (IL-4)-induced IgE synthesis from human peripheral blood mononuclear cells (PBMC) in the presence of fetal calf serum (FCS) was suppressed by HS in a dose-dependent fashion. The following results indicate that this suppression is mediated by IgG: (1) IVIG preparations, which consist mainly of IgG, suppressed the IgE synthesis from IL-4-stimulated PBMC in a dose-dependent way; (2) when HS was fractionated by protein G sepharose or anti-IgG sepharose, the eluate fractions (containing IgG), but not the effluent fractions (void of IgG) suppressed IgE synthesis, whereas the opposite was found when HS was fractionated by FCS-coupled sepharose. We conclude from these data that human IgG preparations suppress the in vitro synthesis not only of the IgG, IgA, and IgM isotypes, but also of the IgE isotype.