IgE-specific suppressor factors in normal human serum.

The effect of normal human serum on in vitro IgE production was studied in an attempt to determine whether IgE-specific suppressor factors are present in the circulation of nonallergic individuals. Sera from 10 nonatopic donors (serum IgE less than 20 I.U./ml) were filtered through Diaflo CF50A membranes (cutoff point 50,000 D) and various dilutions of the IgE-free serum filtrates (less than 150 pg/ml of IgE) were examined for their ability to suppress spontaneous in vitro IgE synthesis by peripheral blood mononuclear cells (PBMC) from patients with hyper-IgE states. Serum filtrates from all 10 nonatopic donors tested suppressed IgE synthesis (mean suppression = 70 +/- 4%). IgE suppression was isotype specific because addition of the serum filtrates to pokeweed mitogen-stimulated normal PBMC or to spontaneously activated B cells from patients with active systemic lupus erythematosus did not suppress IgG or IgM production. The IgE suppressor activity was destroyed by treatment with trypsin but not with neuraminidase or exposure to heat. Substantial suppressor activity bound to IgE-Sepharose but not to a control IgG-Sepharose column. Further evaluation of the IgE-binding serum IgE suppressor factor(s) revealed a marked affinity for peanut agglutinin-Sepharose but minimal binding to lentil lectin-Sepharose. These results suggest that human serum from nonatopic donors contain low molecular weight IgE-binding factors which selectively suppress IgE production but not IgG production. Characterization of ths IgE-binding suppressor factor(s) reveals physicochemical features similar to those previously described for rat T-cell-derived IgE-binding factors with IgE suppressive activity.