Cell surface receptors for IgE were isolated from detergent lysates of iodinated, IgE-saturated, rat basophilic leukemia cells by precipitation with anti-IgE antibodies followed by chromatography at acid pH. The isolated material showed a single 125I-band (m.w. ∼58,000) on gel electrophoresis in sodium dodecyl surfate and was used to immunize a rabbit. The resulting antiserum was reacted with lysates of surface iodinated mouse or rat tumor mast cells. Analysis of the precipitates on (10%) gel electrophoresis revealed one major peak comprising >80% of the detectable counts and having an estimated m.w. of ∼58,000. The antiserum reacted with detergent-solubilized and cell-bound receptors in the presence of absence of excess IgE; it also inhibited the binding of 125I-IgE. Cultured mouse mastocytoma cells never exposed to IgE released 3H-serotonin when incubated with F(ab′)2, but not Fab′ fragments of the antiserum, which had been rigorously freed of IgE and anti-IgE. The release was inhibited in the presence of excess IgE, was Ca++ dependent, and equaled 80% of the maximum obtained with IgE and anti-IgE. We conclude that aggregation of the receptors for IgE provides the critical signals for cell activation.
Parts of this work were presented at the Third International Congress of Immunology, Sydney, Australia, July, 1977, and at the American Society of Biological Chemists/American Association of Immunologists joint meeting in Atlanta, Georgia, June, 1978.