Triggering of cultured neoplastic mast cells by antibodies to the receptor for IgE

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 sulfate 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 or 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. The authors conclude that aggregation of the receptors for IgE provides the critical signal for cell activation.