Figure 3.

Time course of the phosphorylation of receptors in the presence of antigen stimulation and subsequent addition of hapten. RBL-2H3 cells (6.25 × 10⁶/ml), which had been partially sensitized with DNP-specific mouse IgE, were reacted with 0.3 μg/ml rat IgE oligomers at t = 0. At t = 10 min, DNP₆-BSA (100 ng/ml) and monomeric rat IgE (1 μg/ml) were added, and at t = 13 min, excess hapten (100 μM) was added. Hapten (100 μM final) was also added to the solubilization buffer to promote solubilization of antigen-bound receptors. Recovery of the receptors was assessed by the recovery of ¹²⁵I-IgE oligomer. Binding of oligomer was monitored simultaneously, and it was confirmed that binding of oligomer stopped after the addition of monomeric IgE. At each time point, rat and mouse IgE were precipitated with species-specific anti-IgE, and the receptors bound to them were analyzed for phosphotyrosine. The data are the average of two samples. (a) Time course of the phosphorylation of receptors bound by rat IgE oligomers. (b) Time course of the phosphorylation of receptors bound to mouse DNP-specific IgE. In these experiments, the relative phosphorylation of the receptors associated with the mouse (b) and rat IgE (a) approximated 8:1 (cf. Fig. 1 legend)