Inhibition of IL-3–induced  and β chain dimerization and phosphorylation by MoAb BION-1. (A) Immunoprecipitations using anti–IL-3R MoAb, 9F5, or anti-β_c MoAb, 8E4, from ¹²⁵I-surface-labeled MO7e cells preincubated with MoAbs BION-1, control anti-β_c MoAb 1C1, or medium alone (−), before being stimulated (+) or not (−) with IL-3. The radiolabeled proteins were spearated by SDS-PAGE and visualized by PhosphorImaging. The position and molecular weight of marker proteins are shown. (B) Immunoprecipitated proteins were probed using antiphosphotyrosine MoAb 3-365-10.