Phosphorylation of FcγRIIb after mAb binding to B-cell surface receptors at the same level. (A) A488-labeled RTX (solid black line) was titrated on Daudi cells to give the same binding as A488-labeled mAbs (5 μg/mL) specific for a range of other receptors (solid gray line). The binding of a saturating concentration of RTX (5 µg/mL) is included for comparison (dashed line). (B) Daudi cells were treated with A488-labeled RTX (RTX at concentration shown, others at 5 μg/mL) for 30 minutes and lysates were then blotted for pFcγRIIb and α tubulin as a loading control. Two representative examples are shown.