Phosphorylation of FcγRIIb after mAb ligation of B-cell surface receptors. The Burkitt lymphoma cell lines (A) Ramos FcγRIIb2-low transfectants, Raji, and Daudi, and (B) primary CLL cells were treated with 5 µg/mL A488-labeled mAb for 30 minutes. Lysates were then blotted for pFcγRIIb and α tubulin as a loading control. Two representative examples for each cell line are shown.