Trogocytosis is accompanied by CD20 downmodulation on CLL B-cell targets. Purified PMNs were cocultured with CLL B cells at a 1:3 E:T ratio in the presence of 10 µg/mL of anti-CD20 antibodies RTX-WT, RTX-GE, OBZ-WT, OBZ-GE, the CET control antibody, or no mAb. At 3 hours, surface CD20 still available was detected by adding an excess of the same anti-CD20 antibody followed by anti-human IgG fluorescein isothiocyanate. The results are the MFI (of fluorescein isothiocyanate) for CD20 on CLL B-cell targets, observed in wells treated with the indicated antibodies for 3 hours, as a percentage of that in equivalent wells without any antibody added. The results are the means and standard deviations of 5 independent coculture experiments with (A) PMNs and CLL B cells or (B) 6 separate experiments performed in the presence (black bars) or absence (gray bars) of PMNs. *P < .05; **P < .01; ***P < .001.