Neutrophil ADCC of B lymphoma cells is mainly dependent on FcγRI. (A) Neutrophil ADCC of Raji CD47KO cells opsonized with rituximab in the presence of SSG. FcγRI, FcγRIIa, FcγRIIIb or a combination thereof (indicated with “+” or “–”) were blocked on neutrophils using blocking f(ab′)2 fragments (n = 4-14 donors from 10 independent experiments). (B) Neutrophil ADCC of Raji wild type or CD47KO cells opsonized with rituximab or with FcγRI-selective rituximab in the absence or presence of SSG (n = 10 FcγRIIa-131HH–donors from 6 independent experiments). (C-D) Neutrophil trogocytosis and ADCC of 2 patient-derived primary CLL cells (patient 1, open symbols; patient 2, closed symbols) by neutrophils from healthy donors (2 allogeneic FcγRIIa-131HH neutrophil donors (d) per patient) with or without SSG. CLL cells were opsonized with rituximab or FcγRI-selective rituximab. CD47-SIRPα signaling was blocked by incubating the CLL cells with anti-CD47 f(ab′)2 fragments. For trogocytosis, SSG did not significantly enhance trogocytosis in the opsonized conditions. (E) Expression of FcγRIIIb, FcγRIIa, and FcγRI on neutrophils during stimulation with G-CSF and IFN-γ (n = 7 donors from 4 experiments). (F) Neutrophil ADCC of Raji CD47KO cells opsonized with rituximab or with FcγRI-selective rituximab in the absence or presence of SSG, by unstimulated (unstim) neutrophils, neutrophils stimulated for 4 hours, or neutrophils stimulated overnight (O/N) with G-CSF and IFN-γ (n = 7 donors from 3 independent experiments). Data are mean ± SEM. *P ≤ .05; **P ≤ .01; ***P ≤ .001; ****P ≤ .0001.