Isolated neutrophils from healthy donors or from G-CSF–treated patients were compared for expression of FcαRI (A), conventional ADCC via IgA2 (B), or reverse ADCC using either A77 sensitized HB58 target cells (C), or FcαRI-directed BsAb (D). Both effector cell populations expressed similar levels of FcαRI. At constant effector to target cell ratios, G-CSF–primed PMN were less effective than healthy donor PMN, with differences being significant for ADCC against SK-BR–3, either haptenized using anti-NIP IgA or HER-2/neu-directed BsAb (P = .01, or .03, respectively). Results from at least eight experiments are expressed as mean ± SEM. (A) (▪), Relevant antibody; (□), irrelevant antibody. (B through D) (▪), Healthy donor; (□), G-CSF–treated patient.