Effect of the anti-FcR_II MoAb IV.3 (Fab fragments) and anti-FcR_III MoAb 3G8 (F[ab′]₂ fragments) on the GM-CSF–stimulated neutrophil-mediated Lym-1 antibody-dependent cytolysis.⁵¹Cr-labeled Raji cells were at 2 × 10⁴. The neutrophil-Raji cell ratio was 20:1. Lym-1 and GM-CSF were at 10 μg/mL and 1 ng/mL, respectively. The incubation time was 14 hours. (A) The lysis was 15.43 ± 6.17 (mean ± 1 SD, n = 4) with a median of 12.90 (confidence interval 95%, 5.61 to 25.24) in the absence of IV.3 and 0.02 ± 0.05 (mean ± 1 SD, n = 4) with a median of 0.00 (confidence interval 95%, −0.05 to 0.10) in the presence of 4 μg/mL IV.3. Cytolysis in the absence versus that in the presence of IV.3 was P = .0286. (B) The lysis was 16.34 ± 7.10 (mean ± 1 SD, n = 5) with a median of 14.10 (confidence interval 95%, 7.53 to 25.15) in the absence of 3G8 and 19.92 ± 11.43 (mean ± 1 SD, n = 5) with a median of 20.00 (confidence interval 95%, 5.73 to 34.11) in the presence of 4 μg/mL 3G8. Cytolysis in the absence versus that in the presence of 3G8 was P = 1.000.