Higher rates of proliferation and poorer survival of NK cells in the absence of neutrophils. (A and B) Representative FACS profiles of splenic NK cells from WT and Genista (A, or isotype control– and 1A8-treated mice (B) stained with anti-NK1.1 and anti-Ki67 mAb. Data a representative of three independent experiments. n = 3–4. (C and D) CFSE-labeled CD45.1⁺ WT spleen NK cells (donor) were transferred into CD45.2⁺ WT or Genista hosts for 7 d. (C) Representative FACS profiles show the percentage of donor WT NK cells (rectangle) after transfer into WT (top left) or Genista (top right) mice. Histograms of CFSE expression gated on donor CD45.1⁺ WT NK cells after transfer into WT (bottom left) or Genista (bottom right) mice. (D) 7 d after transfer into WT (left) or Genista (right) mice, the frequency of undivided (CFSE^high) or divided (CFSE^diluted) donor WT NK cells producing IFN-γ in response to stimulation with isotype control, anti-NK1.1, or anti-NKp46–coated plates was determined. (top) Representative FACS profile upon NK1.1 activation. (bottom) Statistical comparison of NK cell responsiveness in undivided (CFSE^high) and divided (CFSE^diluted) donor NK cells. Experiments were performed three times. n = 2–4. (E) Representative FACS profiles of WT or Genista NK cells (gated on CD3⁻ NKp46⁺ or NK1.1⁺) stained with anti–Annexin V and propidium iodine (Pi) after overnight incubation with medium, 1,000 U/ml IL-2 or 15 ng/ml IL-15. (F) Frequencies of Pi⁺ NK cells from WT (shaded bars) or Genista (open bars) mice after overnight incubation with medium, 1,000 U/ml IL-2 or 15 ng/ml IL-15. Experiments were repeated three times. n = 7–10. Statistical significance was determined in a Mann-Whitney test. *, P < 0.05; **, P < 0.01; ***, P < 0.005.