Neutrophils are required for terminal NK cell maturation. (A and B) Representative FACS profiles of splenic NK cells stained with anti-CD27 and anti-CD11b mAb from WT and Genista mice (A) or 1A8, RB6-8C5, or isotype control mAb–treated mice (B). Experiments were performed 6–20 times. n = 3–6. (C) Representative FACS histograms of CD43 expression of splenic NK cells from WT (black line) or Genista (gray line). Tinted histogram shows isotype control staining. Data represent at least 20 independent experiments. (C–E) Percentages of splenic NK cells positive for CD43, for WT and Genista mice (C, right); isotype control-, 1A8-, or RB6-8C5–treated mice (D); or donor WT NK cells 7 d after transfer into WT or Genista hosts (E). Experiments were performed three to six times. n = 3–4. Statistical significance was determined in a Mann-Whitney test. *, P < 0.05; **, P < 0.01; ***, P < 0.001. (F) Representative FACS profiles of splenic NK cells (gated on CD3⁻ NKp46⁺ or NK1.1⁺) from WT mice stained for CD43 and intracellular IFN-γ, 4 h after stimulation by incubation in isotype control, anti-NK1.1, or anti-NKp46 mAb-coated plates. (G) Frequencies of IFN-γ–producing splenic NK cells generated from CD43⁺ or CD43⁻ WT NK cells by stimulation on anti-NK1.1 or anti-NKp46 mAb-coated plates. (H) Amount of IFN-γ secreted per CD43⁺ (shaded bars) or CD43⁻ (open bars) NK cell in response to stimulation by incubation in anti-NK1.1 (top) or anti-NKp46 (bottom) mAb-coated plates. The MFI for IFN-γ of IFN-γ⁺ CD43⁻ NK cells was normalized with respect to that for IFN-γ⁺ CD43⁺ NK cells. Experiments were performed twice. n = 5–8. Statistical significance was determined in a Mann-Whitney test. *, P < 0.05; **, P < 0.01; ***, P < 0.001.