Fig. 4: Neutrophils inhibit the tumoricidal activity of NK cells.

a–d Neutrophilia induced effector NK cell suppression in the pre-metastatic lungs. As depicted in a, NOD-scid mice were orthotopically injected with E0771 or E0771-g-csf cells. The mice were sacrificed at day 10. The total numbers of lung-infiltrating NK cells were calculated upon analysis by flow cytometry (b), and the percentages of IFNγ⁺ (c), and CD107a⁺ effector NK cells (d) were determined by flow cytometry. n = 5 mice per group. P values were determined by unpaired two-tailed t-test. e–h Depletion of neutrophils abolished tumor cell G-csf-overexpression-induced NK cell suppression. As depicted in (e), E0771 or E0771-g-csf cells were orthotopically implanted in NOD-scid mice, and the mice received control IgG or anti-Ly6G (Ly6Gab) daily 2 days after tumor cell implantation. The mice were sacrificed at day 10, and the total number of lung-infiltrating NK cells were calculated upon analysis by flow cytometry (f). The percentages of IFNγ⁺ (g) or CD107a⁺ effector NK cells (h) were determined by flow cytometry. n = 5 mice per group. P values were determined by one-way ANOVA with Tukey’s multiple comparisons test. i–k In i, a schematic diagram is to show the experimental design in j, k. Neutrophils were freshly isolated from the lungs of E0771-g-csf orthotopic tumor-bearing NOD-scid mice, and NK cells were derived from spleens of naïve NOD-scid mice. An ex vivo cytotoxicity assay was performed in a co-culture system including neutrophils, NK cells and tumor cells (3 ×  10⁴ AT3 cells or 1 × 10⁴ YAC-1 cells), with the ratios of neutrophil: NK cell: tumor cells at 10:10:1 or 20:20:1. The percentages of AT3 cells (j) and YAC-1 cells (k) killed by neutrophils and NK cells individually or together were determined. P value was determined by one-way ANOVA with Tukey’s multiple comparisons test. Data are represented as mean ± SEM (b–d, f–h) or mean ± SD of four biologically independent cell cultures (j, k). ns not significant. Source data are provided as a Source data file.