Fig. 3. The metastasis-modulating effects by neutrophils occur at the early stage of metastatic colonization.
a Model depicting the dual roles of neutrophils in metastatic colonization. In the absence of NK cells, neutrophils exclusively exert their tumoricidal effect thereby showing a net anti-metastatic effect; in the presence of NK cells, neutrophils are also tumoricidal but they suppress the more tumoricidal NK cells leading to a net pro-metastatic effect. b–e Determination of neutrophilia-induced metastasis regulation at the early stage of colonization. The diagrams in b, d show the experimental designs in c, e, respectively. The representative BLI images (left), and quantification of photon flux (right) in each group at various time points are shown in c, e. n = 5 NOD-scid mice in c and 6 NSG mice in e per group. P values were determined by unpaired two-tailed t-test. f Comparison of the tumoricidal activities of neutrophils isolated from C57BL/6J, NOD-scid and NSG mice. Lung-infiltrating neutrophils were freshly isolated from E0771-g-csf tumor-bearing mice for ex vivo cytotoxic assay against AT3 cells. Statistical significance was determined by two-way ANOVA. Neu: neutrophils. g–i The tumoricidal capacities of neutrophils and NK cells under non-inflammatory and neutrophilhigh inflammatory conditions. E0771 cells and E0771-g-csf cells were orthotopically implanted in NOD-scid mice to induce non-inflammatory and inflammatory tumor-bearing host conditions, respectively, with PBS injection as a control. The mice were sacrificed at the pre-metastatic stage (day 10), and lung-infiltrating neutrophils were isolated for the ex vivo cytotoxic assay against AT3 cells (g). Statistical significance was determined by two-way ANOVA. Lung-infiltrating NK cells were also isolated from the same mice for the ex vivo cytotoxicity assay against AT3 (h) or YAC-1 cells (i). P values were determined by unpaired two-tailed t-test (h, i). Data are represented as mean ± SEM (c, e) or mean ± SD of four biologically independent cell cultures (f–i). ns not significant. Source data are provided as a Source data file.