NK cells inhibited the expansion and function of ILC2s in vitro via IFN-γ. NK cells inhibited the expansion and function of ILC2s in vitro via IFN-γ. ILC2s were cultured alone or with the indicated cells or reagents in the presence of IL-2, IL-7, and IL-33, as well as in the presence of IFN-γ–neutralizing or control Abs, for 3 d. Absolute numbers of ILC2s were assessed. IL-5 and IL-13 concentrations in the culture supernatant were analyzed by ELISA. (A) ILC2s were cultured alone or with the indicated amounts of poly I:C–activated NK cells. (B) ILC2s were cultured with 24-h culture supernatants from poly I:C–activated NK cells or control medium. (C) ILC2s were cultured or not with 50 μg of poly I:C. (D) ILC2s were cultured with IL-12–preactivated or untreated splenocytes, splenocytes from mice depleted of NK cells using PK136, or sorted NK cells at a 1:3 ratio. (E) Percentages of Ki-67–, IL-5–, and IL-13–expressing cells among ILC2s in (D) that were cultured or not with IL-12–preactivated NK cells. (F) Fold intensity of anti–GATA-3 staining relative to the intensity of isotype Ab staining in ILC2s from (D). (G) Fold intensity of anti–arginase-1, CD71, or CD98 staining relative to the intensity of isotype Ab staining in ILC2s from (D). All data in triplicates are representative of three independent experiments and are represented as the mean ± SEM. *p < 0.05, **p < 0.005, ***p < 0.0005. Jiacheng Bi et al. J Immunol 2017;198:3336-3344 Copyright © 2017 by The American Association of Immunologists, Inc.