Fig 1: IL-33 is required for ILC2-mediated enhancement of Th2 cell response(A) WT mice were challenged i.n. with PBS or papain and then sacrificed on day 3 (acute) or 16 (chronic). IL-25, IL-33, and TSLP were measured by ELISA (mean ± SEM; n = 8–14; ns, not significant, **p < 0.01, ****p < 0.0001, Student’s t test).(B) WT mice sensitized with OVA/alum or alum alone on days 0 and 7, followed by four doses of OVA i.n. challenges on days 11–14. These mice were sacrificed on days 11, 13, and 15. IL-25, IL-33, and TSLP were measured by ELISA (mean ± SEM; n = 8–11; ns, not significant, *p < 0.05, **p < 0.01, ****p < 0.0001, Student’s t test).(C and D) WT mice and mice deficient for CIKS, IL-33, and TSLPR are acutely challenged with PBS or papain, and mice were sacrificed on day 3.(C) Eosinophils in BALF and lung were analyzed by flow cytometry. The total numbers were counted and plotted (mean ± SEM; n = 6; ****p < 0.0001, ns, not significant, Student’s t test).(D) Lung cells were stimulated with PMA/ionomycin, and then IL-13-producing ILC2s were analyzed by flow cytometry. Percentages of IL-13+ ILC2s were calculated and plotted (mean ± SEM; n = 5–6; ****p < 0.0001, ns, not significant, Student’s t test).(E–G) Mice were chronically challenged with papain or PBS and sacrificed on day 16.(E) Eosinophils in BALF and lung were analyzed by flow cytometry. The total numbers were counted and plotted (mean ± SEM; n = 5; ****p < 0.0001, ns, not significant, Student’s t test).(F) Th2 cells in the lung were analyzed by flow cytometry. The total numbers were counted and plotted (mean ± SEM; n = 5; *p < 0.05, ns, not significant, Student’s t test).(G) ILC2s in the lung were analyzed by flow cytometry. The total numbers were counted and plotted (mean ± SEM; n = 5; ****p < 0.0001, ns, not significant, Student’s t test).(H) Shown are the microscopic images of lung tissue sections stained with periodic acid-Schiff.(I) Eosinophilic scores and total lung histopathology scores were plotted (mean ± SEM; n = 4–10; *p < 0.05, **p < 0.01, Student’s t test).Results are representative of at least two independent experiments. See also Figures S2 and S4.