IL-21R signaling is required for Th2 responses against Heligmosomoides polygyrus. C57BL/6 and IL-21R–deficient mice were infected by oral gavage with H polygyrus. On day 14 after infection, (A) the proportion of basophils in the blood and spleen were determined by FACS analysis. (B) The proportion of eosinophils circulating in the blood was determined by differential cell counts of blood smears. Data show averages ± SD of a representative experiment using 5 to 6 mice per group. (C) H&E staining of intestinal sections with granuloma indicated by arrows. (D) Granulomas were counted under a dissecting microscope. Splenocytes were cultured for 3 days in the presence of HES, followed by a short restimulation with PMA and ionomycin. (E) The proportion of CD4⁺ T cells producing IFN-γ and IL-4 was determined by intracellular cytokine staining and FACS analysis. (F) IL-4 and (G) IFN-γ from supernatant of the sample cultures were measured by ELISA. Similar results were obtained in a repeat experiment. (D-G) Circles indicate data of individual mice, and horizontal bars indicate averages of a group.