IL-21R signaling is required for Th2 responses against Nippostrongylus brasiliensis. C57BL/6 and IL-21R–deficient mice were infected subcutaneously with Nb. On day 14 after infection, BAL was performed and (A) the total number of eosinophils, lymphocytes, and macrophages was determined by total and differential cell counts. (B) Total IgA, IgG1, and IgE in the BAL fluid were assessed by ELISA. Data show averages ± SD of a representative experiment using 5 to 6 mice per group. Similar results were obtained in an independent experiment.