WASp-deficient CD4⁺ T cells fail to support Th2 immune responses to N brasiliensis infection in vivo. WT or WAS^−/− CD4⁺ T cells (BALB/c) were adoptively transferred into TCR Ca^−/− mice. After 24 hours, mice were infected with 500 infective N brasiliensis third-stage larvae (Nb). Ten days after infection, small intestines were excised for direct counting of adult worms. Symbols represent individual mice, 6 mice per group. *P ≤ .01 for WT versus WAS^−/− CD4-reconstituted; Student t test. (B) Serum IgE levels measured by ELISA 10 days after infection. (C) In vivo cytokine capture for IL-4 in TCR Ca^−/− mice reconstituted with WT or WAS^−/− CD4⁺ T cells, 10 days after Nb infection. (D) Serum IL-13 in TCR Ca^−/− mice reconstituted with WT or WAS^−/− CD4⁺ T cells, 10 days after Nb infection. (E) CD4 T-cell numbers in mesenteric LNs 10 days after Nb infection; symbols represent individual mice. (F) ELISPOT for cytokine-secreting cells from the lungs and mesenteric LNs of infected mice restimulated ex vivo for 18 hours with Nb antigen. Statistical analysis by Student t test: lung tissue, *P < .008; mesenteric LN, *P < .004 for difference between IL-4 production by WT and WAS^−/− cells. Data are from 1 experiment representative of at least 3 independent experiments. (G) Ex vivo ELISPOT for IL-13 with or without addition of blocking anti–MHC class II Ab. (H) mRNA analysis of Th2 cytokine gene expression in WT and WAS^−/− CD4⁺ T cells from the mesenteric LNs of Nb-infected mice at day 10. Transcripts were normalized to HPRT and expressed relative to uninfected CD4⁺ T cells from the mesenteric LN. (I) Innate cell number in the lung, 10 days after Nb infection. Noninfected lungs contained 306 ± 60 basophils, 1130 ± 248 eosinophils, and 507 ± 140 mast cells. Results are the mean of individual mice from 3 independent experiments. Differences between WT and WAS^−/− recipients were not statistically significant. Error bars indicate mean and SEM.