WAS^−/− CD4⁺ T cells exert Th1 effector function in vivo. WT and WAS^−/− CD4⁺ T cells (C57BL/6) were adoptively transferred into Rag-deficient mice. At 24 hours later, mice were infected with 2.0 × 10⁵L major promastigotes. (A) Progression of disease measured by footpad (lesion) size, mean of 4 to 6 mice per group. *P ≤ .05 (Mann-Whitney) for differences between Rag^−/− with no reconstitution and either WT or WAS^−/− CD4 reconstitution. (B) Limiting dilution analysis of parasite load in the footpad. *P ≤ .05 by paired Student t test across 3 independent experiments. (C) Draining LN CD4⁺ T-cell numbers 8 weeks after reconstitution of RAG^−/− mice and L major infection. ns indicates not significant; paired Student t test. (D) ELISPOT analysis of antigen-specific IFNγ-producing cells upon 6 hours of restimulation with SLA. ns indicates P = .5 between WT and WAS^−/− IFNγ production across 3 independent experiments; paired Student t test. Error bars indicate mean and SEM. (E) CSA for IL-4 and IFNγ production by WT and WAS^−/− CD4⁺ T cells in the L major–infected dermis at 8 weeks. Cytokines were measured after 6 hours of restimulation with SLA. Dot plots were gated on CD4⁺ T cells. Numbers in quadrants equal the percentage of CD4⁺ T cells. Data are from 1 experiment representative of at least 3 comparable independent experiments.