IL-15 is required for induction of cytotoxic lineage genes in IL-7Rα–cKO thymocytes. (A) Relative mRNA expression of the indicated genes. IL-7Rα–cKO and γ_c-cKO data from Fig. 5 A are shown compared with TCR-β^hi CD8SP thymocytes sorted from IL-7Rα–cKO–IL-15^−/− mice by gating specifically for IL-7Rα–deleted thymocytes. Data are normalized to Rpl13A and Cre⁻ controls. Means of at least three mice are shown, and error bars represent SEM. All statistically significant changes are marked with asterisks: **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. Any comparisons not marked with asterisks were not significant. (B) Expression of CD122 and CD44 on IL-7Rα–deleted TCR-β^hi CD8SP thymocytes from IL-7Rα–cKO (blue line) and IL-7Rα–cKO–IL-15^−/− (olive green line) mice compared with WT (shaded histograms). Dotted line represents negative staining control. Data are representative of three independent experiments.