IL-2 and IL-15 regulation of S6 ribosomal protein phosphorylation. Flow cytometric analysis of phospho-S6 ribosomal protein in (A) naive CD8⁺ T cells and 2-day antigen-primed P14 LCMV CD8⁺ T cells and in (B) antigen-primed CD8⁺ T cells maintained for another 6 to 24 hours in medium, 20 ng/mL IL-2 (CD8IL-2), or 20 ng/mL IL-15 (CD8^IL-15). (C) Antigen-primed P14 LCMV CD8⁺ T cells maintained for 24 hours in medium or 20 ng/mL IL-2 (CD8^IL-2) ± 10 μM LY294002, a PI3K inhibitor. (D) Antigen-primed P14 LCMV CD8⁺ T cells maintained for 24 hours in 20 ng/mL IL-2 (CD8^IL-2) or 20 ng/mL IL-15 (CD8^IL-15) followed by no further treatment or by activation with 20 nM PdBu for 30 minutes before analysis. FACS histograms are representative of the results of 5 or more experiments.