Expression levels of the cytokine receptor unique α chains IL-2Rα (CD25) and IL-15Rα on T cells cultured in IL-2 or IL-15. (A-B) FACS histograms show expression of IL-2Rα (CD25) and IL-15Rα subunits on antigen-primed P14 LCMV CD8⁺ T cells cultured in 20 ng/mL IL-2 (CD8^IL-2), IL-15 (CD8^IL-15), or medium alone for 24 hours.