TGF-β regulation of IL-2/IL-15Rβ expression on CD8⁺ memory T cells. Purified CD8⁺ T cells from 8- to 10-week-old C57BL/6 mice were incubated in complete mouse media (gray lines), +IL-15 (black lines), or +IL-15 plus TGF-β (dotted lines) for various times. Cell-surface expression of IL-2/IL-15Rβ (first row), IL-15Rα (second row), and TNFRII (third row) were determined by flow cytometric analysis on the CD8⁺, CD44^hi T-cell population (top panels) and the CD8⁺CD44^lo T-cell population (bottom panels). CFSE-labeled CD8⁺ T cells were included in each experiment to measure cell division (bottom row). Experiments were repeated 4 times with similar results.