Kinetics of the change in cell size of antigen-activated CD8⁺ T-cell cultures stimulated with IL-2 or IL-15. (A-B) Data show dot plots and histograms of FSC and SSC of naive P14 LCMV transgenic CD8⁺ T cells or P14 LCMV CD8⁺ T cells activated with LCMV gp33-41 peptide for 2 days. Cells represented in histogram profiles were gated on size, as indicated in dot plots, and equal expression levels of the CD8a surface molecule (data not shown). (C) Cellular protein content (mg/mL) of 10⁶ naive P14 LCMV transgenic CD8⁺ T cells or P14 LCMV CD8⁺ T cells activated with LCMV gp33-41 peptide for 2 days. (D) Data show FSC, SSC, and cellular protein content of 10⁶ peptide-activated P14 LCMV CD8⁺ T cells cultured for 24, 48, and 72 hours in medium alone, 20 ng/mL IL-2 (CD8^IL-2), or IL-15 (CD8^IL-15). (C-D) Error bars indicate SD. (E) FACS dot plots with FSC and SSC profiles of antigen-activated P14 LCMV CD8⁺ T cells cultured in 20 ng/mL IL-15 (CD8^IL-15) for 3 days. After 3 days in culture, CD8^IL-15 cells were washed 3 to 4 times (to remove exogenous cytokine) and were recultured in 20 ng/mL IL-2 (CD8^IL-15 + IL-2) or again in 20 ng/mL IL-15 (CD8^IL-15) for another 48 hours. As a comparison, FSC and SSC profiles are shown of antigen-activated P14 LCMV CD8⁺ T cells maintained only in IL-2 (CD8^IL-2) for 5 days. All histograms, dot plots, and graphs are representative of the results of 4 or more experiments. P < .05 for concentration differences 2-fold or greater.