Effect of IL-15 on T-cell activation. FACS analysis of CD25 expression was performed with a PE-conjugated antihuman CD25 MoAb on T cells, which had been cultured as indicated with medium, anti-CD20, a nonspecific IgG2a isotype control antibody, anti-CD3, anti-CD3 + IL-15 (100 ng/mL, 10 ng/mL, 1 ng/mL, 0.1 ng/mL), anti-CD3 + IL-15 (100 ng/mL) + IL-10 (10 ng/mL), anti-CD3 + IL-2 (100 ng/mL, 10 ng/mL, 1 ng/mL, 0.1 ng/mL and anti-CD3 + IL-2 (100 ng/mL) + IL-10 (10 ng/mL) for 72 hours. Control profiles using PE-conjugated mouse IgG-1 are shown on each panel (light areas). Shown are the results from one representative experiment. A total of four experiments has been performed. Depicted are cell number (Y-axis) and fluorescence intensity of the CD25 staining (X-axis).