1X10^6 anti-CD3/CD28 treated (2 days) C57BL/6 mouse splenocytes were surface stained with 0.25 ug FITC Anti-Rat IgG1 Isotype Control (FITC-65212, Clone: HRPN) (red), or 0.25 ug FITC Plus Anti-Mouse CD25 (PC61.5) (FITC-65137, Clone: PC61.5) (green) or unstained (blue). Cells were not fixed.