Flow cytometry: 1X10^6 Human PBMC (untreated,left) and Human PBMC (treated with 50 ng/mL PMA and 1 µg/mL ionomycin for 6 hours,right) were surface-stained with ABflo® 647 Rabbit anti-Human/Monkey CD4 mAb (A25279,5 μl/Test) , then intracellularly-stained with PE Rabbit anti-Human CD152/CTLA-4 mAb (A23713,5 μl/Test).