Figure 4.

Accessory signaling did not influence PD-1 expression on activated CD8⁺ T cells. Purified naive CD8 T cells were stimulated with anti-CD3 in the presence or absence of anti-CD28. (a) CFSE dilution of CD8 T⁺ cells. The experiments were repeated at least three times with a similar pattern. Representative overlay pictures are shown. (b) MFI of PD-1 expression on CD8⁺ T cells. (c) Living cell percentage determined by Annexin-V staining. For b and c, the cumulative statistical results pooled from three experiments are shown. *P<0.01, ***P<0.001. MFI, mean fluorescence intensity; PD-1, program death 1.