**Figure 2. **Apoptosis and the expressions of PD-1 and PD-L1 on activation-induced apoptotic cells were evaluated by flow cytometry. **A**: Cells considered to be undergoing apoptosis were positive for Annexin V, but negative for PI (the lower right part). **B**: The gated cells represent the expression of Annexin V^{+}PI^{-}PD-1^{+} cells. **C**: The gated cells represent the expression of Annexin V^{+}PI^{-}PD-L1^{+} cells. Results of a representative experiment are shown. **D**: Apoptosis and the expressions of PD-1 and PD-L1 on activation-induced apoptotic lymphocytes are shown by a histogram. All
data shown represent the mean ± SD of at least three independent experiments. *p<0.05 compared with the control group. #p<0.05
compared with the DM-NDR group.