Freshly isolated PBMC and LN single-cell suspensions from naïve and SIV-infected rhesus macaques were stained for analysis of PD-1 expression. (A) Gating strategy used to identify total CD4+ and CD8+ T cells as well as CD4+ and CD8+ Tregs. PD-1 expression was evaluated in CD4+ and CD8+ T cells and Tregs in PBMCs (B) and LN (C) cells. (D) PD-1 expression levels were analyzed in naïve (CD28+ CD95−), central memory (CM, CD28+CD95+), and effector memory (EM, CD28−CD95+) CD4+ and CD8+ T cells. PBMC data are pooled from 10 naïve and 12 SIV-infected macaques. LN data are pooled from 5 naïve and 12 SIV-infected macaques. Data are shown as means ± SEM. *, p<0.05 and **, p<0.01 indicate statistically significant differences between the compared groups by Mann-Whitney Test.