In vitro assays measuring the apoptosis and activation of monkey memory CD4+ T cells by Pf extract. PBMCs from a monkey with chronic SIV infection were isolated and cocultured with Pf extract. After coculture for 24 or 48 hours, the cells were stained with anti-CD4 PE-Cy7, anti-CD95-APC, and annexin V PE or with anti-CD4 PE-Cy7, anti-CD95 APC, anti-CD38 FITC and anti-HLA-DR PE. Memory CD4+ T cells were gated (CD95 + CD4+ T lymphocytes) and examined for the percentages of cells that stained with annexin V. Alternatively, the MFI of CD38 and HLA-DR was measured. (A) Both 10 μg/ml and 50 μg/ml Pf extract could dramatically induce the apoptosis of memory CD4+ T cells after 48 hours of coculture (3.30 ± 0.20% vs. 1.23 ± 0.07% and 4.36 ± 1.10% vs. 1.23 ± 0.07%, respectively, P < 0.001). (B) In this study, 50 μg/ml Pf extract could induce the activation of memory CD4+ T cells, leading to more CD38 (MFI of 100.50 ± 4.50 vs. 75.27 ± 1.25) and HLA-DR (MFI of 226.00 ± 7.00 vs. 146.00 ± 2.000) expression on these cells after 48 hours of coculture. (C) A positive correlation was found between the memory CD4+ T cells’ activation level and apoptosis level. (D) In this study, 50 μg/ml Pf extract could induce more SIV p27 antigen expression after 8 days of coculture (181.70 ± 57.08 vs. 47.11 ± 12.75 pg/ml). The data in this figure are presented as the means with SD. One-way ANOVA was used to compare the variables in A, B and D. Spearman’s correlation analysis was used to analyze the relationship between the parameters in C.