Animals each received a single bolus of BrdU (60 mg/kg) intravenously and EDTA-treated blood samples were collected various days later for antibody staining and flow cytometry analysis. Neutrophils were gated from single cells, FSC/SSChigh/dim, HLA-DR-, CD3-, CD20-, CD123-, and the percentages of BrdU+ cells were gated from the neutrophil population. (A&B) Percentages of BrdU-positive neutrophils four days (A) and seven days (B) after administration of BrdU were compared between the two age groups using the nonparametric Mann-Whitney U test. (C) The kinetics of BrdU-labeled blood neutrophil kinetics were compared between rhesus macaques aged 20–26 years old (red line) and previously reported data from rhesus macaques between 3 to 19 years old (blue line) [5]. Medians and interquartile ranges were shown at different time points after BrdU injection. (D) BrdU-labeled blood neutrophil kinetics of individual rhesus macaques aged 20–26 years old demonstrates in-group variability in this age group. ****, P <0.0001. Medians and interquartile ranges were shown.