Daan Pieren

44 Chapter 2 PD-1 + Th and Tc populations contain less activated cells at old age To verify the findings of our viSNE analyses on an individual mouse level rather than a pooled group of mice, we addressed the frequency of activated (CD25 + CD69 + ) PD-1 + and PD-1 - Th and Tc cells in young and aged mice before and after two days of exposure to an intermediate strength of stimulation ( Figure 7A, B, Supplementary Figure 8 ). The frequency of PD-1 + Th and Tc cells of young mice significantly increased after stimulation, whereas cells of aged mice did not ( Figure 7B ). Th and Tc cells of aged mice have increased expression of CD25 and CD69 within both PD-1 + and PD-1 - subsets observed at time points indicated, but to a lesser extent than cells of young mice ( Figure 7C ).