Daan Pieren

39 Novel features of ageing in murine T cells lower frequencies of CD25 + cells compared to young mice in response to both low and intermediate strength of stimulation. However, high dose stimulation resulted in comparable CD25 + Treg frequencies between young and aged mice ( Figure 4A ), although the expression of CD25 per cell was lower on aged Treg cells (data not shown). CD25 expression CD69 expression A B Low Intermediate High Low Intermediate High Th cells Tc cells Treg cells Time (Days) Young (2 months) Aged (22-24 months) 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 20 40 60 80 100 % CD25 + of Th *** ** * *** * *** * 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 20 40 60 80 100 % CD25 + of Tc *** ** *** *** 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 20 40 60 80 100 % CD25 + of Treg *** ** * ** * * 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 20 40 60 80 100 % CD69 + of Th *** *** * *** *** 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 20 40 60 80 100 % CD69 + of Tc *** *** ** *** 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 20 40 60 80 100 % CD69 + of Treg *** *** *** *** * *** Figure 4. Reduced induction of T-cell activation in aged mice can partially be restored by stronger stimulation. The proportion of CD25 + ( A ) and CD69 + ( B ) Th, Treg, and Tc cells of young (n=6, 2 months old) and aged (n=6, 22-24 months old) mice cultured up to four days with a low, intermediate, or high stimulatory strength. Mean ± SEM; * p < 0.05, ** p < 0.01, *** p < 0.001 for difference between young and aged mice at time points indicated using Two-way ANOVA. Frequencies of cells expressing the early activation marker CD69 on Th and Tc cells were comparable between young and aged mice before stimulation, while the frequency of CD69 + Treg cells of aged mice was significantly higher ( Figure 4B ). At young age, all three T-cell subsets showed a rapid incline in the frequency of CD69 + cells within one day. At old age, Th and Tc cells also 2