Expression of inhibitory receptors on CD8⁺ T cells. (A) Data showing the correlation between KLRG1 expression on CD8⁺ T cells and age. (B) Graph showing the percentage of CD8⁺ T cells expressing KLRG1 in young and old donors on CD28/CD27 subsets. Horizontal lines depict mean values. (C) Graph showing the correlation between PD1 expression on CD8⁺ T cells and age. All P values were calculated using the Student t test.