Fig. 2

Immune checkpoint expression frequencies within CD4+ and CD8+ cells and B cells of young and older adults. Age effects on immune checkpoint expression were determined by flow cytometric staining of whole blood from young and older adults. Graphs represent percentages of CD28+, PD-1+, VISTA+ and CD40L+ cells within total CD4+ (a) and CD8+ T cells (b) and CD40+ cells within total B cells (c). Open and closed circles represent males and females, respectively. Open and closed triangles represent males (n = 2) and females (n = 2), respectively, that were 65 years of age or younger in the OA group. Horizontal bars reflect median percentages. The Mann-Whitney U test was used for comparison between young (YA, n = 20) and older (OA, n = 20) adults. P-values are indicated in the graphs