Fig. 4

Immune checkpoint expression frequencies among naive and memory CD4+ cells of young and older adults. Age effects on CD28, PD-1, VISTA and CD40L expression within naive and memory CD4+ T cells were determined by flow cytometric staining of whole blood. Graphs represent percentages of immune checkpoints within total naive (CD45RA+) and memory (CD45RA-) CD4+ cells. Open and closed circles respectively represent males and females. 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