A) Analysis of CD40L expression. Untreated CD4 T cells from young (left histograms) or old (right histograms) AND mice were adoptively transferred to CD4KO hosts. PCC priming of the host increased the expression of CD40L (light lines) compared to isotype controls (dark lines) on gated CD4VB3+ cells from young, but not from old, donor mice. The histogram bars represent the mean percentage (± SEM) of CD40L(+) of untreated and OSGE-treated cells with respect to isotype controls (C) from 8 young and 4 old AND donor mice. The asterisk (*) indicates statistical significance with respect to untreated young cells in primed hosts, while the (^) represents statistical significance relative to untreated old cells. B) Analysis of PD-1 expression. CD4 cells from the CD40L analysis were further stained for PD-1, showing that PCC priming increased PD-1 expression (light lines) compared to isotype controls (dark lines) on gated CD4VB3+ cells from young and old donor mice. Quantitative analysis from 8 young and 4 old AND mice demonstrated that PCC increased PD-1 expression in all groups, with no significant effect of age or OSGE noted.