Associations between PD-1 expression and effector functions in T cells from aging healthy WT mice and Eµ-TCL1 mice. Fresh splenocytes from 3-, 6, and 12-month-old WT and Eµ-TCL1 mice were processed and stained as described in Figure 2. Ratios for (A) CD107a degranulation, (B) intracellular GrB, (C) IFN-γ, and (D) EdU proliferation were compared between PD-1^high and PD-1^low CD3⁺CD8⁺CD44⁺ cells in WT and Eµ-TCL1 mice. Three-month-old mice had no detectable PD-1 expression; effector function was therefore determined on PD-1^low cells only. All graphs show median with interquartile range. ns, nonsignificant, *P < .05, **P < .001, ***P < .0001.