Aged mice mount normal T_CD8+ cell responses to nonvirulent OPVs or WT ECTV when its replication is curtailed. (A) Young (Y) and aged (A) B6 mice were infected with 3,000 PFU ECTV Δ166 and euthanized 7 dpi. Splenocytes were counted, restimulated with infected cells for 6 h with the addition of brefeldin A during the last hour, and stained for surface CD3 and CD8 and for intracellular IFN-γ and GzB, followed by flow cytometry. Column graphs indicate the mean ± SD for the calculated absolute number of T_CD8+ cells in the spleen that expressed GzB (left) or IFN-γ (right). Representative flow cytometry plots are shown together with a plot corresponding to an uninfected control (U) mouse for comparison. (B) As in A but showing the mean ± SD of the calculated absolute numbers and representative plots of CD8⁺K^b-TSYKFESV⁺ cells in the spleen. Data correspond to the mean ± SD of six individual mice from two independent experiments. (C) As in A but infected with 10⁶ PFU VACV i.p. (D) As in B but infected with VACV i.p. Data correspond to the mean ± SD of six individual mice from three experiments. (E) As in A but infected with WT ECTV and, when indicated, aged mice were treated 2 dpi with 600 µg cidofovir (A+C) i.p. (F) Splenocytes from mice treated as in E were analyzed as in B. Data correspond to the mean ± SD of six individual mice from two experiments.