FIG. 2.

CD25^−/− CD8⁺ T cells can respond to secondary challenge. WT/CD25^−/− chimeric mice were infected with MHV-68 i.n. After 60 days, the percentage of peripheral blood CD8⁺ T cells specific for p79 was determined. Mice were then challenged with rVV p79, and the p79⁺ CD8⁺ population was determined 5 days postchallenge (A). The numbers in the box represent the averages ± standard deviations. The average fold increase was calculated to determine the ability of WT and CD25^−/− CD8⁺ T cells to respond to a secondary challenge (B). Error bars represent standard deviations from the means. Four mice were used per group, and data are representative of at least two experiments.