Tregs permit the generation of secondary responses to CMV antigen. Euthymic or thymectomized Balb/c animals that were co-transplanted with FVB TCD-BM, Tcons, and Tregs (●) or with TCD-BM alone (○) on day 0 and infected with CMV on day 14 or 30 were killed on day 100. Donor splenic lymphocytes were sorted and CMV-specific responses to E1 antigen were measured by Elispot assay for Interferon-γ release. Each symbol represents the Elispot count from a different mouse. Solid line indicates mean number of elipsots. P values: * = .01, ** = .006, *** = .01, ^# = .002, ^## = .001, ^### = .001. P values are not significant between • versus ○, and not significant between euthymic versus thymectomized animals infected on day 30 for both groups. Positive (pos) and negative (neg) controls are as described in “IFN-γ ELISPOT assay.”