In these assays, we compared equal numbers of IFN-c + and IFN-c -Tregs for suppressive function. However, results in Fig. 1 showed that the numbers of Tregs and their relative expression of Foxp3 were diminished in IL-12-treated cultures. Further, a previous report showed that Treg suppressive function was alleviated by IL-12 [12] . To reconcile these disparate results, we assessed Treg suppression in the presence of IL-12 using Tregs and responder T cells enriched from lymph nodes and spleens. Responder T cells were labeled with CFSE and co-cultured with unlabeled Tregs at several cell ratios. We observed diminished suppression of CFSE-labeled CD4 T cells in the presence of IL-12, in agreement with published results (Fig. 5) . Suppression of CD8 T cell proliferation was almost completely abrogated if IL-12 was present in the culture.