IL-12 has also been shown to enhance activation and proliferation of Tconvs even if Tregs are present, possibly reflecting an IL-12-mediated reduction in Treg suppressive function [12] . In other studies, IL-12 was shown to induce IFNc production by Tregs in vitro and in vivo [5, 13] ; IFN-c expression by Tregs may indicate that these cells are transiting to Th1 effector cells [13] . Thus, in apparent conflict with the results using suppression assays, these data suggest that IFN-c expression is a marker for reduced immunosuppressive ability. However whether IFN-c expression actually affects Treg suppressive function has not been assessed experimentally. Collectively these results suggest that IL-12 has independent effects on Tconv and CD8 T cells as opposed to Tregs. Consequently, the effect of IL-12 (or other cytokines) on the T cell response in a total lymphocyte culture will reflect the summation of effects on the different cell types.