Further support for an important role for IL-2R levels on Tconv and CD8 T cells comes from studies of IL-27. IL-27 is a cytokine with pro-and anti-inflammatory properties [42] [43] [44] [45] . Mice transgenic for the expression of IL-27 exhibit diminished IL-2 production, which results in decreased numbers of Tregs and subsequently, a systemic inflammatory disease [46] . We showed that IL-27 diminished IL-2 expression, consistent with these results, but IL-27 only modestly decreased Treg frequency (Fig. 9D ). Consistent with a role for IL-2R expression on non-Tregs, there were minimal changes in IL-2R levels on these cells after IL-27 treatment (Fig. 9E) . Thus, under these conditions, Tregs were presumably able to compete for IL-2 even in the presence of reduced amounts of IL-2.