Loss of Foxp3 expression by Tregs has been demonstrated in vivo, although whether this represents Treg instability is controversial [22] [23] [24] . IL-12 induces IFN-c expression by Tregs (Fig. 1B) ; if IL-12 also mediated Treg conversion, this would contribute to a decrease in Treg, and an increase in Tconv numbers. To examine this possibility, Foxp3 gfp /Thy1.1 Tregs were purified from naïve spleens and incubated with unfractionated lymphocytes from Foxp3 gfp /Thy1.2 mice in the presence of anti-CD3 mAb and IL-12 or media. As shown in Fig. 7 , IL-12 did not induce an appreciable level of Treg (Foxp3 + ) to Tconv (Foxp3 2 ) conversion when compared to samples exposed to medium alone.