We found a substantial reduction in Treg cell numbers in Cd25Y129H mice, indicating that optimal IL-2R signaling is essential for peripheral Treg cell homeostasis, as suggested previously.3,4,6,50 However, unlike mice deficient in IL-2 or IL-2Rα,4,12,13,50Cd25Y129H mice did not exhibit signs of spontaneous autoimmunity. This evidence concerns the gene IL2 and Autoimmunity.