FOXP3 and autoimmune disease: The overall proportion of Foxp3+ Treg cells among CD4+ T cells in the blood of ICOS-neutralized Il2ramut/mutIl15−/− mice was also reduced by ~50%, although mice did not develop autoimmunity (Fig. 6e and Supplementary Fig. 6f), suggesting that none of the proposed mechanisms accounts for the absence of autoimmune disease in Il2ramut/mut mice.