Although no single member of this cytokine family (IL-2, IL-7, or IL-15) is non-redundant in the thymic induction of tTregs, the most significant defect is observed in IL-2−/− or CD25−/− animals, in which Foxp3 expression is reduced by 50% in thymocytes and animals succumb to lethal autoimmune diseases (Sadlack et al., 1993; Willerford et al., 1995; Fontenot et al., 2005b). Here, IL2 is linked to autoimmune disease.