Thus, type I IFNs should be added to the long list of cytokines (IL-1β, IL-4, IL-6, IL-15, IL-21) [64–72] and members of the tumor necrosis factor superfamily (TNFSF) (GITR-L, 4-1BB-L, OX40-L and TNF-α) [73–76] that are purported to decrease Treg suppressive function in autoimmune and infectious disease models. Here, IL21 is linked to infectious disease.