IFIH1 and autoimmune disease: We hypothesized that the Treg-specific constitutive activation of MDA5, by expressing the gain-of function mutant G821S of the Ifih1 gene (referred to as MDA5 G821S) (40), would result in Treg population loss and the onset of autoimmune diseases, similar to that observed in Foxp3ΔAdar1 mice.