The A946T variant of the RNA sensor IFIH1 mediates an interferon program that limits viral infection but increases the risk for autoimmunity.

The single-nucleotide polymorphism rs1990760 in the gene encoding the cytosolic viral sensor IFIH1 results in an amino-acid change (A946T; IFIH1 ^T946 ) that is associated with multiple autoimmune diseases. The effect of this polymorphism on both viral sensing and autoimmune pathogenesis remains poorly understood. Here we found that human peripheral blood mononuclear cells (PBMCs) and cell lines expressing the risk variant IFIH1 ^T946 exhibited heightened basal and ligand-triggered production of type I interferons. Consistent with those findings, mice with a knock-in mutation encoding IFIH1 ^T946 displayed enhanced basal expression of type I interferons, survived a lethal viral challenge and exhibited increased penetrance in autoimmune models, including a combinatorial effect with other risk variants. Furthermore, IFIH1 ^T946 mice manifested an embryonic survival defect consistent with enhanced responsiveness to RNA self ligands. Together our data support a model wherein the production of type I interferons driven by an autoimmune risk variant and triggered by ligand functions to protect against viral challenge, which probably accounts for its selection within human populations but provides this advantage at the cost of modestly promoting the risk of autoimmunity.