In contrast to type I IFNs (IFN-α and IFN-β), which are secreted by infected cells and can result in immunopathology during viral infections, type III IFN (IFNL) responses are restricted primarily to mucosal surfaces and are thought to confer antiviral protection without driving damaging proinflammatory responses (27, 28). Here, IFNB1 is linked to viral infectious disease.