Retinoic acid-inducible gene-I (RIG-I), melanoma differentiation-associated 5 (MDA5), and laboratory of genetics and physiology 2 (LGP2) form a family of DExD/H box RNA helicases. RIG-I-like receptors (RLRs) are expressed ubiquitously at low levels, and their expression is induced by treatment with type I interferon (IFN) or a viral infection. RLRs function as sensors for the detection of viral RNA (such as double-stranded RNA) in the cytoplasm to initiate antiviral responses by producing type I and type III IFNs. Unlike Toll-like receptors, which sense exogenous pathogen-associated molecular patterns, RLRs detect cytoplasmic viral RNA. Because RLRs are IFN-inducible viral sensors, they are critical in amplifying antiviral responses.
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