Self RNA Sensing by RIG-I-like Receptors in Viral Infection and Sterile Inflammation

The innate immune system uses pattern recognition receptors to survey the intracellular and extracellular environment for signs of infection. Viral infection is detected through the presence of viral nucleic acids in infected cells. Pattern recognition receptor activation by viral nucleic acids induces the expression and secretion of type I IFNs (IFN-Is), important mediators of antiviral immunity. RIG-I-like receptors (RLRs) are RNA sensors that detect viral RNA in the cytosol and induce an IFN-I response. Viral RNAs contain features that set them apart from host RNAs, allowing RLRs to discriminate between cellular/self and viral/non-self RNA. The notion emerged that self RNAs can also engage RLRs and modulate the IFN-I response, indicating that the distinction between self and non-self RNA is not watertight. We review how self RNAs regulate RLR activation and the IFN-I response during viral infection and how recognition of self RNAs by RLRs is implicated in autoinflammatory disorders and cancer.