A rapid RIG-I signaling relay mediates efficient antiviral response.

RIG-I is essential for host defense against viral pathogens, as it triggers the release of type I interferons upon encounter with viral RNA molecules. In this study, we show that RIG-I is rapidly and efficiently activated by small quantities of incoming viral RNA and that it relies exclusively on the constitutively expressed resident pool of RIG-I receptors for a strong antiviral response. Live-cell imaging of RIG-I following stimulation with viral or synthetic dsRNA reveals that RIG-I signaling occurs without mass aggregation at the mitochondrial membrane. By contrast, interferon-induced RIG-I protein becomes embedded in cytosolic aggregates that are functionally unrelated to signaling. These findings suggest that endogenous RIG-I efficiently recognizes viral RNA and rapidly relays an antiviral signal to MAVS via a transient signaling complex and that cellular aggregates of RIG-I have a function that is distinct from signaling.