Fig. (1) Detection of viral RNA. Double stranded RNA (dsRNA) from a virus is detected either by TLR7 in the endosome or via the RNA helicase RIG-I. RNA bound RIG-I translocates to the mitochondria and binds to VISA via CARD-CARD interactions. This then activates a signalling cascade, which, like TLR7 signalling, results in transcription of interferon α and interferon β, which then go on to activate the type I interferon response, resulting in upregulation of proapoptotic genes and inflammatory cytokines.