Université Lyon-I FRE3011, CNRS ; Inserm U758, CERVI, 21, avenue Tony-Garnier, 69007 Lyon
In response to a viral infection, the host immediately triggers the innate immune response with the production of interferon (IFN). Microbial associated molecular patterns (MAMPs) are detected by the cytoplasmic RIG-I like receptors (RLRs) identified in 2004. Three RLRs are known, RIG-I, MDA5 and LGP2. They are RNA-helicases made of two or three types of domain. The C-terminal CTD (or RD) and helicase domains bind to viral RNA in that order. The two CARD domains recruit the signalling cascade. The involvement of each of the three RLRs in recognizing the infection varies according to virus families. Using chemically and enzymatically synthesized RNAs, the moieties required for activating RIG-I have been defined as a 5’triphosphate end adjacent to a short stretch of double stranded RNA. The true viral RNAs that are present in an infected cell and harbouring these RNA features are at best predicted. Both of the signalling cascade activated by the RLRs and the panel of the viral counter-measures benefit from a continuous flow of new knowledge. The ligand and protein partnership of virus and/or cell origin involved in the induction of the IFN response by RLRs are reviewed here with the latest information available.