RIGI and infection: RIG-I and MDA5 have nonredundant functions, where RIG-I is activated by dsRNAs containing a blunt-end and 5′-triphosphate group (5′ppp), such as panhandle structures of viral genomes [47] or copy-back defective interfering particles [48,49], and thereby contribute to infection variability [50], while MDA5 requires several hundred base pairs of duplex RNA stem structures, which occur as replication intermediates, for example in picornaviruses or coronaviruses [51,52].