RIG-I is essential for the recognition of a series of RNA viruses, which include Sendai virus, Newcastle disease virus, influenza virus, vesicular stomatitis virus and Japanese encephalitis virus (27) . MDA5 is required for the recognition of other RNA viruses, including picornaviruses such as encephalomyocarditis virus, Mengo virus and Theiler virus (13, 27) . Thus, RIG-I and MDA5 have specificities in their detection of RNA viruses, presumably through recognition of distinct structures of viral RNA (24, 28) .