Identification of a cross-species entry factor for bat influenza virus

Influenza A viruses were recently discovered in bats. Birds are thought to be the main reservoir for influenza A viruses, and avian influenza viruses use sialic acid receptors to infect avian or mammalian cells. Bat influenza A viruses do not use sialic acid receptors to infect cells. Silke Stertz and colleagues now show that these bat viruses make use of MHC class II to enter cells. They also show that these bat viruses can infect the upper airways of mice in an MHC-class-II-dependent manner, and that MHC class II proteins from a broad range of species (including pigs and humans) can facilitate entry of these bat viruses into cells. The work raises the possibility that zoonotic transfer of bat influenza viruses to humans may be possible, although whether this would result in a pathogenic infection is not clear.