Identification of cellular genes that affect host range restriction of influenza virus

Influenza viruses pose a pandemic threat to human health because avian influenza viruses can sometimes acquire the ability to replicate in and transmit between people. Since humans have no pre-existing immunity to these strains, the whole world is susceptible and the virus spreads rapidly causing excess morbidity and mortality. The way in which this might happen is for a strain of bird flu to acquire a mutation in its genetic makeup that helps it replicate faster in human cells. We know about some of the mutations by which this switch is achieved, but we do not understand the mechanism behind them. In this project we will identify genes from the chicken and from the human host which might be important in determining whether a particular virus can replicate in either host. Then we will design experiments to discover why they are important for influenza virus replication. This basic scientific information will allow us to understand how to predict which strains of virus are the ones most likely to cause pandemics, and will also assist design of novel antiviral compounds that target essential steps of the virus cycle.

The H5N1 avian strain of influenza A virus is posing a pandemic threat. It is paramount to understand and predict the mechanism by which the virus might acquire increased replicative ability and thus transmit between humans. Avian influenza viruses are usually restricted in their replication in humans but it is well documented that mutations in the PB2 component of the heterotrimeric polymerase complex can adapt the virus for replication in humans. However the mechanism by which that occurs is not clear. We hypothesize that the polymerases of avian influenza viruses do not interact efficiently with a cellular component in human cells and that this interaction would be required during replication. We seek to identify such genes and discover their role in enhancing influenza virus replication. The approach we will take has proved successful in a preliminary study. We supply fragments of chicken chromosome as a cDNA library to mammalian cells which otherwise are not permissive to avian influenza, and screen for those cells in which replication is enhanced. Isolation of individual chicken cDNAs will allow their identification and experiments designed to uncover why such genes enhance avian virus replication will be performed. Understanding these mechanisms are of basic scientific interest, but will also inform surveillance and may direct strategies for novel antiviral therapies.