Modulation of the interferon response during henipavirus infection

© 2011 Dr. Elena R. VirtueHendra and Nipah viruses, members of the genus Henipavirus within the family Paramyxoviridae, cause lethal infection in humans and animals. The exact mechanism of pathogenesis for these viruses is unknown. Bats are natural reservoirs for a spectrum of infectious zoonotic diseases including the recently emerged henipaviruses. Henipaviruses have been observed both naturally and experimentally to cause serious and often fatal disease in many different mammal species, including humans. Interestingly, infection of the flying fox with henipaviruses occurs in the absence of clinical disease. The extreme variation in the disease pattern between humans and bats has led to an investigation into the effects of henipavirus infection on the innate immune response in both human and bat cell lines. This is the first report of henipavirus infection in bat cells specifically investigating aspects of the innate immune system. Henipaviruses are capable of making several proteins (SB, C, V and W) which are not essential for virus replication, but are believed to play a role in virulence or pathogenesis. Viral proteins that act as IFN antagonists are important virulence factors, and their identification and characterisation should provide valuable insights into viral pathogenesis. Due to the ability to conduct BSL-4 infection experiments, this thesis has investigated the ability of the viruses to antagonise the interferon pathways and will provide important insights into the pathogenesis, treatment and future prevention of henipavirus infection. In this study, we have infected both human and bat cell lines to examine the level of activation and/or antagonism of the interferon response. We found that following infection of human cells with henipaviruses, the interferon production pathway is antagonised; however the interferon signalling pathway remains active. We then identified subtle differences between human and bat cells following henipavirus infection, in which the interferon signalling pathway in bats is blocked. These results begin to elucidate mechanisms by which bats may evade acute infection. Prior to this study, analysis of the P gene products had been carried out by utilising mammalian expression from transfected single genes; however examination of function during infection was not possible due to the lack of a reverse genetics system allowing for the manipulation of individual genes. In this study, a minigenome assay has been utilised to assess functionality of the polymerase complex components without the need for the high level of biocontainment required when working with infectious virus particles. Optimisation of the minigenome system has underpinned the further development of the full-length rescue system in which recombinant wild-type and mutant infectious viruses will be recovered. Development of the reverse genetics system will allow further investigation into the function of the P gene accessory proteins and additional pathogenicity determinants of the henipaviruses