Innate Immunity in Influenza Virus Infection of Mammalian Airways
Emerging influenza A virus (FLUAV) infections pose a considerable health threat to mankind. The molecular determinants governing increased virulence of emerging virus strains in humans are presently not well understood. FLUINNATE proposes to identify and study the essential viral and host factors that determine the outcome of infection. FLUAV enters the human respiratory tract and must replicate in the face of multiple innate immune defence mechanisms to establish infection in vivo.
Successful viruses must adapt to intrinsic cellular restriction factors and evolve the capacity of circumventing the antiviral interferon (IFN) response, either by limiting IFN production or by blocking IFN actions. We will test the hypothesis that the speed and efficiency by which a given virus circumvents these early host responses are critical determinants in its host range and pathogenicity. In this respect, the crucial role of the virus polymerase and its cellular interactors will be analysed. Likewise, the importance of the IFN-inducible Mx GTPase as a major anti-FLUAV effector molecule will be evaluated.
Virus-induced inflammatory cytokines and chemokines exert powerful effects against FLUAV in lung epithelial cells. However, they may be detrimental to the host, causing accelerated influenza pathogenesis in the human respiratory tract. We will analyse viral factors governing the innate antiviral cytokine response and determine the impact of these factors on virus growth, cell survival and pathogenicity. Human, avian and porcine FLUAV will be used in animal models and in cell culture systems, such as human airway epithelium. The present studies should generate important information that will help to better understand the processes involved in the emergence of lethal influenza viruses and to develop efficient control measures against these devastating pathogens.[+] Read More
Influenza is a highly contagious, acute respiratory illness that is still a major health problem. Epidemics caused by influenza A viruses occur regularly, often leading to excess mortality in susceptible populations. In addition, influenza A viruses can cause devastating pandemics in humans. An avian influenza A virus originating from Asia and currently circulating among domestic birds in Europe and neighbouring countries makes headlines because of its potential to infect and kill people. If further adaptation to humans occurs, this virus strain might become the origin of a future pandemic.
Although influenza viruses belong to the best studied viruses, the host adaptation processes which enable influenza viruses to jump from one species to another are largely unknown. Likewise, the properties required for host-to-host transmission are presently not understood. Moreover, efficient control of influenza virus infections is still not possible. Immunisation regimes are continually being confronted with the extreme antigenic variability of influenza A viruses brought about by antigenic drift and shift. It is evident that new approaches and reagents to control influenza are urgently needed.
The FLUINNATE objectives focus on the identification of influenza A virus genes and gene products which contribute to virulence/pathogenicity in experimental animal and tissue culture models. The required animals are available and will consist of mice with the wild-type Mx1 gene as part of the full innate immune response, various strains with targeted mutations in specific genes and pigs as natural hosts and 'mixing vessels' for influenza A viruses. In addition, human airway and porcine epithelial cell cultures will be established and characterised. Human airway epithelial cell cultures are a rare but most precious substrate to study the biology of influenza virus infection.
The influenza viruses used will be human, avian and swine strains, some of which will be generated by reverse genetics entirely from plasmids. Stock viruses and single and multi-segment reassortants will be produced and fully characterised together with the parental strains with respect to growth kinetics in tissue culture and in vivo, the capacity to induce or respond to interferon, and the capacity to induce disease or death in experimental animals. The technology for expressing, purifying and analysing the viral RNA polymerase complex will be established and further refined, as well as biochemical and biophysical approaches to identify co-purifying host cellular factors. Advanced tests for protein-protein interactions such as the yeast three-hybrid system will be set up and candidate interactors evaluated in functional tests, based on transfection experiments. The real-time RT-PCR methodology will be optimised for the analysis of interferon and cytokine responses and gene array data will be generated.
It is expected that FLUINNATE will provide innovative vistas on the immunopathology of influenza infection as well as candidate new markers and possibly therapeutic agents. Using cutting-edge technology (such as reverse genetics systems) useful recombinant viruses will be produced and provided to the scientific community for research purposes. Results on antiviral host restriction factors and viral virulence determinants will be of great interest to epidemiologists and healthcare authorities and may have an impact on future pandemic planning.