Our lab is investigating the structural correlates of human pandemic influenza viruses (H1N1, H2N2, H3N2), as well as other emerging viruses (such as H5N1, H7N7, H9N2, and recently discovered novel flu A viruses from bats) that have the potential to cause severe or lethal human infection, to elucidate the key factors that contribute to host specificity, antigenicity, replication and virulence. This studies seek to provide valuable insights into influenza virus neutralization, tropism and pathogenesis that can be used to design novel strategies to control and combat highly lethal influenza virus infections in the event of a new pandemic, as well as aid in preventing epidemics that arise from seasonal flu.
Influenza A is an infection of the respiratory tract affecting millions every year. Influenza, together with subsequent complications of infection by bacterial pneumonia (Streptococcus pneumoniae and Staphylococcus aureus), is among the top 10 leading causes of deaths in the US, killing more than 50,000 people per annum and, in pandemic years, from 1 million (1957-58) to 50 million (1918-1919). The 1918 ‘Spanish’ flu was the most devastating outbreak of any infectious disease in recorded history. With more pandemics predicted, the ongoing question is where and when the next virus will emerge. Multiple factors contribute to the virulence of any single virus and an understanding of how a virus attains pandemic potential can only be fully understood if the entire complement of viral proteins is investigated. Influenza is a negative-strand RNA virus that has 8 gene segments that code for 12 proteins.
Influenza A viruses exhibit extreme diversity via multiple serotypes of the hemagglutinin (HA 1-16) and neuraminidase (NA 1-9) surface antigens. To date, only three of the possible 144 combinations found in bird and animal reservoirs have been associated with human pandemics (H1N1, H2N2, H3N2). Recently, a distinct lineage of influenza A viruses has been identified in bats, further increasing the spectrum of possible zoonotic viruses that could infect humans. Our labroratory seeks to elucidate at the structural level, key sites of vulnerability on influenza virus for development of a sustainable cross-serotype immune response, and understand activity relationships of the surface glycoproteins (HA, NA) and ribonucleoprotein (RNP) complex, including the polymerase (PA, PB1, PB2), that underlie the pathogenicity and transmissibility of pandemic and seasonal influenza viruses. Antibody-mediated neutralization of influenza virus is a complex combinatorial problem for the human immune system as it is presented with diverse, highly variable and constantly evolving viruses. While neutralizing antibodies against human flu are traditionally regarded as being strain specific, recent studies have shown that a much broader response can be mounted over decades of evolution of a particular subtype (e.g. H3N2), across group 1 or group 2, and even across two major phylogenetic groups (I and 2). While these examples provide compelling evidence that the immune system is capable of mounting a sustained, cross-serotype response against influenza, how to elicit broadly neutralizing antibodies by vaccination is poorly understood. Therefore, we seek to determine the structural basis of broad neutralization and delineate the sites of vulnerability on the HA to enable development of novel vaccine scaffolds and even small molecule inhibitors that ameliorate or prevent disease progression. Furthermore, because we do not understand why certain viruses, such as the recent H1N1 2009 swine flu, are able to enter the human population and cause pandemics, we will also study the molecular basis of pathogenicity. Using a novel strategy to investigate both HA and NA substrate specificity and activity using newly designed glycan microarrays, we will assess the functional relationships between NA and HA activity. In this way, we will test the hypothesis that efficient infection of humans by influenza viruses requires a functional balance between the binding and specificity of HA and enzymatic activity of the NA with host glycan receptors. Another key factor in host-specific pathogenicity is the replication machinery composed of the RNP with associated polymerase, where mutations can alter polymerase activity and interaction with host cell factors. Structural and functional understanding of the RNP will enable other approaches to combat influenza infection. A combined biophysical and biochemical approach from three laboratories employing state of the art X-ray crystallography, electron microscopy and glycan array technologies are being used to provide key insights into influenza virus neutralization, tropism and pathogenesis, to reveal novel strategies to control and combat future pandemics.
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