Ducks are the primary host of influenza virus. They can be infected with all strains of influenza, and most cause them little harm. We are interested in both the host-pathogen interactions that permit re-infection, and understanding how the duck successfully clears the virus. Lessons from ducks may identify new strategies to prime our immune defenses against deadly influenza.
Recent and on-going projects.
Ducks, but not chickens, have a functional influenza sensor RIG-I that contributes to the innate immune response to influenza.
We showed by bioinformatics and Southern blotting that chickens do not
have the RIG-I gene. We can reconstitute chicken cells using duck RIG-I,
which is functional in chicken embryonic fibroblast DF-1 cells (a
spontaneously immortalized chicken cell line) and confers detection of
RIG-I ligand (Barber et al., 2010). This provides a simple explanation for why ducks are resistant to strains of flu that would kill chickens in a few days.
Our goal is to understand how RIG-I is regulated in an influenza infection in ducks. We examined regulation by ubquitination, and showed that ubiquitination is not needed for activation of duck RIG-I (Domingo Miranzo Navarro, PDF PLOS One, 2014). We expect influenza can interfere in the pathway in many ways. Projects underway in the lab involve examining host-pathogen interactions at the protein level (Danyel Evseev, MSc candidate and David Tetrault, MSc candidate.
Genes expressed in antiviral defenses against highly pathogenic avian influenza. In an international collaboration, we will compare genes expressed in response to highly pathogenic avian influenza versus low pathogenic strains, and use these to complete the duck genome sequence (Huang et al., 2013). We also characterized the genes upregulated in chicken cells with and without the duck RIG-I, as a way to see which genes are under control of the RIG-I pathway (Barber et al., 2013). Using differential subtractive screening we identified genes upregulated in antiviral responses, and characterized them by real-time PCR (Hillary Vanderven, MSc) (Vanderven et al., 2012). Candidate antiviral genes will be tested for function (Alysson Blaine, MSc., Graham Blyth, MSc. candidate). We will also examine gene regulation of key antiviral genes (Yanna Xiao, Ph.D. candidate).
MHC class I gene organization and diversity in ducks
We showed that the organization of the MHC class I region in ducks has functional implications for severe limitation of the nature of the antigens that can be transported and presented in ducks (Mesa et al., 2004; Moon et al., 2005). This helps us understand the weak memory responses that allow ducks to be continually re-infected with influenza viruses. Only one MHC class I gene is highly expressed, while 4 others are not. Graduate student Luke Chan is characterizing the MHC class I promoters to understand their regulation. We are also examining the genetic diversity of the antigen presenting and processing genes in wild mallards (Shawna Jensen MSc and Kristina Petkau, MSc). Some allelic variants of these genes may be better at defense against influenza. In addition, features of the duck antibody response contribute to the poor defenses against influenza(Magor, 2011).
Immune gene discovery through genomics projects. We use expressed sequence tag (EST) projects to discover immune relevant genes (Xia et al., 2007). We are particularly interested in genes that allow us to manipulate dendritic cell function, since this is key to successful vaccination. Two ESTs encoded DCIR and DCAR. DCIR is an endocytic receptor on dendritic cells that influences antigen presentation. The closest mammalian homologue of DCAR is BDCA-2, which controls the interferon response. We have sequenced a duck genomic clone containing DCIR, and two DCAR genes to clarify the identity of the genes and examine the evolutionary history of the locus (Guo et al., 2008).
Two ESTs encoded CCL19 and CCL21, homologues of mammalian chemokines involved in the recruitment of naïve lymphocytes and dendritic cells to lymphoid tissues. We showed that CCL19/21 expression is upregulated in influenza-infected tissues and absent in the putative duck lymph nodes (Fleming-Canepa et al., 2011).
PhD student Janet Haley Sperling is using high throughput sequencing technology to survey microbes carried by Canadian ticks. Through this work we hope to determine the incidence of bacterial and viral infections carried by ticks.