2007 - 2009
Immunology of T cell-mediated immune response to avian influenza virus in the chicken
Principal Investigator: Shayan Sharif, University of Guelph
ObjectiveThe long-term objective of this project is to develop effective, broad-spectrum vaccines against avian influenza (AI) virus.
BackgroundThere is relatively little known about the chicken’s immune response to AI virus infection. The immediate objectives of this project, therefore, are to identify the molecular determinants that confer immunity to the virus and identify the immune system cells that see these determinants. The project is also aimed at determining the dynamics of immune system cells in response to AI virus infection and to elucidate the genetic pathways that control that response. A better understanding of the immunology of AI is required before rational control strategies can be developed.
Research ProgressThe direction of this research program is ever-evolving as more information about AI and potential measures for its control are gained worldwide. There are a number of approaches to AIV vaccines under development, such as inactivated viral vectors expressing AIV antigens, naked DNA or recombinant proteins. There are even a few commercially available (not in Canada) AIV vaccines. None of the approaches or vaccines thus far are without their shortcomings. We need to know more about the biology of AIV to develop more efficient control measures.
Studies on the chicken’s immune response to AIV infection suggests that antibodies produced against AIV HA antigens are the most important in eliciting a protective response. NA antigens elicit production of neutralizing antibodies that appear to reduce virus shedding from infected individuals, and may have a synergistic protective effect as well. Dr. Sharif wants to produce a vaccine that presents one or both of these antigens (and perhaps as well immune system molecules such as cytokines). Dr. Sharif worked with Eva Nagy at Guelph to construct fowlpox virus (FPV) vectors expressing AIV proteins (HA, NA etc.). Two HA sequences from Canadian H5N1 isolates were integrated into the system, but the resulting vector was not stable. Dr. Sharif’s team therefore adapted an in vitro protein expression system to produce the antigens. Their intent is to use the antigens to stimulate AIV-specific T-cells in vitro. In order to do so, they need a line of these cells that is stable in culture. Dr. Sharif has developed cell lines before and has established proof-of-principle on using reticuloendothelial virus (REV) to transform a cell line. Assays were developed that measure a number of these cells’ responses (e.g. expression of cytokine genes, transcripts of cytokine genes, pathway signals etc.).
Parallel to the studies described above, Dr. Sharif’s group looked at immune responses to commercial vaccines that are based on FPV. (little is known about responses to recombinant FPV). They immunized immune-defined chickens with rFPV vectors expressing HA antigen from H5 AIV. Spleen cells from these birds were treated in vitro with a range of small protein fragments of the HA antigen. They identified a peptide that could elicit an increase in cytokine expression. This immune trigger or “epitope” appears to be conserved among various H5 AIVs. The epitope is not, however, immunogenic in chickens on its own, but could elicit a low T-cell response when introduced with adjuvants. This epitope may be used to broaden the immune response and therefore protective effect of future vaccines.
Future WorkThe information gained from this research adds to the overall understanding of the chicken’s response to AIV infection. The research group identified a molecular determinant within the HA antigen that will serve in future studies as a candidate vaccine against high path AIV.
Funding$359,400 (CPRC $59,800, PIC $60,000, NSERC/AAFC $239,600)