Selection and antigenic characterization of immune-escape mutants of H7N2 low pathogenic avian influenza virus using homologous polyclonal sera

Virus Res. 2020 Dec;290:198188. doi: 10.1016/j.virusres.2020.198188. Epub 2020 Oct 10.


Understanding the dynamics of the selection of influenza A immune escape variants by serum antibody is critical for designing effective vaccination programs for animals, especially poultry where large populations have a short generation time and may be vaccinated with high frequency. In this report, immune-escape mutants of A/turkey/New York/4450/1994 H7N2 low pathogenic avian influenza virus, were selected by serially passaging the virus in the presence of continuously increasing concentrations of homologous chicken polyclonal sera. Amino acid mutations were identified by sequencing the parental hemagglutinin (HA) gene and every 10 passages by both Sanger and deep sequencing, and the antigenic distance of the mutants to the parent strain was determined. Progressively, a total of five amino acid mutations were observed over the course of 30 passages. Based on their absence from the parental virus with deep sequencing, the mutations appear to have developed de novo. The antigenic distance between the selected mutants and the parent strain increased as the number of amino acid mutations accumulated and the concentration of antibodies had to be periodically increased to maintain the same reduction in virus titer during selection. This selection system demonstrates how H7 avian influenza viruses behave under selection with homologous sera, and provides a glimpse of their evolutionary dynamics, which can be applied to developing vaccination programs that maximize the effectiveness of a vaccine over time.

Keywords: Antigenic cartography; Low pathogenic avian influenza; Polyclonal sera; Viral mutant selection; Virus evolution.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acids / genetics
  • Animals
  • Antibodies, Viral / blood
  • Antigenic Variation / genetics*
  • Antigenic Variation / immunology
  • Hemagglutinin Glycoproteins, Influenza Virus / genetics
  • Hemagglutinin Glycoproteins, Influenza Virus / immunology
  • Immune Evasion*
  • Immune Sera*
  • Influenza A Virus, H7N2 Subtype / genetics*
  • Influenza A Virus, H7N2 Subtype / immunology*
  • Influenza A Virus, H7N2 Subtype / pathogenicity
  • Influenza Vaccines / administration & dosage
  • Influenza Vaccines / immunology
  • Influenza in Birds / virology*
  • Mutation*
  • Poultry / immunology
  • Poultry / virology*
  • Specific Pathogen-Free Organisms
  • Vaccination


  • Amino Acids
  • Antibodies, Viral
  • Hemagglutinin Glycoproteins, Influenza Virus
  • Immune Sera
  • Influenza Vaccines