title: The Molecular Determinants of Antibody Recognition and Antigenic Drift in the H3 Hemagglutinin of Swine Influenza A Virus.
abstract: Influenza A virus (IAV) of the H3 subtype is an important respiratory pathogen that affects both humans and swine. Vaccination to induce neutralizing antibodies against the surface glycoprotein hemagglutinin (HA) is the primary method used to control disease. However, due to antigenic drift, vaccine strains must be periodically updated. Six of the 7 positions previously identified in human seasonal H3 (positions 145, 155, 156, 158, 159, 189, and 193) were also indicated in swine H3 antigenic evolution. To experimentally test the effect on virus antigenicity of these 7 positions, substitutions were introduced into the HA of an isogenic swine lineage virus. We tested the antigenic effect of these introduced substitutions by using hemagglutination inhibition (HI) data with monovalent swine antisera and antigenic cartography to evaluate the antigenic phenotype of the mutant viruses. Combinations of substitutions within the antigenic motif caused significant changes in antigenicity. One virus mutant that varied at only two positions relative to the wild type had a >4-fold reduction in HI titers compared to homologous antisera. Potential changes in pathogenesis and transmission of the double mutant were evaluated in pigs. Although the double mutant had virus shedding titers and transmissibility comparable to those of the wild type, it caused a significantly lower percentage of lung lesions. Elucidating the antigenic effects of specific amino acid substitutions at these sites in swine H3 IAV has important implications for understanding IAV evolution within pigs as well as for improved vaccine development and control strategies in swine.
  
  
  
  A key component of influenza virus evolution is antigenic drift mediated by the accumulation of amino acid substitutions in the hemagglutinin (HA) protein, resulting in escape from prior immunity generated by natural infection or vaccination. Understanding which amino acid positions of the HA contribute to the ability of the virus to avoid prior immunity is important for understanding antigenic evolution and informs vaccine efficacy predictions based on the genetic sequence data from currently circulating strains. Following our previous work characterizing antigenic phenotypes of contemporary wild-type swine H3 influenza viruses, we experimentally validated that substitutions at 6 amino acid positions in the HA protein have major effects on antigenicity. An improved understanding of the antigenic diversity of swine influenza will facilitate a rational approach for selecting more effective vaccine components to control the circulation of influenza in pigs and reduce the potential for zoonotic viruses to emerge.
authors.affiliation: Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa, USA.
authors.forename: Eugenio J
authors.initials: EJ
authors.lastname: Abente
authors.affiliation: Department of Population Health, Poultry Diagnostic and Research Center, College of Veterinary Medicine, University of Georgia, Athens, Georgia, USA.
authors.forename: Jefferson
authors.initials: J
authors.lastname: Santos
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Nicola S
authors.initials: NS
authors.lastname: Lewis
authors.affiliation: Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA.
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Gauger
authors.affiliation: Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa, USA.
authors.forename: Jered
authors.initials: J
authors.lastname: Stratton
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Eugene
authors.initials: E
authors.lastname: Skepner
authors.affiliation: Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa, USA.
authors.forename: Tavis K
authors.identifier: 0000-0002-3138-5535
authors.initials: TK
authors.lastname: Anderson
authors.affiliation: Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa, USA.
authors.forename: Daniela S
authors.initials: DS
authors.lastname: Rajao
authors.affiliation: Department of Population Health, Poultry Diagnostic and Research Center, College of Veterinary Medicine, University of Georgia, Athens, Georgia, USA.
authors.forename: Daniel R
authors.identifier: 0000-0002-6569-5689
authors.initials: DR
authors.lastname: Perez
authors.affiliation: Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa, USA amy.vincent@ars.usda.gov.
authors.forename: Amy L
authors.initials: AL
authors.lastname: Vincent
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology*; D000956:Antigens, Viral / Q000235:genetics / Q000276:immunology*; D040961:Genetic Drift; D006385:Hemagglutination Inhibition Tests; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000276:immunology*; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology*; D008168:Lung / Q000473:pathology; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000276:immunology; D009976:Orthomyxoviridae Infections / Q000473:pathology / Q000635:transmission / Q000662:veterinary / Q000821:virology; D059386:Reverse Genetics; D013552:Swine; D013553:Swine Diseases / Q000473:pathology / Q000821:virology; D014774:Virulence; D017201:Virus Shedding
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D050505:Mutant Proteins