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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.

SUBMITTER: Abente EJ

PROVIDER: S-EPMC5008105 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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The Molecular Determinants of Antibody Recognition and Antigenic Drift in the H3 Hemagglutinin of Swine Influenza A Virus.

Abente Eugenio J EJ Santos Jefferson J Lewis Nicola S NS Gauger Phillip C PC Stratton Jered J Skepner Eugene E Anderson Tavis K TK Rajao Daniela S DS Perez Daniel R DR Vincent Amy L AL

Journal of virology 20160826 18

<h4>Unlabelled</h4>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 swi ...[more]

PMID: 27384658

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Project description:The continuous antigenic variation of influenza A viruses remains a major hurdle for vaccine selection; however, the molecular determinants and mechanisms of antigenic change remain largely unknown. In this study, two escape mutants were generated by serial passages of the Eurasian avian-like H1N1 swine influenza virus (EA H1N1 SIV) A/swine/Henan/11/2005 (HeN11) in the presence of two neutralizing monoclonal antibodies (mAbs) against the hemagglutinin (HA) protein, which were designated HeN11-2B6-P5 and HeN11-4C7-P8, respectively. The HeN11-2B6-P5 mutant simultaneously harbored the N190D and I230M substitutions in HA, whereas HeN11-4C7-P8 harbored the M269R substitution in HA (H3 numbering). The effects of each of these substitutions on viral antigenicity were determined by measuring the neutralization and hemagglutination inhibition (HI) titers with mAbs and polyclonal sera raised against the representative viruses. The results indicate that residues 190 and 269 are key determinants of viral antigenic variation. In particular, the N190D mutation had the greatest antigenic impact, as determined by the HI assay. Further studies showed that both HeN11-2B6-P5 and HeN11-4C7-P8 maintained the receptor-binding specificity of the parent virus, although the single mutation N190D decreased the binding affinity for the human-type receptor. The replicative ability in vitro of HeN11-2B6-P5 was increased, whereas that of HeN11-4C7-P8 was decreased. These findings extend our understanding of the antigenic evolution of influenza viruses under immune pressure and provide insights into the functional effects of amino acid substitutions near the receptor-binding site and the interplay among receptor binding, viral replication, and antigenic drift. IMPORTANCE The antigenic changes that occur continually in the evolution of influenza A viruses remain a great challenge for the effective control of disease outbreaks. Here, we identified three amino acid substitutions (at positions 190, 230, and 269) in the HA of EA H1N1 SIVs that determine viral antigenicity and result in escape from neutralizing monoclonal antibodies. All three of these substitutions have emerged in nature. Of note, residues 190 and 230 have synergistic effects on receptor binding and antigenicity. Our findings provide a better understanding of the functional effects of amino acid substitutions in HA and their consequences for the antigenic drift of influenza viruses.

Project description:BackgroundIn early 2020, a novel H9N2 AIV immune escape variant emerged in South China and rapidly spread throughout mainland China. The effectiveness of the current H9N2 vaccine is being challenged by emerging immune escape strains. Assessing key amino acid substitutions that contribute to antigenic drift and immune escape in the HA gene of circulating strains is critical for understanding virus evolution and in selecting more effective vaccine components.MethodsIn this study, a representative immune escape strain, A/chicken/Fujian/11/2020 (FJ/20), differed from current H9N2 vaccine strain, A/chicken/Anhui/LH99/2017 (AH/17) by 18 amino acids in the head domain in HA protein. To investigate the molecular determinants of antigenic drift of FJ/20, a panel of mutants were generated by reverse genetics including specific amino acids changes in the HA genes of FJ/20 and AH/17. The antigenic effect of the substitutions was evaluated by hemagglutination inhibition (HI) assay and antigenic cartography.ResultsFujian-like H9N2 viruses had changed antigenicity significantly, having mutated into an antigenically distinct sub-clade. Relative to the titers of the vaccine virus AH/17, the escape strain FJ/20 saw a 16-fold reduction in HI titer against antiserum elicited by AH/17. Our results showed that seven residue substitutions (D127S, G135D, N145T, R146Q, D179T, R182T and T183N) near the HA receptor binding sites were critical for converting the antigenicity of both AH/17 and FJ/20. Especially, the combined mutations 127D, 135G, 145N, and 146R could be a major factor of antigenic drift in the current immune escape variant FJ/20. The avian influenza A (H9N2) variant virus need further ongoing epidemiological surveillance.ConclusionsIn this study, we evaluated the relative contributions of different combinations of amino acid substitutions in the HA globular head domain of the immune escape strain FJ/20 and the vaccine strain AH/17. Our study provides more insights into the molecular mechanism of the antigenic drift of the H9N2 AIV immune escape strain. This work identified important markers for understanding H9N2 AIV evolution as well as for improving vaccine development and control strategies in poultry.

Dataset Information

The Molecular Determinants of Antibody Recognition and Antigenic Drift in the H3 Hemagglutinin of Swine Influenza A Virus.

Publications

The Molecular Determinants of Antibody Recognition and Antigenic Drift in the H3 Hemagglutinin of Swine Influenza A Virus.

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