The molecular determinants of antigenic drift in a novel avian influenza A (H9N2) variant virus

Abstract

Background In 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. Methods In 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. Results Fujian-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. Conclusions In 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.

Antigenic mapping of the hemagglutinin of the H9 subtype influenza A viruses using sera from Japanese quail (Coturnix c. japonica)

“…The current literature shows different approaches employed for the antisera generation, including live virus inoculation and inactivated/adjuvanted virus vaccination to study antigenicity of the HA of influenza viruses. Still, none have used quail sera as a model (16,(24)(25)(26)(27). The results validate using the quail model to study the antigenicity of H9N2 as well as other viral properties such as virus replication, pathogenesis, and transmission.…”

“…Quail show wide distribution in the respiratory tract of both avian-like (SAα2.3) and human-like (SAα2.6) sialic acid receptors, which may have contributed to the emergence of the poultry-adapted H9N2 strains with human-like receptor preference (22,23). Anti-H9 sera have been raised by different approaches and regimes, which act as confounding factors to assess antigenicity faithfully (16,(24)(25)(26)(27). Immunization approaches have included either live virus challenge or most typically inactivated/adjuvanted viruses in either single or prime and boost infection or vaccina tion.…”

Unleashing the Immune Arsenal: Development of Broad-spectrum Multiepitope Bluetongue Vaccine Targeting Conserved T Cell Epitopes of Structural Proteins

“…Collectively, the comprehensive profiling of our vaccine constructs underscores their potential as promising candidates for effective BT vaccine development. With a focus on cell-mediated immunity, which has demonstrated its importance in providing cross-protection against various BTV serotypes in prior research (Umeshappa, Singh et al 2010, singh 2011, Umeshappa, Singh et al 2011, Rojas, Rodriguez-Calvo et al 2017, Potter 2019, Evseev and Magor 2021, Rodríguez-Martín D 2021, Wang, Tang et al 2022, Zheng, Guo et al 2022…”

“…Collectively, the comprehensive profiling of our vaccine constructs underscores their potential as promising candidates for effective BT vaccine development. With a focus on cell-mediated immunity, which has demonstrated its importance in providing cross-protection against various BTV serotypes in prior research (Umeshappa, Singh et al 2010, singh 2011, Umeshappa, Singh et al 2011, Rojas, Rodriguez-Calvo et al 2017, Potter 2019, Rijn 2019, Evseev and Magor 2021, Rodríguez-Martín D 2021, Wang, Tang et al 2022, Zheng, Guo et al 2022), our vaccine design strategy emphasizes targeting conserved immunogenic cytotoxic T lymphocyte (CTL) and T-helper-1 cell epitopes to develop a highly effective pan-BTV vaccine. Including T-helper epitopes is crucial, as CD4+ T-helper-1 cells play a vital role in supporting the function of anti-viral CD8+ CTLs (Umeshappa, Huang et al 2009, Umeshappa and Xiang 2011, Sokke Umeshappa, Hebbandi Nanjundappa et al 2012, Umeshappa, Xie et al 2013).…”

Evolutionary Events Promoted Polymerase Activity of H13N8 Avian Influenza Virus

“…Since first identified in United States turkeys in 1966, H9N2 AIVs have spread widely around the world [ 9 , 10 , 11 ]. H9N2 AIVs are the most prevalent subtypes in China and are endemic in multiple avian species [ 12 , 13 ]. Meanwhile, H9N2 AIVs have acquired the ability to overcome species barriers, resulting in infections in pigs, dogs, and even humans [ 14 ].…”