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Reverse genetics in virology: A double edged sword. BIOSAFETY AND HEALTH 2022. [DOI: 10.1016/j.bsheal.2022.08.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Li J, Zhang C, Cao J, Yang Y, Dong H, Cui Y, Yao X, Zhou H, Lu L, Lycett S, Wang X, Song H, Liu W, Gao GF, Shi W, Bi Y. Re-emergence of H5N8 highly pathogenic avian influenza virus in wild birds, China. Emerg Microbes Infect 2021; 10:1819-1823. [PMID: 34392820 PMCID: PMC8451669 DOI: 10.1080/22221751.2021.1968317] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
In mid-November 2020, deaths of whooper swan were reported in the Yellow River Reservoir Area, China. In the present study, we describe the genetic characterizations and phylogenetic relationships of four clade 2.3.4.4b H5N8 highly avian influenza viruses (HPAIVs) identified from a sick whooper swan and environmental samples collected in the Yellow River Reservoir Area in late November 2020. They were closely related to recent H5Nx HPAIVs causing outbreaks in Eurasia in the 2020-2021 influenza season, suggesting these isolates might be imported into China via migratory birds. The newly identified H5N8 HPAIVs possessed Q226 and G228 (H3 numbering), indicating that they prefer to avian-like receptors. However, they had three mutations falling within known antigenic regions, including T144A in antigenic region A, T192I in antigenic region B, and N240D in antigenic region D. Our study highlights the risk of the rapid global spread of H5N8 HPAIVs and the necessity for continuous monitoring of avian influenza viruses in wild birds.
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Affiliation(s)
- Juan Li
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271016, China
| | - Chunge Zhang
- Key Laboratory of Applied Technology on Green-Eco-Healthy Animal Husbandry of Zhejiang Province, College of Animal Science and Technology & College of Veterinary Medicine of Zhejiang A&F University, Lin'an 311300, China.,CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Center for Influenza Research and Early-warning (CASCIRE), CAS-TWAS Center of Excellence for Emerging Infectious Diseases (CEEID), Chinese Academy of Sciences, Beijing 100101, China
| | - Jian Cao
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Center for Influenza Research and Early-warning (CASCIRE), CAS-TWAS Center of Excellence for Emerging Infectious Diseases (CEEID), Chinese Academy of Sciences, Beijing 100101, China.,University of Chinese Academy of Sciences, Beijing 101409, China
| | - Yongchun Yang
- Key Laboratory of Applied Technology on Green-Eco-Healthy Animal Husbandry of Zhejiang Province, College of Animal Science and Technology & College of Veterinary Medicine of Zhejiang A&F University, Lin'an 311300, China
| | - Hui Dong
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271016, China.,School of Public Health, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271000, China
| | - Yanan Cui
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271016, China.,School of Public Health, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271000, China
| | - Xue Yao
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271016, China
| | - Hong Zhou
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271016, China
| | - Lu Lu
- Usher Institute of Population Health Sciences & Informatics, Ashworth Laboratories, Kings Buildings, University of Edinburgh, United Kingdom
| | | | - Xiaodu Wang
- Key Laboratory of Applied Technology on Green-Eco-Healthy Animal Husbandry of Zhejiang Province, College of Animal Science and Technology & College of Veterinary Medicine of Zhejiang A&F University, Lin'an 311300, China
| | - Houhui Song
- Key Laboratory of Applied Technology on Green-Eco-Healthy Animal Husbandry of Zhejiang Province, College of Animal Science and Technology & College of Veterinary Medicine of Zhejiang A&F University, Lin'an 311300, China
| | - Wenjun Liu
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Center for Influenza Research and Early-warning (CASCIRE), CAS-TWAS Center of Excellence for Emerging Infectious Diseases (CEEID), Chinese Academy of Sciences, Beijing 100101, China.,University of Chinese Academy of Sciences, Beijing 101409, China
| | - George F Gao
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Center for Influenza Research and Early-warning (CASCIRE), CAS-TWAS Center of Excellence for Emerging Infectious Diseases (CEEID), Chinese Academy of Sciences, Beijing 100101, China.,University of Chinese Academy of Sciences, Beijing 101409, China
| | - Weifeng Shi
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271016, China.,School of Public Health, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian 271000, China
| | - Yuhai Bi
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Center for Influenza Research and Early-warning (CASCIRE), CAS-TWAS Center of Excellence for Emerging Infectious Diseases (CEEID), Chinese Academy of Sciences, Beijing 100101, China.,University of Chinese Academy of Sciences, Beijing 101409, China
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Abstract
The HA protein of influenza A viruses is the major viral antigen. In this study, we simultaneously introduced mutations at 17 amino acid positions of an H5 HA expected to affect antigenicity. Viruses with ≥13 amino acid changes in HA were viable, and some had altered antigenic properties. H5 HA can therefore accommodate many mutations in regions that affect antigenicity. The substantial plasticity of H5 HA may facilitate the emergence of novel antigenic variants. Since the emergence of highly pathogenic avian influenza viruses of the H5 subtype, the major viral antigen, hemagglutinin (HA), has undergone constant evolution, resulting in numerous genetic and antigenic (sub)clades. To explore the consequences of amino acid changes at sites that may affect the antigenicity of H5 viruses, we simultaneously mutated 17 amino acid positions of an H5 HA by using a synthetic gene library that, theoretically, encodes all combinations of the 20 amino acids at the 17 positions. All 251 mutant viruses sequenced possessed ≥13 amino acid substitutions in HA, demonstrating that the targeted sites can accommodate a substantial number of mutations. Selection with ferret sera raised against H5 viruses of different clades resulted in the isolation of 39 genotypes. Further analysis of seven variants demonstrated that they were antigenically different from the parental virus and replicated efficiently in mammalian cells. Our data demonstrate the substantial plasticity of the influenza virus H5 HA protein, which may lead to novel antigenic variants.
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Li J, Gu M, Liu K, Gao R, Sun W, Liu D, Jiang K, Zhong L, Wang X, Hu J, Hu S, Liu X, Shi W, Ren H, Peng D, Jiao X, Liu X. Amino acid substitutions in antigenic region B of hemagglutinin play a critical role in the antigenic drift of subclade 2.3.4.4 highly pathogenic H5NX influenza viruses. Transbound Emerg Dis 2019; 67:263-275. [PMID: 31484213 DOI: 10.1111/tbed.13347] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2019] [Revised: 08/06/2019] [Accepted: 08/26/2019] [Indexed: 01/04/2023]
Abstract
As one of the important control strategies for highly pathogenic avian influenza (HPAI) in China, vaccination has been implemented compulsively in poultry flocks since 2004. However, the emergence and dominance of the circulating antigenic variants require the update of vaccines periodically. In order to investigate the key molecular sites responsible for the antigenic drift, a total of 13 amino acid positions divergent between clade 2.3.4 H5 viruses and their descendent subclade 2.3.4.4 variants in or around the recognized antigenic epitopes A-E were initially identified through inspecting a comprehensive HA sequence alignment of the H5 subtype HPAI viruses. Subsequently, a panel of single-site or multi-site HA mutants was constructed by reverse genetics with two H5N1 viruses of S (clade 2.3.4) and QD1 (subclade 2.3.4.4) as the HA backbone to study their antigenic variations, respectively. The hemagglutination-inhibition assay revealed an evident impact of mutations at sites 88, 156, 205, 208, 239 and 289 to the HA antigenicity and highlighted that the amino acid substitutions located in the antigenic region B, especially the combined mutations at sites 205 and 208, were the major antigenic determinant which was also consistent with results from flow cytometry and antigenic mapping. Our findings provided more insights into the molecular mechanism of antigenic drift of the H5 subtype HPAI virus, which would be helpful for the selection of vaccine candidates and accordingly for the prevention and control of this devastating viral agent.
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Affiliation(s)
- Juan Li
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan, China
| | - Min Gu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Kaituo Liu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China
| | - Ruyi Gao
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China
| | - Wenqiang Sun
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China
| | - Dong Liu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China
| | - Kaijun Jiang
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China
| | - Lei Zhong
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China
| | - Xiaoquan Wang
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Jiao Hu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Shunlin Hu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Xiaowen Liu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Weifeng Shi
- Key Laboratory of Etiology and Epidemiology of Emerging Infectious Diseases in Universities of Shandong, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan, China
| | - Hongguang Ren
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Biotechnology, Beijing, China
| | - Daxin Peng
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Xinan Jiao
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
| | - Xiufan Liu
- Key Laboratory of Animal Infectious Diseases, Ministry of Agriculture, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China.,Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture, Yangzhou University, Yangzhou, China
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Structural and functional definition of a vulnerable site on the hemagglutinin of highly pathogenic avian influenza A virus H5N1. J Biol Chem 2019; 294:4290-4303. [PMID: 30737282 PMCID: PMC6433081 DOI: 10.1074/jbc.ra118.007008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Revised: 01/19/2019] [Indexed: 01/07/2023] Open
Abstract
Most neutralizing antibodies against highly pathogenic avian influenza A virus H5N1 recognize the receptor-binding site (RBS) on the globular head domain and the stem of H5N1 hemagglutinin (HA). Through comprehensive analysis of multiple human protective antibodies, we previously identified four vulnerable sites (VS1-VS4) on the globular head domain. Among them, the VS1, occupying the opposite side of the RBS on the same HA, was defined by the epitope of antibody 65C6. In this study, we report the crystal structures of two additional human H5N1 antibodies isolated from H5N1-infected individuals, 3C11 and AVFluIgG01, bound to the head at 2.33- and 2.30-Å resolution, respectively. These two new antibody epitopes have large overlap with and extend beyond the original VS1. Site-directed mutagenesis experiments identified eight pivotal residues (Ser-126b, Lys-165, Arg-166, Ser-167, Tyr-168, Asn-169, Thr-171, and Asn-172) critical for 65C6-, 3C11-, and AVFluIgG01-binding and neutralization activities. These residues formed a unique "Y"-shaped surface on H5N1 globular head and are highly conserved among H5N1 viruses. Our results further support the existence of a vulnerable site distinct from the RBS and the stem region of H5N1 HA, and future design of immunogens should take this particular site into consideration.
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Guo C, Xie X, Li H, Zhao P, Zhao X, Sun J, Wang H, Liu Y, Li Y, Hu Q, Hu J, Li Y. Prediction of common epitopes on hemagglutinin of the influenza A virus (H1 subtype). Exp Mol Pathol 2014; 98:79-84. [PMID: 25533547 DOI: 10.1016/j.yexmp.2014.12.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Accepted: 12/18/2014] [Indexed: 11/25/2022]
Abstract
Influenza A virus infection is a persistent threat to public health worldwide due to hemagglutinin (HA) variation. Current vaccines against influenza A virus provide immunity to viral isolates similar to vaccine strains. Antibodies against common epitopes provide immunity to diverse influenza virus strains and protect against future pandemic influenza. Therefore, it is vital to analyze common HA antigenic epitopes of influenza virus. In this study, 14 strains of monoclonal antibodies with high sensitivity to common epitopes of influenza virus antigens identified in our previous study were selected as the tool to predict common HA epitopes. The common HA antigenic epitopes were divided into four categories by ELISA blocking experiments, and separately, into three categories according to the preliminary results of computer simulation. Comparison between the results of computer simulations and ELISA blocking experiments indicated that at least two classes of common epitopes are present in influenza virus HA. This study provides experimental data for improving the prediction of HA epitopes of influenza virus (H1 subtype) and the development of a potential universal vaccine as well as a novel approach for the prediction of epitopes on other pathogenic microorganisms.
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Affiliation(s)
- Chunyan Guo
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Xin Xie
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, College of Life Science, Northwest University, Xi'an 710069, China; Department of Translational Medicine, Institute of Integrated Medical Information, Xi'an 710016, China
| | - Huijin Li
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Penghua Zhao
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Xiangrong Zhao
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Jingying Sun
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Haifang Wang
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Yang Liu
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Yan Li
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Qiaoxia Hu
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
| | - Jun Hu
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China.
| | - Yuan Li
- Central Laboratory, Shaanxi Provincial People's Hospital, Third Affiliated Hospital of the School of Medicine, Xi'an Jiaotong University, Xi'an 710068, China; Key Laboratory of Infection and Immunity Disease of Shaanxi Province, Xi'an, 710068, China
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Donis RO. Antigenic analyses of highly pathogenic avian influenza a viruses. Curr Top Microbiol Immunol 2014; 385:403-40. [PMID: 25190014 DOI: 10.1007/82_2014_422] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
Abstract
In response to the ongoing threat to animal and human health posed by HPAI endemic in poultry, Asia (H5N1) and North America (H7N3) have revived efforts to reduce pandemic risk by disease control at the source and improved pandemic vaccines. Discovery of conserved neutralization epitopes in the HA, which mediate broad protection within and across HA subtypes have changed the paradigm of "broadly reactive" or "universal" vaccine design. Development of such vaccines would benefit from comparative antigenic analysis of viruses with increasing divergence within (and between) HA subtypes. A review of recent work to define the antigenic properties of HPAI viruses revealed data generated through an array of experimental approaches. This information has supported diagnostics and vaccine development for animal and human health. Further harmonization of analytical methods is needed to determine the antigenic relationships among multiple lineages of rapidly evolving HPAI viruses.
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Affiliation(s)
- Ruben O Donis
- Influenza Division, Centers for Disease Control and Prevention, 1600 Clifton Road NE Mailstop A20, Atlanta, GA, 30333, USA,
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The antigenic architecture of the hemagglutinin of influenza H5N1 viruses. Mol Immunol 2013; 56:705-19. [PMID: 23933511 DOI: 10.1016/j.molimm.2013.07.010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 07/06/2013] [Accepted: 07/14/2013] [Indexed: 11/22/2022]
Abstract
Human infection with the highly pathogenic avian influenza A virus H5N1 is associated with a high mortality and morbidity. H5N1 continues to transmit from poultry to the human population, raising serious concerns about its pandemic potential. Current influenza H5N1 vaccines are based upon the elicitation of a neutralizing antibody (Ab) response against the major epitope regions of the viral surface glycoprotein, hemagglutinin (HA). However, antigenic drift mutations in immune-dominant regions on the HA structure allow the virus to escape Ab neutralization. Epitope mapping using neutralizing monoclonal antibodies (mAb) helps define mechanisms of antigenic drift, neutralizing escape and can facilitate pre-pandemic vaccine design. This review explores the current knowledge base of the antigenic sites of the H5N1 HA molecule. The relationship between the epitope architecture of the H5N1 HA, antigenic evolution of the different H5N1 lineages and the antigenic complexity of the H5N1 virus lineages that constitute potential pandemic strains are discussed in detail.
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