title: Characterization of H5N1 influenza virus variants with hemagglutinin mutations isolated from patients.
abstract: A change in viral hemagglutinin (HA) receptor binding specificity from α2,3- to α2,6-linked sialic acid is necessary for highly pathogenic avian influenza (AI) virus subtype H5N1 to become pandemic. However, details of the human-adaptive change in the H5N1 virus remain unknown. Our database search of H5N1 clade 2.2.1 viruses circulating in Egypt identified multiple HA mutations that had been selected in infected patients. Using reverse genetics, we found that increases in both human receptor specificity and the HA pH threshold for membrane fusion were necessary to facilitate replication of the virus variants in human airway epithelia. Furthermore, variants with enhanced replication in human cells had decreased HA stability, apparently to compensate for the changes in viral receptor specificity and membrane fusion activity. Our findings showed that H5N1 viruses could rapidly adapt to growth in the human airway microenvironment by altering their HA properties in infected patients and provided new insights into the human-adaptive mechanisms of AI viruses.
  
  
  OBJECTIVE
  Circulation between bird and human hosts may allow H5N1 viruses to acquire amino acid changes that increase fitness for human infections. However, human-adaptive changes in H5N1 viruses have not been adequately investigated. In this study, we found that multiple HA mutations were actually selected in H5N1-infected patients and that H5N1 variants with some of these HA mutations had increased human-type receptor specificity and increased HA membrane fusion activity, both of which are advantageous for viral replication in human airway epithelia. Furthermore, HA mutants selected during viral replication in patients were likely to have less HA stability, apparently as a compensatory mechanism. These results begin to clarify the picture of the H5N1 human-adaptive mechanism.
authors: nabe@biken.osaka-u.ac.jp.
authors: Yohei
authors: Y
authors: Watanabe
authors: Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.
authors: Yasuha
authors: Y
authors: Arai
authors: Department of Infectious Diseases, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors: Tomo
authors: T
authors: Daidoji
authors: Norihito
authors: N
authors: Kawashita
authors: Department of Microbiology and Immunology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt.
authors: Madiha S
authors: MS
authors: Ibrahim
authors: Department of Microbiology and Immunology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt.
authors: Emad El-Din M
authors: Eel-D
authors: El-Gendy
authors: Health Scientific Hills, College of Life and Health Sciences, Chubu University, Aichi, Japan.
authors: Hiroaki
authors: H
authors: Hiramatsu
authors: Kanonji Institute, The Research Foundation for Microbial Diseases of Osaka University, Kagawa, Japan.
authors: Ritsuko
authors: R
authors: Kubota-Koketsu
authors: Tatsuya
authors: T
authors: Takagi
authors: Department of Applied Biological Chemistry, Faculty of Agriculture, Shizuoka University, Shizuoka, Japan.
authors: Takeomi
authors: T
authors: Murata
authors: Department of Infectious Diseases, Osaka Prefectural Institute of Public Health, Osaka, Japan.
authors: Kazuo
authors: K
authors: Takahashi
authors: Kanonji Institute, The Research Foundation for Microbial Diseases of Osaka University, Kagawa, Japan.
authors: Yoshinobu
authors: Y
authors: Okuno
authors: Department of Infectious Diseases, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors: Takaaki
authors: T
authors: Nakaya
authors: Health Scientific Hills, College of Life and Health Sciences, Chubu University, Aichi, Japan.
authors: Yasuo
authors: Y
authors: Suzuki
authors: Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.
authors: Kazuyoshi
authors: K
authors: Ikuta
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000821:virology; D014644:Genetic Variation; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics*; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000145:classification* / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D007251:Influenza, Human / Q000821:virology*; D008807:Mice, Inbred BALB C; D020125:Mutation, Missense; D009976:Orthomyxoviridae Infections / Q000821:virology; D016019:Survival Analysis
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; C109963:hemagglutinin, avian influenza A virus