title: Re-emergence of H3N2 strains carrying potential neutralizing mutations at the N-linked glycosylation site at the hemagglutinin head, post the 2009 H1N1 pandemic.
abstract: Seasonally prevalent H1N1 and H3N2 influenza A viruses have evolved by antigenic drift; this evolution has resulted in the acquisition of asparagine (N)-linked glycosylation sites (NGSs) in the globular head of hemagglutinin (HA), thereby affecting the antigenic and receptor-binding properties, as well as virulence. An epidemiological survey indicated that although the traditional seasonal H1N1 strain had disappeared, H3N2 became predominant again in the seasons (2010-11 and 2011-12) immediately following the H1N1 pandemic of 2009. Interestingly, although the 2009 pandemic H1N1 strain (H1N1pdm09) lacks additional NGSs, clinically isolated H3N2 strains obtained during these seasons gained N (Asn) residues at positions 45 and 144 of HA that forms additional NGSs.
  
  
  
  To investigate whether these NGSs are associated with re-emergence of H3N2 within the subtype, we tested the effect of amino acid substitutions on neutralizing activity by using the antisera raised against H3N2 strains with or without additional NGSs. Furthermore, because the N residue at position 144 of HA was identified as the site of mismatch between the vaccine and epidemic strains of 2011-2012, we generated mutant viruses by reverse genetics and tested the functional importance of this particular NGS for antibody-mediated neutralization by intranasal inoculation of mice.
  
  
  
  The results indicated that amino acid substitution at residue 144 significantly affected neutralization activity, acting as an escape mutation.
  
  
  
  Our data suggest that the newly acquired NGSs in the HA globular head may play an important role in the re-emergence of endemic seasonal H3N2 strain by aiding the escape from humoral immunity.
authors: Department of Microbiology, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors: Hiroshi
authors: H
authors: Ushirogawa
authors: Department of Microbiology, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors: Tadasuke
authors: T
authors: Naito
authors: Department of Hematology, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors: Hirotoshi
authors: H
authors: Tokunaga
authors: Department of Pediatrics, Shizuoka Kosei Hospital, 23 Kitaban-cho, Aoi-ku, Shizuoka, 420-8623, Japan.
authors: Toshihiro
authors: T
authors: Tanaka
authors: Department of Pediatrics, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors: Takashi
authors: T
authors: Nakano
authors: Department of Pediatrics, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors: Kihei
authors: K
authors: Terada
authors: Department of Microbiology, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan.
authors: Masanobu
authors: M
authors: Ohuchi
authors: Department of Microbiology, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama, 701-0192, Japan. mineki@med.kawasaki-m.ac.jp.
authors: Mineki
authors: M
authors: Saito
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D057134:Antibodies, Neutralizing / Q000276:immunology; D016208:Databases, Factual; D006031:Glycosylation; D006385:Hemagglutination Inhibition Tests; D006388:Hemagglutinins / Q000235:genetics* / Q000276:immunology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics* / Q000276:immunology; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics* / Q000276:immunology; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology / Q000821:virology*; D007564:Japan / Q000453:epidemiology; D051379:Mice; D009154:Mutation; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012621:Seasons; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D057134:Antibodies, Neutralizing; D006388:Hemagglutinins; D037521:Virulence Factors
keywords: Escape mutation; H3N2; HA globular head; Influenza A; N-glycosylation