title: Epitope specificity of anti-HA2 antibodies induced in humans during influenza infection.
abstract: BACKGROUND
  The conserved, fusion-active HA2 glycopolypeptide (HA2) subunit of influenza A hemagglutinin comprises four distinct antigenic sites. Monoclonal antibodies (MAbs) recognizing three of these sites are broadly cross-reactive and protective.
  
  
  OBJECTIVE
  This study aimed to establish whether antibodies specific to these three antigenic sites were elicited during a natural influenza infection or by vaccination of humans.
  
  
  METHODS
  Forty-five paired acute and convalescent sera from individuals with a confirmed influenza A (subtype H3) infection were examined for the presence of HA2-specific antibodies. The fraction of antibodies specific to three particular antigenic sites (designated IIF4, FC12, and CF2 here) was investigated using competitive enzyme immunoassay.
  
  
  RESULTS
  Increased levels of antibodies specific to an ectodomain of HA2 (EHA2: N-terminal residues 23-185 of HA2) were detected in 73% of tested convalescent sera (33/45), while an increased level of antibodies specific to the HA2 fusion peptide (N-terminal residues 1-38) was induced in just 15/45 individuals (33%). Competitive assays confirmed that antibodies specific to the IIF4 epitope (within HA2 residues 125-175) prevailed in 86% (13/15) over those specific to the other two epitopes during infection. However, only a negligible increase in HA2-specific antibodies was detectable following vaccination with a current subunit vaccine.
  
  
  CONCLUSIONS
  We observed that the antigenic site localized within N-terminal HA2 residues 125-175 was more immunogenic than that within residues 1-38 (HA2 fusion protein), although both are weak natural immunogens. We suggest that new anti-influenza vaccines should include HA2 (or specific epitopes localized within this glycopolypeptide) to enhance their cross-protective efficacy.
authors.affiliation: Institute of Virology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Staneková
authors.forename: Vojtech
authors.initials: V
authors.lastname: Mucha
authors.forename: Tatiana
authors.initials: T
authors.lastname: Sládková
authors.forename: Hana
authors.initials: H
authors.lastname: Blaškovičová
authors.forename: František
authors.initials: F
authors.lastname: Kostolanský
authors.forename: Eva
authors.initials: E
authors.lastname: Varečková
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D000939:Epitopes / Q000276:immunology*; D005260:Female; D006389:Hemagglutinins, Viral / Q000276:immunology*; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology; D007251:Influenza, Human / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D000939:Epitopes; D006389:Hemagglutinins, Viral; D007252:Influenza Vaccines; C452559:hemagglutinin HA-2 fusogenic peptide, Influenza virus