title: Cross-reactive immunity against influenza viruses in children and adults following 2009 pandemic H1N1 infection.
abstract: 2009 H1N1 pandemic influenza (A(H1N1)pdm09) virus infected large numbers of people worldwide. Recent studies suggest infection with A(H1N1)pdm09 virus elicited cross-reactive anti-hemagglutinin (HA) memory B cell response to conserved regions of HA. However, the breadth and magnitude of cross-reactive immunity in children and adults following A(H1N1)pdm09 infection are unknown.
  
  
  METHODS
  We investigated serum anti-HA immunity to a number of group-1 and -2 viruses in children and adults using hemagglutination inhibition (HAI), enzyme-linked immunosorbent assay and virus neutralization assay.
  
  
  RESULTS
  Applying hemagglutination inhibition (HAI) titers ⩾40 against A(H1N1)pdm09 as threshold of sero-positivity, we observed significantly higher levels of anti-HA antibodies to a number of virus subtypes, including those neutralizing H5N1, in subjects with HAI titer ⩾40 than those with HAI <40. Adults demonstrated broader and stronger cross-reactive anti-HA antibodies than children, including cross-reactive anti-HA1 and -HA2 antibodies. By comparison, individuals with serologic evidence of recent exposure to seasonal H1N1 or H3N2 did not show such broad cross-reactive immunity.
  
  
  CONCLUSIONS
  Our results suggest individuals exposed to A(H1N1)pdm09 virus developed a broad and age-associated cross-reactive anti-HA immunity which may have important implications for future vaccination strategies to enable protection against a broader range of influenza viruses.
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Muhammad S
authors.initials: MS
authors.lastname: Ahmed
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Jacques
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Waleed
authors.initials: W
authors.lastname: Mahallawi
authors.affiliation: Viral Pseudotype Unit, School of Pharmacy, University of Kent, Kent, United Kingdom.
authors.forename: Francesca
authors.initials: F
authors.lastname: Ferrara
authors.affiliation: Viral Pseudotype Unit, School of Pharmacy, University of Kent, Kent, United Kingdom.
authors.forename: Nigel
authors.initials: N
authors.lastname: Temperton
authors.affiliation: ENT Department, Alder Hey Children's Hospital, Liverpool, United Kingdom.
authors.forename: Nav
authors.initials: N
authors.lastname: Upile
authors.affiliation: ENT Department, Alder Hey Children's Hospital, Liverpool, United Kingdom.
authors.forename: Casey
authors.initials: C
authors.lastname: Vaughan
authors.affiliation: ENT Department, Alder Hey Children's Hospital, Liverpool, United Kingdom.
authors.forename: Ravi
authors.initials: R
authors.lastname: Sharma
authors.affiliation: ENT Department, Royal Liverpool and Broadgreen University Hospital, Liverpool, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Beer
authors.affiliation: Respiratory Virus Unit, Public Health England, London, United Kingdom.
authors.forename: Katja
authors.initials: K
authors.lastname: Hoschler
authors.affiliation: Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Paul S
authors.initials: PS
authors.lastname: McNamara
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom. Electronic address: Qibo.Zhang@liverpool.ac.uk.
authors.forename: Qibo
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood / Q000276:immunology; D002648:Child; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006385:Hemagglutination Inhibition Tests; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000276:immunology*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology*; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology* / Q000821:virology; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus
keywords: Anti-hemagglutinin antibody; Cross-reactive immunity; Influenza virus; Pandemic H1N1 infection; Serum antibody; Virus neutralization