title: Complex patterns of human antisera reactivity to novel 2009 H1N1 and historical H1N1 influenza strains.
abstract: BACKGROUND
  During the 2009 influenza pandemic, individuals over the age of 60 had the lowest incidence of infection with approximately 25% of these people having pre-existing, cross-reactive antibodies to novel 2009 H1N1 influenza isolates. It was proposed that older people had pre-existing antibodies induced by previous 1918-like virus infection(s) that cross-reacted to novel H1N1 strains.
  
  
  RESULTS
  Using antisera collected from a cohort of individuals collected before the second wave of novel H1N1 infections, only a minority of individuals with 1918 influenza specific antibodies also demonstrated hemagglutination-inhibition activity against the novel H1N1 influenza. In this study, we examined human antisera collected from individuals that ranged between the ages of 1 month and 90 years to determine the profile of seropositive influenza immunity to viruses representing H1N1 antigenic eras over the past 100 years. Even though HAI titers to novel 2009 H1N1 and the 1918 H1N1 influenza viruses were positively associated, the association was far from perfect, particularly for the older and younger age groups.
  
  
  CONCLUSIONS
  Therefore, there may be a complex set of immune responses that are retained in people infected with seasonal H1N1 that can contribute to the reduced rates of H1N1 influenza infection in older populations.
authors: Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors: Donald M
authors: DM
authors: Carter
authors: Hai-Rong
authors: HR
authors: Lu
authors: Chalise E
authors: CE
authors: Bloom
authors: Corey J
authors: CJ
authors: Crevar
authors: Joshua L
authors: JL
authors: Cherry
authors: David J
authors: DJ
authors: Lipman
authors: Ted M
authors: TM
authors: Ross
mesh_terms: D000914:Antibodies, Viral / Q000276:immunology*; D003429:Cross Reactions; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000276:immunology; D006801:Humans; D007106:Immune Sera / Q000276:immunology*; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D013045:Species Specificity; D014765:Viral Vaccines / Q000276:immunology
chemical_list: D000914:Antibodies, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007106:Immune Sera; D014765:Viral Vaccines