title: Age-related sensitivity and pathological differences in infections by 2009 pandemic influenza A (H1N1) virus.
abstract: BACKGROUND
  The highly pandemic 2009 influenza A H1N1 virus infection showed distinguished skewed age distribution with majority of infection and death in children and young adults. Although previous exposure to related antigen has been proposed as an explanation, the mechanism of age protection is still unknown.
  
  
  METHODS
  In this study, murine model of different ages were inoculated intranasally with H1N1 (A/Beijing/501/09) virus and the susceptibility and pathological response to 2009 H1N1 infection were investigated.
  
  
  RESULTS
  Our results showed that the younger mice had higher mortality rate when infected with the same dose of virus and the lethal dose increased with age. Immunohistochemical staining of H1N1 antigens in mice lung indicated infection was in the lower respiratory tract. Most bronchial and bronchiolar epithelial cells in 4-week mice were infected while only a minor percentage of those cells in 6-month and 1-year old mice did. The young mice developed much more severe lung lesions and had higher virus load in lung than the two older groups of mice while older mice formed more inducible bronchus-associated lymphoid tissue in their lungs and more severe damage in spleen.
  
  
  CONCLUSIONS
  These results suggest that young individuals are more sensitive to H1N1 infection and have less protective immune responses than older adults. The age factor should be considered when studying the pathogenesis and transmission of influenza virus and formulating strategies on vaccination and treatment.
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
authors.forename: Shihui
authors.initials: S
authors.lastname: Sun
authors.forename: Guangyu
authors.initials: G
authors.lastname: Zhao
authors.forename: Wenjun
authors.initials: W
authors.lastname: Xiao
authors.forename: Jingya
authors.initials: J
authors.lastname: Hu
authors.forename: Yan
authors.initials: Y
authors.lastname: Guo
authors.forename: Hong
authors.initials: H
authors.lastname: Yu
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wu
authors.forename: Yadi
authors.initials: Y
authors.lastname: Tan
authors.forename: Yusen
authors.initials: Y
authors.lastname: Zhou
mesh_terms: D000367:Age Factors; D000818:Animals; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000472:pathogenicity / Q000502:physiology*; D007251:Influenza, Human / Q000453:epidemiology / Q000401:mortality / Q000473:pathology* / Q000821:virology*; D008168:Lung / Q000473:pathology / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D058873:Pandemics; D014774:Virulence