title: Study on age-dependent pre-existing 2009 pandemic influenza virus T and B cell responses from Chinese population.
abstract: The outbreak of the 2009 H1N1 influenza pandemic (H1N1pdm) affected thousands of people in Mexico and the United States, and spread rapidly throughout the world from April 2009 to July 2010. To explore the age-specific prevalence of seroprotection against H1N1pdm infection, we estimated pre-existing humoral and cellular immunities of residents in Northern China against H1N1pdm and seasonal H1N1 virus in an age-dependent manner.
  
  
  
  Anonymous serum samples were collected from 1425 to 1434 adult healthy individuals before and after the pandemic outbreak, and then grouped by birth year 1913-1990. The antibody titers of H1N1pdm and seasonal H1N1 were determined using microneutralization (MN) assays, and the proportion of seropositive was estimated based on the year of birth. Separately, another 63 blood samples were collected in 2006 and prepared for analysis of virus specific memory B and IFN-γ+T cells using the ELISpot assays.
  
  
  
  The prevalence of pre-existing H1N1pdm-specific sero-antibodies in the elderly population (>60 years old) was 7.8%. The younger group, aged 19 to 60 years, exhibited a significant increase in seropositivity for H1N1pdm after the pandemic (4.9% before pandemic and 18.9% after pandemic, p < 0.05). The prevalence of H1N1pdm specific MBCs before the pandemic in the elderly (>60 years) and younger populations (<60 years) was 38% (8/21) and 48% (20/42), respectively (p = 0.6). The IFN-γ+T cell responses to the pandemic and seasonal viruses were significantly lower in the elder group than those in the younger group (<60 years) (p < 0.05).
  
  
  
  Pre-existing serum antibodies and memory B cells against H1N1pdm were low in all age group, whereas diminished memory T cell responses to this virus were observed in the elderly population both before and after the pandemic.
authors.affiliation: The General Hospital of PLA Rocket Force, 16 Xin Jie Kou Wai Street, Hai-Dian District, Beijing, 100088, People's Republic of China.
authors.forename: Jin
authors.initials: J
authors.lastname: Lv
authors.affiliation: Beijing Center for Disease Prevention and Control, Beijing, 100013, People's Republic of China.
authors.forename: Zhen-Yong
authors.initials: ZY
authors.lastname: Ren
authors.affiliation: The General Hospital of PLA Rocket Force, 16 Xin Jie Kou Wai Street, Hai-Dian District, Beijing, 100088, People's Republic of China.
authors.forename: Ying-Ying
authors.initials: YY
authors.lastname: Zhang
authors.affiliation: The General Hospital of PLA Rocket Force, 16 Xin Jie Kou Wai Street, Hai-Dian District, Beijing, 100088, People's Republic of China.
authors.forename: Yun-E
authors.initials: YE
authors.lastname: Liu
authors.affiliation: The General Hospital of PLA Rocket Force, 16 Xin Jie Kou Wai Street, Hai-Dian District, Beijing, 100088, People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Gao
authors.affiliation: National Development and Reform Commission Hospital, Beijing, People's Republic of China.
authors.forename: Kun
authors.initials: K
authors.lastname: Yao
authors.affiliation: Chinese PLA General Hospital, 28 Fu-Xing Road, Hai-Dian District, Beijing, 10853, People's Republic of China.
authors.forename: Dan
authors.initials: D
authors.lastname: Feng
authors.affiliation: The General Hospital of PLA Rocket Force, 16 Xin Jie Kou Wai Street, Hai-Dian District, Beijing, 100088, People's Republic of China.
authors.forename: Zhen-Yuan
authors.initials: ZY
authors.lastname: Li
authors.affiliation: The General Hospital of PLA Rocket Force, 16 Xin Jie Kou Wai Street, Hai-Dian District, Beijing, 100088, People's Republic of China. fengxin722@aliyun.com.
authors.forename: Xin
authors.initials: X
authors.lastname: Feng
authors.affiliation: Chinese PLA General Hospital, 28 Fu-Xing Road, Hai-Dian District, Beijing, 10853, People's Republic of China. yunxiliu6511@sohu.com.
authors.forename: Yun-Xi
authors.initials: YX
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da Street, Fengtai District, Beijing, 100071, People's Republic of China. jiana79_41@hotmail.com.
authors.forename: Na
authors.initials: N
authors.lastname: Jia
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000097:blood*; D001402:B-Lymphocytes / Q000276:immunology; D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000097:blood / Q000453:epidemiology*; D008875:Middle Aged; D015995:Prevalence; D013601:T-Lymphocytes / Q000276:immunology; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral
keywords: Age-dependent; ELISpot; IFN-γ+ T cell; Memory B cell; Pandemic influenza