title: H. pylori-infection and antibody immune response in a rural Tanzanian population.
abstract: BACKGROUND
  Helicobacter pylori (H. pylori) infection is ubiquitous in sub-Saharan Africa, but paradoxically gastric cancer is rare.
  
  
  METHODS
  Sera collected during a household-based survey in rural Tanzania in 1985 were tested for anti-H. pylori IgG and IgG subclass antibodies by enzyme immunoassay. Odds ratios (OR) and confidence intervals (CI) of association of seropositivity with demographic variables were computed by logistic regression models.
  
  
  RESULTS
  Of 788 participants, 513 were aged < or = 17 years. H. pylori seropositivity increased from 76% at 0-4 years to 99% by > or = 18 years of age. Seropositivity was associated with age (OR 11.5, 95% CI 4.2-31.4 for 10-17 vs. 0-4 years), higher birth-order (11.1; 3.6-34.1 for > or = 3rd vs. 1st born), and having a seropositive next-older sibling (2.7; 0.9-8.3). Median values of IgG subclass were 7.2 for IgG1 and 2.0 for IgG2. The median IgG1/IgG2 ratio was 3.1 (IQR: 1.7-5.6), consistent with a Th2-dominant immune profile. Th2-dominant response was more frequent in children than adults (OR 2.4, 95% CI 1.3-4.4).
  
  
  CONCLUSIONS
  H. pylori seropositivity was highly prevalent in Tanzania and the immunological response was Th2-dominant. Th2-dominant immune response, possibly caused by concurrent bacterial or parasitic infections, could explain, in part, the lower risk of H. pylori-associated gastric cancer in Africa.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, Rockville, Maryland, USA. mbulaits@mail.nih.gov
authors.forename: Sam M
authors.initials: SM
authors.lastname: Mbulaiteye
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Gold
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Pfeiffer
authors.forename: Glen R
authors.initials: GR
authors.lastname: Brubaker
authors.forename: John
authors.initials: J
authors.lastname: Shao
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Biggar
authors.forename: Michie
authors.initials: M
authors.lastname: Hisada