Niche and neutral effects of acquired immunity permit coexistence of pneumococcal serotypes

Science. 2012 Mar 16;335(6074):1376-80. doi: 10.1126/science.1215947. Epub 2012 Mar 1.


Over 90 capsular serotypes of Streptococcus pneumoniae, a common nasopharyngeal colonizer and major cause of pneumonia, bacteremia, and meningitis, are known. It is unclear why some serotypes can persist at all: They are more easily cleared from carriage and compete poorly in vivo. Serotype-specific immune responses, which could promote diversity in principle, are weak enough to allow repeated colonizations by the same type. We show that weak serotype-specific immunity and an acquired response not specific to the capsule can together reproduce observed diversity. Serotype-specific immunity stabilizes competition, and acquired immunity to noncapsular antigens reduces fitness differences. Our model can be used to explain the effects of pneumococcal vaccination and indicates general factors that regulate the diversity of pathogens.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptive Immunity*
  • Adult
  • Antigenic Variation
  • Antigens, Bacterial / immunology*
  • Bacterial Capsules / immunology
  • Carrier State / immunology
  • Carrier State / microbiology*
  • Child
  • Child, Preschool
  • Computer Simulation
  • Humans
  • Immunity, Innate
  • Infant
  • Models, Biological
  • Nasopharynx / microbiology*
  • Pneumococcal Infections / immunology
  • Pneumococcal Infections / microbiology*
  • Pneumococcal Vaccines / immunology
  • Serotyping
  • Streptococcus pneumoniae / classification
  • Streptococcus pneumoniae / immunology*
  • Streptococcus pneumoniae / physiology*
  • Time Factors


  • Antigens, Bacterial
  • Pneumococcal Vaccines