Serum samples from infants vaccinated with a pneumococcal conjugate vaccine, PncT, protect mice against invasive infection caused by Streptococcus pneumoniae serotypes 6A and 6B

J Infect Dis. 2001 Jan 15;183(2):253-260. doi: 10.1086/317934. Epub 2000 Dec 8.


Streptococcus pneumoniae serogroup 6 is an important cause of respiratory tract disease worldwide. Vaccination with 6B polysaccharide induces antibody response to the cross-reacting serotype 6A, but the protective capacity of 6A antibodies induced in infants remains unknown. In this study, passive immunization with serum samples obtained from infants vaccinated with an octavalent polysaccharide protein conjugate vaccine, PncT, protected mice against bacteremia and/or lung infection caused by intranasal challenge with serotypes 6B and 6A. Protective infant serum samples had significantly higher serotype-specific IgG levels and opsonic activity than did nonprotective serum samples. The protective level to either serotype was approximately 1 microg of specific IgG antibodies injected per mouse (corresponding to approximately 0.3 microg/mL). The protection was strongly related to opsonophagocytic antibody levels measured in vitro. These results demonstrate that PncT induces antibodies in infants that protect mice against invasive disease caused by the homologous serotype and by the cross-reacting serotype 6A.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Bacterial / blood
  • Antibodies, Bacterial / immunology*
  • Antibody Affinity
  • Bacteremia / immunology
  • Bacteremia / microbiology
  • Bacteremia / prevention & control
  • Female
  • Humans
  • Immunization, Passive*
  • Immunoglobulin G / blood
  • Immunoglobulin G / classification
  • Immunoglobulin M / blood
  • Infant
  • Lung Diseases / immunology
  • Lung Diseases / microbiology
  • Lung Diseases / prevention & control
  • Mice
  • Opsonin Proteins / immunology
  • Pneumococcal Infections / immunology
  • Pneumococcal Infections / microbiology
  • Pneumococcal Infections / prevention & control*
  • Pneumococcal Vaccines / immunology*
  • Serotyping
  • Streptococcus pneumoniae / classification
  • Streptococcus pneumoniae / immunology
  • Streptococcus pneumoniae / pathogenicity
  • Tetanus Toxoid / immunology
  • Vaccines, Conjugate / immunology*


  • 23-valent pneumococcal capsular polysaccharide vaccine
  • Antibodies, Bacterial
  • Immunoglobulin G
  • Immunoglobulin M
  • Opsonin Proteins
  • Pneumococcal Vaccines
  • Tetanus Toxoid
  • Vaccines, Conjugate