title: Inhibition of dendritic cell maturation by group A Streptococcus.
abstract: BACKGROUND
  Exposure to group A Streptococcus (GAS) has been shown to induce maturation of dendritic cells (DC).
  
  
  METHODS
  To identify bacterial determinants that modulate DC activation in response to GAS infection, we analyzed the induction of maturation in human monocyte-derived DC following exposure to GAS clinical isolates.
  
  
  RESULTS
  Unexpectedly, only 6 of 24 GAS strains tested induced surface expression of major histocompatibility complex class II and costimulatory molecules CD80 and CD83 to levels consistent with DC maturation. Rather, the majority of the strains did not promote DC maturation, and many triggered DC apoptosis. GAS strains that failed to induce DC maturation were those that produced abundant hyaluronic acid (HA) capsular polysaccharide and/or large amounts of the cytotoxin streptolysin O (SLO). By use of isogenic mutants deficient in HA and/or SLO, we determined that GAS inhibits DC maturation through 2 distinct mechanisms: (1) inhibition of bacterial binding and/or phagocytosis by the HA capsule and (2) SLO-mediated induction of DC apoptosis by intracellular GAS.
  
  
  CONCLUSIONS
  These results demonstrate that GAS virulence factors modulate maturation and survival of human DC, effects that are likely to have a critical impact on activation of innate and adaptive immune responses to this important human pathogen.
authors.affiliation: Division of Infectious Diseases, Children's Hospital Boston, Boston, Massachusetts 02115, USA.
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Cortés
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wessels
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000166:cytology* / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006801:Humans; D006820:Hyaluronic Acid / Q000378:metabolism; D010587:Phagocytosis; D013297:Streptococcus pyogenes / Q000502:physiology*; D013301:Streptolysins / Q000235:genetics / Q000378:metabolism; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D013301:Streptolysins; D037521:Virulence Factors; C025964:streptolysin O; D006820:Hyaluronic Acid