title: Bacterial-induced protection against allergic inflammation through a multicomponent immunoregulatory mechanism.
abstract: BACKGROUND
  Airborne microbial products have been reported to promote immune responses that suppress asthma, yet how these beneficial effects take place remains controversial and poorly understood.
  
  
  METHODS
  We exposed mice to the bacterium Escherichia coli and subsequently induced allergic airway inflammation through sensitization and intranasal challenge with ovalbumin.
  
  
  RESULTS
  Pulmonary exposure to the bacterium Escherichia coli leads to a suppression of allergic airway inflammation. This immune modulation was neither mediated by the induction of a T helper 1 (Th1) response nor regulatory T cells; however, it was dependent on Toll-like receptor 4 (TLR4) but did not involve TLR desensitisation. Dendritic cell migration to the draining lymph nodes and activation of T cells was unaffected by prior exposure to E. coli, while dendritic cells in the lung displayed a less activated phenotype and had impaired antigen presentation capacity. Consequently, in situ Th2 cytokine production was abrogated. The suppression of airway hyper-responsiveness was mediated through the recruitment of gd T cells; however, the suppression of dendritic cells and T cells was mediated through a distinct mechanism that could not be overcome by the local administration of activated dendritic cells, or by the in vivo administration of tumour necrosis factor a.
  
  
  CONCLUSIONS
  Our data reveal a localized immunoregulatory pathway that acts to protect the airways from allergic inflammation.
authors.affiliation: Institute of Integrative Biology, Molecular Biomedicine, ETH Zürich, Switzerland.
authors.forename: Chiara
authors.initials: C
authors.lastname: Nembrini
authors.forename: Anke
authors.initials: A
authors.lastname: Sichelstiel
authors.forename: Jan
authors.initials: J
authors.lastname: Kisielow
authors.forename: Michael
authors.initials: M
authors.lastname: Kurrer
authors.forename: Manfred
authors.initials: M
authors.lastname: Kopf
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Marsland
mesh_terms: D000818:Animals; D001249:Asthma / Q000276:immunology / Q000473:pathology / Q000517:prevention & control*; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology / Q000378:metabolism; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology / Q000276:immunology; D003713:Dendritic Cells / Q000276:immunology*; D004195:Disease Models, Animal; D004926:Escherichia coli / Q000276:immunology* / Q000302:isolation & purification / Q000378:metabolism; D005434:Flow Cytometry; D056747:Immunomodulation / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018418:Th2 Cells / Q000276:immunology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; C419843:TLR protein, bacteria