title: Physiologic TLR9-CpG-DNA interaction is essential for the homeostasis of the intestinal immune system.
abstract: BACKGROUND
  Cytosine-guanosine dinucleotide (CpG) motifs are immunostimulatory components of bacterial DNA and activators of innate immunity through Toll-like receptor 9 (TLR9). Administration of CpG oligodeoxynucleotides before the onset of experimental colitis prevents intestinal inflammation by enforcement of regulatory mechanisms. It was investigated whether physiologic CpG/TLR9 interactions are critical for the homeostasis of the intestinal immune system.
  
  
  METHODS
  Mesenteric lymph node cell and lamina propria mononuclear cell (LPMC) populations from BALB/c wild-type (wt) or TLR9 mice were assessed by flow cytometry and proteome profiling. Cytokine secretion was determined and nuclear extracts were analyzed for nuclear factor kappa B (NF-κB) and cAMP response-element binding protein activity. To assess the colitogenic potential of intestinal T cells, CD4-enriched cells from LPMC of wt or TLR9 donor mice were injected intraperitoneally in recipient CB-17 SCID mice.
  
  
  RESULTS
  TLR9 deficiency was accompanied by slight changes in cellular composition and phosphorylation of signaling proteins of mesenteric lymph node cell and LPMC. LPMC from TLR9 mice displayed an increased proinflammatory phenotype compared with wt LPMC. NF-κB activity in cells from TLR9 mice was enhanced, whereas cAMP response-element binding activity was reduced compared with wt. Transfer of lamina propria CD4-enriched T cells from TLR9 mice induced severe colitis, whereas wt lamina propria CD4-enriched T cells displayed an attenuated phenotype.
  
  
  CONCLUSIONS
  Lack of physiologic CpG/TLR9 interaction impairs the function of the intestinal immune system indicated by enhanced proinflammatory properties. Thus, physiologic CpG/TLR interaction is essential for homeostasis of the intestinal immune system as it is required for the induction of counterregulating anti-inflammatory mechanisms.
authors.affiliation: *Departments of Internal Medicine I, and †Internal Medicine III, Regensburg University Medical Center, Regensburg, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Hofmann
authors.forename: Nadja
authors.initials: N
authors.lastname: Dunger
authors.forename: Kristina
authors.initials: K
authors.lastname: Doser
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Lippert
authors.forename: Sebastian
authors.initials: S
authors.lastname: Siller
authors.forename: Matthias
authors.initials: M
authors.lastname: Edinger
authors.forename: Werner
authors.initials: W
authors.lastname: Falk
authors.forename: Florian
authors.initials: F
authors.lastname: Obermeier
mesh_terms: D000818:Animals; D003092:Colitis / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D004247:DNA / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D006706:Homeostasis; D007107:Immune System / Q000378:metabolism* / Q000473:pathology; D007249:Inflammation / Q000378:metabolism / Q000473:pathology; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000276:immunology; D007963:Leukocytes, Mononuclear / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008198:Lymph Nodes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008643:Mesentery / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D016513:Mice, SCID; D009838:Oligodeoxyribonucleotides / Q000378:metabolism*; D040901:Proteomics; D051217:Toll-Like Receptor 9 / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C408982:CPG-oligonucleotide; D009838:Oligodeoxyribonucleotides; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; D014157:Transcription Factors; D004247:DNA