Commensal microflora induce host defense and decrease bacterial translocation in burn mice through toll-like receptor 4.
BACKGROUND
Major burn is associated with decreased gut barrier function and increased bacterial translocation (BT). This study is to investigate whether commensal microflora induce host defense and decrease BT in burn mice.


METHODS
First, we treated Wild type (WT) mice with antibiotics in drinking water for 4 weeks to deplete gut commensal microflora. At week 3, drinking water was supplemented with lipopolysaccharide (LPS); a ligand for TLR4, to trigger TLRs in gut. The intestinal permeability, glutathione level, NF-kappaB DNA-binding activity, TLR4 expression of intestinal mucosa, BT to mesenteric lymph nodes (MLNs), and bacterial killing activity of peritoneal cells were measured after thermal injury. Second, lung of animals were harvested for MPO activity and TNFalpha mRNA expression assay. Third, WT animals were treated with oral antibiotics with or without LPS supplement after burn. At 48 hr after burn, TLR4 expression of intestinal mucosa and bacterial killing activity of cells were examined. Finally, bacterial killing activity and BT to MLNs after thermal injury in C3H/HeJ (TLR4 mutant) mice were measured.


RESULTS
Burn induced BT to MLNs in WT mice. Commensal depletion decreased TLR4 expression as well as NF-kappaB activation of intestine, myeloperoxidase (MPO) activity as well as TNFalpha expression of lung, and bacterial killing activity of peritoneal cells. Oral LPS supplement markedly reduced 81% of burn-induced BT and increased TLR4 expression, MPO activity of lung, as well as bacterial killing activity of peritoneal cells. LPS supplement did not change BT or bacterial killing activity in C3H/HeJ mice.


CONCLUSIONS
Collectively, commensal microflora induce TLR4 expression of intestine and bacterial killing activity of inflammatory cells in burn. TLR4 ligand increases bacterial killing activity and decreases burn-induced BT. Taken together with the abolition of LPS effect in TLR4 mutant mice, we conclude that commensal microflora induce host defense and decrease bacterial translocation in burn mice through toll-like receptor 4.
Chen
Lee-Wei
LW
Institute of Emergency and Critical Care Medicine, National Yang-Ming University, Taipei, Taiwan. chenlw2001@yahoo.com.tw
Chang
Wei-Jung
WJ
Chen
Pei-Hsuan
PH
Hsu
Ching-Mei
CM
D000818:Animals; D001419:Bacteria / Q000276:immunology*; D001483:Base Sequence; D002056:Burns / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D017931:DNA Primers / Q000235:genetics; D005978:Glutathione / Q000378:metabolism; D007113:Immunity, Innate; D007422:Intestines / Q000276:immunology / Q000382:microbiology; D008024:Ligands; D008070:Lipopolysaccharides / Q000008:administration & dosage; D008168:Lung / Q000276:immunology / Q000378:metabolism; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008817:Mice, Mutant Strains; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D017931:DNA Primers; D008024:Ligands; D008070:Lipopolysaccharides; D050505:Mutant Proteins; D016328:NF-kappa B; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D018808:Transcription Factor AP-1; D014409:Tumor Necrosis Factor-alpha; D009195:Peroxidase; D005978:Glutathione