title: Linking the "two-hit" response following injury to enhanced TLR4 reactivity.
abstract: Severe injury can initiate an exaggerated systemic inflammatory response and multiple organ failure (MOF) if a subsequent immune stimulus, "second hit", occurs. Using a mouse thermal injury model, we tested whether changes in innate immune cell reactivity following injury can contribute to the development of heightened inflammation and MOF. Using high-purity Escherichia coli lipopolysaccharide (LPS) to selectively stimulate Toll-like receptor 4 (TLR4), we demonstrate augmented interleukin (IL)-1beta, tumor necrosis factor alpha (TNF-alpha), and IL-6 production by 1 day but particularly, at 7 days after injury. The in vivo significance of enhanced TLR4 responsiveness was explored by challenging sham or burn mice with LPS at 1 or 7 days after injury and determining mortality along with in vivo cytokine and chemokine levels. Mortality was high (75%) in LPS-challenged burn but not sham mice at 7 days, although not at 1 day, after injury. Death was associated with leukocyte sequestration in the lungs and livers along with increased proinflammatory cytokine and chemokine levels in these organs. Blocking TNF-alpha activity prevented this mortality, suggesting that excessive TNF-alpha production contributes to this lethal response. These findings demonstrate the potential lethality of excessive TLR4 reactivity after injury and provide an explanation for the exaggerated inflammatory response to a second hit, which can occur following severe injury.
authors.affiliation: Department of Surgery (Immunology), Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115,USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Murphy
authors.forename: Hugh M
authors.initials: HM
authors.lastname: Paterson
authors.forename: Sara
authors.initials: S
authors.lastname: Kriynovich
authors.forename: Yan
authors.initials: Y
authors.lastname: Zang
authors.forename: Evelyn A
authors.initials: EA
authors.lastname: Kurt-Jones
authors.forename: John A
authors.initials: JA
authors.lastname: Mannick
authors.forename: James A
authors.initials: JA
authors.lastname: Lederer
mesh_terms: D000818:Animals; D002056:Burns / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D007375:Interleukin-1 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D007962:Leukocytes / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008099:Liver / Q000293:injuries / Q000378:metabolism / Q000473:pathology; D008168:Lung / Q000378:metabolism / Q000473:pathology; D055370:Lung Injury; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015996:Survival Rate; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014947:Wounds and Injuries / Q000150:complications / Q000276:immunology*
chemical_list: D007375:Interleukin-1; D015850:Interleukin-6; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha