title: Interleukin 10 overexpression alters survival in the setting of gram-negative pneumonia following lung contusion.
abstract: OBJECTIVE
  Lung contusion injury produces a vulnerable window within the inflammatory defenses of the lung that predisposes the patient to pneumonia. Interleukin 10 (IL-10) is a known anti-inflammatory mediator produced by macrophages and capable of downregulating acute lung inflammation. We investigated the impact of increased levels of IL-10 within the lung on survival and the host response to trauma in the setting of lung contusion (LC) and gram-negative pneumonia.
  
  
  METHODS
  A bitransgenic, tetracycline-inducible, lung-specific human IL-10 overexpression (IL-10 OE) mouse model and single transgenic (TG-) control mice were used. Mice underwent LC injury or sham injury (sham) at time -6 h. At time 0, animals were inoculated intratracheally with 500 colony-forming units of Klebsiella pneumoniae (pneu). Bronchoalveolar lavage fluid, lung tissue specimens, or purified macrophages were collected. Lung tissue and blood bacteria levels were quantified. Cytokine levels were assayed by enzyme-linked immunosorbent assay, and gene expression levels were evaluated by real-time polymerase chain reaction. Cell-type identification and quantification were done using real-time polymerase chain reaction and flow cytometry.
  
  
  RESULTS
  Interleukin 10 OE mice demonstrated decreased 5-day survival compared with TG- mice following LC + pneu (0 vs. 30%, P < 0.0001). Interleukin 10 OE mice had significantly higher lung bacteria counts (P = 0.02) and levels of bacteremia (P = 0.001) at 24 h. The IL-10 OE mice recruited more neutrophils into the alveoli as measured in bronchoalveolar lavage fluid compared with TG- mice. Alveolar macrophages from IL-10 OE mice displayed increased alternative activation (M2 macrophages, P = 0.046), whereas macrophages from TG- mice exhibited classic activation (M1 macrophages) and much higher intracellular bacterial killing potential (P = 0.03). Interleukin 6, keratinocyte-derived chemokine, and macrophage inflammatory protein 2 levels were significantly elevated in IL-10 OE LC + pneu animals (P < 0.05).
  
  
  CONCLUSIONS
  Lung-specific IL-10 overexpression induces alternative activation of alveolar macrophages. This shift in macrophage phenotype decreases intracellular bacterial killing, resulting in a more pronounced bacteremia and accelerated mortality in a model of LC and pneumonia.
authors.affiliation: Departments of *Surgery and †Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, Michigan.
authors.forename: Vladislav A
authors.initials: VA
authors.lastname: Dolgachev
authors.forename: Bi
authors.initials: B
authors.lastname: Yu
authors.forename: Lei
authors.initials: L
authors.lastname: Sun
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Shanley
authors.forename: Krishnan
authors.initials: K
authors.lastname: Raghavendran
authors.forename: Mark R
authors.initials: MR
authors.lastname: Hemmila
mesh_terms: D000818:Animals; D058491:Bacterial Load; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D003288:Contusions / Q000150:complications* / Q000276:immunology / Q000473:pathology; D016905:Gram-Negative Bacterial Infections / Q000209:etiology / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D016753:Interleukin-10 / Q000378:metabolism*; D055370:Lung Injury / Q000150:complications* / Q000276:immunology / Q000473:pathology; D008262:Macrophage Activation / Q000276:immunology; D016676:Macrophages, Alveolar / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010641:Phenotype; D018410:Pneumonia, Bacterial / Q000209:etiology / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D016019:Survival Analysis
chemical_list: D016753:Interleukin-10