Intratracheal IL-6 protects against lung inflammation in direct, but not indirect, causes of acute lung injury in mice

PLoS One. 2013 May 8;8(5):e61405. doi: 10.1371/journal.pone.0061405. Print 2013.


Introduction: Serum and bronchoalveolar fluid IL-6 are increased in patients with acute respiratory distress syndrome (ARDS) and predict prolonged mechanical ventilation and poor outcomes, although the role of intra-alveolar IL-6 in indirect lung injury is unknown. We investigated the role of endogenous and exogenous intra-alveolar IL-6 in AKI-mediated lung injury (indirect lung injury), intraperitoneal (IP) endotoxin administration (indirect lung injury) and, for comparison, intratracheal (IT) endotoxin administration (direct lung injury) with the hypothesis that IL-6 would exert a pro-inflammatory effect in these causes of acute lung inflammation.

Methods: Bronchoalveolar cytokines (IL-6, CXCL1, TNF-α, IL-1β, and IL-10), BAL fluid neutrophils, lung inflammation (lung cytokines, MPO activity [a biochemical marker of neutrophil infiltration]), and serum cytokines were determined in adult male C57Bl/6 mice with no intervention or 4 hours after ischemic AKI (22 minutes of renal pedicle clamping), IP endotoxin (10 µg), or IT endotoxin (80 µg) with and without intratracheal (IT) IL-6 (25 ng or 200 ng) treatment.

Results: Lung inflammation was similar after AKI, IP endotoxin, and IT endotoxin. BAL fluid IL-6 was markedly increased after IT endotoxin, and not increased after AKI or IP endotoxin. Unexpectedly, IT IL-6 exerted an anti-inflammatory effect in healthy mice characterized by reduced BAL fluid cytokines. IT IL-6 also exerted an anti-inflammatory effect in IT endotoxin characterized by reduced BAL fluid cytokines and lung inflammation; IT IL-6 had no effect on lung inflammation in AKI or IP endotoxin.

Conclusion: IL-6 exerts an anti-inflammatory effect in direct lung injury from IT endotoxin, yet has no role in the pathogenesis or treatment of indirect lung injury from AKI or IP endotoxin. Since intra-alveolar inflammation is important in the pathogenesis of direct, but not indirect, causes of lung inflammation, IT anti-inflammatory treatments may have a role in direct, but not indirect, causes of ARDS.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Kidney Injury / complications
  • Acute Lung Injury / etiology*
  • Acute Lung Injury / metabolism*
  • Analysis of Variance
  • Animals
  • Blood Urea Nitrogen
  • Bronchoalveolar Lavage Fluid / immunology
  • Creatinine / blood
  • Cytokines / immunology
  • Endotoxins / toxicity
  • Interleukin-6 / blood
  • Interleukin-6 / immunology*
  • Interleukin-6 / metabolism
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Pneumonia / etiology*
  • Pneumonia / metabolism*
  • Trachea / metabolism


  • Cytokines
  • Endotoxins
  • Interleukin-6
  • endotoxin, Escherichia coli
  • Creatinine