• Vladislav A Dolgachev, Bi Yu, Julia M Reinke, Krishnan Raghavendran, and Mark R Hemmila.
• Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109-5033, USA.
• J Trauma Acute Care Surg. 2012 Mar 1;72(3):614-22; discussion 622-3.

BackgroundLung contusion (LC) induces inflammation with high local concentrations of proinflammatory mediators stimulating chemotaxis and activation of neutrophils. LC is also a risk factor for development of pneumonia; however, the reason for this increased susceptibility is not clearly identified. We hypothesize that LC creates acute changes in the host pulmonary innate immune system that leads to vulnerability from a "second" hit bacterial infection.MethodsFemale C57Bl/6 mice underwent LC injury at time -6 hours. At 0 hours, these mice were inoculated intratracheally with 1,000 colony forming unit (CFU) of Klebsiella pneumoniae (LC+Pneu) or vehicle (LC). Control animals underwent a sham LC injury followed by pneumonia (Sham+Pneu). Bronchoalveolar lavage (BAL) fluid and lung tissue specimens were collected. Lung bacteria levels were quantified by serial dilution, plating, and counting CFUs. Cytokine levels were assayed by ELISA. Cell type identification and quantification was performed using flow cytometry.ResultsSurvival at 72 hours was markedly different for the LC, Sham+Pneu, and LC+Pneu groups (100%, 80%, 20%, p < 0.05 Sham+Pneu vs. LC+Pneu). LC+Pneu animals had decreased pulmonary bacterial clearance at 24 hours compared with the Sham+Pneu group (4 × 10(7) vs. 8 × 10(6) CFUs, p < 0.05). BAL levels of IL-1β, IL-6, and keratinocyte chemoattractant were all significantly elevated in LC+Pneu mice compared with the Sham+Pneu group at 24 hours. Conversely, the Sham+Pneu mice had increased levels of macrophage inflammatory protein-2, total cells, macrophages, and neutrophils in BAL compared with the LC+Pneu group at 24 hours. LC+Pneu animals demonstrated changes in macrophage apoptosis and necrosis in BAL samples obtained 2 hours after induction of pneumonia when compared with the Sham+Pneu group. Both Sham+Pneu and LC+Pneu animals demonstrated an increase in the level of IL-10 in BAL fluid compared with LC animals.ConclusionAcute inflammation after LC acts to modulate the presence of inflammatory cells necessary to combat gram-negative bacteria. This results in decreased bacterial clearance and increased mortality from pneumonia.

30 keywords...

hide…