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Original Research: Critical Care |

Ventilator-Associated Pneumonia Is Characterized by Excessive Release of Neutrophil Proteases in the LungNeutrophils in Ventilator-Associated Pneumonia

Thomas S. Wilkinson, PhD; Andrew Conway Morris, MD, PhD; Kallirroi Kefala, MD; Cecilia M. O’Kane, MD, PhD; Norma R. Moore, BSc; Nuala A. Booth, PhD; Daniel F. McAuley, MD; Kevin Dhaliwal, MD; Timothy S. Walsh, MD; Christopher Haslett, MD; Jean-Michel Sallenave, PhD; A. John Simpson, MD, PhD
Author and Funding Information

From the Medical Research Council Centre for Inflammation Research (Drs Wilkinson, Conway Morris, Kefala, Dhaliwal, Walsh, Haslett, and Simpson), University of Edinburgh, Edinburgh, Scotland; Institute of Life Science (Dr Wilkinson), Medical Microbiology and Infectious Disease, Swansea University, Swansea, Wales; Centre for Infection and Immunity (Drs O’Kane and McAuley), Queen’s University of Belfast, Belfast, Northern Ireland; Institute of Medical Sciences (Ms Moore and Dr Booth), University of Aberdeen, Aberdeen, Scotland; Unité de Défense Innée et Inflammation (Dr Sallenave), INSERM U874, Paris, France; and the Institute of Cellular Medicine (Dr Simpson), Newcastle University, Newcastle upon Tyne, England.

Correspondence to: John Simpson MD, PhD, 4th Floor, William Leech Bldg, Institute of Cellular Medicine, Medical School, Framlington Place, Newcastle upon Tyne, NE2 4HH, England; e-mail: j.simpson@newcastle.ac.uk.


For editorial comment see page 1365

Drs Wilkinson, Conway Morris, and Kefala contributed equally to this manuscript.

Funding/Support: This study was funded by the Sir Jules Thorn Charitable Trust.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2012;142(6):1425-1432. doi:10.1378/chest.11-3273
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Background:  Ventilator-associated pneumonia (VAP) is characterized by neutrophils infiltrating the alveolar space. VAP is associated with high mortality, and accurate diagnosis remains difficult. We hypothesized that proteolytic enzymes from neutrophils would be significantly increased and locally produced inhibitors of human neutrophil elastase (HNE) would be decreased in BAL fluid (BALF) from patients with confirmed VAP. We postulated that in suspected VAP, neutrophil proteases in BALF may help identify “true” VAP.

Methods:  BAL was performed in 55 patients with suspected VAP and in 18 control subjects. Isolation of a pathogen(s) at > 104 colony-forming units/mL of BALF dichotomized patients into VAP (n = 12) and non-VAP (n = 43) groups. Matrix metalloproteinases (MMPs), HNE, inhibitors of HNE, and tissue inhibitors of matrix metalloproteinases (TIMPs) were quantified. Plasminogen activator (PA) activity was estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and zymography.

Results:  Neutrophil-derived proteases HNE, MMP-8, and MMP-9 were significantly increased in cell-free BALF from patients with VAP as compared with those without VAP (median values: HNE, 2,708 ng/mL vs 294 ng/mL, P < .01; MMP-8, 184 ng/mL vs 5 ng/mL, P < .01; MMP-9, 310 ng/mL vs 11 ng/mL, P < .01). HNE activity was also significantly increased in VAP (0.45 vs 0.01 arbitrary units; P < .05). In contrast, no significant differences were observed for protease inhibitors, TIMPs, or PAs. HNE in BALF, at a cutoff of 670 ng/mL, identified VAP with a sensitivity of 93% and specificity of 79%.

Conclusions:  Neutrophil proteases are significantly elevated in the alveolar space in VAP and may contribute to pathogenesis. Neutrophil proteases appear to have potential in suspected VAP for distinguishing true cases from “non–VAP” cases.

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