Ventilator-associated pneumonia is characterized by excessive release of neutrophil proteases in the lung.
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.
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland; Institute of Life Science, Medical Microbiology and Infectious Disease, Swansea University, Swansea, Wales.
Thomas S
TS
Wilkinson
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland.
Andrew
A
Conway Morris
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland.
Kallirroi
K
Kefala
Centre for Infection and Immunity, Queen's University of Belfast, Belfast, Northern Ireland.
Cecilia M
CM
O'Kane
Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland.
Norma R
NR
Moore
Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland.
Nuala A
NA
Booth
Centre for Infection and Immunity, Queen's University of Belfast, Belfast, Northern Ireland.
Daniel F
DF
McAuley
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland.
Kevin
K
Dhaliwal
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland.
Timothy S
TS
Walsh
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland.
Christopher
C
Haslett
Unité de Défense Innée et Inflammation, INSERM U874, Paris, France.
Jean-Michel
JM
Sallenave
Medical Research Council Centre for Inflammation Research, University of Edinburgh, Edinburgh, Scotland; Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, England. Electronic address: j.simpson@newcastle.ac.uk.
A John
AJ
Simpson
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001992:Bronchoalveolar Lavage Fluid; D016022:Case-Control Studies; D002465:Cell Movement; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008168:Lung / Q000201:enzymology* / Q000473:pathology; D008297:Male; D020784:Matrix Metalloproteinase 8 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D008875:Middle Aged; D009504:Neutrophils / Q000201:enzymology* / Q000473:pathology; D010196:Pancreatic Elastase / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D053717:Pneumonia, Ventilator-Associated / Q000175:diagnosis* / Q000201:enzymology* / Q000473:pathology; D019714:Tissue Inhibitor of Metalloproteinases / Q000378:metabolism
D019714:Tissue Inhibitor of Metalloproteinases; D010447:Peptide Hydrolases; D010196:Pancreatic Elastase; D020784:Matrix Metalloproteinase 8; D020780:Matrix Metalloproteinase 9