The role of coagulation in ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in the intensive care unit, and it is associated with prolonged hospitalization, increased health care costs, and high attributable mortality. Inflammatory changes in the pulmonary compartment as observed in acute lung injury are also often seen in VAP, and similar observations are now made regarding pulmonary coagulation changes. In the current review we will discuss the role of these coagulation changes in VAP (coagulopathy). We will discuss how mechanical ventilation affects both VAP and coagulopathy. As well as the role of anticoagulant therapies to reduce coagulopathy; from a theoretical perspective and from limited experimental research. And finally we will outline future research in this field

Local dornase alfa treatment reduces NETs-induced airway obstruction during severe RSV infection

Respiratory syncytial virus (RSV) infection is characterised by airway obstruction with mucus plugs, containing DNA networks in the form of neutrophil extracellular traps (NETs). We investigated the effect of dornase alfa on histopathological NETs-induced airway obstruction and viral load in an age-relevant calf model of severe bovine RSV disease. As compared with the control animals, dornase alfa treatment resulted in a strong reduction of NETs-induced airway obstruction. Viral load in the lower respiratory tract was not different between the two groups. We conclude that NETs form a relevant target for treatment of airway obstruction in severe RSV disease.</p

Semi-survival experiment.

<p>Kaplan-Meier curves showing the percentages of BALBc mice (solid lines) and C57Bl6 mice (dashed lines) treated with either 1A8 mAb (black, N = 5-6/group) or isotype control antibody (grey, N = 5-6/group) reaching the end point of a clinical score of ≥ 4 and/or > 20% weight loss after PVM inoculation (not significant).</p

Neutrophil subset responses in infants with severe viral respiratory infection

Neutrophils are the predominant inflammatory cells recruited to the respiratory tract as part of the innate immune response to viral infections. Recent reports indicate the existence of distinct functional neutrophil subsets in the circulatory compartment of adults, following severe inflammatory conditions. Here, we evaluated the occurrence of neutrophil subsets in blood and broncho-alveolar lavage fluid during severe viral respiratory infection in infants based on CD16/CD62L expression. We show that during the course of severe respiratory infection infants may develop four heterogeneous neutrophil subsets in blood (mature, immature, progenitor, and suppressive neutrophils), each with distinct activation states. However, while isolated viral respiratory infection was characterized by a relative absence of suppressive neutrophils in both blood and lungs, only patients with bacterial co-infection were shown to produce suppressive neutrophils. These data suggest the occurrence of distinct and unique neutrophil subset responses during severe viral and (secondary) bacterial respiratory infection in infant

Pneumovirus-Induced Lung Disease in Mice Is Independent of Neutrophil-Driven Inflammation

<div><p>The human pneumovirus respiratory syncytial virus (RSV) is the most common pathogen causing lower respiratory tract disease in young children worldwide. A hallmark of severe human RSV infection is the strong neutrophil recruitment to the airways and lungs. Massive neutrophil activation has been proven detrimental in numerous diseases, yet in RSV the contribution of neutrophils to disease severity, and thereby, the relevance of targeting them, is largely unknown. To determine the relevance of potential neutrophil targeting therapies, we implemented antibody-mediated neutrophil depletion in a mouse pneumonia virus of mice (PVM) model. PVM is a host specific murine pneumovirus closely related to human RSV, which reproduces many of the features of RSV infection, such as high viral replication and neutrophil recruitment. Clinical disease and markers of lung inflammation and injury were studied in PVM-infected mice treated with either depleting or isotype control antibodies. To confirm our results we performed all experiments in two mice strains: C57Bl6 and BALBc mice. Neutrophil depletion in blood and lungs was efficient throughout the disease. Remarkably, in both mouse strains we found no difference in clinical disease severity between neutrophil-depleted and control arms. In line with this observation, we found no differences between groups in histopathological lung injury and lung viral loads. In conclusion, our study shows that in mice neutrophil recruitment to the lungs does not affect disease outcome or viral clearance during severe PVM infection. As such, this model does not support the notion that neutrophils play a key role in mouse pneumovirus disease.</p></div

NET production.

<p><b>(A)</b> Citrullinated histone H3 staining of a non-infected lung tissue section, no NETs are visible (magnification 200×). <b>(B,C)</b> Citrullinated histone H3 staining of PVM infected C57Bl6 (day 8) and BALBc (day 7) mice (non-lavaged lung sections, magnification 200×) shows scarce NET formation (insets, magnification 1200×) without airway occlusion (asterisk).</p

Lung histopathology.

<p><b>(A,C)</b> Representative image of HE-staining of C57Bl6 mice (day 8), showing interstitial cellular infiltrates and proteinacious debris <b>(B,D)</b> HE-staining of BALBc mice (day 7), showing hemorrhaging and proteinacious debris (magnification 400×).</p

BAL cellularity, cytokines and neutrophil activation.

<p>BAL cellularity, cytokines and neutrophil activation.</p

Neutrophil depletion during severe PVM disease in mice.

<p>Percentage of neutrophils present in blood <b>(A)</b> and total number of neutrophils per mL of BAL <b>(B)</b> in C57Bl6 and BALBc mice treated with either 1A8 mAb (grey circles, N = 6/group) or isotype control antibody (white circles, N = 6/group), measured on day 8 (C57Bl6, blood p = 0.002, BAL p = 0.009) and day 7 (BALBc, blood p = 0.002, BAL p = 0.008) after PVM inoculation. <b>(C)</b> Representative images of Ly6C/G-staining of lung tissue sections showing minimal interstitial neutrophil numbers in the 1A8 mAb treated animals on day 8 (C57Bl6) and day 7 (BALBc) after inoculation (magnification 200×). Data are shown as individual values and median with bars depicting IQR. ** p < 0.01</p

Clinical PVM disease severity.

<p><b>(A-B)</b> Weight loss and clinical score of illness as measured by the modified Cook’s score <b>(C-D)</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0168779#pone.0168779.ref025" target="_blank">25</a>] in C57Bl6 and BALBc mice treated with either 1A8 mAb (grey circles, N = 6) or isotype control antibody (white circles, N = 6) during the course of severe PVM disease. No significant differences between groups. Data are shown as median with bars depicting IQR.</p