ABSTRACT
Mechanical ventilation (MV) is a life-saving therapy for respiratory failure but also leads to severe
physiological and morphological alterations in the lung, known as ventilator-induced lung injury (VILI).
Inflammation is a key component of acute lung injury (ALI), and work from our group and others has
shown that MV leads to hypoxemia, cytokine production, neutrophil recruitment, and lung injury, even
at low tidal volumes. Although neutrophils are most often associated with the pathology of VILI, our
proposed study aims to demonstrate a regulatory, tissue-reparative function of neutrophils in the
context of VILI and susceptibility to infection. Indeed, the immunomodulatory effects of MV with
regards to infection remain unknown. Preliminary data from our lab show that MV stimulates rapid
but transient neutrophil recruitment, activation and deposition of extracellular DNA in the airspaces,
termed neutrophil extracellular traps (NETs), and we found that these NETs provide protection
against infection with Pseudomonas aeruginosa. In particular, this protective effect of neutrophil
activity lasts several days after MV, at a time when neutrophils can no longer be detected in the
airspaces. Thus, we propose the novel hypothesis that MV-induced neutrophil activation and NET
deposition in the airways constitute an innate immune response to tissue damage that
counterbalances post-trauma susceptibility to infection. In Specific Aim 1, we will demonstrate
that neutrophils are the source of MV-induced NETs using depletion, adoptive transfer and PCR-
based methods to detect NET-DNA, as well as quantify the half-life of NETs in the airspaces. Despite
the known antibacterial properties of NETs and their induction in response to MV, no study has
investigated the impact of NETs on subsequent infection. Thus, in Specific Aim 2, we will
experimentally ablate NETs and NET components, both in vivo and in vitro, to determine their impact
on bacterial infection of the lung. Thus, using MV as a model of sterile ALI with transient neutrophil
extravasation into the air spaces, our work aims to identify an as-yet-unidentified protective effect of
NET production and thereby improve the design of future clinical treatments to increase lung function
and prevent infection.