Preferential activation of alveolar macrophages versus epithelial cells during initiation of ventilator-induced lung injury in mice

Background: It has been suggested that stretch-induced deformation of alveolar epithelial cells (AEC) plays a role in the initiation of ventilator-induced lung injury (VILI). In vitro stretch of AEC upregulates intracellular mitogen-activated protein kinases (MAPK) leading to mediator release, but this may not reflect the situation in vivo . We have developed a novel method to measure MAPK intermediates within discrete lung cell populations following in vivo VILI. Methods: Anaesthetised C57BL6 mice were ventilated with high (Vt=40ml/kg) or low stretch (Vt=10ml/kg). At various time points lungs were removed and single cell suspensions were produced by mechanical disruption, with cells immediately fixed and permeabilised. Levels of intracellular phosphorylated (p-) p38 and MK2 in alveolar macrophages (AM, CD11c+ cells), type I (T1α+) and II (Pro-SPC+) AEC were determined by flow cytometry. Results: p-p38 and p-MK2 expression (mean fluorescence intensity, MFI) increased in AM within 5 minutes of high stretch. In contrast, both type I and II AEC showed little p38 and MK2 phosphorylation, even up to 1 hour. View this table: MAPK phosphorylation Conclusion: Contrary to previous suggestions that stretch-induced activation of AEC is the key initiator of VILI, our results indicate an immediate, direct activation of AM with high stretch, placing AM as potentially more important than AEC in triggering the early inflammatory response during VILI.