Background:Subsequent neutrophil (polymorphonuclear neutrophil [PMN])-predominant inflammatory response is a predominant feature of ventilator-induced lung injury (VILI),and mesenchymal stem cell (MSC) can improve mice survival model of endotoxin-induced acute lung injury,reduce lung impairs,and enhance the repair of VILI.However,whether MSC could attenuate PMN-predominant inflammatory in the VILI is still unknown.This study aimed to test whether MSC intervention could attenuate the PMN-predominate inflammatory in the mechanical VILI.Methods:Sprague-Dawley rats were ventilated for 2 hours with large tidal volume (20 mL/kg).MSCs were given before or after ventilation.The inflammatory chemokines and gas exchange were observed and compared dynamically until 4 hours after ventilation,and pulmonary pathological change and activation of PMN were observed and compared 4 hours after ventilation.Results:Mechanical ventilation (MV) caused significant lung injury reflected by increasing in PMN pulmonary sequestration,inflammatory chemokines (tumor necrosis factor-alpha,interleukin-6 and macrophage inflammatory protein 2) in the bronchoalveolar lavage fluid,and injury score of the lung tissue.These changes were accompanied with excessive PMN activation which reflected by increases in PMN elastase activity,production of radical oxygen series.MSC intervention especially pretreatment attenuated subsequent lung injury,systemic inflammation response and PMN pulmonary sequestration and excessive PMN activation initiated by injurious ventilation.Conclusions:MV causes profound lung injury and PMN-predominate inflammatory responses.The protection effect of MSC in the VILI rat model is related to the suppression of the PMN activation.