Objective To investigate the effect of exogenous protectin DX (PDX) on acute lung injury in septic mice.Methods Thirty male C57BL/6 mice,aged 6-8 weeks,weighing 20-25 g,were randomly divided into 3 groups (n =10 each) using a random number table:sham operation group (Sham group),sepsis group (S group) and PDX group.Sepsis was produced by cecum ligation and puncture (CLP) in the mice anesthetized with pentobarbital sodium.At 1 h after CLP,PDX 300 ng was injected intraperitoneally in PDX group,and the equal volume of normal saline was given in Sham and S groups.At 24 h after CLP,the mice were sacrificed,and the broncho-alveolar lavage fluid (BALF) was collected for determination of interleukin-1beta (IL-1β),tumor necrosis factor-alpha (TNF-α),IL-6 and IL-10 concentrations,and the lungs were removed for microscopic examination and for determination of the myeloperoxidase (MPO) activity,wet/dry lung weight ratio (W/D ratio) and phosphorylation of nuclear factor-kappa B (NF-κB) p65.Lung injury scores were calculated.Results Compared with Sham group,the lung injury score,MPO activity,W/D ratio,phosphorylation of NF-κB p65,and concentrations of protein and inflammatory factors in BALF were significantly increased in S and PDX groups (P＜0.05).Compared with S group,the lung injury score,MPO activity,W/D ratio,phosphorylation of NF-κB p65,and concentrations of protein,IL-1β,TNF-α and IL-6 in BALF were significantly decreased,and the concentration of IL-10 in BALF was significantly increased in PDX group (P＜0.05).Conclusion Exogenous PDX can alleviate acute lung injury through inhibiting NF-κB activity in the lung tissues of septic mice.