Objective To evaluate the effects of transplantation of endothelial progenitor cells (EPCs) on inflanmatory responses during acute lung injury (ALI) induced by oleic acid in rabbits.Methods Ninety-six New Zealand male rabbits,aged 7-10 months,weighing 2.5-3.0 kg,were randomly divided into 4 groups using a random number table:control group (group C,n =16),transplantation of EPC group (group EPC,n =32),ALI group and ALI + transplantation of EPC group (group ALI + EPC,n =32).ALI was induced by iv 20％ emulsified oleic acid 75 mg/kg.EPCs (106 cells,in 1 ml of PBS) or the equal volume of PBS was administered intravenously at 0.5 h after iv oleic acid injection.Eight animals were randomly chosen at 6,12,24 and 48 h after oleic acid injection (T1-4) in LI and ALI+ EPC groups,or at T3,4 in C and EPC groups,and then sacrificed.The lungs were removed for determination of the expression of NF-κB mRNA (by RT-PCR),TNF-α,IL-1β and activity of NF-κB (by Western blot),and for microscopic examination of pathological changes of lung tissues (using HE staining).Diffuse alveolar damage (DAD) score was carried out.Results Compared with group C,the expression of NF-κB mRNA,IL-1β and TNF-α was significantly up-regulated,and NF-κB activity and DAD score were increased at T3,4 in ALI and ALI + EPC groups,and no significant change was found in the parameters mentioned above in EPC group.Compared with ALI group,the expression of NF-κB mRNA,TNF-α and IL-1β was significantly down-regulated,and NF-κB activity and DAD score were decreased at T1-4 in ALI + EPC group.Conclusion The mechanism by which EPCs mitigate ALI induced by oleic acid is related to inhibition of inflammatory responses in rabbits.