Objective To investigate the effect of bone marrow mesenchymal stem cells(BMSCs)on the inflamma-tory response of lipopolysaccharide(LPS)induced acute lung injury(ALI)in mice.Methods 32 SPF KM mice,aged 4 weeks were randomly divided into four groups,control group,LPS group,dexamethasone treatment group(LPS+DEX)and BMSCs treatment group(LPS+BMSCs).The latter three groups were injected with LPS by tra-cheal puncture to establish mouse ALI model 24 h after modeling,BMSCs isolated from the femur of mice were in-jected into the caudal vein,and DEX were injected into caudal vein at the same time in LPS+DEX group for 3 consecutive days.On the 4th day after cell transplantation or 24 h after DEX injection,the survival quantity of mice was recorded,lung function was detected,and the wet/dry weight ratio(W/D)of lung was measured.Then in-flammatory cells in bronchoalveolar lavage fluid(BALF),lung pathological changes and serum inflammatory cyto-kines were collected.Green fluorescent protein(GFP)staining was used to observe the homing of BMSCs in lung tissues.The mRNA and protein expression of TLR4,MyD88 and NF-κB in lung tissues were detected by RT-PCR and Western blot assay respectively.Results Compared with the control group,LPS model group showed de-creased lung function,significantly increase in the W/D weight ratio of lung,inflammatory cytokines in serum and inflammatory cells in BALF,and severe damage in lung tissue.Compared with LPS group,LPS+DEX group and LPS+BMSCs group showed improved lung function,reduced lung tissue damage,significantly decrease in the W/D weight ratio of lung,inflammatory cytokines in serum and inflammatory cells in BALF.And the expression of TLR4-MyD88-NF-κB signaling pathway-related genes and proteins decreased,the survival quantity increased.Conclusion Homologous BMSCs transplantation can effectively treat LPS-induced acute lung injury,and the mechanism may be related to the regulation of TLR4-MyD88-NF-κB signaling pathway and the reduction of inflam-matory response.These findings provide the experimental basis for BMSCs homologous transplantation for ALI.