RESUMO
@#【Objective】 To investigate whether mesenchymal stem cells （MSC）can alleviate acute lung injury by inducing alveolar macrophages to polarize to M2 phenotype. 【Methods】 Umbilical cord MSC was extracted by adherent method and cell phenotypes were analyzed by flow cytometry. The differentiation along osteogenic and adipogenic pathways were assessed by histological staining in vitro. Mouse alveolar macrophage cell line（MH- S cells）which was stimulated by LPS was isolated co-culture with MSC and MSC soluble factor inhibitor was added. We set up three groups （LPS， LPS+MSC ，and MSC inhibitor）. After being cultured for 48 hours ，the macrophage polarization was analyzed by flow cytometry and qPCR. Thirty balb/c male mice were randomly divided into control group（n = 10），ALI group（n = 10）， and ALI+MSC group（n = 10）. LPS was instilled intranasally to establish acute lung injury model in mice. After treatment with MSC for 48 hours ，HE staining of lung tissue was performed for damage assessment. The alveolar lavage fluid （BALF）was obtained and the cells in BALF were analyzed by flow cytometry and qPCR to detect the expression of M2-type macrophage markers including CD206，IL10 and Arg1. The concentration of M1-type macrophage marker TNF-α in the supernatant was measured by ELISA. 【Results】 MSC showed adherent growth and had the ability of osteogenic and adipogenic differentiation. MSC can induce MH- S cells to polarize to M2 type and with a significant increase of CD206 positive proportion cells （P<0.05）. Prostaglandin E2 （PGE2） inhibitors can reverse this effect. Mouse ALI model was successful. After treatment with MSC，the pathology and lung injury score was significantly improved. The proportion of CD206 positive macrophages in alveolar lavage fluid in ALI + MSC group was significantly higher than that in ALI group. The expression of CD206 and IL-10 in mRNA level was significantly higher in ALI+MSC group than that in ALI group. The concentration of inflammatory cytokine TNF- α in alveolar lavage fluid was significantly lower in the ALI+ MSC group than in the ALI group（P<0.05）.【Conclusion】Umbilical cord mesenchymal stem cells can effectively alleviate acute lung injury induced by LPS in mice via PEG2 to induce macrophage to polarize to M2 type.