BACKGROUND:M2 macrophages have the function of reducing inflammatory factors and promoting tissue healing.Therefore,how to regulate M2 polarization of macrophages has been a hot research topic in recent years,and some miRNAs have been found to have this function. OBJECTIVE:To investigate the effects of miR-378a on the polarization of the Raw264.7 macrophage cell line. METHODS:The M1 polarization of macrophages was induced by lipopolysaccharide and interferon-γ.Interleukin-4 induced M2 polarization and the expression of endogenous miR-378a in each cell type was detected using qRT-PCR to verify whether miR-378a was involved in the polarization of macrophages.By transfection with lentivirus as the vector of overexpression of miR-378a,the stable expression of miR-378a cell lines was screened.Macrophage M1 polarization was induced synergically by lipopolysaccharide and interferon-γ.Macrophage M2 polarization was induced by interleukin-4.The levels of M1/M2 polarization-related cytokines in the supernatant of the macrophage culture medium were determined by enzyme-linked immunosorbent assay.qRT-PCR was used to detect the polarization characteristics of M1/M2-type macrophages and the mRNA expression levels of related cytokines. RESULTS AND CONCLUSION:(1)The expression level of endogenous miR-378a in Raw264.7 cells of each group increased after macrophage polarization.(2)Compared with the non-transfected group,the expressions of proinflammatory cytokine-induced nitric oxide synthase,tumor necrosis factor-α,interleukin-6 and interleukin-1β in macrophage M1 induced polarization were significantly decreased in the miR-378a transfection group(P<0.05);the levels of inducible nitric oxide synthase,tumor necrosis factor-α and interleukin-6 in cell supernatant were also significantly decreased(P<0.05).(3)Compared with the non-transfected group,the expressions of CD206,interleukin-10 and arginase-I in macrophage M2 induced polarization were significantly increased(P<0.05);the levels of CD206 and interleukin-10 in cell supernatant were also significantly increased(P<0.05)in the miR-378a transfection group.(4)It is indicated that overexpression of miR-378a promotes the M2 polarization of macrophages and inhibits the M1 polarization of macrophages.