['Alcoholic liver disease (ALD) ranges from fatty liver to inflammation and cirrhosis. miRNA-155 is an important regulator of inflammation. In this study, we describe the in vivo role of miR-155 in ALD.', 'Wild-type (WT) (C57/BL6J) or miR-155 knockout (KO) and TLR4 KO mice received Lieber DeCarli diet for 5weeks. Some mice received corn oil or CCl4 for 2 or 9weeks.', 'We found that miR-155 KO mice are protected from alcohol-induced steatosis and inflammation. The reduction in alcohol-induced fat accumulation in miR-155 KO mice was associated with increased peroxisome proliferator-activated receptor response element (PPRE) and peroxisome proliferator-activated receptors (PPAR)α (miR-155 target) binding and decreased MCP1 production. Treatment with a miR-155 inhibitor increased PPARγ expression in naïve and alcohol treated RAW macrophages. Alcohol increased lipid metabolism gene expression (FABP4, LXRα, ACC1 and LDLR) in WT mice and this was prevented in KO mice. Alcohol diet caused an increase in the number of CD163(+) CD206(+) infiltrating macrophages and neutrophils in WT mice, which was prevented in miR-155 KO mice. Kupffer cells isolated from miR-155 KO mice exhibited predominance of M2 phenotype when exposed to M1 polarized signals and this was due to increased C/EBPβ. Pro-fibrotic genes were attenuated in miR-155 KO mice after alcohol diet or CCl4 treatment. Compared to WT mice, attenuation in CCl4 induced hydroxyproline and α-SMA was observed in KO mice. Finally, we show TLR4 signaling regulates miR-155 as TLR4 KO mice showed no induction of miR-155 after alcohol diet.'] Do the pro-inflammatory effects of miR-155 promote liver fibrosis and alcohol-induced steatohepatitis?