MicroRNA-155 promotes autoimmune inflammation by enhancing inflammatory T cell development. This study shows that miR-155 is involved in the development of inflammatory T cells, including Th17 and Th1 cells, during autoimmune inflammation. Mice lacking miR-155 (Mir155⁻/⁻) are resistant to experimental autoimmune encephalomyelitis (EAE), a model of autoimmune disease. The resistance is due to reduced development of inflammatory T cells and decreased production of cytokines by dendritic cells that support Th17 cell formation. The study also shows that miR-155 functions in CD4+ T cells to promote EAE. Additionally, miR-155 is required for the production of inflammatory cytokines by dendritic cells, which are essential for Th17 cell development. These findings suggest that miR-155 may be a promising therapeutic target for autoimmune disorders. The study also demonstrates that miR-155 is involved in the development of Th17 cells in vivo and in vitro, and that its expression is increased in response to inflammatory signals. The results indicate that miR-155 plays a critical role in the development of inflammatory T cells and the progression of autoimmune diseases.MicroRNA-155 promotes autoimmune inflammation by enhancing inflammatory T cell development. This study shows that miR-155 is involved in the development of inflammatory T cells, including Th17 and Th1 cells, during autoimmune inflammation. Mice lacking miR-155 (Mir155⁻/⁻) are resistant to experimental autoimmune encephalomyelitis (EAE), a model of autoimmune disease. The resistance is due to reduced development of inflammatory T cells and decreased production of cytokines by dendritic cells that support Th17 cell formation. The study also shows that miR-155 functions in CD4+ T cells to promote EAE. Additionally, miR-155 is required for the production of inflammatory cytokines by dendritic cells, which are essential for Th17 cell development. These findings suggest that miR-155 may be a promising therapeutic target for autoimmune disorders. The study also demonstrates that miR-155 is involved in the development of Th17 cells in vivo and in vitro, and that its expression is increased in response to inflammatory signals. The results indicate that miR-155 plays a critical role in the development of inflammatory T cells and the progression of autoimmune diseases.