Th17 cells: inflammation and regulation

IL-17-producing CD4+ T cells (Th17 cells) are understood to be a distinct lineage of CD4+ T helper (Th) cells, which play an important role in the host defense, tissue inflammation and autoimmunity. The identification of Th17 cells collapsed the concept of the previously held Th1/Th2 paradigm in infection and autoimmunity. Recent studies have provided new information on the role of Th17 cells in different autoimmune diseases and the mechanisms of Th17 cell differentiation. Th17 cells contribute to the exacerbation of autoimmune disease, whereas they possess a protective aspect against microbes such as bacteria and fungi. This suggests that Th17 cells can be broadly categorized as pathogenic or non-pathogenic. Naïve CD4+ T cells can differentiate into Th17 cells in synergy with IL-6 and TGF-β, while TGF-β induces regulatory T cells (iTreg), which appear to be mutually exclusive to Th17 cells. Here we describe the detail molecular mechanism of Th17 cell differentiation, including recently identified molecules, and discuss different roles of Th17 cells in infection, inflammation and autoimmunity in a cytokine milieu