T helper cells (Th cells) are T-lymphocytes, a type of white blood cell, belonging to the CD4+ subset. They play an important role in the immune system, particularly in the adaptive immune system. They help the activity of other immune cells by releasing T cell cytokines, which stimulate the helped cells.
T helper 17 (Th17) cells are a subset of effector T helper cells which protect surfaces (e.g. skin, lining of the intestine) against extracellular bacteria. The key regulator of Th17 is the ROR-gamma-t transcription factor. The ROR-gamma-t transcription factor can be expressed in some extent by the TGF-beta and IL-6 but Th17 requires both TGF-beta and IL-6 for its induction. The stimulated Th17 cells produce Th17 cytokines such as IL-17A, IL-17F and IL-22.
These cytokines stimulate epithelial cells to produce anti-microbial proteins to fight microbial infection.