T helper 17 cell

T helper 17 cells (T_h17) are a subset of interleukin 17-producing T helper cells. They are considered developmentally distinct from T_h1 and T_h2 cells and are thought to play a key role in autoimmune disease.^[1][2]

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Differentiation

Activation of precursor T helper cells in the presence of TGF-beta and IL-6 is thought to drive differentiation of T_h17 cells. Aside from cytokine environment, it is unclear whether any other elements of the initial activation of T_h17 cells differ from those of other T helper cells. It has been suggested that IL-23 is involved in the expansion of established T_h17 populations. IL-21, a cytokine produced by T_h17 cells themselves, has also been shown to initiate an alternative route for the activation of T_h17 populations.^[3] Both Interferon gamma and IL-4, the main stimulators of T_h1 and T_h2 differentiation respectively, have been shown to negatively regulate T_h17 differentiation.

Functions

On initial characterisation, T_h17 cells were broadly implicated in autoimmune disease and auto-specific T_h17 were shown to be highly pathogenic. A more natural role for T_h17 cells is suggested by studies which have demonstrated preferential induction of IL-17 in cases of host infection with various bacterial and fungal species. T_h17 primarily produce two main members of the IL-17 family; IL-17A and IL-17F which are involved in the recruitment, activation and migration of neutrophils.

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