Wednesday 10 November 2010
T helper cells that produce interleukin-17 (IL-17) (Th17 cells) have recently been identified as the third distinct subset of effector T cells, the differentiation of which depends on specific transcription nuclear factor retinoic acid-related orphan nuclear receptor-gammat.
Th17 cells play an important role in innate immunity, adaptive immunity and autoimmunity.
Interestingly, there is a reciprocal relationship between Th17 cells and regulatory T cells (Treg), not only in development, but also in their effector function.
Transforming growth factor (TGF)-beta induces Treg-specific transcription factor Forkhead box P3(FOXP3), while the addition of IL-6 to TGF-beta inhibits the generation of Treg cells and induces Th17 cells.
It is proposed that the fine balance between Th17 and Treg cells is crucial for maintenance of immune homeostasis.
In addition to IL-6, other factors such as retinoic acid, rapamycin, or cytokines (e.g., IL-2 and IL-27) could dictate the balance between Th17 and Treg cells.
Since Treg cells play an important role in hepatic immunity with overregulation in chronic viral hepatitis and hepatic carcinoma, and inadequate inhibition in autoimmune liver diseases, graft rejection and acute liver failure, it is reasonable to assume that Th17 cells may play a reciprocal role in these diseases.
Th17 cells: the emerging reciprocal partner of regulatory T cells in the liver. Zhao L, Qiu de K, Ma X. J Dig Dis. 2010 Jun;11(3):126-33. PMID: 20579216