T H 17 cell

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T H 17 cells are a special type of T helper cells . They are named after the interleukin IL-17 they produce and play an important role in the activation of neutrophils , but are also associated with the development of chronic inflammation and autoimmune diseases . The T H 17 differentiation pathway is a differentiation pathway for T helper cells that is outside the previously known T H 1 / T H 2 system.

Emergence

T H 17 cells develop from so-called naive T helper cells, i.e. T helper cells that have not yet had contact with their specific antigen , only after they have been activated by antigen contact. For the differentiation of T H 17 cells, IL-6 and TGF-β are necessary, which activates the transcription factor RORgt in the cells . Interleukin IL-23 , which has long played a role in the development of autoimmune diseases, is still required for the cells to survive .

effect

The main secretion product of T H 17 cells is the eponymous IL-17 , which is a cytokine family with various messenger substances from IL-17A to IL-17F, with the secretion of IL-17A and IL-17F in T H 17 cells dominates. Receptors for IL-17 are located on different cell types of the immune system, for example on myeloid cells, which include neutrophils, and on lymphocytes . But epithelial and endothelial cells as well as fibroblasts also have corresponding receptors. Other secretion products from T H 17 cells are TNF -α and IL-6.

The messenger substances cause inflammatory processes in which neutrophils play a dominant role. IL-17 causes G-CSF , IL-6 and IL-8 to be released in the target cells mentioned , which bring this cell type to immigration and activate it. In addition, pro-inflammatory proteins such as IL-1 , IL-6, PGE-2 , cyclooxygenase 2 and matrix metalloproteases are increasingly expressed . The structure of connective and bone tissue is also modulated by IL-17. It activates the formation of osteoclasts and inhibits the synthesis of proteoglycans . At the same time, the breakdown of proteoglycans and the formation of aggrecanase are promoted.

Another effect of T H 17 cells is the prevention of an efficient fight against intracellular pathogens by suppressing the formation of T H 1 cells.

function

The physiological function of T H 17 cells appears to be the initiation of defense against extracellular bacteria in peripheral organs by neutrophils. The suppression of T H 1 cells can lead to persistence of pathogens or antigens and thus to chronic inflammation. T H 17 cells are also believed to be involved in the development of autoimmune diseases such as rheumatoid arthritis .

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