Since then researchers have tried to find origin and function of Th17 cells and have been trying to use them in therapy. Specific molecules regulating Th17 cells functions and properties have become more interesting, after discovery that Th17 cells take part in pathomechanisms of many diseases. Th17, like other Th cells, need specific cytokines and transcription factors for activation and proliferation. Both of them are pro-inflammatory cytokines IL-21 helps to restore the balance between Th17 and Treg cells and IL-22 is a member of IL-10 cytokine family, which is linked to chronic inflammation and participates in pathogenesis of many autoimmune diseases. This special population of CD4 + T cells produces also IL-21 (Pelletier and Girard 2007) and IL-22 (Pan et al. Some researchers have recently shown that IL-17A and/or IL-17F are responsible for development of inflammation in many disorders, especially in autoimmune diseases like rheumatoid arthritis (RA), psoriasis, juvenile idiopathic arthritis (JIA), CrohnвЂ™s disease and many others (Adami et al. Both of them are pro-inflammatory cytokines. There are six known isoforms of IL-17, from A to F, but Th17 cells are able to produce only IL-17A and IL-17F (Tesmer et al. Subsequently the presence of a novel Th cell subpopulation (Th17), able to produce IL-17, was revealed. However, in the nineties of the past century a new cytokine, interleukin (IL)-17, was identified (Rouvier et al.

In 1989 Mosmann and Coffman ( 1989) described the relationship between functional properties of Th1 and Th2 cells and cytokines produced by them (Mosmann et al. In the late twentieth century some changes in T helper cellвЂ™s classification have been introduced. In this review, we attempt to summarize researches focused on the importance of Th17 cells in development of human autoimmune diseases as well as effectiveness of targeting IL-17 and its pathways in pre-clinical and clinical studies. Therapies based on inhibition of Th17-dependent pathways are associated with clinical benefits, but on the other hand are frequently inducing adverse effects. These findings made Th17 cells and pathways regulating their development and function a good target for therapy. Numerous publications based on animal and human models confirmed their pivotal role in pathogenesis of human systemic and organ-specific autoimmune diseases. High abilities to stimulate acute and chronic inflammation made these cells ideal candidate for crucial player in development of autoimmune disorders. The identification of the new subpopulation of T helper cells producing IL-17 modified model of Th1вЂ“Th2 paradigm and it was named Th17. The end of twentieth century has introduced some changes into T helper (Th) cells division.

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