Helper T cell 17 (Th17) being a new cell subset of CD4+T in the body, which is different from Th1 and Th2 cells, have independent mechanisms of differentiation and developmental regulation. Th17 cells mainly secrete various cytokines such as IL-17, IL-6 and TNF-α, which induce inflammation. Treg cells are T cells with high expression of CD25 differentiated by T cells under the action of certain cytokines, namely CD4+CD25+(hi) Foxp3+T cells, which can regulate the immune response mediated by effector cells and are an important line of defense for human autoimmune. Therefore, Treg cells play an important role in maintaining immune tolerance of the body. As an important subset of T cells, Treg cells have an inhibitory effect on inflammation. Its working principle is to selectively inhibit autoreactive T cells and effector T cells so as to maintain the body's immune balance, and normal quantity and function help the immune system to its antigen stimulation, establishing a good state of tolerance. The expression of Treg cells increased, can avoid the occurrence of autoimmune diseases. Treg cells inhibit the differentiation of Th17 cells by down-regulating the expression of IL-23 and IL-17 or by its specific transcription factor Foxp3; similarly, inhibition of Th17 cell production can promote the development of Treg cells. Both Th17 and Treg cells are functionally inhibited. Th17 cells promote inflammatory reaction, and Treg cells suppress immune reaction. Numerous cytokines are involved in regulation. For example, IL-6 and IL-21 can inhibit Foxp3 and promote the expression of RORγt, thereby inhibiting Treg cells and inducing the differentiation of Th17 cells. In the absence of IL-6 and other pro-inflammatory factors, TGF-β enhances the inhibitory effect of Foxp3 on RORγt and promotes the growth and development of Treg cells. The anti-inflammatory factor IL-10 also induces Treg cells to inhibit the reaction of Th17 cells. The effects of Treg and Th17 cells are normally in a dynamic equilibrium. Once the balance is imbalanced, autoimmune diseases will occur. This article reviews the differentiation, function and research progress of Th17/Treg cells in autoimmune diseases.

As being one of the most common diseases in autoimmune thyroid disease (AITD), Hashimoto's thyroiditis (HT) is an organ-specific autoimmune disease. It is mostly related to genetics, infection, and excessive iodine, but the exact pathogenesis has not yet clear. As one of the most important immune cells, T cells play an important role in the human immune. Helper T cells (Th) and regulatory T cells (Treg) are two important subgroups of T cells. The former include Th1, Th2, Th17 and other cells. HT patients is mainly characterized by expressing Th1 cytokines. The imbalance of Th1/Th2 ratio can induce abnormal immune response, which is closely related to the incidence of HT. Th17/Treg cells are mutually restricted in differentiation and mutually antagonistic in function. IL-17 secreted by Th17 cells directly promotes the inflammatory response of thyroid tissue and accelerates the damage of thyroid tissue. Abnormal Treg cell function cannot effectively inhibit the occurrence of autoimmune reactions and promote immune tolerance. Th17/Treg constitute a relatively independent group of cell networks except Th1/Th2. Under normal circumstances, Th1/Th2 and Th17/Treg cells maintain a dynamic balance. However, once unbalanced, they will lead to immune dysfunction and participate in the development of HT. This article reviews the mechanisms of Th1/Th2 and Th17/Treg cells and their cytokines in the pathogenesis of HT.

Regulatory T cells (Treg) are a subset of T cells with immunosuppressive functions. According to the source and mechanism of Treg cells, they are divided into natural regulatory T cells (nTreg) and induced regulatory T cells (iTreg). According to the different properties of secreted cytokines, they are divided into two types: pro-inflammatory and anti-inflammatory cells. Pro-inflammatory Treg cells that secrete IFN-ã are closely related to the development of autoimmune diseases, while anti-inflammatory Treg cells that secrete IL-10 can reduce the development of slow inflammation. In addition to secreting a variety of inhibitory cytokines such as IL-10 and TGF-â, Treg cells also exert immunosuppressive effects through direct contact among cells to jointly maintain the body's immune tolerance and suppress immune responses. By suppressing the autoimmune response of effector T cells and promoting immune tolerance, it has a very important role in maintaining the homeostasis of the body. The differentiation and regulation of Treg cells and their relationship with autoimmune diseases have been hotspots in the field of immunology in recent years. This article reviews the source of Treg, differentiation regulation, classification, markers, functions and mechanisms of action so as to deepen the understanding of Treg cell differentiation and immune regulation mechanisms, and further broaden the research horizon and thinking.

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