The phenomenon of autoimmunity develops as a result of the triggering factor released by damaged cells. This leads to an infiltration of CD4+ cells involved in stimulating the effector cells cytotoxicity and stimulating the humoral response. One of the most common autoimmune disorders are autoimmune thyroid diseases, including Hashimoto's thyroiditis and Graves's diseases. Helper T lymphocytes, which are divided into Th1, Th2, Tregs, and the relatively new groups Th17, Th22, and Th9, are involved in the pathogenesis of AITD. CD4+ cell subtypes mature and differentiate by specific transcription factors and in a specific interleukin environment. Not only are Th1 and Th2 cells involved in the development of AITD, but also Th17, Th22, and Th9 lymphocytes and their correlation to Tregs lymphocytes. The plasticity of the CD4+ cells is very important, affecting the balance between these cells, as well the factors modulating their phenotypic variability. Patients with AITD have an increased percentage of Th17, Th22, and Th9 cells as well as defective function of Tregs lymphocytes. The balance between Th17 cells (and also other cytotoxic T cells) and Treg cells is also very important. Understanding the role of CD4 cells in the pathogenesis of AITD may be important not only for the development of the knowledge, but also for determining therapeutic targets.
Keywords: CD4+ T cell; Th lymphocytes; Treg lymphocytes; autoimmune thyroid disease.