T regulatory (Treg) and T helper 17 (Th17) lymphocytes in thyroid autoimmunity

Different immune cell subsets have a relevant role in the pathogenesis of and tissue damage seen in autoimmune thyroid diseases (AITD), including T regulatory (Treg) lymphocytes and T helper (Th) 17 cells. There are several types of CD4+ Treg cells (Foxp3+, CD69+, Tr1), which are able to prevent the appearance of autoimmune diseases, down regulating the immune response and the inflammatory phenomenon. However, despite their presence in peripheral blood and thyroid tissue from patients with AITD, these cells are apparently unable to put down the autoimmune process. Moreover, many reports indicate the involvement of Th17 cells in chronic inflammatory diseases, including AITD. Nevertheless, it is now evident that these lymphocytes show a remarkable plasticity, giving rise to anti-inflammatory (including Treg lymphocytes) and pro-inflammatory cell subtypes. Nowadays, both Treg and Th17 cells must be considered as key elements in the pathogenesis of AITD as well as plausible potential targets for the next generation of therapeutic options of this condition.