The role of the immune system and cytokines involved in the pathogenesis of autoimmune thyroid disease (AITD).

Autoimmune thyroid disease (AITD) is the most common organ-specific autoimmune disorder. AITD development occurs due to loss of immune tolerance and reactivity to thyroid autoantigens: thyroid peroxidase (TPO), thyroglobulin (TG) and thyroid stimulating hormone receptor (TSHR). This leads to infiltration of the gland by T cells and B cells that produce antibodies specific for clinical manifestations of hyperthyroidism in Graves' disease (GD) and chronic autoimmune thyroiditis (cAIT). In addition, T cells in Hashimoto's thyroiditis induce apoptosis in thyroid follicular cells, leading ultimately to the destruction of the gland. Cytokines are involved in the pathogenesis of thyroid diseases working in both the immune system and directly targeting the thyroid follicular cells. They are involved in the induction and effector phase of the immune response and inflammation, playing a key role in the pathogenesis of autoimmune thyroid disease. The presence of multiple cytokines has been demonstrated: IL-1alpha, IL-1b, IL-2, IL-4 , IL-6, IL-8, IL-10, IL-12, IL-13, IL-14, TNF-alpha and IFN-gamma within the inflammatory cells and thyroid follicular cells. Finally, cytokines derived from T cells can directly damage thyroid cells, leading to functional disorders and may also stimulate the production of nitric oxide (NO) and prostaglandin (PG), thus increasing the inflammatory response in AITD. Immunological mechanisms involved in the pathogenesis of AITD are strongly related to each other, but differences in the image of cAIT and GD phenotype are possibly due to a different type of immune response observed in these two counteracting clinical thyroid diseases. This article describes the potential role of cytokines and immune mechanisms in the pathogenesis of AITD.