Role of cytokines in the pathogenesis and suppression of thyroid autoimmunity.

Autoimmune thyroid diseases (AITD) are one of the most common organ-specific autoimmune disorders, of which Hashimoto's thyroiditis (HT) and Graves' disease (GD) are 2 of the most common clinical expressions. HT is characterized by hypothyroidism that results from the destruction of the thyroid by thyroglobulin-specific T cell-mediated autoimmune response. In contrast, GD is characterized by hyperthyroidism due to excessive production of thyroid hormone induced by thyrotropin receptor-specific stimulatory autoantibodies. Cytokines play a crucial role in modulating immune responses that affect the balance between maintenance of self-tolerance and initiation of autoimmunity. However, the role of cytokines is often confusing and is neither independent nor exclusive of other immune mediators. A regulatory cytokine may either favor induction of tolerance against thyroid autoimmune disease or favor activation and/or exacerbation of autoimmune responses. These apparently contradictory functions of a given cytokine are primarily influenced by the nature of co-signaling delivered by other cytokines. Consequently, a thorough understanding of the role of a particular cytokine in the context of a specific immune response is essential for the development of appropriate strategies to modulate cytokine responses to maintain or restore health. This review provides a summary of recent research pertaining to the role of cytokines in the pathogenesis of AITD with a particular emphasis on the therapeutic applications of cytokine modulation.