Vitamin D and autoimmune thyroid diseases (part 1)

Autoimmune thyroiditis (AIT) and Graves’ disease (GD) are common autoimmune diseases, and their prevalence assessed as 5 % of general population. Currently, selective immunosuppressive agents for pathogenetic treatment of autoimmune pathology are being developed. Vitamin D with the known anti­inflammatory and immunoregulatory properties, is also of great interest. The first part of the article reviews the roles of various immune cells in the pathogenesis of autoimmune thyroid diseases, which is necessary to reveal the therapeutic potential of calcitriol in these disorders. Classically, AIT was considered to be mediated by T­helpers type 1 (Th1), and GD — by T­helpers type 2 (Th2). This misunderstanding was based on the idea that humoral immunity is controlled by Th2 cytokines, and cellular immunity — by Th1. In the past decades, the role of new subsets of immune cells in the pathogenesis of autoimmune thyroid diseases is being studied, displacing the traditional paradigm of Th1/Th2 dichotomy. It has been established that T­helpers type 17 (Th17) play an important role in the development of various inflammatory and autoimmune diseases, previously classified as Th1­dependent pathologies. The involvement of T­ and B­regulatory lymphocytes in the autoimmune process is also of particular interest. It was found that these cells accumulate in inflamed thyroid tissue in patients with thyroid pathology, but they are unable to suppress the immune response effectively. Further research will help to find out which immune cells can become targets for vitamin D agonists in the complex treatment of autoimmune diseases.