Infection and Autoimmune Thyroid Diseases

The etiology of the autoimmune thyroid diseases (AITDs) remains unclear, but it is now generally believed that both genetic and environmental factors contribute to their development. Previous findings have begun to directly and indirectly implicate infectious agents in the pathogenesis of AITD, and these data serve as the basis for this review. Classical AITDs (i.e., Graves' disease and Hashimoto's thyroiditis) have been shown to be associated with a variety of infectious agents. However, a causative role for infectious agents in AITD has not been definitively demonstrated in humans. Infectious agents may induce thyroid autoimmunity by a variety of diverse mechanisms, such as inducing modifications of self-antigens, mimicking self-molecules, altering the idiotypic network, forming immune complexes, and inducing expression of MHC molecules on thyroid epithelial cells. While indirect data suggesting the involvement of the infecting organisms in the pathogenesis of human AITD are abundant, only a limited number of studies have employed direct approaches. It is this area of research where further studies are needed.