Infection and Autoimmune Thyroid Diseases

The autoimmune thyroid diseases (AITD) include a number of conditions which have in common cellular and humoral immune responses targeted at the thyroid gland. The AITD include Graves' disease (GD) and Hashimoto's thyroiditis (HT), both of which involve infiltration of the thyroid by T and B cells reactive with thyroid antigens, production of thyroid autoantibodies, with the resultant clinical manifestations (hyperthyroidism in GD and hypothyroidism in HT). This chapter points to the possibility of involvement of an infectious agent in the pathogenesis of. Several studies point to the involvement of bacterial and viral agents in the pathogenesis of Graves' and Hashimoto's diseases. Various mechanisms have been proposed to explain induction of autoimmunity by infection, but it seems that two possibilities may be important to thyroid autoimmunity-amely, molecular mimicry (perhaps to retroviruses) and MHC class II antigen induction. However, it should be remembered that the association between AITD and infections may be merely coincidental and not etiological.