Environmental factors that may contribute to the pathogenesis of Graves' disease. Environmental factors involved in Graves' disease are listed in Fig. 17.15. Iodine has an immune-stimulant effect, and the autoimmune thyroid diseases are rare in areas of iodine deficiency. Cigarette smoking has been associated with Graves' ophthalmopathy, possibly via an effect on immune-competent cells. Precipitation of disease by environmental stress such as bereavement has been suggested but is difficult to substantiate. Infectious agents are involved in the development of autoimmune thyroid disease in animals, and molecular mimicry or non-specific immune stimulation by bacteria or viruses is a likely environmental trigger. Induction of class II antigen expression on thyroid follicular cells for example, in response to a viral infection, could lead to perpetuation of the immune process.
