Autoimmune thyroid disease: propagation and progression.

Autoimmune thyroid disease is the archetype for organ-specific autoimmune disorders. Progress in treating these disorders lies in improvements of our understanding of the predisposing factors responsible, the mechanisms responsible for progression of disease, and the interaction between thyroid antigens and the immune system at the level of the T cell and antibody. In common with other autoimmune diseases, genetic, environmental and endogenous factors are required in an appropriate combination to initiate thyroid autoimmunity. At present the only genetic factors which have been confirmed lie in the HLA complex and CTLA-4 or a closely linked gene. Identifying other predisposing genes will require large-scale family studies, or further insights into likely candidate genes. A number of environmental factors are known to predispose to autoimmune thyroid disease, including smoking, stress and iodine intake, while immunomodulatory treatments are revealing new pathways for disease emergence. The thyroid cell itself appears to play a major role in disease progression, interacting with the immune system through expression of a number of immunologically active molecules including HLA class I and II, adhesion molecules, cytokines, CD40 and complement regulatory proteins. New techniques, in particular phage display libraries, are providing the methods with which to identify autoantibody diversity in autoimmune thyroid disease and to provide tools for mapping autoantigenic epitopes. Application of these techniques is likely to lead to an understanding of how TSH receptor antibodies interact with the receptor to cause Graves' disease and also to the identification of novel orbital autoantigens in thyroid-associated ophthalmopathy.