Concept of a multigenic basis for the pathogenesis of spontaneous autoimmune thyroiditis.

The review presents a concept for the pathogenesis of spontaneous, organ-specific autoimmune diseases that take into account an altered immune regulation, modulating hormonal influences and a genetically determined primary susceptibility of the target organ for the autoimmune attack. The concept is exemplified by means of the Obese strain (OS) chicken model which develops a spontaneous hereditary autoimmune thyroiditis. In respect to the the altered function of the immune system both, MHC associated (Ir) and non-MHC associated genes are involved. The MHC, i.e. a certain haplotype, only plays a modulatory role in determining the frequency and severity of spontaneous autoimmune thyroiditis, while the presence of certain non-MHC associated genes is a absolute prerequisite for the emergence of the disease. The latter is also true for the genetically determined target organ susceptibility, while hormonal factors, notably sex-steroids and glucocorticoids, again only have a facultative, modulatory effect. Only if an appropriate genetic constellation concerning the non-MHC encoded aberrant immunological function and genes coding for the susceptibility of the thyroid gland for the autoimmune process is present, severe autoimmune thyroids develops.