Thyroid autoimmunity and polyautoimmunity

Thyroid autoimmunity is a pathological process caused by T-cell and B-cell self-reactivity against the thyroid gland. The pathogenesis is most often multifactorial including genetic susceptibility (i.e., HLA-DR3 alleles), environmental factors (iodine consumption, smoking) and endogenous factors (female sex, previous pregnancies, increasing age). Several clinically overt, common, and distinct thyroid diseases result from thyroid autoimmunity, although there are also many individuals who have subclinical evidence of thyroid autoimmunity. Autoimmune thyroid diseases are the most common autoimmune diseases and are often involved in polyautoimmunity, where T cells or autoantibodies react with self-antigens from different organ systems in the body. Such polyautoimmunity indicates that the patients suffer from a more generalized dysregulation of the immune system. Apart from the specifically recognized polyglandular autoimmune syndromes, thyroid autoimmunity is the most common co-existing autoimmunity in other autoimmune diseases and is, thus, essential in the understanding of polyautoimmunity.