Thyroid cell apoptosis - A new understanding of thyroid autoimmunity

Apoptosis is a highly regulated mechanism of cell death involved in normal development, immune regulation, and homeostasis. Abnormal apoptotic activit y has been implicated in a variety of diseases including cancer, autoimmuni ty, and degenerative disorders. In the thyroid, altered cell death may play a role in the pathogenesis of autoimmune disorders such as Hashimoto's thy roiditis and Graves' disease. Apoptosis-signaling pathways can be initiated through activation of death receptors or in response to cellular damage, s uch as in gamma irradiation. It has been demonstrated that Fas, tumor necro sis factor, and tumor necrosis factor-related apoptosis-inducing ligand pat hways are present and functional in the thyroid, although the expression of these molecules and their roles in thyroid autoimmunity have been debated. Thyroid apoptosis is regulated at multiple levels, including receptor and ligand expression, and the expression of anti-apoptotic proteins, such as F AP-1 and Bcl-2. These factors may provide potential mechanisms for modifyin g the pathogenesis of autoimmune thyroid disease.