Which substance is considered the primary autoantigen of the thyroid gland?

The primary autoantigen of the thyroid gland is thyroglobulin. This large protein is synthesized by the follicular cells of the thyroid and serves as the precursor for the synthesis of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). In autoimmune thyroid diseases, such as Hashimoto's thyroiditis and Graves’ disease, antibodies may develop against thyroglobulin, leading to an autoimmune response that can damage the thyroid tissue.

Understanding the role of thyroglobulin as an autoantigen is key in diagnosing and managing thyroid-related autoimmune conditions. It not only acts as a target for immune attack but also is a useful marker in evaluating autoimmune thyroid disorders.

Other substances like thyroid peroxidase, the TSH receptor, and calcitonin play roles in thyroid function and autoimmunity but are not regarded as the primary autoantigen. Thyroid peroxidase is also a common target for autoantibodies but is secondary to thyroglobulin in terms of its classification as a primary autoantigen. The TSH receptor is involved in the regulation of thyroid hormone production, and calcitonin is important in calcium homeostasis, but neither functions as the main autoantigen