Autoantibodies to the thyrotropin receptor

Area of Science:

• Endocrinology
• Immunology
• Thyroidology

Background:

• Thyroid-stimulating hormone receptor antibodies (TRAb) play a key role in thyroid autoimmune diseases.
• Accurate measurement and understanding of TRAb properties are crucial for diagnosis and management.

Purpose of the Study:

• To review recent advancements in TRAb measurement, action, and synthesis.
• To elucidate the clinical significance of TRAb in Graves' disease and hypothyroidism.
• To describe the structure of the TSH receptor.

Main Methods:

• Utilized two novel assay methods: receptor assays inhibiting TSH binding and bioassays measuring cAMP release.
• Studied TRAb action (agonist/antagonist) in patients with Graves' hyperthyroidism and hypothyroidism.
• Investigated TRAb synthesis sites using evidence of thyroid lymphocyte production.
• Employed affinity labeling to determine TSH receptor structure.

Main Results:

• New assays offer improved sensitivity, specificity, precision, and ease of TRAb measurement.
• TSH receptor antibodies predominantly act as TSH agonists in Graves' hyperthyroidism.
• TRAb measurements can predict treatment outcomes in iodine-sufficient areas but may be less reliable in iodine-deficient regions.
• Approximately 20% of hypothyroid patients have TRAb antagonists (blocking antibodies), potentially causing neonatal hypothyroidism.
• Direct evidence confirms TRAb synthesis by thyroid lymphocytes.
• The TSH receptor has a two-chain structure (A and B subunits) with the TSH binding site on the extracellular A subunit.

Conclusions:

• Enhanced TRAb assays provide valuable tools for managing thyroid autoimmune disorders.
• Understanding TRAb agonist and antagonist activities is critical for predicting disease course and treatment response.
• Thyroid lymphocytes are the primary site of TRAb synthesis.
• Elucidation of TSH receptor structure offers insights into antibody-thyroid interactions.