[Apoptosis and the thyroid: the Fas pathway].
THE APOPTOTIC FAS/FAS-L PATHWAY: Represents a major apoptotic pathway and involves the specific interaction between a membrane receptor, Fas, harbored by the target cell and a membrane ligand, Fas-L, harbored by the cytotoxic cell. FAS AND NORMAL THYROID GLAND: Normal thyrocytes express Fas receptor but not its ligand. The control of thyroid gland volume results from an equilibrium between the trophic action of TSH and thyrocyte apoptosis, which is limited to some extent by resistance to Fas activation by producing an inhibitor of the apoptotic signal transduction. FAS AND HASHIMOTO'S THYROIDITIS: Aberrant expression of Fas-L by thyrocytes induces their fratricide apoptosis. Thyroid-infiltrating lymphocytes are resistant to apoptosis by overexpressing the antiapoptotic protein Bcl2. FAS AND GRAVES' DISEASE: Autoantibody-dependant stimulation of the thyrotropin receptor favors goiter formation by reducing thyrocyte apoptosis. It induces repression of Fas expression and production of a soluble Fas, whose serum levels are correlated with clinical course. FAS AND THYROID CANCER: Tumoral cells are resistant to apoptosis by inhibiting the apoptotic signal transduction and exert Fas counter-attack by inducing apoptosis of antitumoral lymphocytes.