[Can growth-stimulating immunoglobulins (TGI) explain sporadic euthyroid goiters?].

IgGs capable of stimulating thyroid growth have been demonstrated (thyroid growth stimulating IgG-TGI) using a cytochemical bioassay based upon measurement of DNA synthesis in slices of guinea-pig thyroid. This activity has been confirmed by measurement of 3H-thymidine incorporation into DNA, in rat dispersed thyroid follicles cultured in suspension. Circulating TGI has been observed in patient with "simple" goitre, Graves' disease and more rarely in Hashimoto's thyroiditis. TGI titers are correlated with goitre size or lack of suppressibility by exogenous thyroid hormones rather than with thyroid function as assessed by circulating hormone levels. In patients with primary myxoedema and thyroid atrophy, existence of TGI-blocking IgGs has also been demonstrated. Existence of natural TGI has been corroborated by experimental production of a monoclonal anti-TSH receptor antibody with thyroid growth activity. These observations raise several points: --relationship of TGI to other thyroid antibodies, specially to anti-TSH receptor antibodies; --is "simple" goitre, either diffuse or nodular, an auto-immune thyroid disorder? How to explain the usual functional and structural heterogeneity of these goitres?; --metabolic relationship between DNA synthesis and activity of glucose-6-phosphate deshydrogenase involved in hormonogenesis; mechanism of the apparent uncoupling between cell multiplication and secretory activity.