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Incidence of Antibodies Blocking Thyrotropin Effect In Vitro in Patients with Euthyroid or Hypothyroid Autoimmune Thyroiditis^*

Cattedra di Endocrinologia e Medicina Costituzionale, University of Pisa Pisa, Italy

Address all correspondence and requests for reprints to: Dr. Luca Chiovato, Cattedra di Endocrinologia e Medicina Costituzionale, Isti-tuto di Endocrinologia, Metodologia Clinica e Medicina del Lavoro, University of Pisa, viale del Tirreno 64, 56018, Tirrenia-Pisa, Italy.

Autoantibodies blocking the TSH-dependent production of cAMP in thyroid cells (TSH-BAb) have been described in atrophic thyroiditis (AT; idiopathic myxedema) and in neonates with transient hypothyroidism, but their incidence in autoimmune thyroiditis in relation to thyroid status remains to be completely established. To this purpose TSH-BAb were evaluated in a group of 140 consecutive patients with autoimmune thyroiditis, which included 26 cases of AT and 114 subjects with goitrous Hashimoto's thyroiditis (HT); among the goitrous group 27 were euthyroid (HT-E), 32 had subclinical hypothyroidism (HT-SH), and 55 had clinical hypothyroidism (HT-H). TSH-BAb were measured in immunoglobulin G prepared by DEAE-Sephadex A-50 by determining their ability to inhibit TSH-dependent cAMP production in a differentiated strain of cultured rat thyroid cells (FRTL-5). Using this sensitive and reproducible method, TSH-BAb were detected in 12 of 26 (46%) patients with AT, in 1 of 27 (3.7%) subjects with HT-E, in 3 of 32 (9.4%) with HT-SH, and in 20 of 55 (36%) with HT-H. The prevalence of TSH-BAb was higher in AT vs. HT-H (P < 0.001), HT-SH (P < 0.001), or HT-E (P < 0.001), and in HT-H vs. HT-SH (P < 0.001) or HT-E (P < 0.001). Mean TSH-BAb levels in AT were higher than those in HT-H (P < 0.005) and HT-SH (P < 0.025); the difference was not significant between HT-H and HT-SH. An inverse correlation was found between TSH-BAb levels and estimated goiter weight (P < 0.005). The results of the present study indicate that 1) in autoimmune thyroiditis TSH-BAb are detectable almost exclusively in hypothyroid patients, their prevalence being higher in overt hypothyroidism than in subclinical thyroid failure; 2) the prevalence of TSH-BAb and their mean levels are higher in hypothyroid patients with AT than in those with HT; and 3) therefore, the presence of circulating TSH-BAb appears to be related to the development of hypothyroidism and thyroid atrophy.

^* This work was supported by grants from the Consiglio Nazionale delle Ricerche, Progetti Finalizzati: Medicina Preventiva e Riabilita-tiva, Sottoprogetto 2 (Meccanismi di Invecchiamento; Grant 84.02464.56); Biotecnologie e Biostrumentazione, Sottoprogetto 6 (Bio-farmaci: Biotecnologie e Meccanismo D'azione dei Farmaci e Fattori di Crescita); and the Ministero Pubblica Istruzione, Rome, Italy.

Received August 4, 1989.

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