Heterogeneity of TSH receptor-binding antibodies in Hashimoto's thyroiditis and Graves' disease

Dermatologic aspects of thyroid disease

Thyroid disorders commonly have dermatologic manifestations. The purpose of the present chapter is to review and emphasize potential clinical dermatologic findings that can occur with Graves' disease, hypothyroidism and thyroid cancer. In autoimmune diseases such as Graves' disease and Hashimoto's thyroiditis the skin manifestations may be related to either thyroid hormone levels themselves or to the associated T and/or B cell abnormalities. Thyroid cancer may be associated with various syndromes that could have significant skin manifestations.

Graves disease in childhood: a review of the options for diagnosis and treatment

While diagnosing Graves disease in childhood and adolescence does not usually present specific problems, the treatment of hyperthyroidism is still controversial. In particular, with regard to the use of radioiodine therapy, strategies vary between many European and North American pediatric endocrinology centers. After the diagnosis is made, antithyroid drug treatment with methimazole (thiamazole), carbimazole, or propylthiouracil should be performed with caution, in particular, because of severe adverse effects, such as agranulocytosis or hepatitis, that are found in up to 1% of patients. Antithyroid drug treatment should not be continued long-term, particularly since definitive remission cannot be expected in more than 30-40% of patients. In contrast, the risk of severe adverse effects is still present, and the risk of thyroid carcinoma increases with time and appears to be considerably higher than after radioiodine treatment. To a great extent, the success of surgery depends on the skills of a trained surgeon. The question of whether to perform total or subtotal thyroidectomy is yet to be resolved. Surgery should be considered in patients with a large thyroid gland (>80g), severe ophthalmopathy, and a lack of remission on antithyroid drug treatment. Success rates have increased to up to 97%, while severe adverse effects (laryngeal nerve palsy, hypoparathyroidism) occur in approximately 4% of patients. Mortality is below 0.1%. Radioiodine treatment in children >5 years of age does not appear to be associated with an increased risk of thyroid carcinoma; however, long-term data are lacking. Compared with the surgical approach, success rates are lower, particularly if low doses of radioiodine are used. In general, adverse effects are less prevalent than in patients who have undergone surgery.

Diagnosis and management of juvenile hyperthyroidism in Germany: a retrospective multicenter study

This retrospective multicenter study was designed to survey the management of childhood and adolescent hyperthyroidism in six pediatric endocrinological units in Germany. Fifty-six patients aged between 1.1 and 17.0 yr (median 10.5 yr) were enrolled. Data were collected retrospectively from the patients' records by a trained pediatric endocrinologist using standardized questionnaires. After the diagnosis of hyperthyroidism was established on the basis of clinical and biological findings, treatment with antithyroid drugs (carbimazole, methimazole, thiamazole, propylthiouracil) was started in all patients. In 55/56 of the patients treated with antithyroid drugs, euthyroidism was achieved (98%). However, 26 patients (47%) were still hyperthyroid after discontinuation of the medication. Eight children with continued hyperthyroidism ultimately underwent subtotal thyroidectomy 13-136 (median 28) months after the initial diagnosis. Management principles of the participating centers were heterogeneous. As a consequence, prospective multicenter studies are urgently needed to establish clear standards for the diagnosis and therapy of childhood hyperthyroidism.

Recombinant human TSH receptor expressed in E. coli

We expressed the extracellular domain (20-408 aa, (T) of human TSH receptor (TSHR) in E. coli to detect TSHR autoantibodies (TRAb) and, moreover, we expressed the two portions (20-218 aa (5') and 217-408 aa (3')) of the extracellular domain thought to distinguish thyroid stimulating antibodies (TSAb) from blocking antibodies (TSBAb), using pGEX.3X as the expression vector. Using Western blotting analysis of the sera from patients with autoimmune thyroid disease, sera from Graves' patients and patients with idiopathic myxedema who had TSBAb reacted with the fusion protein (T), but none of the control sera reacted with it. We further evaluated whether or not the positive sear for T recognized fusion proteins (5') or (3'). The sera from Graves' patients reacted with both fusion proteins (5') and (3'). The sera from patients with idiopathic myxedema did not react with either of fusion proteins (5') or (3'). These findings suggest that these recombinant TSHR proteins could be used as antigens to detect TRAb, and differentiate TSABb from patients with idiopathic myxedema.

Precipitations of thyrotropin receptor-related peptides by immunoglobulin G of patients with Hashimoto's thyroiditis

In order to study whether specific binding sites for Hashimoto's IgG exist in TSH receptor, we have examined the TSH receptor binding activity of IgG of patients with Hashimoto's thyroiditis using synthetic peptides corresponding to the amino acid sequences in the extracellular domain of human TSH receptor. Eight different peptides were synthesized, radiolabeled and examined by immunoprecipitation assay. Among the peptides studied, peptide (352-378) was significantly precipitated by IgG of patients with Hashimoto's thyroiditis compared with control subjects. Ten out of twenty patients with Hashimoto's thyroiditis showed more precipitations of peptide (352-378) than mean + 2SD of those of control subjects. Peptide (352-378) was precipitated by IgG in a dose dependent manner and the binding of peptide (352-378) to IgG was displaced by the addition of increased amount of cold peptide (352-378). Precipitations of peptide (352-378) positively correlates with both TGHA and MCHA titers. Two out of fourteen patients with Graves' disease, one out of seven patients with subacute thyroiditis and none of eleven patients with thyroid tumor showed more precipitations of peptide (352-378) than mean + 2SD of those of control subjects. These results suggest that one of binding sites for Hashimoto's IgG is present in the amino acid sequence of 352-378 in the extracellular domain of TSH receptor.

Thyroid peroxidase antibodies in children with autoimmune thyroiditis

AIMS

To compare the prevalence of thyroid peroxidase antibodies in 25 children with autoimmune thyroid disorders and in 41 children and young adults with type 1 diabetes, and to test the prevalence of thyrotropin receptor antibodies.

METHODS

Two commercially available radioimmunoassays for antibodies to thyroid peroxidase, a commercially available agglutination test of particles coated with thyroid microsomal antigens, and a radioimmunoassay for thyrotropin receptor antibodies were used. Patients and controls were studied.

RESULTS

One of the radioimmunoassays detected thyroid peroxidase antibodies not only in all children with autoimmune thyroid disorders and children and young adults with type 1 diabetes and thyroid microsomal antibodies, but also in 20% of healthy control children without microsomal antibodies. With this thyroid peroxidase assay and with microsomal agglutination, 94% of the children with autoimmune thyroiditis, 71% of those with Graves' disease, and over 90% of those with type 1 diabetes and thyroid dysfunction tested positive. In the other radioimmunoassay for thyroid peroxidase antibodies thyroid peroxidase antibody titres in half or more of the children with microsomal antibodies failed to reach the level of positivity given by the producers. Eighty five percent of children with Graves' disease and 71% of those with autoimmune thyroiditis had thyrotropin receptor antibodies but so did 35% of children studied for other endocrinological disorders such as delayed growth or puberty.

CONCLUSIONS

Testing patients with well characterised disorders of thyroid function and with other endocrine disorders is important in evaluating the efficacy of new diagnostic tests for thyroid autoantibodies.

Binding domains of stimulatory and inhibitory thyrotropin (TSH) receptor autoantibodies determined with chimeric TSH-lutropin/chorionic gonadotropin receptors

We examined the relative effects of thyrotropin (TSH) and TSH receptor autoantibodies in the sera of patients with autoimmune thyroid disease on three TSH-lutropin/chorionic gonadotropin (LH/CG) receptor extracellular domain chimeras. Each chimera binds TSH with high affinity. Only the chimera with TSH receptor extracellular domains ABC (amino acids 1-260) had a functional (cAMP) response to thyroid stimulatory IgG. The chimeras with TSH receptor domains CD (amino acids 171-360) and DE (amino acids 261-418) were unresponsive. The lack of response of the chimera with TSH receptor domains DE was anticipated because it fails to transduce a signal with TSH stimulation, unlike the other two chimeras. A different spectrum of responses occurred when the TSH-LH/CG chimeras were examined in terms of autoantibody competition for TSH binding. IgG with TSH binding-inhibitory activity when tested with the wild-type TSH receptor also inhibited TSH binding to the chimera with TSH receptor domains DE. Dramatically, however, these IgG did not inhibit TSH binding to the chimera with TSH receptor domains CD, and had weak or absent activity with the chimera with TSH receptor domains ABC. Chimeras with TSH receptor domains ABC and DE were equally effective in affinity-purifying IgG with thyroid-stimulatory and TSH binding-inhibitory activities. Nonstimulatory IgG with TSH binding-inhibitory activity inhibited the action of stimulatory IgG on the wild-type TSH receptor, but not with the chimera containing TSH receptor domains ABC. In summary, TSH receptor autoantibodies and TSH bind to regions in both domains ABC and DE of the TSH receptor extracellular region. Stimulatory and inhibitory TSH receptor autoantibodies, as well as TSH, appear to bind to different sites in domains ABC, but similar sites in domains DE, of the receptor. Alternatively, TSH and the different TSH receptor antibodies bind with differing affinities to the same site in the ABC region.

Structural/functional relationships between internal and external MSH receptors: modulation of expression in Cloudman melanoma cells by UVB radiation

Expression of internal receptors for MSH is an important criterion for responsiveness to MSH by Cloudman melanoma cells (Orlow et al: J. Cell. Physiol., 142:129-136, 1990). Here, we show that internal and external receptors for MSH are of identical molecular weights (50-53 kDa) and share common antigenic determinants, indicating a structural relationship between the 2 populations of molecules. The internal receptors co-purified with a sub-cellular fraction highly enriched for small vesicles, many of which were coated. Ultraviolet B light (UVB) acted synergistically with MSH to increase tyrosinase activity and melanin content of cultured Cloudman melanoma cells, consistent with previous findings in the skin of mice and guinea pigs (Bolognia et al: J. Invest. Derm., 92:651-656, 1989). Preceding the rise in tyrosinase activity in cultured cells, UVB elicited a decrease in internal MSH binding sites and a concomitant increase in external sites. The time frame for the UVB effects on MSH receptors and melanogenesis, 48 hours, was similar to that for a response to solar radiation in humans. Together, the results indicate a key role for MSH receptors in the induction of melanogenesis by UVB and suggest a potential mechanism of action for UVB: redistribution of MSH receptors with a resultant increase in cellular responsiveness to MSH.