Acta endocrinologica. Supplementum最新文献

Studies of the TSH receptor using affinity labelling with photoactive derivatives of TSH and analysis by SDS-PAGE have shown that the receptor contains 2 subunits (A and B), linked by a disulphide bridge. Similar results are obtained with TSH receptors from human, porcine and guinea pig thyroid tissue and from guinea pig fat. Analysis of affinity labelled receptors under non-denaturing conditions suggest that subunits additional to the A and B subunits are not present. Hydrodynamic measurements indicate that the receptor A subunit has an approximately spherical structure (Stokes' radius 70 A) and when this interacts with TSH (an elongated structure with Stokes' radius 56A) a very elongated complex (Stokes' radius 104A) is formed. Isoelectric focusing studies of the TSH receptor A subunit, TSH and TSH receptor antibodies indicate that charge-charge interactions are of considerable importance in the binding of hormone and antibody to the receptor.

Using a number of immunologic and biochemical approaches, we have identified a number of [125I]bTSH binding peptides with Mr approximately 45,000, 66,000-70,000, approximately 95,000; larger conjugates capable of binding the hormone have not been excluded. A conservative interpretation of the data suggest a basic receptor unit of Mr approximately 95,000 of which Mr 45,000 and 66,000-70,000 are proteolytic products of membrane-bound proteases. The association of two intact subunits by strong noncovalent forces may generate more than 3 TSH binding sites.

The effects of insulin, the tumour promotor tetradecanoyl phorbol acetate (TPA), TSH and combinations of these factors on growth and DNA synthesis have been examined in the FRTL-5 cell strain and in sheep thyroid cells. In addition the regulation of the production by sheep thyroid cells of the insulin-like growth factors (IGF) by TSH and their possible autocrine roles have been investigated. We found that insulin and the IGF's stimulated DNA synthesis in both rat FRTL-5 cells and sheep cells. TPA also stimulated growth in both cell types, and its effects were additive to those of insulin. In the FRTL-5 cells, TPA was a less potent stimulator of growth than TSH, but the effects of TPA and TSH were not additive which may imply growth stimulation through a common pathway. In sheep cells TSH was not mitogenic and did not appear to activate protein kinase C, the receptor for TPA. Sheep cells, unlike FRTL-5 cells, were found to produce IGF-I and IGF-II, and their syntheses were regulated by TSH. Sheep cells were also found to produce IGF-binding proteins which may modulate the biologic effects of the IGF's. Sheep thyroid IGF binding proteins were found to copurify with urokinase-like plasminogen activator on immunoaffinity chromatography. The production of this serine protease has also been shown to be regulated by TSH.

Since the aberrant HLA-DR expression on thyroid follicular cells (TFC) has been found in glands already having an ongoing immune response, the possibility exists that this ectopic expression is not the primary event leading to the infiltration by autoreactive lymphocytes, but rather a consequence of that infiltration. We have explored that possibility in studies on the behaviour of TFC from normal and autoimmune glands with respect to their expression of HLA-DR antigens when they are cultured with or without autologous mononuclear cells from the intrathyroidal infiltrates or peripheral blood. Our findings suggest that 1) the ectopic expression of class II HLA antigens by TFC in autoimmune conditions is not the result of a primary or intrinsic defect of those cells but a consequence of their response to an environmental stimulus operating in situ; 2) this stimulus appears to be the lymphoid infiltration itself; 3) there are no significant differences in the responses given by TFC from autoimmune and normal glands. In alopecia areata, another presumably autoimmune condition characterized by the presence of lymphoid infiltration precedes that ectopic HLA-DR expression in vivo. In addition, we have found that human adrenocortical cells in the zona reticularis of adult glands normally express HLA-DR antigenic determinants. Therefore, the co-existence of both HLA-DR and potentially autoantigenic cell-surface constituents does not seem to be a sufficient stimulus to trigger an organ-specific autoimmune response.

Our results show evidence for regulation of Graves' disease remission by anti-idiotypic antibodies in a biologic assay. The polyclonality and functional heterogeneity of thyroid receptor antibodies is most likely the reason why evidence for idiotypic-anti-idiotypic regulation can be demonstrated in the autologous but not consistently in the homologous system.

In a patient with Graves' disease who underwent thyroidectomy with subsequent radioiodine therapy thyroid receptor antibody could be detected by radioligand assay. No thyroid tissue could be detected by 131I-scintiscanning. Thyroglobulin was repeatedly negative. Biologic activity of this patients serum could be demonstrated in the nude mice bio assay. 131I-incorporation and secretion of human thyroglobulin could be stimulated by injecting thymusdysplastic nude mice with transplants of thyroid tissue from a patient with Graves' disease with the athyroid patients serum. These results demonstrate evidence for extrathyroidal production and biological activity of TRAb in vivo.

The monoclonal antibody 11E8 (Kohn et al. 1984) is a novel proof of the actions of thyroid stimulator, since it is not only a potent stimulator of thyroid cells but also an inhibitor for TSH-binding. This might reflect an interaction of 11E8 with a discrete domaine of the TSH receptor, which is an essential component for TSH but not for TSab actions. These unique properties of 11E8 can be applied to the characterization of other thyroid stimulators which may interact with different domaines of the receptor. Moreover, 'TSab-like' stimulators, such as the sheep anti-TSH antiserum, could potentially be identified by 11E8.