Thyroid-stimulating immunoglobulin

Graves disease An autoimmune disease in which the B lymphocytes synthesize an immunoglobulin (thyroid-stimulating immunoglobulin, TSIg) that binds to and activates the TSH receptor in such a way that the thyroid hormones do not feedback inhibit the receptor-effector interaction, leading to a hyperthyroid condition. 

In Graves disease, hyperthyroidism results from the action of thyroid-stimulating antibodies (TSAb) directed against the thyrotropin receptor on the surface of the thyroid cell. These immunoglobulin G antibodies bind to the receptor and activate the enzyme adenylate cyclase in the same manner as TSH. 

TSH receptor-stimulating antibody or thyroid-stimulating immunoglobulin (TSI) < 125% Test not indicated Elevated in Graves disease... 

The excessive production of thyroid hormone in Graves disease is associated with an enlarged thyroid gland, but in this case a circulating immunoglobulin that mimics the activity of thyroid stimulating hormone (TSH) is implicated. Finally, we saw in an earlier section how an inappropriate steroid hormone may be secreted in excessive amounts when specific enzymes in the adrenal steroid biosynthetic pathway are present at inadequate levels. 

Biochemical mechanism The most frequent cause of hyperthyroidism, Graves disease, is an autoimmune process in which thyroid hypersecretion is caused by circulating immunoglobulins that bind to the TSH receptor on the thyroid follicular cells and stimulate thyroid hormone production. The diagnosis is confirmed by increased thyroid stimulating IgG antibodies and is frequently seen in other family members. 

Many different types of proteins are glycoproteins. For example, stractural proteins such as collagen, proteins found in mucous secretions, immunoglobulins, folhcle-stimu-lating hormone and thyroid-stimulating hormone, interferon (an antiviral protein), and blood plasma proteins are all glycoproteins. One of the functions of the polysaccharide chain is to act as a receptor site on the cell surface in order to transmit signals from hormones and other molecules across the cell membrane into the cell. The carbohydrates on the surfaces of cells also serve as points of attachment for other cells, vimses, and toxins. 

It is probable that the more recently discovered immunoglobulins, all in the IgG class, such as long-acting thyroid stimulator (LATS) and LATS protector, should be classified as thyroid autoantibodies and discussion on these follows in the next section. 

Recent years have seen exciting advances in the recognition of thyroid-stimulating immunoglobulins of the IgG class, which have an extremely important bearing on the etiology of Graves disease. It would be premature for clinical chemistry departments, except those with special inter-... 

M16a. Mukhtar, E. D., Smith, B. R., Pyle, G. A., Hall, R. and Vice, P., Relation of thyroid stimulating immunoglobulins to thyroid function and effects of surgery, radio-iodine and antithyroid drugs. Lancet 1, 713-715 (1975). 

Incubation of thyroid-stimulating immunoglobulin G (IgG) found in the blood of patients with Graves disease... 

By determining the radioactivity in blood samples 9-24 h after the material to be assayed has been injected, it is also possible to assay the long-acting thyroid-stimulating immunoglobulin (LATS). 

Adrenocorticotropic hormone, a-amylase, atrazineAriazines, 2,4-dinitrophenyl lysine, human chorionic gonadotropin, human serum albumin, immunoglobulin G, isoproturon, parathyroid hormone, testosterone, theophylline, thyroid stimulating hormone, thyroxine, transferrin, transferrin, trinitrotoluene... 

Graves disease. In this autoimmune condition the thyroid gland is stimulated by an immunoglobulin called long-acting thyroid stimulator (LATS). 

Mehdi, S. Q., and Kriss, J. P., 1978, Preparation of radiolabeled thyroid-stimulating immunoglobulins (TSI) by recombining TSI heavy chains with I-labeled light chains Direct evidence that the product binds to the membrane thyrotropin receptor and stimulates adenylate cyclase. Endocrinology 103 296. 

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