Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.11.1.8 (thyroid peroxidase)
3,116 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Autoantibodies directed against the thyroid peroxidase (TPO), the thyroid microsomal antigen, are widely used to diagnose human autoimmune thyroid disease. A cloned 3.088 kb cDNA coding for the entire mature human TPO was isolated from a cDNA library derived from a pathological thyroid gland of a Graves' disease patient and used further to generate a so-called TPO epitope cDNA library in order to map linear autoantigenic epitopes involving a recombinant molecular biology approach. The TPO epitope cDNA library consisting of randomly fragmented cDNA sequences inserted in the expression vector pGEX-2T was expressed in Escherichia coli and screened with characterized anti-TPO autoantisera from Hashimoto's disease patients. All the sera were positively tested with a purified thyroid microsomal antigen fraction (TMA/TPO). Only about 1% of examined autoantisera were able to recognize bacterial expressed recombinant TPO representing sequential antigenic determinants. A corresponding autoantigenic epitope with 61 amino acids in length was located at the C-terminus of human TPO.
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PMID:Mapping of a linear autoantigenic epitope within the human thyroid peroxidase using recombinant DNA techniques. 137 23

To define the epitope(s) on human thyroid peroxidase (TPO) recognized by antibodies in the sera of patients with autoimmune thyroid disease, we constructed and screened a human TPO cDNA sublibrary containing 3.8 million random fragments of human TPO cDNA, each 200-500 basepairs in length. These fragments would code for TPO polypeptides of 66-166 amino acid residues. The validity of this approach was first tested with a murine monoclonal antibody against the denatured human thyroid microsomal antigen (TPO). Analysis of the nucleotide sequence of 14 clones selected from this library enabled molecular identification of the epitope recognized by this monoclonal antibody. In contrast to the data obtained with the monoclonal antibody, sera from patients with Hashimoto's thyroiditis containing polyclonal antimicrosomal/TPO antibodies did not recognize the TPO protein fragments generated by this library. These results differ from previous data obtained with recombinant human TPO fragments generated as bacterial fusion proteins. Our data suggest that, contrary to previous concepts, the natural B-cell epitope(s) on human TPO may be highly conformational (requiring a complex 3-dimensional structure) or may be discontinuous (formed by distant regions of the linear polypeptide chain being brought into apposition by protein folding).
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PMID:Evidence for the highly conformational nature of the epitope(s) on human thyroid peroxidase that are recognized by sera from patients with Hashimoto's thyroiditis. 169 26

The close relationship between thyroid microsomal antigen and thyroid peroxidase (TPO) is now well established. The present study evaluates the significance of autoantibodies against TPO (anti-TPO-Abs) in the various forms and stages of autoimmune thyroid disease with respect to a possible heterogeneous nature and particularly to their influence on TPO activity. When measured by a RIA using purified human TPO, anti-TPO-Abs were highly correlated with microsomal antibodies determined by enyzme-linked immunosorbant assay (r = 0.96; P less than 0.0001) and with the results of a TPO immunoprecipitation assay using crude microsomal preparations (r = 0.76; P less than 0.001). Relating the results of these assays to the reactivities of patients' sera with thyroid microsomes in immunoblot under nonreducing and reducing conditions, discordant results could be observed in a few cases. Further analysis of these data indicate a heterogeneous nature of anti-TPO-Abs, which react with at least two antigenic domains of the TPO molecule. The comparative analysis of patients with hyperthyroid Graves' disease, patients with Graves' disease in clinical remission, and patients with hypothyroid Hashimoto's thyroiditis revealed no significant differences in the antibody spectrum. When evaluating the direct influence of anti-TPO-Abs on the activity of TPO under a rigorous methodological approach, we found no significant inhibition of the enzymatic activity by any of the sera investigated from patients with autoimmune thyroid disease compared to that in sera from normal controls. In conclusion, the data indicate a heterogeneous nature of anti-TPO-Abs. The spectrum of antigenic epitopes recognized by anti-TPO-Abs seems not to be significantly different in the various forms and stages of autoimmune thyroid disease. The lack of an inhibitory effect of autoantibodies on TPO activity argues against direct binding of autoantibodies to the enzymatic sites of TPO and indicates that they are not important factors in producing thyroid dysfunction in autoimmune thyroid disease.
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PMID:Heterogeneity of autoantibodies against thyroid peroxidase in autoimmune thyroid disease: evidence against antibodies directly inhibiting peroxidase activity as regulatory factors in thyroid hormone metabolism. 170 46

We have studied the role of eye muscle and thyroid autoimmunity in patients with Graves' hyperthyroidism with or without ophthalmopathy in an area of relatively low iodine intake. Antibody dependent cell mediated cytotoxicity (ADCC) and complement mediated antibody dependent cytotoxicity (CMAC) against thyroid and eye muscle cells, and levels of antibodies against TSH receptor antigen and the thyroid microsomal antigen (thyroid peroxidase) were determined in three groups of patients: (1) thyrotoxic with exophthalmos (TX, n = 28), (2) thyrotoxic without ophthalmopathy (GR, n = 10), and (3) euthyroid ophthalmopathy (EU, n = 12). The thyroid glandular mass of the EU group was significantly less (P less than 0.01) compared with TX or GR. Mean (+/- SD) TSH receptor antibody (TRAb) level was 27 +/- 14% in EU which was significantly lower compared with TX (52.4 +/- 20%) and GR (59 +/- 18%). The prevalence of microsomal antibodies were similar and not significantly different in the three groups. On the other hand the prevalence of positive ADCC and CMAC tests was significantly greater, and at higher levels, in EU (ADCC THY CELLS 10.9 +/- 8.9% SL, ADCC Eye muscle = 25.9 +/- 20% SL, CMAC = 70.2 +/- 43% SL) and TX (ADCC THY CELLS = 9.3 +/- 9.2% SL, ADCC Eye muscle = 20.1 +/- 19% SL, CMAC = 62.4 +/- 30% SL) compared to GR (ADCC THY CELLS = 4.4 +/- 9.5% SL, ADCC Eye muscle = 7.7 +/- 6.7% SL, CMAC = 24.7 +/- 23% SL).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Immunologically mediated cytotoxicity against human eye muscle and thyroid cells in euthyroid and thyrotoxic Graves' ophthalmopathy. 195 9

Recently, thyroid microsomal antigen was identified as thyroid peroxidase, and thyroid microsomal antibody was found to inhibit thyroid peroxidase activity in vitro. We investigated the possibility that anti-microsomal antibody inhibits the iodination of tyrosine, in vivo. Immunoglobulin G with or without anti-microsomal antibody from hypothyroid patients with goitrous Hashimoto's thyroiditis inhibited thyroid hormone synthesis in cultured slices of normal human thyroid tissue. IgGs with anti-microsomal antibody inhibited 125I thyroidal uptake and thyroid hormone synthesis stimulated by TSH more than normal IgG did. However, the same results were obtained with IgGs without anti-microsomal antibody. This effect did not involve anti-microsomal antibody, anti-thyroglobulin antibody, TSH-binding inhibitor immunoglobulin, thyroid stimulation-blocking immunoglobulin, or the cAMP level of the thyroid tissue. The ratio of organic I to inorganic I with stimulation by TSH in slices incubated with IgG from hypothyroid patients with goitrous Hashimoto's thyroiditis or normal IgG was not significantly different, but was significantly higher in slices incubated with methylmercaptoimidazole. Therefore, IgG from hypothyroid patients with goitrous Hashimoto's thyroiditis mainly suppressed 125I thyroidal uptake, rather than inhibiting thyroid peroxidase activity. In addition, this IgG was present in the serum of 11 of the 12 hypothyroid patients with Hashimoto's thyroiditis studied. This IgG may be involved in the mechanism that causes hypothyroidism in some patients with goitrous Hashimoto's disease.
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PMID:Inhibition by immunoglobulin G of synthesis of thyroid hormone in thyroid cultures from hypothyroid patients with goitrous Hashimoto's thyroiditis. 197 65

The aim of this chapter was to present a theory or concept of autoimmune disease that, in a sense, deemphasized the importance of immunoregulatory defects but rather concentrated on defects and/or changes in a target organ that might stimulate immune responses. Defects in immune regulation were not discussed because there is little evidence that generalized defects in immunoregulation occur in patients with autoimmune thyroid disease (38). There is some evidence of decreased numbers of thyroid-antigen-specific T-suppressor cells in patients with autoimmune thyroid disease; however, this has been detected only after the appearance of frank disease (38). Thus a reduction of T-suppressor cells specific for the thyroid microsomal antigen at a time when the immune system is responding vigorously to that antigen is to be expected and cannot a priori be assumed to be the reason for the immune response. One other reason for questioning the role of defective antigen-specific T-suppressor cells as an initiating event is that individual patients with autoimmune thyroid disease produce antibodies to a variety of unrelated thyroid antigens (Tg, microsomal antigen, which is now known to be thyroid peroxidase, TSH receptor, and others) (39). One would have to assume that the majority of thyroid patients spontaneously lose several unrelated clones of specific suppressor T cells. An alternative scenario of events in the pathogenesis of autoimmune disease is as follows: An environmental agent, whether it be iodide, alone, or in combination with high TSH, or a virus causes damage to the thyroid gland. The iodide-induced damage, perhaps mediated by hydroxyl radicals (40), is more severe and/or prolonged if the gland has a defect in iodide organification or perhaps, as seen in some susceptible chicken strains, partially autonomous thyroid function. As a result of the damage, leukocytes migrate into the gland. Once leukocytes arrive, a number of interesting phenomena occur. First, monocytes may secrete IL-1, which is directly cytotoxic for endocrine cells (41) and provides an accessory signal to T-helper cells. Second, T and B cells migrate into the damaged gland and into the follicles, where at least two of the important thyroid antigens are located, thyroglobulin and thyroid peroxidase. These two proteins are highly immunogenic: the thyroglobulin due to its increased iodine content and the thyroid peroxidase because it is a membrane-bound antigen sequestered in thyroid follicles. Third, the T cells, once activated, provide help to B cells and secrete gamma interferon, which induces the expression of class II MHC antigens on the thyroid epithelial cells (42).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Iodine in autoimmune thyroiditis. 215 Nov 26

The inheritance of autoantibodies to thyroglobulin and thyroid peroxidase (thyroid microsomal antigen) has been reevaluated with newly developed ultrasensitive assays that depend on the direct interaction between antibody and radiolabeled antigen. In a study of 16 families with autoimmune thyroid disease, autoantibodies to thyroid peroxidase (TPO) were found to be inherited as a dominant Mendelian trait in females with reduced penetrance in males. Similar results were obtained with thyroglobulin (Tg) autoantibodies. Genetic linkage analysis of the loci for TPO and Tg autoantibodies with 28 polymorphic serological markers (including HLA and Gm allotypes) was carried out in 9 families. LOD scores for some serological markers (such as Gm) were uninformative, but linkage with other markers, notably the HLA antigens -A, B, -DR, -DQ, and BF on chromosome 6, could be excluded. Further studies using a comprehensive panel of gene probes to analyze DNA from families with autoimmune thyroid disease should permit the localization of the gene cluster responsible for regulating the ability to produce autoantibodies to TPO and Tg in man.
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PMID:Autosomal dominant transmission of autoantibodies to thyroglobulin and thyroid peroxidase. 230 28

We have isolated highly purified thyroid peroxidase (TPO) from human thyroid tissue to study further the relationship between TPO and the thyroid microsomal antigen that elicits the production of microsomal autoantibodies in patients with autoimmune thyroid disease. Serum samples were obtained from 24 patients with suspected autoimmune thyroid disease, and from 7 normal subjects. Microsomal autoantibodies in the patient sera, as determined by the microsomal hemagglutination assay (MCHA), varied between 1:100 and 1:102,400. Antithyroglobulin antibodies, however, were very low (less than 1:100). Binding of serum autoantibodies to purified human TPO, as determined by enzyme-linked immunosorbent assay, correlated fairly well with MCHA titers (r = 0.72; P less than 0.001). An immunoblot procedure was developed to study the binding of serum antibodies to the major active fragment of TPO (93 kDa), after sodium dodecyl sulfate-polyacrylamide gel electrophoresis under both reducing and nonreducing conditions. Binding under both conditions correlated very well with MCHA titers (r = 0.80-0.84; P less than 0.001). Studies were performed to determine the inhibitory effect of patient serum on the enzymatic activity of purified human TPO. A marked inhibitory effect on guaiacol activity was observed when TPO was preincubated with as little as 10 microL high titer serum. There was a significant correlation (r = 0.47; P less than 0.01) between MCHA titer and inhibitory effect. The addition of 2 micrograms purified human TPO completely or almost completely inhibited the binding of serum antibodies to thyroid microsomes (enzyme-linked immunosorbent assay) in 10 of 11 patient sera with high MCHA titers (1:25,600 or greater).
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PMID:Studies with purified human thyroid peroxidase and thyroid microsomal autoantibodies. 230 29

A detailed examination of the epitopes recognized by autoantibodies (aAbs) to the thyroid microsomal antigen/thyroid peroxidase (TMA/TPO) in patients with thyroid autoimmune disease has been made using a combination of immunochemical and enzymatic techniques. Our results demonstrate the the autoimmune response to thyroid microsomal antigen/thyroid peroxidase (TMA/TPO) is multifocal and far more heterogeneous than hitherto recognized. By immunoblotting with aAbs, antigenic determinants on the TMA/TPO have been recognized that are either susceptible to polypeptide denaturation and/or sensitive to the effects of reducing agents. Furthermore, these aAbs can inhibit, to varying degrees, the enzymatic activity of solubilized preparations of TPO in microsomes, as ascertained by peroxidation of guaiacol and iodide. A large proportion of the autoimmune response is directed to the guaiacol peroxidation site. The data support the view that the autoimmune reactivity to the TMA/TPO is a specific polyclonal response with a minimum of six distinct, independent determinants that are recognized by aAbs.
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PMID:Autoantibodies to the thyroid microsomal/thyroid peroxidase antigen are polyclonal and directed to several distinct antigenic sites. 245 86

Previous studies carried out by screening a lambda gt11 human thyroid cDNA library with serum samples from selected patients with Hashimoto's thyroiditis and a polyclonal antibody to porcine thyroid peroxidase (TPO) confirmed, at the molecular level, that TPO is a major component of the thyroid microsomal antigen (M). That investigation led to the isolation of a clone (C2) which encodes an 85-amino acid segment of TPO and harbors a major epitope recognized by serum from several patients with autoimmune thyroid disease that contained anti-M autoantibodies (MAb). In this study, C2 antigen that was produced as a beta-galactosidase fusion protein was used to establish an enzyme-linked immunoabsorbent assay for the detection of anti-C2 autoantibodies (C2Ab). C2Ab then were assayed in 191 patients with different autoimmune and nonautoimmune thyroid disorders, and 50 patients with nonthyroidal autoimmune diseases. The results were compared with the titers of anti-TPO antibodies (TPOAb; as detected by monoclonal antibody-assisted RIA) and MAb (as detected by passive hemagglutination). Positive C2Ab was found in the serum of 85 of 136 (63%) patients whose serum contained TPOAb and/or MAb. A significant positive correlation was found between the levels of C2Ab and those of TPOAb (r = 0.76; P less than 0.001) or MAb (r = 0.69; P less than 0.001), which was independent of the type of underlying autoimmune thyroid disorder. Low levels of C2Ab also were found in 10 of 105 (9%) serum samples that did not contain TPOAb. Western blot analysis carried out on the latter samples showed that in 2 samples the apparent C2Ab reactivity was due to the presence of antibodies reacting with beta-galactosidase. In conclusion, we confirmed the validity of screening lambda gt11 cDNA human thyroid libraries to better characterize thyroid autoantigens and demonstrated the feasibility of using recombinant proteins to establish diagnostic assays for autoantibodies.
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PMID:Antibodies to human thyroid peroxidase in autoimmune thyroid disease: studies with a cloned recombinant complementary deoxyribonucleic acid epitope. 247 Jul 71


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