Autoantibody stimulation of the human thyrotropin receptor: regulation of adenylate cyclase activity, thyroglobulin and thyroid peroxidase mRNA levels in primary cultures of Graves' thyroid tissue

ASSOCIATION OF SERUM AUTO-ANTIBODIES AND THYROID FUNCTION TEST IN PATIENTS WITH NON-NEOPLASTIC THYROID DISEASES IN SHENDI LOCALITY, SUDAN

Background:  Thyroid disorders are the most second endocrine problem after diabetes mellitus in society. Environmental, immunological, and genetic factors   lead to the development of thyroid disorders.  Objectives: The study intended to evaluate the role of thyroid antibodies and hormones in the diagnosis of thyroid diseases, as well as the prevalence of thyroid antibodies in patients having thyroid disorders living   in Shendi locality. Study design: The current research was prospective, case - control, hospital-based study carried out from 2013-2017, in El-Mek Nimir Uiversity Hospital in Shendi town- Northern Sudan.-. River Nile State. Two hundred and eighty-three (283) participants selected randomly as study population, of whom Hundred and eleven (111) patients with hypothyroidism; Seventy-two (72) patients with hyperthyroidism; Hundred (100) healthy normal subjects as control group.  Participants were recruited from outpatient clinics in El-Mek Nimir Uiversity Hospital in Shendi Thyroid hormones profile (TSH, T4, T3, fT3, and fT4) and Thyroid antibodies (Anti-thyroid peroxidase and antithyroglobulin) were measured. Results: The study revealed that (60.7%) had hypothyroidism, (39.3%) had hyperthyroidism, (91.9%) of hypothyroidism were female, and only (8.1%) were male, while (84.7%) of hyperthyroidism were female while male represented only (15.3%) of them. The current study revealed that 107 of the case group (58.5%) were positive when evaluated for thyroid peroxidase antibodies (TPO Ab), with level more than (40.0 IU/ml).  72 (64.9%) of them were hypothyroidism, whereas a 35 (48.6%) of them were hyperthyroidism. As regard Thyroglobulin antibodies (Tg Ab), 73 (39.9%) of the case studied were positive, 51 (69.9%) of them were hypothyroidism, and 22 (30.1%) of them were hyperthyroidism. The study also revealed statistically significant positive correlation between the presence of TPO Ab and the values of fT3

Autoimmune thyroid disorders

Purpose of Review. Studies have been published in the field of autoimmune thyroid diseases since January 2005. The review is organized into areas of etiology, autoimmune features, autoantibodies, mechanism of thyroid cell injury, B-cell responses, and T-cell responses. Also it reviews the diagnosis and the relationship between autoimmune thyroid disease, neoplasm, and kidney disorders. Recent Findings. Autoimmune thyroid diseases have been reported in people living in different parts of the world including North America, Europe, Baalkans, Asia, Middle East, South America, and Africa though the reported figures do not fully reflect the number of people infected per year. Cases are unrecognized due to inaccurate diagnosis and hence are treated as other diseases. However, the most recent studies have shown that the human autoimmune thyroid diseases (AITDs) affect up to 5% of the general population and are seen mostly in women between 30 and 50 years. Summary. Autoimmune thyroid disease is the result of a complex interaction between genetic and environmental factors. Overall, this review has expanded our understanding of the mechanism involved in pathogenesis of AITD and the relationship between autoimmune thyroid disease, neoplasm, and kidney disease. It has opened new lines of investigations that will ultimately result in a better clinical practice.

Autoimmune thyroid disorders-An update

BACKGROUND

Autoimmune thyroid disease (AITD), a common organ specific autoimmune disorder is seen mostly in women between 30-50 yrs of age. Thyroid autoimmunity can cause several forms of thyroiditis ranging from hypothyroidism (Hashimoto's thyroiditis) to hyperthyroidism (Graves'Disease). Prevalence rate of autoimmune mediated hypothyroidism is about 0.8 per 100 and 95% among them are women. Graves' disease is about one tenth as common as hypothyroidism and tends to occur more in younger individuals. Both these disorders share many immunologic features and the disease may progress from one state to other as the autoimmune process changes. Genetic, environmental and endogenous factors are responsible for initiation of thyroid autoimmunity. At present the only confirmed genetic factor lies in HLA complex (HLA DR-3) and the T cell regulatory gene (CTLA 4). A number of environmental factors like viral infection, smoking, stress & iodine intake are associated with the disease progression. The development of antibodies to thyroid peroxidase (TPO) thyroglobulin (TG) and Thyroid stimulating hormone receptor (TSH R) is the main hallmark of AITD. Circulating T Lymphocytes are increased in AITD and thyroid gland is infiltrated with CD4+ and CD8+ T Cells. Wide varieties of cytokines are produced by infiltrated immune cells, which mediate cytotoxicity leading to thyroid cell destruction. Circulating antibodies to TPO and TG are measured by immunofluorescense, hemagglutination, ELISA & RIA. TSHR antibodies of Graves' disease can be measured in bioassays or indirectly in assays that detect antibody binding to the receptor.

Thyroid autoantibody profiles in ophthalmic dominant and thyroid dominant Graves' disease differ and suggest ophthalmopathy is a multiantigenic disease

BACKGROUND

Thyroid-associated ophthalmopathy (TAO) occurs in 25-50% of patients with Graves' disease (GD) and is occasionally seen in hypothyroid Hashimoto's disease or euthyroid individuals. The link between TAO and hyperthyroidism remains unclear. We hypothesized that qualitative or quantitative differences in thyroid antibodies might determine individual predisposition to these features.

METHODS

In a prospective study over 3 years, thyroid antibody levels were measured in all patients diagnosed at the Singapore National Eye Centre to have GD. These patients had no known history of thyroid disease, presented with eye complaints and diagnosis was made by an ophthalmologist. A total of 31 patients were identified. Antibody levels were compared against 71 consecutive patients referred to a thyroid clinic (TC) for thyrotoxic symptoms in whom the diagnosis of GD was confirmed by a thyroidologist.

FINDINGS

Thyroid autoantibody profiles of patients diagnosed at the ophthalmology centre (OC) and TC differed markedly. OC patients had significantly higher TSI (P = 0.003) but lower TPOAb (P = 0.008) and TgAb levels (P < 0.001). In contrast, TC patients had higher free T4 (P = 0.048) and higher TBII levels (P < 0.001). Antibody levels were correlated with four parameters of ophthalmopathy--chronic lid retraction, lid swelling, proptosis and extraocular myopathy (EOM). On univariate logistic regression analysis, TSI was a positive predictor and TPOAb and TgAb negative predictors of all four features. In the absence of TgAb, the odds ratios for individual TAO features ranged from 2.8 to 7.9, with corresponding values of 3.9-10.2 when TPOAb was absent. In stepwise logistic regression analysis, TSI was the strongest independent predictor of all aspects studied: lid fullness P = 0.001, proptosis P = 0.001, lid retraction P = 0.008, EOM P = 0.009. Among smokers, TPOAb were significantly lower (P = 0.044) but no association between smoking and the other antibodies was observed.

INTERPRETATION

The study demonstrates markedly different thyroid autoantibody profiles in newly diagnosed GD patients with ophthalmic dominant as opposed to thyroid dominant features. It suggests differing antibody patterns are associated with predisposition to hyperthyroidism and orbitopathy. In addition, an association between smoking and low TPOAb levels was noted.

A method for identification of the peptides that bind to a clone of thyroid-stimulating antibodies in the serum of Graves' disease patients

A method was developed for identification of the peptide sequences that bind to thyroid-stimulating antibody (TSAb) clones from phage-displayed peptide library. Immunoglobulin G (IgG) was purified from the serum of a Graves' disease patient that stimulates the synthesis of cAMP in the cells that express TSH receptor (TSHR). The IgG that binds to TSHR was purified by an affinity column packed with the resin cross-linked with the extracellular domain of human TSHR. The receptor-binding IgG was then mixed with phages that display linear or cyclic peptides at the end of tail protein pIII. The bound phages were eluted with acidic glycine after extensive washing. From sequencing of the pIII gene of the bound phages, one can deduce the sequences of the peptides that bind to the receptor-binding IgG. Each peptide sequence was then tested for inhibition of the synthesis of cAMP from thyroid cells induced by the serum of a Graves' patient. In this way, one can obtain the peptides that bind to a clone of TSAb. We obtained a peptide sequence that inhibits the action of TSAb at an extremely low concentration (<10(-14) M). Such a peptide will be useful for various studies on TSAb.

Identification of the peptides that inhibit the function of human monoclonal thyroid-stimulating antibodies from phage-displayed peptide library

Autoantibodies against TSH receptor (TSHR) are known to be involved in the occurrence of Graves' disease. It is obvious that mapping of epitopes of the autoantibodies found in the patients with Graves' disease is an important step in elucidating possible mechanism of generation of the autoantibodies against TSHR as well as in developing effective diagnostic and therapeutic approaches for Graves' disease. In this report we have identified the peptide sequences that bind to two human monoclonal thyroid-stimulating antibodies (mTSAbs; B6B7 and 101-2) from a disulfide-constrained phage-displayed peptide library. The peptides selected by three rounds of biopanning showed half-maximal inhibitory activities for cAMP synthesis induced by mTSAbs at about 0.1 micromol/L. SPWTLGA and TQWNMQH selected for B6B7 and 101-2, respectively, show specificity for their respective antibodies. This means that different clones of mTSAbs may have different epitopes for TSHR. The IgG of the patient from whom B6B7 was derived binds with specificity to the respective immobilized peptide in an enzyme-linked immunosorbant assay format, and its cAMP generation was also inhibited by selected peptide. It may be possible that the epitopes of TSAbs identified from the phage-displayed peptide library could be used for the classification of different clones of TSAbs present in patients with Graves' disease and for development of drugs to treat Graves' disease.

Different bioactivities of human thyrotropin receptors with different signal peptides

For investigation of the mechanism and pathogenesis of Graves' disease, availability of a large amount of functional human thyrotropin receptor (TSHR) capable of recognition by Graves' autoantibodies is essential. Many attempts have been made to produce the extracellular domain of TSH receptor (TSHRE) in a baculovirus expression system. However, the receptor is expressed as an insoluble form and the refolded protein is often not recognized by the autoantibodies. In this study, we found that the TSHRE expressed with its own signal peptide (VL3-RE) in insect cells is retained inside of the cells and found in both soluble and insoluble fractions in equal proportion. The signal peptide is not removed. The receptor in the soluble fraction is not recognized by either TSH or Graves' autoantibodies. The TSHRE with an insect-specific mellitin signal peptide (Mel-RE) is also retained inside of the cell and found in both the soluble and insoluble fractions in equal proportion. However, the signal peptide is removed and the receptor is recognized by the Graves' autoantibodies but not by TSH. Also, the amount of Mel-RE expressed was 5-10-fold higher than VL3-RE. The two receptor preparations apparently have the same degree of glycosylation as evidenced by the same increased mass (approximately 15 kDa) due to glycosylation. However, the two receptors have different affinity for an anion-exchange resin and different pI. Deglycosylated receptors have the same pI. This suggests that the composition of sugars may be different. Taken together, the results suggest that the two receptors are modified and folded differently by different pathways due to the presence of different signal peptides. Use of an insect-specific signal peptide is recommended for expression of TSHR that is recognized by Graves' autoantibodies in a baculovirus system.

Increased expression of the Na+/I- symporter in cultured human thyroid cells exposed to thyrotropin and in Graves' thyroid tissue

The Na+/I- symporter (NIS) is important in hormone synthesis in the thyroid gland. NIS activity, as reflected by I- uptake, was increased by TSH (1 mU/mL) or forskolin (10 mumol/L) in primary cultured human thyroid cells. Northern blot analysis revealed that incubation of these cells with TSH or forskolin for 24 h increased the abundance of NIS messenger ribonucleic acid (mRNA) 2.3- and 2.5-fold, respectively. Immunoblot analysis revealed 2.7- and 2.4-fold increases, respectively, in the amount of NIS protein after 48 h, suggesting that elevated levels of intracellular cAMP induced the expression of NIS in human thyrocytes. We then studied the levels of NIS mRNA and protein in Graves' thyroid tissue and found that the amount of NIS mRNA in thyroid tissue from individuals with Graves' disease (n = 5) was 3.8 times that in normal thyroid tissue (n = 5). The abundance of NIS mRNA was significantly correlated with that of thyroid peroxidase or thyroglobulin mRNAs, but not with that of TSH receptor mRNA, in the Graves' and normal thyroid tissue specimens. The amount of NIS protein was also increased 3.1-fold in Graves' thyroid tissue compared with that in normal thyroid tissue. The increased expression of NIS may thus contribute to the development of Graves' disease.

TSH-receptor expression and human thyroid disease: relation to clinical, endocrine, and molecular thyroid parameters

Thyrotropin receptor (TSH-R) gene expression can be positively or negatively regulated by TSH and stimulating TSH-R antibodies (TSAbs) in immortalized thyroid cell lines such as rat FRTL-5 cells. However, regulation is less clear in other mammalian cells including cultures of human thyroid cells. Additionally, it has been suggested, based on FRTL-5 cell data, that TSH-R gene negative regulation by TSH or TSAbs might be lost in Graves' disease. The present study evaluated TSH-R gene transcript levels in thyroids from patients with Graves' disease to correlate in vivo data with in vitro observations or hypotheses. TSH-R mRNA levels were characterized in a total of 66 human thyroid glands with particular concern to levels in Graves' patients. Results were related to clinical parameters, transcript levels of thyroglobulin (TG), and thyroid peroxidase (TPO), as well as transcript levels of thyroid transcription factor 1 (TTF-1) which regulates the expression of all three genes and paired box-gene 8 (Pax-8) which regulates TG and TPO gene expression. Northern blot analyses showed that TSH-R expression was significantly increased, 2.2-fold, in Graves' thyroids (p = 0.0098, n = 35) by comparison to normals (n = 6). TSH-R mRNA levels were decreased to 30% and 7% of normal levels in Hashimoto's thyroids (p = 0.0281, n = 5) and anaplastic carcinomas (p = 0.0033, n = 6), respectively. No significant changes were seen in endemic goiters (n = 8) and in thyroid autonomy (n = 6). TSH-R RNA levels were higher, 3.6-fold, in thyroids of a subgroup of Graves' patients that had not been pretreated with iodide before surgery (n = 10) by comparison to thyroids from those that had been treated before surgery, 1.7-fold (n = 25). TSH-R antibodies exhibited a nonsignificant tendency toward a negative correlation. All other clinical or endocrine parameters showed no clear relation to TSH-R mRNA levels. Pax-8 and TTF-1 transcripts were detectable in normal thyroids; however, Pax-8 expression was increased in Graves' thyroids (3.8-fold), whereas TTF-1 expression was only minimally changed in all thyroids investigated. Changes of the two did not correlate. Pax-8 expression correlated with TG and TPO expression (in all cases, p = 0.0001); TTF-1, despite its minimal change, still correlated with TG (p = 0.0471) but not with TPO expression (p = 0.0984). TTF-1, again despite its minimal changes, correlated positively with TSH-R gene expression (p = 0.0251); however, surprisingly, Pax-8, which does not regulate TSH-R gene expression, correlated even better with TSH-R transcript levels (p = 0.0001). We conclude that augmentation of TSH-R expression levels, and thus potential ligand binding sites, may indicate an important regulatory principle in the pathogenesis of autoimmune hyperthyroidism in vivo: the responsiveness of the TSH-R to TSH and TSAb induced negative regulation is lost. This increase of TSH-R expression levels is not due to an ongoing transcriptional activation of the TTF-1 gene. Pax-8, though positively correlated with TSH-R RNA levels, cannot be the factor either, because Pax-8 does not upregulate TSH-R expression. This predicts that other factors involved in TSH-R induced negative regulation are abnormal and must be searched for and evaluated.

A polyclonal T cell repertoire of V-alpha and V-beta T cell receptor gene families in intrathyroidal T lymphocytes of Graves' disease patients

We have examined for the presence or absence of T cell receptor V-alpha (VA) and V-beta (VB) gene expression in infiltrating T lymphocytes (ITL) isolated from Graves' thyroid glands in comparison to paired peripheral blood lymphocyte (PBL) samples using a qualitative based polymerase chain reaction (PCR) assay. Sequence specific oligonucleotides for VA and VB T cell receptor gene (TCR) families that had previously been validated in other studies, were used for the PCR analysis, followed by Southern blot hybridization with a labelled, internal C-region primer. A total of seven Graves' disease patients who had been treated with carbimazole were studied. T cell receptor VA and VB gene usage was examined in freshly isolated, unstimulated ITLs from five patients. A widespread usage of VA and VB gene families with 12 to 18 families being used was apparent. Use of oligo-dT or C-region priming of the mRNA prior to reverse transcription of the mRNA did not have any significant affect on the results nor did the use of whole Graves' thyroid mRNA as the starting material (n = 2) or perfusion of one gland with saline to remove as much of the contaminating blood from the gland. Our results contrast with those of Davies and colleagues who have previously shown a restricted repertoire of VA gene families in ITLs in comparison to autologous PBLs, and are much more in line with other recent reports indicating a diverse VA repertoire of the infiltrating T cells in Graves' thyroid glands derived from patients treated with anti-thyroid drugs.

Thyroid autoimmunity

Antigenic structure remains a major focus in thyroid immunology. The genes for three major thyroid antigens--thyroglobulin, thyroid peroxidase and the thyrotropin receptor--were sequenced in the late 1980's, and epitopes for antibody and T cells have been reported within the last year. In addition, new evidence for selective use of T-cell receptor V gene segments in human thyroid infiltrates may point the way to specific immunotherapy.