Comparison of LATS activity and TSH receptor antibody in Graves' disease

TSH-receptor antibody (TRAb) activity and LATS activity of Graves' sera were compared. All of 50 LATS-positive cases were TRAb positive, although only 63% of LATS-negative cases were TRAb positive. Binding of 125I-TSH to the TSH receptors was inhibited dose-dependently by LATS-immunoglobulin. However, no correlation between TRAb activity and LATS activity was observed. TRAb was positive in 2 LATS-positive cases even when the symptoms of hyperthyroidism were controlled by treatment (antithyroid or radioisotope). The positive TRAb was not changed in 4 Graves' disease patients whose LATS activity had disappeared following antithyroid treatment. These clinical studies show that TRAb is more sensitive than LATS and suggest that LATS may be one of a heterogenous population of antibodies to the TSH receptor in Graves' disease.     

Thyroid autoantigens and their relevance in the pathogenesis of thyroid autoimmunity

Humoral and cellular immune responses are both involved in autoimmune disorders of the thyroid gland. In the last five years, new substantial data have been obtained on the nature and the expression of thyroid cell surface autoantigens and on the demonstration of the functional heterogeneity of autoantibodies to the thyroid stimulating hormone (TSH) receptor. In the present report, attention will be mainly focused on recent studies carried out in our laboratory. The main autoantigens so far identified include the 'microsomal' antigen, thyroglobulin and the TSH receptor. For many years the 'microsomal' antigen (M) was considered a poorly characterized constituent of the cytoplasm of the thyroid cell. In the last five years, several lines of evidence were provided indicating that M is also well represented on the surface of the follicular cell and is identical to thyroid peroxidase (TPO). The use of anti-TPO monoclonal antibodies, presently available, have confirmed this antigenic identity. Microsomal (anti-TPO) antibodies are very useful markers of autoimmune thyroid disorders and are generally present in Hashimoto's thyroiditis, idiopathic myxedema and Graves' disease. TSH receptor antibodies (TRAb) are present in the sera of patients with Graves' disease. TRAb are able to stimulate thyroid adenylate cyclase and also to mimic TSH in its thyroid growth stimulation. Thus, these antibodies may have a pathogenetic role in goiter formation and in thyroid hyperfunction in Graves' disease. TRAb were also shown to inhibit both TSH binding to its receptor and TSH-stimulated adenylate cyclase activity. Recently TRAb, which inhibited TSH-stimulated adenylate cyclase activity, were found in idiopathic myxedema patients and may be responsible for impairment of thyroid function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of M22-based ELISA and human-TSH-receptor-based luminescence assay for the measurement of thyrotropin receptor antibodies in patients with thyroid diseases.

Previously, a new procedure for measuring serum TSH receptor autoantibodies (TRAb) was reported in which the autoantibodies inhibit binding of a human monoclonal thyroid stimulating antibody M22 to TSHR-coated ELISA plate wells (TRAb ELISA). The aim of the present study was to evaluate the clinical performance of this assay in comparison to the second generation TRAb assay (TRAb LIA) based on the recombinant human TSH-receptor and chemiluminescence technology (TRAb LIA). Among the 158 patients, 84 patients suffered from Graves' disease (GD), 34 patients had Hashimoto's thyroiditis (HT), and 40 patients had euthyroid nodular thyroid disease (NTD) without signs of autoimmunity. TRAb measurements were performed according to the manufacturer's instructions. Out of 84 GD patients, 80 (95.2%) were TRAb positive as detected by the TRAb LIA. One GD patient had TRAb values within the grey zone (1.0-1.5 IU/l). All patients with HT and NTD were negative except in 6 (8.1%) cases whose TRAb values were within the grey zone. On the basis of the recommended cutoff value (TRAb 1.0 IU/l), the TRAb ELISA found 78 of 84 (92.9%) GD patients to be TRAb positive. None of the patients with HT, but two cases (5.0%) with NTD were TRAb positive. The diagnostic sensitivity of the TRAb LIA and TRAb ELISA assays was 95.2 and 92.9%, while the specificity was 100% and 97.3%, respectively. There was a close correlation (r=0.968, p<0.0001) between both assays in 84 patients with GD. Additionally, the between-run imprecision close to the cutoff limit was assessed. The calculated between-run coefficient of variation (CV) of the TRAb ELISA was 28.2% at the recommended cutoff value of 1.0 IU/l. Due to the evaluated imprecision data we propose a higher cutoff value correlating with a between-run CV of 20% (functional assay sensitivity). Our results indicate that due to a worse imprecision the TRAb ELISA has a slightly lower sensitivity and specificity compared to the TRAb LIA assay. These findings suggest that the M22 monoclonal antibody-based TRAb ELISA is not as reliable as other second generation TRAb assays in the diagnosis of Graves' diseases.     

Thyrotropin receptor non-mediated thyroid stimulating immunoglobulin in Graves' disease.

There exists a consensus that hyperthyroid Graves' disease is caused by thyrotropin receptor (TSH-R) autoantibodies. To test the possibility that the TSH-R is the sole antigen for thyroid stimulating antibodies (TSAb), we compared bioactivities of Graves' IgGs between non-thyroid mammalian cells transfected with human TSH-R cDNA and the reference thyroid bioassay. A Graves' IgG with TSH-binding inhibitor immunoglobulin (TBII) activity (89%) markedly stimulated cAMP formation in both CHO-K1 cells transfected with TSH-R cDNA (340 microU/ml of TSH equivalent) and rat thyroid cells, FRTL-5, (410 microU/ml of TSH equivalent). In contrast, a TBII negative (-1.5%) IgG from another patient with Graves' disease showed a strong thyroid stimulating activity (87 microU/ml of TSH equivalent) when FRTL-5 cells were used for the assay. But no stimulating activity was observed in this IgG when CHO-K1 cells transfected with TSH-R cDNA were used, suggesting a possible existence of TSH-R non-mediated thyroid stimulating immunoglobulin in some cases of Graves' disease.     

An attempt to analyze various thyroid stimulators by the receptor assay using hTSH radioimmunoassay.

In an attempt to analyze thyroid stimulators in serum we developed an assay procedure using hTSH radioimmunoassay (RIA) in combination with receptor competition. The principle of this method is the determination by RIA of hTSH displaced by other thyroid stimulators from a thyroidal receptor preparation which previously bound unlabelled hTSH. Practically 4 microunits of hTSH were bound with human or bovine receptor, and then hTSH displaced by addition of test serum (0.1 ml) or samples dissolved in serum (0.1 ml) was measured by RIA. This assay can determine the thyroid stimulators other than hTSH in serum that has the displacement activity of 0.5-4.0 microunits of hTSH in the useful range, such as mU/ml level of bovine TSH or rat TSH. Cholera toxin that has the thyroid stimulating activity like TSH also showed the displacement of the bound hTSH. This assay is not applicable for the human serum with more than 5 microunits/ml of TSH, because the assay value is over estimated by the free hTSH derived from the test serum. On the other hand, eighteen sera with high LATS activity and 42 sera with negative LATS activity from patients with untreated hyperthyroidism did not show any displacement. This might be due to the lower binding activity of LATS with hTSH receptor or the lower sensitivity of this assay method. Although it is difficult to use this assay clinically because of its low sensitivity, increased TSH in animal serum can be determined by this assay. The principle of this method may be also useful for examining the receptor binding of other peptide hormone that can be determined by an RIA method.     

The thyroid "microsomal" antigen is an epitope on the thyrotropin receptor

Antimicrosomal antibodies are present in the sera of most patients with autoimmune thyroiditis, and Graves' disease. It has, in general, been difficult to separate antimicrosomal activity from that directed against the thyrotropin (TSH) receptor in Graves' IgG preparations. The "microsomal" antigen has been localized to the endoplasmic reticulum and microfollicular aspect of thyrocytes; its structure is however unknown. In an attempt to identify the thyroid microsomal antigen, we studied the interaction of Hashimoto's IgG with high microsomal antibody titre and negative for thyroglobulin with purified thyroid plasma and light microsomal membranes. We allowed Hashimoto's, Graves', and control IgGs to bind to protein blots of thyroid plasma membranes resolved on SDS-PAGE under non-reducing conditions. All seven Hashimoto's IgG at a concentration of 2 mg/ml interacted with an M approximately 197,000 polypeptide corresponding to the TSH holoreceptor. By contrast to Graves' IgG (which were positive at 1 mg/ml), however, this binding was not blocked by pretreatment of the protein blots with TSH. Normal IgGs showed no binding at concentrations of up to 2 mg/ml. Both Hashimoto's and Graves' IgG interacted with TSH-affinity column-purified receptor preparations. Two of the Hashimoto's IgGs induced adenylate cyclase activation in thyroid plasma membranes, three inhibited TSH-stimulated enzyme activation, and two were without effect. Two classes of autoantibodies, other than TSH receptor directed, were encountered; one class raised to antigens common to all seven patients and another class unique to individual patients, eg, Mr 210,000 and Mr 20,000 polypeptides. We propose that the TSH receptor has multiple epitopes (functional domains), and the one to which antimicrosomal antibody bind is likely to be spatially separated from that with which Graves' IgG and TSH interact. Differences in affinity or number of sites allows for the demonstration of Graves' IgG against a background of antimicrosomal antibody.     

Second-generation thyrotropin receptor antibodies assay and quantitative thyroid scintigraphy in autoimmune hyperthyroidism.

Graves' disease (GD) is characterized by circulating TSH receptor antibodies (TRAb), and so-called hyperthyroid autoimmune thyroiditis (H-AIT) generally shows negative TRAb results with first-generation assays. However, a positive titer was observed in up to 13% of patients with euthyroid or hypothyroid autoimmune thyroiditis (AIT) by second-generation TRAb assays, and a larger increase is expected in hyperfunctioning forms. A thyroid 99mTc-pertechnetate uptake (TcTUs) cutoff of 2% previously was shown to accurately discriminate between GD and H-AIT. Here we evaluated the relationship between second-generation TRAb assays and TcTUs in 139 patients with untreated autoimmune hyperthyroidism. An increase in TRAb levels was found in 114 of 139 patients (82%). All patients with TcTUs >2% and 66% of those with lower values had positive TRAb measurements. When the cutoff was increased to 5.9 U/l, positive TRAb occurred in 92.6% of those having higher TcTUs and in 1.4% of those with lower TcTUs. TRAb levels significantly increased in patients with TcTUs higher than 2% as compared with those having lower values, while no differences occurred in patients with TcTUs ranging from 0 to 1%, from 1.1 to 1.5%, or from 1.6 to 2%. A significant relationship between TRAb and TcTUs (as well as fT3, fT4, and thyroid volume) was found. TcTUs, fT4, fT3, and thyroid volume significantly increased in patients with positive TRAb (cutoff 1.5 U/l) compared with those testing negative. Our data indicate that a large proportion of patients with hyperthyroidism and hypoechoic thyroid, including those previously diagnosed as having H-AIT, actually have circulating TRAb. TRAb levels predicate the degree of iodine uptake (as measured by TcTUs) and thyroid hyperfunction. The role of baseline TRAb measurement by second-generation assays to predict patients' outcome needs to be further evaluated and compared with TcTUs in prospective studies.     

Stimulation of iodine organification in porcine thyroid cells by thyroid stimulators

Several Graves' sera were simultaneously assessed in a bioassay based on the ability of porcine thyroid cells to organify 125I and in a radioreceptor assay for TSH receptor binding activity. Both assay systems were sensitive to 1 mcU/ml (final concentration) of unlabelled bovine TSH. Six Graves' sera were studied in detail over a wide (0-1.0 mcl sera) dose response range in repeat determinations. Two sera exhibited parallel binding and stimulating. However, two sera revealed significant inhibition of 125I-TSH binding prior to the demonstration of stimulation and the other two sera showed stimulatory capabilities before significant binding was evident. IgG was prepared from one serum by ammonium sulphate precipitation and chromatography on Sepharose 6B and then subjected to preparative isoelectric focusing. The isoelectric distribution of the two activities were found to be identical with major peaks of activity at pl=9.5 and pl=8.5. In summary: 1) each Graves' sera exhibits different dose-response curves with respect to binding and stimulation, 2) at certain concentrations of sera, only binding or stimulation were evident, 3) neither assay was consistently more sensitive for the presence of Graves' immunoglobulins, 4) for one Graves' sera, binding and stimulation could not be separated by isoelectric focusing. These studies would suggest each Graves' immunoglobulin has inherently different characteristics in its interaction with the TSH receptor.     

A case of Graves' disease with false hyperthyrotropinemia who developed silent thyroiditis.

We encountered a patient who developed silent thyroiditis during the course of Graves' disease. The diagnosis of silent thyroiditis was made on the basis of a low thyroidal 131I uptake, no response to the thyrotropin releasing hormone (TRH) test, and subsequent hypothyroidism despite the presence of high titers of thyrotropin (TSH) receptor antibody (TRAb) and thyroid stimulating antibody (TSAb). The patient, in addition, had a discrepancy between serum TSH and thyroid hormone values. This was due to the presence of interfering substances that react to mouse IgG in the sera since serum TSH levels were decreased in a dose dependent manner by the addition of increasing amounts of mouse IgG to the sera. It should therefore be noted that silent thyroiditis can develop in patients with Graves' disease. Furthermore, clinicians should be aware that two-site immunoassay kits that use mouse monoclonal antibodies are subject to interference by some substances, possibly antibodies which react to mouse IgG.     

Activity of thyroid stimulating antibody and thyroid stimulation blocking antibody determined by radioiodine uptake into FRTL-5 cells

To investigate the pathophysiology of patients with autoimmune thyroid diseases, we measured serum thyroid stimulating antibody (TSAb) activity and thyroid stimulation blocking antibody (TSBAb) activity by determining the radioiodine (125I) uptake into FRTL-5 cells. FRTL-5 cells were pre-incubated for seven days with 5H medium and then incubated for 48 hours with patients' crude IgG prepared by polyethylene glycol precipitation. In order to measure TSBAb, 10 microU/ml TSH was also added. 125I was added one hour before the end of the 48 hour incubation period. After the incubation, the medium was aspirated, and the radioactivity in the cells was counted. In patients with untreated hyperthyroid Graves' disease, TSAb was detectable in 18 of 20 patients, the detectability being 90%, and activity showed a statistically significant positive correlation with TSAb activity determined by c-AMP accumulation. Out of 41 patients with hypothyroidism, TSBAb determined by 125I uptake was positive in six cases, the detectability being 14.6%. The inhibition of 125I uptake by one of these six IgGs was suggested to be at the TSH receptor level because it inhibited TSH induced c-AMP accumulation and showed positive thyrotropin binding inhibitor immunoglobulin (TBI I) activity, but did not inhibit the forskolin- and (Bu)2cAMP-induced 125I uptake. Inhibition of another IgG was suggested at the post-receptor level because it did not inhibit TSH induced cAMP accumulation and showed negative TBI I activity, but inhibited forskolin- and (Bu)2cAMP-induced 125I uptake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Similar triiodothyronine releasing activity of thyroid stimulating antibodies in human and porcine thyroid slices

In an approach to addressing species specificity of thyroid stimulating antibodies (TSAb) stimulation of T3 release by Graves' sera was comparatively studied in human and porcine thyroid slices. A high sensitivity and specificity was found for the T3 bioassay independently on the use of human or porcine thyroid. Moreover, activity indices of the individual sera in both tissues were significantly correlated to each other and to circulating hormone levels in untreated disease. In conclusion, we suppose a lack of functionally relevant differences between target antigens, brought about probably by the TSH receptor itself and other membrane components, in human and porcine thyroid. Thus, for clinically applicable T3 releasing bioassay porcine thyroid may be alternatively used. In addition, this bioassay renders the advantage of reflecting the activity of disease.     

Relationship among thyrotropin (TSH), thyroid stimulating immunoglobulins, and results of triiodothyronine (T3) suppression test in patients with Graves' disease

To investigate the relationship between TSH and abnormal thyroid stimulator(s) in patients with hyperthyroid Graves' disease in whom normal thyroid hormone levels in the serum were maintained by antithyroid drug therapy and in patients with euthyroid Graves' disease, determinations were made of the TSH concentration, action of thyroid stimulating immunoglobulins (TSAb and TBII), and T3 suppression. Out of thirty-three patients with hyperthyroid Graves' disease, twelve patients with subnormal TSH levels were all non-suppressible according to the T3 suppression test results and the detectability of TSAb and/or TBII was as high as 75%. In three out of five patients with euthyroid Graves' disease, the serum TSH level was subnormal. All three showed non-suppressibility in the T3 suppression test and positive action of either TSAb or TBII. One of them became clinically thyrotoxic when the TSAb activity was further increased and TBII became positive, and was therefore diagnosed as having hyperthyroid Graves' disease. The present findings suggest that there are still abnormal thyroid stimulator(s) in patients with hyperthyroid Graves' disease who have low TSH, even if their thyroid hormone concentrations remain normal. Moreover, it is likely that some of the patients with euthyroid Graves' disease are actually in a state of subclinical hyperthyroidism because of the presence of abnormal thyroid stimulator(s).     

Demonstration by immunoblotting of heterogeneity in the autoantibody response directed against fat cells in Graves' disease

Guinea pig fat cell membranes (FCM) have been widely used in preference to thyroid membranes as a source of TSH receptors to investigate TSH receptor antibodies in Graves' disease, because FCM are ostensibly free of other thyroid antigens. However, by FCM immunoblotting we have found: 8 of 10 normal sera bound to determinants at 38 and 190 kDa; 17 other determinants were recognised by 60% of Graves' or Hashimoto sera and by 20% of normal sera; three determinants at 65-90 kDa were recognised by 5 of 13 Graves' but by none of the normal or Hashimoto sera; and none of the determinants recognised appeared to be related to the TSH receptor.     

TSBAb (TSH-stimulation blocking antibody) and TSAb (thyroid stimulating antibody) in TSBAb-positive patients with hypothyroidism and Graves' patients with hyperthyroidism.

There are two types of TSH receptor antibodies (TRAb); thyroid stimulating antibody (TSAb) and TSH-stimulation blocking antibody (TSBAb). TSAb causes Graves' hyperthyroidism. TSBAb causes hypothyroidism. Both TSAb and TSBAb block TSH-binding to thyroid cells as TSH receptor antibodies (TRAb). TSBAb-positive patients with hypothyroidism and Graves' patients with hyperthyroidism may have both TSBAb and TSAb. We studied TSBAb and TSAb in 43 TSBAb-positive patients with hypothyroidism and in 55 untreated Graves' patients with hyperthyroidism. TSBAb-activities were expressed as percentage inhibition of bovine (b) TSH-stimulated cAMP production by test IgG. Two formulas were used to calculate TSBAb-activities; TSBAb-A (%) = [1 - (c - b)/(a - b)] x 100 and TSBAb-B (%) = [1 - (c - d)/(a - b)] x 100, where a: cAMP generated in the presence of normal IgG and bTSH, b: cAMP generated in the presence of normal IgG, c: cAMP generated in the presence of test IgG and bTSH, and d: cAMP generated in the presence of test IgG. TSAb (%) = [d/b] x 100. All of the 43 TSBAb-positive patients with hypothyroidism had strongly positive TSBAb-A and -B. Some of them had weakly positive TSAb (<240%). All 55 untreated Graves' patients had positive TSAb (205-2509%). Some of them had both TSAb and TSBAb. TSBAb-positive patients with hypothyroidism had a limited distribution of TSBAb- and TSAb-activities (TSBAb-A + 75 - + 103%, TSBAb-B + 87 - + 106%, TSAb 92-240%), but Graves' patients with hyperthyroidsim had a wide distribution of TSAb- and TSBAb-activities (TSAb 205-2509%, TSBAb-A - 158 - + 43%, TSBAb-B - 14 - + 164%). TSBAb-A ignores TSAb activity in serum, and might give low TSBAb activity. However, TSBAb-A clearly differentiates TSBAb-positive patients with hypothyroidism from Graves' patients with hyperthyroidism; thus, we favor TSBAb-A over TSBAb-B. Some of TSBAb-positive patients with hypothyroidism and Graves' patients with hyperthyroidism have both TSBAb and TSAb.     

Continuously increasing sensitivity over three generations of TSH receptor autoantibody assays

Thyroid stimulating hormone (TSH) receptor (TSHR) antibodies (TRAb) are the hallmarks in serological diagnosis of Graves' disease (GD, autoimmune hyperthyroidism). In the 1980s, the first generation liquid-phase TRAb assay with detergent solubilized porcine TSHR was introduced into routine thyroid serology and proved to be highly specific for GD, albeit with moderate sensitivity. In the 1990 s, second generation solid-phase TRAb assays with immobilized porcine or recombinant human TSHR became available, and were clearly more sensitive for Graves' disease without loss of specificity. Recently, third generation TRAb assays have been developed, in which the human thyroid stimulating monoclonal antibody M22 replaces bovine TSH as the competing reagent for TRAb binding to TSHR. Again, an improvement in functional sensitivity was reported for this latest assay generation. To investigate the analytical (aas) and functional assay sensitivity (fas) over 3 generations of TRAb assays, pooled serum samples from patients with GD were measured 10-fold in different assay lots over a few months. The 20% inter-assay coefficients of variation (CV) were calculated and compared taking into account the different calibrations of the assay generations. The fas continuously increased from about 8 U/l of MRC B65/122 in liquid phase TRAb assays, to about 1.0 IU/l (NIBSC 90/672) in TSH based solid phase TRAb assays and to about 0.3 IU/l (NIBSC 90/672) in the M22 based TRAb assay finally. In conclusion, the fas of TRAb measurements has been improved continuously over the last 3 decades.     

Similarity and dissimilarity between clinical and laboratory findings, especially anti-thyrotropin receptor antibody in ophthalmic Graves' disease without persistent hyperthyroidism and hyperthyroid Graves' disease

The aim of this study was to investigate thyroid states, significance of anti-TSH receptor antibodies and the clinical courses of patients with euthyroid Graves' ophthalmopathy. The clinical and laboratory finding of 30 patients with euthyroid Graves' ophthalmopathy were briefly as follows: 1) normal sized thyroid or small goiter; 2) negative or weakly positive thyrotropin binding inhibitor immunoglobulin (TBII); 3) normal thyroid [99 m-Tc] pertechnetate uptake; and 4) frequent observations of low serum TSH values. Besides TBII, thyroid stimulating antibody (TSAb) was measured under low salt and isotonic conditions using FRTL-5 rat thyroid cells. Both TBII and TSAb titers were lower in euthyroid Graves' ophthalmopathy than in hyperthyroid Graves' disease. Serum TSH levels frequently became low in patients considered as euthyroid upon the first examination as well as in Graves' patients in remission, reflecting preceding or mild hyperthyroidism. In follow-up studies, these patients with mildly elevated thyroid hormone levels and low TSH levels seldom reached a state of persistent hyperthyroidism, when TBII was negative or only weakly positive.     

Pathophysiological role of thyroid blocking antibody in patients with primary hypothyroidism

The pathophysiological role of thyroid blocking antibody (TBAb) in patients with adult primary hypothyroidism and the mechanism of TBAb action were studied. A sensitive bioassay for TBAb, which inhibits the TSH-induced cAMP accumulation, was established using normal human thyroid cells in culture. Thirty-four patients with primary hypothyroidism consisting of 17 goitrous and 17 non-goitrous patients were examined. Two out of 17 goitrous patients (11.8%) and three out of 17 non-goitrous patients (17.6%) were TBAb positive. There were no significant differences between TBAb positive and negative patients in terms of the severity of hypothyroidism or the titers of MCHA or TGHA. Four out of the five TBAb-positive IgGs had strongly positive thyrotropin binding inhibitor immunoglobulin activities. All five TBAb-positive IgGs inhibited the cAMP increase induced by Graves' IgG, but did not affect the action of either prostaglandin E1 or cholera toxin. However, three TBAb positive IgG also inhibited the cAMP increase induced by forskolin. These findings indicate: 1) TBAb is present in hypothyroid patients with autoimmune thyroiditis and TBAb may play a role in the pathophysiology of these patients. 2) TBAb may inhibit the action of TSH not only at the level of the TSH receptor, but also at a different site from the TSH receptor.     

Possible binding site of thyrotropin binding inhibitor immunoglobulin (TBII) on the thyrotropin (TSH) receptor, which is different from TSH binding site

A synthetic decapeptide, P-194, which has the sequence No. 103 to 111 of hTSH receptor structure with an additional N-terminal tyrosine, did not bind TSH nor affected its receptor binding and thyroid stimulating activity. Preincubation of P-194 with sera from thyroid patients caused a significant decrease in TBII activity in almost all 12 TBII positive sera and an increase of thyroid stimulating activity in 3 of 7 Graves' IgG studied. In addition, [125I] P-194 bound to serum IgG fraction from thyroid patients with a positive correlation with TBII (N = 35, r = 0.509, p less than 0.01). The P-194 portion may be, at least a part of, TBII binding site distinct from the TSH binding site on the TSH receptor.     

Effects of Long-acting Thyroid Stimulator (LATS) and LATS Protector on Human Thyroid Adenyl Cyclase Activity

The long-acting thyroid stimulator (LATS) has been thought to be responsible for the hyperthyroidism of Graves''s disease. It is detected by its effect on the mouse thyroid gland but cannot be found in all patients with hyperthyroidism. In an attempt to clarify the problem of LATS-negative hyperthyroidism, serum was obtained from untreated patients and its effect in vitro on human thyroid tissue examined, using the activation of adenyl cyclase as a measure of stimulation. Human thyroid adenyl cyclase was activated by both thyroid-stimulating hormone (TSH) and LATS. Thyroid tissue obtained from patients with Graves''s disease was relatively less responsive to LATS than was non-toxic thyroid tissue. Of the 24 samples studied five contained LATS and all of these activated adenyl cyclase. The presence of LATS protector in LATS-negative hyperthyroid patients was confirmed but LATS-negative sera had no effect on human thyroid adenyl cyclase activity.