Clinical Usefulness oftsh Receptor Autoantibody Using Different Assay Systems

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1 Clinical Usefulness oftsh Receptor Autoantibody Using Different Assay Systems Yukari MIMURA, Toshio OGURA* and Fumio OTSUKA** Abstract Thyroid stimulating hormone receptor antibody (TRAb) plays an important role in Graves' disease (GD). A second-generation measurement system has been developed and we have gotten a benefit by the system clinically. In this study, we determined 4 kinds of TRAb in 42 GD patients using the current and second-generation measurement systems to investigate the differences between them. The secondgeneration measurement system exhibited higher positive rates and inhibition rates of thyroid stimulating hormone (TSH) binding than those of the current system. Furthermore, 42 patients with GD were classified into 4 groups by GD activity. The actual values of all TRAbs and positive rates exhibited a tendency to increase significantly with GD activity. Of significance, 2 TRAbs in the second-generation measurement system exhibited high positive rates. However, all actual values of patients did not necessarily agree with these tendencies. The values of TRAb-human detecting anti-human TSH receptors at an approximate cut-off value reflected GD activity more accurately than those of TRAb-CT detecting anti-porcine TSH receptor. This suggests the possibility of specific differences between TSH receptors and further studies are required to further examine these effects. Keywords: Graves' disease, human-trab, TSAb Introduction The TSH receptor is one of the major autoantigens in autoimmune thyroid disease and the pathogenetic role of autoantibodies to the TSH receptor (TRAb) in sera from patients with autoimmune hyperthyroidism has been clearly established l ). Historically, there are two established methods for the detection of TRAb 2 ). One is the classical radioreceptor assay of Smith 3 ), based on the porcine TSH receptor, where autoantibodies and labeled bovine TSH compete for the binding sites of the receptor. The other method is based on the ability of some autoantibodies similar to TSH to induce the second messenger camp. These bioassays are able to distinguish between stimulating or blocking autoantibodies, based on their biological activity to either enhance or inhibit the production of camp4). Although other detection systems have been described, such as autoantibody detection by FACS5), immunocytochemistry6), or imrnunoprecipitation7), these methods are still in an experimental state Clinical Usefulness of TSH Receptor Autoantibody Using Different Assay Systems Yukari MIMURA, Toshio OGURA * and Fumio OTSUKA * * Division of Developmental Studies and Support, Okayama University Graduate School of Education, * Health and Medical Center, Okayama University, * * Department of Medicine and Clinical Science, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences Division of Developmental Studies and Support, Okayama University Graduate School of Education Tsushima-naka, Kita-ku, Okayama city

2 Yukari MIMURA, Toshio OGURA, and Fumio OTSUKA and are not available for routine commercial use. In a recent report, Costagliola and co-workers 8 ) demonstrate a second generation TSH binding inhibitory assay using the human recombinant TSH receptor with a significant gain in sensitivity compared to the conventional porcine antigen-based system. A new coatedtube radioreceptor assay for measurement of TRAb using porcine TSH receptor has also recently been developed 9J These assays have been reported to exhibit high sensitivity in untreated Graves' disease (GD) patients without loss of specificity in healthy individuals 8. 9 ). However, the usefulness in GD with various clinical states remains controversial. Then the aim of this study was to evaluate the TRAb assay for various clinical states of GD. Subjects and methods Patients Serum samples from 42 patients with GD were examined (mean age, 47.7 year old [range; 17-82]; 11 male and 31 female). These patients attended our thyroid clinic from September to October 02. Among them, 5 were untreated GD and others were GD that had been treated for months (88.4 ± 15.8, mean ± SD). TSH ATD Dosp Change of TSH TSAb Group I ] [ Group II I [Group III I [Group IV I Figure 1. according to TSH, ATD dose, change of TSH, and TSAb. Table 1. Characteristic features in the patient groups. Group n MJF Age (years) TSH (pu/ml) IT3 (pglml) I 12 1/ ± 4.6 <0.01 ± ± 1.25 II 15 6/ ± ± ± 0.16 III 8 4/ ± ± ± 0.26 IV 7 0/ ± ± ± 0.08 Twenty-nine patients had taken thiamazole (MMI) and 8 patients had taken propilthiouracil (PTU). Patients were grouped according to their state of GD, which was determined by the serum TSH level, dose of antithyroid drug (ATD) etc. (Fig 1). Briefly, all patients were initially divided according to their serum TSH levels, and patients whose TSH were suppressed to the undetectable range, belonged to Group 1. Patients with detectable TSH levels were then sub-divided according to the daily dose of ATD, and if they took over 3 tablet of ATD (over 15mglday MMI or 150mglday PTU), they belonged Group II. The change of serum TSH (LlTSH) was then compared between the last and present data. Those patients with negative!'>tsh values also belonged to Group II. Lastly, those patients positive or negative for TSAb were sub-divided into Groups III or IV, respectively. The groups are summarized in Table 1. Patients' samples were collected at the department of endocrinology according to the institutional guidelines for ethical conduct. All samples were frozen immediately, free T3, free T4 and TSH were measured by the ECLIA assay system simultaneously, and stored at - C for further assays. TRAb detection We measured anti-tsh receptor antibodies (TRAb) from 4 different methods and thyroid stimulating antibody (TSAb). Two TRAb methods utilized the conventional radio receptor assay with the porcine TSH receptor. TRAb-D was measured using the TRAb DADE (Dade Ltd, Tokyo, Japan) and TRAb-III was measured using the Cosmic TRAb III (Cosmic Ltd, Tokyo, Japan). The results were expressed as the percentage inhibition of TSH binding. The suggested cut-off was 15% and 10%, respectively. Two additional TRAb methods IT4 (ngldl) 1.92 ± ± ± ± 0.07 TSAb (%) 356 ± ± 43 3 ± ± 21 ATD Dose (tablets/day) 4.5 ± ± ± ±

3 Clinical Usefulness of TSH Receptor Autoantibody Using Different Assay Systems utilized second-generation assays for anti TSH receptor antibodies in coated tubes. TRAb-CT and TRAb-human were used to detect the porcine and human recombinant TSH receptors, respectively. These results were also expressed as the percentage inhibition of TSH binding. The suggested cut-off was 10% for each of these procedures. Additionally, the TRAb-human assay results were expressed in international unit (IU) based on the WHO standard 21, with a cut-off of 1.0 lull, and a "gray zone" of lull. TRAb-CT and TRAb-human were measured using the Cosmic TRAb CT (Cosmic Ltd, Tokyo, Japan) and DYNOtest TRAK human (BRAHMS AG, Berlin, Germany), respectively. We also measured TSAb using the TSAb assay kits (Yamasa Co., Tokyo, Japan). The suggested cut-off for TSAb is 180%. Results Detection TRAb and correlation between d~[ferent assays The results of TRAb and positive ratio, which were determined in accordance with the recommended cut-off values, are presented in Table 2. Among the 4 TRAb assays, the data from the TRAb-CT and TRAb-human assays were higher than that of the TRAb-D (p<o.ol). The highest positive ratio was TRAb-CT with a ratio of 73.8%. The lowest positive ratio was TRAb-D. Table 2. Serum autoantibodies related to thyroid disease. Assay kit Positive ratio (%) TRAb-D (%) 9.7 ± TRAb-III (%) 24.0 ± 4.0* 57.1 TRAb-human (%) 28.7 ± 6.4** 57.1 (lull) 11.2 ± TRAb-CT (%) 35.5 ± 4.5** 73.8 Data expressed mean ± SEM. *p< 0.05, ** p< 0.01 vs TRAb-D. As shown in Figure 2, simple regression analysis demonstrated that the % inhibition in TRAb-human correlated positively with those of TRAb-CT (r=0.965, p<o.oool; Fig. 2F), TRAb-III (r=0.893, p<o.oool; Fig. 2C) and TRAb-D (r=0.842, p<o.ooo1; Fig. 2E), respectively. These findings in TRAb-CT also correlated positively with those of TRAb-III (r=0.940, p<o.oool; Fig. 2B) and TRAb-D (r=0.888, p<o.oool; Fig. 2D), respectively. The findings from TRAb-III also A B C ~100 \00 ~1 o -;J2 80 '" ~ 80 e...-,100 Q 60 0 ~ 60 ~ se 40 Eo-< U 60 R=O.940 ;:l ~ 40 Eo-< _-_. _. 40 P<O.OOOl R=O.967 Ct:: n=42 P<O.OOOl Eo-< 0 ~ 40 0 n=40 Eo-< R=O.893 P<O.OOOl n= SO so so 100 TRAb-II1 (%) TRAb-II1 (%) TRAb-II1 (%) D E F ~ so ,-..,.- e., 80,-.., so 60 tr Eo-< 60 Q '-' U Eo-< R=O.888 ~ 40 U 40 ~ P<O.OOOl..6 R=O.965 Ct:: Eo-< < n=40 P<O.OOOl Eo-< so so a SO TRAb-D (%) TRAb-human (%) TRAb-hurnan (%) Figure 2. Correlation between the two different TRAbs. (A) TRAb-O and TRAb-lIl, (8) TRAb-CT and TRAb-llI, (C) TRAb-human and TRAb-llI, (0) TRAb-CT and TRAb-D, (E) TRAb-D and TRAb-human, and (F) TRAb-CT and TRAb-human f= 0

4 Yukari MIMURA, Toshio OG URA, and Fumio OTSUKA correlated positively with that of TRAb-D ~r=0.~67, p<o.oool; Fig. 2A). All 4 TRAb assays exhibited significant correlations, and the correlations were greater between TRAb-D and TRAb-III or between TRAb-CT and TRAb- human. The strong correlation was thought to be associated with the assay method. TSAb in all patients was 274 ± 28%, and the positive ratio was 69.0%. Positive correlations were also evident between TSAb and the 4 methods of TRAb, but the correlatiuns were weak compared with that between TRAbs (r= ). The strongest correlation was that between TSAb and TRAb-hwnan. Table 3. Oiffereces in 4 assay of TRAb TRAb-D TRAb-III TRAb-human TRAb-CT «15%) «100AJ) «1.5 IUIL) l < 10%) TRAb in activity of CD The summary of the TRAb assays in 42 patients is presented in Table 3. In those patients with negative TRAb-CT (n=11), the other 3 TRAb assays were also negative. In the patients with positive TRAb-D (n=13), the uther 3 TRAb assays were also positive. TRAb-D exhibited the lowest detectiun rate, with only 10 negative patients. Among TRAb-III, TRAb-CT and TRAb-human, there were 8 patients that were positive in one or two TRAb assays. The TRAb levels are shown below Table 3. Almost all values were close to the cut-off value. Thus, if the cut-off were to be altered, the positive ratio would be different. I umber of cases negative negative nf'gative negative 11 negative negative negative positive I negative positive negativp positive T negative negative positive positive negative positive positive positive T 10 positive positive positive positive 1 14 A B c D..;.:::;.=--:"'----"-'-"--'- ~ JTRA~b-~Il~I...\..o'--"-YoL-, Gil 10 -J-l--.il '" 40 OJ II III IV * The rat io of The ratio of The ratio of The ratio of aboy<' the normal range (%) above the normal range (%) above the normal range (%) above the normal range (%) loor o I II III rv 1 II III TV Activity of (~ll *p<o.05 and **p<o.o 1vs Group I o #p...:o.05 vs Group II Figure 3. Level and positive ratio of (A) TRAb-D, (8) TRAb-lIl, (C) TRAb-CT, and (0) TRAb-human. Data are presented as the mean + SEM. *p<o.05 and **p<o.01 vs Group I. #p<o.05 vs Group II. - B8 -

5 Clinical Usefulness of TSH Receptor Autoantibody Using Different Assay Systems The various TRAbs according to GD activity are shown in Figure 3. In all TRAb assays, the levels of TRAb and positive ratio decreased gradually according to the decline in activity of GD. Groups III and IV were significant lower compared with Group I. In Group I, in which the patients were considered to be in an active state of GD, both TRAb-human and TRAb-CT exhibited a high positive ratio, 83.3%. On the other hand, in Group IV, in which patients were considered to be in a non-active state of GD, although the TRAb-D and TRAb-human exhibited a low positive ratio, 14.3%, the TRAbeT exhibited a high positive ratio, 57.1%. D-ifferencp between the TRAb assa~/s The changes of individual data of different TRAb are shown in Figure 4. The % inhibition of TRAb-D, TRAb-III and TRAb-CT increased gradually, but that of TRAb-human did not exhibit this tendency, especially around the cutoff value. We then detected and further examined 24 patients whose TRAb-III were from 0 to %. The data, which was calculated when the individual TRAb-III was 0%, are shown in Figures 5A and 5B. Although the data of TRAb--CT tended to increase, that of TRAbhuman tended to be distributed widely, from negative to positive. We analyzed the difference between TRAb-III and TRAb-CT or TRAbhuman according to the activity of GD (Fig. 5(' ,--.. e 60, c 40 ;D ffi f-<... 0 c 0-3 :0 -:W ~ ' J TRAb-O TRAb-1II ~~~i-1 cut offvajue TRAb-human TRAb CT Figure 4. Comparison of all TRAb in indibidual subject. The lines represent the cut off value. The cut off for TRAb-D was 15%, and for TRAb-llI, TRAb-CT, and TRAbhuman the cut off valueswere 10%. A (%) , B (%) o I-~~~~~=---..., - '-- -=_--J TRAb-III TRAb-human Oi----iIiii -' ' TRAb-1II TRAb-CT C (%) o r---l...l----ll----l...=;==j -10 -'-- --J D (%) o I 1 II T II T Figure 5. Relative values of TRAb-human (A) and TRAb-CT (B) when the value of TRAb-11I was 0%. Value of TRAb-human (C) and TRAb-CT (D) based on GD activity

6 Yukari MIMURA, Toshio OGURA, and Fumio OTSUKA and 5D). Both TRAb-CT and TRAb-human decreased gradually according to the GD activity, but the grade was greater for TRAbhuman compared with TRAb-CT. Discussion The TSH receptor is one of the major autoantigens in autoimmune thyroid disease, and autoantibodies acting as TSH receptor agonists can lead to the clinical symptoms of GDIO). There are two established principles used to detect autoantibodies to the TSH receptor 2 l, and they are generally used to diagnose GD, understand the severity of disease, and to determine the effectiveness and time to cease administration of ATD. Recently, a new, second generation TSH binding inhibitory assay system using coated tubes was developed, that improved sensitivity without loss of specificity in healthy individuals~j). Furthermore, a full-length human recombinant TSH receptor was developed and has been used routinely in laboratories 8, llj. Several reports have described the clinical usefulness of the new assay systems, especially in the diagnosis of GD2, 8, 9, 11-1;)). However, the relationship between new TRAb assay and the severity of GD has not yet been established. We therefore evaluated the relationship between TRAb and GD activity with 4 different TRAb assays and TSAb simultaneously in GD patients. Among the 4 assays of TRAb, the detection rate was high for TRAb-CT, TRAb-human, TRAb-III, and TRAb-D in all patients. The detection rate of TRAb- CT and TRAb-human was high compared with the other 2 methods in Group I, which exhibited high GD activity, and that of TRAb-CT was also high in Group IV, which exhibited low GD activity. A high positive ratio was reported, % in untreated GD, % in treated GD, and % in healed GD9, 13). The reason for the high sensitivity in the solid-phase assay was ascribed to decrease non- specific binding following washing of the tube, and the prevention of contamination with TSH binding agents, such as anti TSH antibodysl. In fact, there was one present case with an anti TSH antibody, for which level of TRAb-D was -51.3% but the TRAb-CT and TRAb-human were positive, suggesting that the influence of the anti TSH antibody was negligible. A small proportion (0.3-18%) of GD patients has been reported to have an anti TSH antibodyi4-16\ so it was important to measure the TRAb exactly and not disregard this subset of patients. We can take the very useful tool, on the contrary, we were at a loss what to do. Since the patients belong Group IV were formerly considered to exhibit decreased activity, with negative TSAb and low dose ATD (1.1 tablet/day), we could not cease treatment with ATD, due to positive TRAb findings. We observed a fine correlation between the individual TRAb assays (r>0.8), and the correlation between TRAb-D and TRAb-III or TRAb-CT and TRAb-human were stronger (r>0.95). Since these two methods utilized similar assay systems, respectively, we considered that to be responsible for the high correlation. There was also a strong correlation between the solid-phase assay (TRAb-CT) and the conventional method (TRAb-III) (r=0.940). The correlation between the 4 TRAb assays and TSAb were weak, as previously reported I7 ). We attempted to examine the clinical data and detection ratio in GD activity, by classifying the patients into 4 groups. We classified the patients according to serum TSH, the dose of ATD, change of TSH compared to 2-3 months ago, and TSAb. The TSAb and dose of ATD gradually decreased in the four groups, supporting the influence of GD activity, although containing patients with transient hypothyroidism following treatment with large doses of ATD. In all assay methods, the parameters and detection rate decreased gradually, and the parameters were significantly lower in Groups III and IV compared to Group I. Although they were considered to be influenced by GD activity, since the detection rate oftrab CT and TRAb-human was higher in Group I, the two new assay methods were useful to diagnose GD. Second generation assays exhibited a high

7 Clinical Usefulness of TSH Receptor Autoantibody Using Different Assay Systems detection rate in untreated GD, and were effective in distinguishing GD from silent thyroiditis9, 13, IS, 19). There were 8 cases (19.0%) that exhibited different results with the different assay methods. Most of these were positive with TRAb-CT or TRAb-human, and were negative with the other assays. However, the titer was almost at the cut-off level, so if the cut-off level were to be changed, the detection would have been changed. Kasagi also described the estrangement of the results ) due to similar mechanisms. With treatment of GD, we were able to observe the transition of the assay data, and we were careful to administer ATD for a long term. When reducing ATD, we should consider not only TRAb, but also goiter size, thyroidal radioactive iodine uptake and serum Tg, in the decision-making process 13,21). When we examined the individual data, TRAb CT, which used porcine TSH receptor, was higher than TRAb-D and TRAb-III. However, the data of TRAb-human, which used the human recombinant TSH receptor, both increased and decreased compared with TRAb-III. Especially, the tendency was strong for the data around the cut-off values with the conventional TRAb-III methods, and we considered this to be greatly influenced by GD activity. Although the TRAbhuman data is generally expressed in lull, we used % inhibition to be able to compare the results with the other assay methods. The % inhibition was calculated without considering non-specific binding (NSB) in the other 3 methods, but in this study we calculated the data of TRAb-human considering NSB according to the manufacturer's instructions. We observed similar results even when we did not account for NSB (data not shown). Some reports have described that the species of THS receptor did not impact the assay results, due to the good correlation between the porcine and human TRAb assayss,22-24). However, the cloning of the TSH receptor ) demonstrated that the human and porcine TSH receptors were similar to in the extracellular domain, and 92.1% in the transmembrane region 2S ). In other words, TSH in human is 15% different from porcine TSH in the extracellular domain. Although this difference appears to be minimal, researchers still do not know the precise functional conformation and the exact location of the relevant TRAb epitopes 2S ). Further, differences in the epitopes of TSAbs from GD patients were apparent in untreated patients, and also after antithyroid drug treatment 29 ). So, although the positive frequency of TRAb or TSAb was similar, individual patients tend to exhibit variability. Functional heterogeneity of TRAbs has been reported 30 ). The TSH receptor is highly homologous between species, such as bovine, human, porcine and rat. However, following TSH cloning of the human and porcine genes, differences were evident on 15% in the extracellular domain and 8% in the transmembrane region 2S ). Some authors described that TSH binding sensitivity was improved when they used the human TSH receptor ). The detection of various TRAb with the human TSH receptor was useful and improves the clinical relevance. In this study, cases that were borderline using the conventional TRAb assay were divided into two groups for TRAb-human, the high clinical activity group exhibited a high TRAb-human titer and the low activity group exhibited a low titer. We thought that this difference might be due to the species of TSH receptor. Komori et az. also described poor correlation in patients with low TRAb-III titers (0-3OO16)1S). However, a larger sample size of similar cases will be required to validate these findings. We hypothesized that these TRAbs could be useful as an indication to stop ATD or relapse of GD. However, we did not obtain the TRAb of patients in Group IV that did not correlate one year after thyroid function (data not shown). Some authors have also reported that the use of the second generation TRAb assays for the precise prediction of relapse or remission in the follow up of GD patients was questionable 35,36). Since the remission and relapse of GD depend on the size of thyroid gland, period of medication, etc. 13, 21), we should consider when the ATD was ceased. In summary, new assay systems using the

8 Yukari MIMURA, Toshio OGURA, and Furnio OTSUKA coated tubes were highly sensitive in GD patients, and were influenced by GD activity. Furthermore, TRAb-human exhibited some specific advantages, which separated it from the other assays. Acknowledgment We would like to thank Yamasa Co., and Cosmic Co., for their technical support in the study. References 1. Weetman AP, McGregor AM : Autoimmune thyroid disease: further developments in our understanding. Endocr Rev 15: , Morgenthaler NG : New assay systems for thyrotropin receptor antibodies. Curr Opin Endocrinol Diab 6: , Smith BR, Hall R : Thyroid-stimulating immunoglobulins in Graves' disease. Lancet 2: , Morgenthaler NG, Pampel I, Aust G, Seissler J, Scherbaum WA : Application of a bioassay with CHO cells for the routine detection of stimulationg and blocking autoantibodies to the TSH-receptor. Horm Metab Res 30: , Patibandla SA, Dallas JS, Seetharamaiah GS, Tahara K, Kohn LD, Prabhaker BS : Flow cytometric analyses of antibody binding to Chinese hamster ovary cells expressing human thyrotropin receptor. J Clin Endocrinol Metab 82: , De Forteza R, Smith CU, Amin J, McKenzie JM, Zakarija M : Visualization of the thyrotropin receptor on the cell surface by potent autoantibodies. J Clin Endocrinol Metab 78: , Morgenthaler NG, Tremble J, Huang GC, Scherbaum WA, McGregor AM, Banga JP : Binding of anti-thyrotropin receptor autoantibodies in Graves' disease serum to nascent, in vitro translated thyrotropin receptor; ability to map epitopes recognished by antibodies. J Clin Endocrinol Metab 81: , Costagliola S, Morgenthaler NG, Hoermann R, Badenhoop K, Struck J, Freitag D, Poertl S, Weglohner W, Hollidt JM, Quadbeck B, Dumont JE, Schumm-Draeger PM, Bergmann A, Mann K, Vassart G, Usadel KH : Secondgeneration assay for thyrotropin receptor antibodies has superior diagnostic sensitivity for Graves' disease. J Clin Endocrinol Metab 84: 90-97, Kubota S, Sasaki I, Oe H, Fukada S, Kuma K, Miyauchi A : Evaluation ofhigh sensitive TRAb measurement assay by radio receptor assay method, "TRAb CT 'Cosmic'.. : Comparison with solid phase assay method. Jpn J Med Pharm Sci 48: , 02. (in Japanease) 10. Rapoprt B, Chazenbalk GD, Jaume JC, McLachlan SM : The thyrotropin (TSH) receptor: interaction with TSH and autoantibodies. Endocr Rev 19: , Scott M, Feldkamp J, Bathan C, Fritzen R, Scherbaum WA, Seissler J : Detecting TSHreceptor antibodies with the receombinant TBII assay: Techinical and clinical evaluation. Horm Metab Res 32: , Morgenthaler NG, Nagata A, Katayama S, Bergmann A, Iitaka M : Detection of low titer TBII in patients with Graves' disease using recombinant human TSH receptor. Clin Endocrinol57: , Misaki T, Ikawa K, Ono Y, Kobayashi K, Kasagi K, Kousaka T, Konishi J : Basic evaluation and clinical assessment of a new coated-tube radioreceptor assay for measurement of TSH binding inhibitor immunoglobulins: With special attention to its correlation withconventional precipitation method and ELISA. Jpn J Med Pharm Sci 48: ,02. (in Japa.nease) 14. Akamizu T, Mori T, Ishii H, Yokota T, Nakamura H, Imura H : Clinical significance of elevated labeled TSH binding (LTB) activity in srea of patients with Graves' disease and other thyroid disorders. J Endocrinol Invest 10: , Ochi Y, Nagamune T, Nakajima Y, Ishida M, Kajita Y, Hachiya T, Ogura H : Anti-TSH antibodies in Graves' disease and their failure

9 Clinical Usefulness of TSH Receptor Autoantibody Using Different Assay Systems to interact with TSH receptor antibodies. Acta Endocrinol (Gopenh) 1: , Noh J, Hamada N, Saito H, Oyanagi H, Ishikawa N, Momotani N, Ito K, Mori H : Evidence against the importance in the disease process of antibodies to bovine thyroid-stimulating hormone found in some patients with Graves' disease. J Glin Endocrinol Metab 68: , Kamijo K : Fundamental and clinical studies on TBII assay by TRAb ELISA (Cosmic Corporation). Jpn J Med Pharrn Sd 45: ,01. (in Japanease) 18. Komori A, Jibiki K, Yamaguchi N, Sato K, Odagiri E, Takano K, Takasaki K : Fundamental and clinical studies of thyrotoropin binding inhibition assay by recombinant human thyrotropin receptors. Jpn J Med Pharm Sci 46: ,01. (i.njapanease) 19. Noh JY, Hamada N, Shimizu T, Ishikawa N, Ito K, Ito K : Establishment of cut off value and clinical effect by TRAb measurement kit ushing human recombinant TSH receptor. Jpn J Med Pharm Sci 47: , 02. (in,japanease). Kasagi K : Evaluation of new sensitive solidphase assays for TSH binding inhibitor immunoglobulins; Comparison between DYNOtest TRAb Human (Yamasa) and TRAb CT (Cosmic) kits. Hormon to Rinsyo 51: , Ikenoue H, Okamura K, Sato K, Kuroda T, Yoshinari M, Tokuyama T, Nakagawa M, Fujishima M : Prediction of relapse in drugtreated Graves' disease using thyroid stimulation indices. Acta Endocrinol 125: , Kakinuma A, Morimoto I, Kuroda T, Fujihira T, Eto S, Sander MM, Rapoport B : Comparison of recombinant human thyrotropin receptors versus porcine thyrotropin receptors in the thyrotropin binding inhibition assay for thyrotropin receptor autoantibodies. Thyroid 9: , Kamij 0 K : TSH-receptor antibody measurement in patients with various thyrotoxicosis and Hashimoto's thyroiditis: a comparison of two two-step assyas, coated plate ELISA using porcine TSH-receptor and coated tube radioassay using human recombinant TSH-receptor. Endocrine J 50: , Kasagi K, Misaki T, Konishi J : A sensitive solid-phase assay for TSH binding inhibitor immunoglobulons using recombinant human TSH receptor. Jpn J Med Pharm Sci 47: ,02. (in Japanease) 25. Nagayama Y, Kaufman KD, Seto P, Rapoport B : Molecular cloning, sequence and functional expression of the cdna for the human thyrotropin receptor. Biochem Biopys Res Gommun 165: , Libert F, Lefort A, Gerard C, Parmentier M, Perret J, Ludgate M, Dumont JE, Vassart G : Cloning, sequencing and expression of the human thyrotropin (TSH) receptor: evidence for binding of autoantibodies. Biochem Biopys Res Gommun 165: , Misrahi M, Loosfelt H, Atger M, Sar S, Guiochon GA, Milgrom F : Cloning, sequencing and expression of human TSH receptor. Biochem Biopys Res Gommun 166: , Sanders J, Oda Y, Roberts SA, Maruyama M, Furmaniak J, Smith BR : Understanding the thyrotropin receptor function-structure relationship. Bailliere's Glin Endocrinol Metab 11: , Kim TY, Park do J, Chung HK, Kim WB, Kohn LD, Cho BY : Epitope heterogeneity of thyroid-stimulation antibodies predicts longterm outcome in Graves' patients treated with antithyroid drugs. J Glin Endocrinol Metab 88: , Kim WB, Chung HK, Lee HK, Kohn LD, Tahara K, Cho BY : Changes in epitopes for thyroid-stimulating antibodies in Graves' disease sera during treatment of hyperthyroidism: Therapeutic implications. J Glin Endocrinol Metab 82: , Endo T, Ohmori M, Ikeda M, Anzai E, Onaya T : Heterogeneous responses of recombinant human thyrotropin receptor to immunoglobulins from patients with Graves' disease. Biochem Biophys Res Gommun 186: ,

10 Yukari MIMURA, Toshio OGURA, and Fumio OTSUKA 32. Kakinuma A, Chazenbalk GD, Jaume JC, Rapoport B, McLachlan SM : The human thyrotropin (TSH) receptor in a TSH binding inhibition assay for TSH receptor autoantibodies. J Clin Endocrinol Metab 82: , Sato K, Yamazaki K, Yamada E, Kanaji Y, Miura M, Obara T : Immunoglobulins of untreated Graves' patients with or without thyrotropin receptor antibody (determined by porcine thyrocytes) universally elicit potent thyroid hormone-releasing activity in cultured human thyroid follicles. Thyroid 9: , Murakami M, Miyashita K, Kakizaki S, Saito S, Yamada M, Irluchijima T, Takeuchi T, Morl M : Clinical usefulness of thyroid-stimulation antibody measurement using Chinese hamster ovary cells expressing human thyroid receptors. Europe J Endocrinol 133: 80-86, Zimmermann BT, Nygaard B, Rasmussen AK, Rasmussen UF : Use of the 2nd generation TRAK human assay did not improve prediction of relapse after antithyroid medical therapy of Graves' disease. Europe J Endocrinol 146: , Schott M, Morgenthaler NG, Fritzen R, Feldkamp J, Willenberg HS, Scherbaum WA, Seissler : Levels of autoantibodies against human TSH receptor predict relapse of hyperthyroidism in Graves' disease. Horm Metab Res 36: 92-96,