Thyroid Stimulation Blocking Antibody Research Articles

Low response of the thyroid gland to endogenous thyrotropin increased by thyrotropin-releasing hormone in patients with euthyroid Graves' disease.

Euthyroid Graves' disease is defined as Graves' ophthalmopathy without hyperthyroidism, and the thyroid-stimulating antibody (TSAb) has been known to be a good marker for diagnosis. However, the question of why TSAb does not cause hyperthyroidism arises. To settle this, we examined thyroid responsiveness to endogenous thyrotropin (TSH) increased by thyrotropin-releasing hormone (TRH) in 23 patients with euthyroid Graves' disease. Nineteen patients (83%) had positive TSAb and 21 (91%) had at least one of the autoantibodies to the thyroid gland. Only one patient (4%) had positive thyroid-stimulation blocking antibody (TSBAb). Basal levels of free thyroxine (FT4), free triiodothyronine (FT3), and thyrotropin (TSH) in patients were not different from those in age- and sex-matched normal controls (n = 25). Response of TSH to TRH was normal; however, an increase of FT3, either absolute or as a multiple of baseline, in the TRH test in these patients (0.46+/-0.23 pg/mL, P < 0.001; 1.14+/-0.09 fold, p < 0.001) was significantly lower than that in controls (0.86+/-0.19 pg/ml; 1.26+/-0.07 fold). There was no correlation between the deltaFT3/deltaTSH ratio and TSAb activity. It is concluded that thyroid responsiveness in euthyroid Graves' disease is lower than in normal controls and this explains the euthyroid function in the patients even in the presence of TSAb.

Effect of Solubilization of Porcine Thyrotropin (TSH) Receptor on TSH Binding and on Radio-Receptor Assay for Anti-TSH Receptor Antibodies

The effect of solubilization of porcine thyrotropin receptor (TSHR) on TSH binding and on the radio-receptor assay for anti-TSHR antibodies was examined. After TSHR solubilization with 1% dodecylpolyethyleneglycoether, TSH binding affinity was increased, from Kd = 1.15nM to 0.45nM, and TSH binding capacity was slightly increased, from 0.15nM to 0.19nM. With a particulate membrane suspension from thyroid cells, blocking of TSH binding to the membrane suspension by anti-thyrotropin receptor antibody was observed only for thyroid stimulation blocking antibody (TSBAb), not for thyroid-stimulating antibody (TSAb). After the solubilization of TSHR, both TSBAb and TSAb blocked TSH-binding to the solubilized TSHR. We speculate that TSAb interacts with the TSHR in the native conformation without interfering with TSH binding, and that after the solubilization, any anti-TSHR antibody interferes with TSH-binding due to the conformational change in TSHR. With these particulate thyroid cell membrane preparations, we can detect only TSBAb by the radio-receptor assay.

A change from stimulatory to blocking antibody activity in Graves' disease during pregnancy.

Remission of Graves' disease (GD) during pregnancy with recrudescence after delivery is commonly observed. However, as pregnancy is associated with type 2 rather than type 1 cytokine production, a decrease in thyroid-stimulating antibody (TSAb) activity alone is unlikely to account for the remission during pregnancy. We hypothesized that a change in the antibody characteristics may occur as pregnancy advances. Fifteen women were studied in the first, second, and third trimesters of pregnancy and 4 months postpartum. TSH receptor antibodies were determined using human thyroid cell cultures, and lymphocyte subsets were measured by flow cytometry. Median TSAb (determined by cAMP release) decreased from 280% (96-3200) to 130% (range, 35-350; P < 0.05) during pregnancy, but no significant change was noted with the TSH binding inhibitory antibody (TBII; determined by RRA). Thyroid stimulation-blocking antibody (TSBAb; inhibition of TSH-stimulated cAMP release) increased from 16 +/- 9% to 43 +/- 16% (mean +/- SD; P < 0.005). The increase in TSBAb was observed even among those patients who were in clinical remission before pregnancy. Overall, a negative correlation was observed between TSBAb activities and free T4 levels during pregnancy (r = -0.279; P < 0.05). Reciprocal changes in TSAb, TBII, and TSBAb levels were observed in the seven patients who relapsed during the postpartum period. In comparison, the healthy pregnant women (n = 14) were all negative for TSAb, TBII, and TSBAb throughout pregnancy. The absolute number of T lymphocytes, T helper cells, and natural killer cells, but not B cells, decreased significantly during pregnancy in both healthy women and GD patients. GD patients had significantly more CD5+ B cells at all stages of pregnancy compared to controls. In conclusion, a change in specificity from stimulatory to blocking antibodies was observed in GD patients during pregnancy and may contribute to the remission of GD during pregnancy.

Demonstration of fragments with thyroid stimulating activity from thyroid stimulation blocking antibodies-IgG molecules by papain digestion.

Thyroid stimulation blocking antibodies (TSBAb) inhibit TSH action and may have a role in the pathogenesis of hypothyroidism. In order to study the relationship between blocking and stimulating activities we have examined the biologically active fragments in TSBAb-IgG molecules after papain digestion. Both thyroid stimulating (TS) activity (cAMP production in thyroid cells) and TSH binding inhibitory (TBI) activity (determined by TSH receptor assay) in sera from patients with primary hypothyroidism were examined after digestion with papain-Sepharose in the presence of cysteine. The digested IgG was separated into unbound (UF) and bound (BF) fractions on a Protein A-Sepharose column. Each fraction was then gel-filtrated on a Sephadex G-100 column. TS activity was found within one hour after hydrolysis in 5 out of 7 antibodies, then gradually decreased after more prolonged incubation. Both TS and TBI activities in the UF and the BF from Protein A were found in Feb (Mr 50 kD) and the second protein peak (Fc with trace amounts of Fab), respectively. The biological activity in the second protein peak was suggested as being derived from Fab fraction, because the activity bound to the anti-F(ab')2 column. However, the first peak (undigested IgG) in the BF had neither TS nor TSB activity. The TS activity in the retarded fraction (less than Mr 20 kD) in the UF gradually increased with prolonged digestion. The conversion of Thyroid stimulation blocking antibodies activity to thyroid stimulating activity by papain digestion suggests that the inherent thyroid stimulating activity located in the Fab portion of the IgG molecule is unmasked by papain cleavage. We also suggest that the thyroid stimulating activity in the retarded fraction in the unbound fraction may be released from hydrolysis of the Fab portion of the IgG molecule.

Familial Clustering of Thyroid Stimulation-Blocking Antibody

Thyroid stimulation—blocking antibody (TSBAb), an antibody that blocks stimulation of thyroid adenylate cyclase induced by thyrotropin stimulation, 1 has been considered to play some pathogenetic role in atrophic autoimmune primary hypothyroidism. 2,3 We describe a familial clustering of TSBAb that affected 4 members of 1 family. We believe that these cases provide a novel mechanism of hereditary hypothyroidism. Report of Cases. The proband, a 63-year-old woman, presented with general malaise and edema. Her goiter was not palpable. She was found to have hypothyroidism (free thyroxine, 4 pmol/L [0.3 ng/dL]; thyrotropin, 149 mU/L) and was positive for both thyrotropin receptor antibody (88.1%) and TSBAb (92.8%). Serologic tests were also positive for antithyroglobulin and antithyroid microsomal antibodies (X200 and X200). Her daughter, who had been diagnosed as having hypothyroidism with TSBAb (73.0%), had been treated with levothyroxine (100 μg/d) for several years. Her son had once been treated in another clinic under

Subtypes of Anti-TSH Receptor Antibodies Classified by Various Assays Using CHO Cells Expressing Wild-Type or Chimeric Human TSH Receptor

To analyze the heterogeneity of anti-TSH receptor antibodies (TSHRAb), we measured serum TSH-binding inhibitory immunoglobulin (TBII), thyroid-stimulating antibody (TSAb), and thyroid stimulation blocking antibody (TSBAb) activities in 31 patients with positive TSHRAb, using CHO cells expressing wild-type TSHR (WT) or TSHR chimera (Mc2) wherein residues 90-165 were substituted by the LH/CG receptor. Using membranes from WT cells, we detected TBII activity in all 31 patients; 10 (32%), all with TSAb activity only, completely lost TBII activity using Mc2 membranes. TSAb activity was found in 26 sera using WT cells; 20 (77%) completely lost TSAb activity in Mc2 cells. Comparisons of TBII and TSAb activity in WT cells did not exhibit a strong positive correlation (r = 0.52). Of the 20 sera that completely lost TSAb activity in Mc2 cells, 10 retained some TBII activity in Mc2 cells. In each of the sera with retained TBII activity, TSAb activity was recovered in Mc2 cells using the conversion assay, which measures the conversion of a nonstimulating TSHRAb to a TSAb by the action of an anti-human IgG. Additionally, the TBII and conversion assay values in Mc2 cells exhibited a strong positive correlation (r = 0.86). Of the 31 sera, TSBAb was found in 7 samples, with no difference in WT and Mc2 cells. TBII activity was detected in all 7 sera with WT cells; TSAb activity in only 2. In the 5 sera with TSBAb but no TSAb activity, and with only a minimal or no decrease in TBII activity in Mc2 cell membranes, the in vitro conversion assay uncovered TSAb activity. Analyzing these data, we classify the sera into 5 groups containing multiple, different TSHR autoantibodies, including two different TSAbs, three different TBIIs, and one nonfunctional antibody. The heterogeneity of TBIIs as well as TSAbs provides a basis to explain the lack of correlation between TBII and TSAb activities in some past studies of Graves' sera.

A Case of Subacute Thyroiditis Accompanied by Thyroid Stimulating Antibodies and Thyroid Stimulation-Blocking Antibodies

After one month of suffering from cervical pain, subfever, palpitation and tachycardia, a 78-year-old woman came to our hospital. Tenderness was noted when we palpated her diffuse goiter. Thyroid stimulating hormone (TSH) level was less than 0.1μU/ml with high serum levels of free T3 (9.8pg/ml) and free T4 (4.4ng/dl), showing hyperthyroid state. Microsome test and thyroid test were both negative, with C-reactive protein (CRP) at 3.1mg/dl, erythrocyte sedimentation rate (ESR) at 139mm/hr and immunosuppressive acidic protein (IAP) at 881μg/ml. She was diagnosed as having subacute thyroiditis. However, thyroid scanning with 123I revealed normal uptake. TSH binding inhibitor Immunoglobulin (TBII) activity was 71.8%. Thyroid stimulating antibody (TSAb) was positive (869%). Thyroid stimulation-blocking antibody (TSBAb) was 22%. The histological examination by needle biopsy showed thyroid follicular cell destruction and appearance of giant cells, compatible with subacute thyroiditis. After administration of anti-inflam-matory drug alone, the cervical pain disappeared and CRP, ESR and IAP levels were normalized. Three months later, serum TSH level was 45.2μU/ml, free T3 was 2.4pg/ml and free T4 was 0.4ng/dl, showing hypothyroid state. TBII was 75.9%, TSAb was negative (122%) and TSBAb was positive (86%). Six months later, TBII, TSAb and TSBAb became negative and the thyroid function returned to normal. The occurrence of subacute thyroiditis may induce transitional multifunctional TSH-receptor antibody appearance.

A Case of Graves' Disease in which Hypothyroidism First Developed, Followed by Hyperthyroidism, and Finally Hypothyroidism Recurred: A Four-year Follow up

A 63-year-old female with a diffuse goiter was referred for evaluation of her thyroid function. When she visited the hospital in January 1991, her serum levels of free T3 (FT 3), free T4 (FT 4), and TSH were 3.1 pmol/l, 12 pmol/l, and less than 0.10 mU/l, respectively. Her thyroid function was thought to have changed from thyrotoxic to euthyroid or hypothyroid since she had been diagnosed as subclinically hyperthyroid at another clinic in November 1990. Her TSH level later increased to 83.2 mU/l. Treatment with T3 was started in March 1991. The T3 administration was terminated in January 1992, when her FT 4 level had increased to 8 pmol/l. Histological examination revealed the presence of chronic thyroiditis in January 1992. She developed mild hyperthyroidism in February 1992, followed by recurrent hypothyroidism in May 1993. The 24-hour thyroidal radioactive iodine uptake (RAIU) was 32.1% in March 1992. Treatment with T3 was restarted in June 1993. T3 therapy was replaced with T4 therapy in August 1994 since her FT 4 level remained low up to July 1994. Ultrasonography of the thyroid revealed diffuse low echogenicity in the hypothyroid state (January 1991 and March 1994). On the other hand, an ultrasonogram obtained during the mild hyperthyroid state (January 1993) showed echo levels increased in the anterior half of the thyroid. C-reactive protein (CRP) was positive at the first visit, in May 1993 when hypothyroidism recurred and in February and March 1994 when her thyroid function deteriorated. However, she did not complain of neck pain during the course of her illness. The results of TSH-binding inhibitor immunoglobulins (TBII) and thyroid-stimulating antibodies (TSAb) were strongly positive at her first visit. Their activities remained high through the end of 1991 and then gradually decreased, indicating that she had Graves' disease. Thyroid-stimulation-blocking antibodies (TSBAb) were not detected throughout the investigation period. The present findings indicate that her thyroid function changed depending on the balance between TSAb activities and the destructive changes in the thyroid. Inflammation might have played a role in the destruction of the thyroid.

High prevalence and little change in TSH receptor blocking antibody titres with thyroxine and antithyroid drug therapy in patients with non-goitrous autoimmune thyroiditis.

We have reevaluated the prevalence and pathogenetic importance of TSH receptor blocking antibodies (TRBAb) in autoimmune hypothyroidism, and investigated the changes in TRBAb activities during thyroxine and antithyroid drug treatment. Serum TSH binding inhibitor immunoglobulin (TBII) and thyroid stimulation blocking antibody (TSBAb) were measured serially in all patients with non-goitrous autoimmune thyroiditis (AT) and measured monthly during methimazole treatment in 6 patients. Ninety patients with non-goitrous AT and 95 patients with goitrous AT were entered consecutively into this study. All patients with non-goitrous AT were treated with thyroxine and followed at intervals of 6 months for 2 years initially and then yearly intervals. The duration of follow-up was 1-8 years. Six patients from the TRBAb-positive non-goitrous AT group who were treated with thyroxine were randomly selected and given additional treatments with methimazole (40 mg per day) for 6 months. Serum TBII was measured by a radioreceptor assay, TSBAb by using FRTL-5 cells, and antithyroid peroxidase and antithyroglobulin antibodies by radioimmunoassay. The prevalences of TBII and TSBAb is non-goitrous AT were 47.8 and 58.9%, respectively, which were significantly higher than those in goitrous AT (6.3% for TBII, 10.5% for TSBAb). All but one patient showed persistent TBII and TSBAb activities during the thyroxine treatment for up to 8 years. A high dose of methimazole (40 mg per day) did not affect the titres of TBII and TSBAb in 5 out of 6 patients with non-goitrous AT tested. However, antithyroid peroxidase and antithyroglobulin antibodies activities were significantly decreased during the methimazole treatment. The high prevalence of TSH receptor blocking antibodies (TRBAb) suggests that TRBAb may play a major role in the development of hypothyroidism and thyroid atrophy in the vast majority of patients with non-goitrous autoimmune thyroiditis. Most TRBAb activities are stable for at least 8 years and are now affected by thyroxine and antithyroid drug treatment.

Scintigraphic findings of the thyroid in hypothyroid patients with blocking-type TSH-receptor antibodies

The present study was designed to analyse the scintigraphic appearance of the thyroid in hypothyroid patients with blocking-type TSH receptor antibodies (TRAbs). Eleven hypothyroid patients with autoimmune thyroiditis positive for TSH binding inhibitor immunoglobulins (TBII) [80% +/- 12 (SD)%; normal < 11%] and for thyroid stimulation-blocking antibodies (TSBAbs) (90% +/- 9%: normal < 32%) were studied. Thyroid scanning was performed using technetium-99m or iodine-123, when the patients were hypothyroid. Analysis of the scan images revealed the presence of localized functioning areas in six patients (group 1), and no visualization of the thyroid in the remaining five patients (group 2). Patients in group 1 showed significantly higher uptake of 99mTc than those in group 2 (P < 0.05). Interestingly, three patients in group 1 were positive for thyroid-stimulating antibodies (TSAbs) (249% +/- 17%; normal < 145%), which were not detected in the remaining eight patients. Antibodies against thyroglobulin and microsomal antigens were detected in nine nine (81.8%) and 11 (100%) patients, respectively, but neither of these titres correlated with the scan image. Three patients in group 1 underwent scintigraphy again after treatment with thyroxine, at which time the functioning lesion was not noted. Fourteen hypothyroid patients with negative TBII displayed no such scintigraphic findings. Chronic stimulation of the thyroid by TSAbs and/or TSH might be responsible for the presence of the functioning lesion, but clarification of the mechanism requires further studies. In summary (1) TSAbs were detected in three (27.3%) of 11 hypothyroid patients with blocking TRAbs; (2) thyroid scintigraphy revealed the presence of localized functioning area(s) in approximately half of these cases.

Studies on the Action of Thyroid Stimulation Blocking Antibody (TSBAb) on Thyroid Cell Membrane

The effect of thyroid stimulation blocking antibody (TSBAb) on stimulated cyclic AMP (cAMP) production induced by adenylate cyclase stimulators in porcine thyroid membrane (PTM) and porcine thyroid cells (PTC) has been studied. Ten TSBAbs with high TSH binding inhibitory immunoglobulin (TBII) activities significantly blocked TSH-stimulated cAMP production in PTC. The blocking effect of TSBAb on the cAMP increase induced by forskolin or GTP-gamma S stimulation in PTC was found in a few cases. However, there was no blocking action of TSBAb on the cAMP increase stimulated by forskolin, GTP gamma S, or NaF in isolated PTM. When TSBAb-globulin was absorbed with PTM or guinea pig epididymal fat membrane (GPFM), the TBII activity in TSBAb-globulin was significantly absorbed by these membranes. A decrease of TSBAb activity (blocking activity for TSH-stimulated cAMP production in PTC) by PTM absorption, but no decrease by GPFM absorption, was found in six cases. This suggests that the potent TSBAb-neutralizing component may be associated with a non-TSH receptor site in the thyroid membrane. The other four cases showed a decrease of TSBAb activity by absorption with both PTM and GPFM. This suggests that the TSBAb-neutralizing activity may be associated with the TSH receptor site of both PTM and GPFM. The results of the present study suggest that TSBAb may block TSH action either via the TSH receptor itself or via a non-TSH receptor component of the thyroid membrane and not at a postreceptor level.

Studies of Human Thyroid Xenografts from Hashimoto's Thyroiditis in Severe Combined Immunodeficient (SCID) Mice: Detection of Thyroid Stimulation-Blocking Antibody

Human thyroid xenografts from 7 patients with Hashimoto's thyroiditis (HT) and 3 normal persons (N) were xenografted into severe combined immunodeficient (SCID) mice to study the intrathyroidal lymphocytes that were expected to survive in these animals. Human IgG was detected in all mice engrafted with HT thyroid tissue peaking at 6-10 weeks after xenografting. Thyroperoxidase-antibody (TPO-Ab) was also detected in all mice with HT thyroid grafts peaking at 4-6 weeks after xenografting, reaching up to 44% of donors' original concentrations. In contrast, maximal thyroglobulin (Tg)-Ab production in some SCID mice with HT thyroid grafts was higher than the donors' original level, and was detectable in mice with thyroid grafts from Tg-Ab-negative HT donors. Thyroid stimulation-blocking antibody (TSBAb) was found in 2 mice with thyroid xenografts from 1 HT patient whose original serum TSBAb and thyrotropin-binding inhibitor immunoglobulin (TBII) had been positive; the maximal TSBAb level in SCID mice exceeded the donor's original level. TSBAb production in SCID mice reached its peak at 10 weeks after xenografting, i.e., later than that of thyroid-stimulating antibody (TSAb) observed in our recent report, suggesting the existence of distinct intrathyroidal B cell autoreactive clones of different life span responsible for secreting TSAb or TSBAb. When autologous peripheral blood mononuclear cells (PBMC) were engrafted alone (without thyroid tissue), TSBAb was undetectable.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient congenital hypothyroidism due to maternal thyrotrophin binding inhibiting immunoglobulin

Transient congenital hypothyroidism due to maternal thyrotrophin binding inhibitor immunoglobulin (TBII), a thyroid-stimulating hormone (TSH)-receptor blocking antibody, is described in three male siblings born to a mother with autoimmune thyroiditis. These cases are believed to be the first described in Australia. The first child was found to have a serum TSH of 565 mU/L and had a negative thyroid scan when presented for neonatal screening. He was treated with thyroxine but became thyrotoxic at 3 months of age when he was on a dosage of 85 micrograms/m2 of body surface area. He was euthyroid 6 months after discontinuation of therapy. Nine years later a second hypothyroid sibling was born, with a serum TSH of 709 mU/L on day 4. Both mother and child were demonstrated to be strongly positive for TBII. Again this child was able to cease therapy by the age of 9 months. A third sibling, also TBII positive, was born 12 months after the second. His TSH was 90 mU/L and his serum thyroxine (T4) was 169 nmol/L. On this occasion, thyroid stimulation-blocking antibody was found to be present in the serum of both mother and child. Thyroxine therapy was ceased at 1 month. The family present a picture of varying degrees of transient neonatal hypothyroidism due to the transplacental passage of a maternal receptor blocking antibody. The condition is self-limiting, resolving when the immunoglobulin is cleared from the infant's circulation.

Hyperthyroidism with Potent Thyroid-Stimulation-Blocking Antibodies and Negative Thyroid-Stimulating Antibodies after Subtotal Thyroidectomy for Graves'' Disease with Follicular Thyroid Carcinoma

A 39-year-old woman with Graves' disease associated with follicular thyroid carcinoma underwent subtotal thyroidectomy. TSH-binding inhibitor immunoglobulins (TBII) were positive, whereas thyroid-stimulating antibodies (TSAb) and thyroid-stimulation-blocking antibodies (TSBAb) were both negative before the operation. After the operation, TBII markedly increased above the pretreatment value. TSBAb became positive 3 months after the operation and then their activity increased, while TSAb remained negative after the operation. Subtotal thyroidectomy may have influenced the development of TSBAb in this patient. Irrespective of these findings, the patient became hyperthyroid again several months after the operation.

Identification of separate determinants on the thyrotropin receptor reactive with Graves' thyroid-stimulating antibodies and with thyroid-stimulating blocking antibodies in idiopathic myxedema: these determinants have no homologous sequence on gonadotropin receptors.

Deletions, substitutions, or mutations of the rat TSH receptor extracellular domain between residues 20 and 107 (all residue numbers are determined by counting from the methionine start site) have been made by site-directed mutagenesis of receptor cDNA. After transfection in Cos-7 cells, constructs were evaluated for their ability to bind [125I]TSH or respond to TSH and thyroid-stimulating antibodies (TSAbs) from Graves' patients in assays measuring cAMP levels of the transfected cells. Assay results were compared to results from Cos-7 cells transfected with wild-type receptor constructs or vector alone. We identify threonine-40 as a TSAb-specific site whose mutation to asparagine, but not alanine, reduces TSAb activity 10-fold, but only minimally affects TSH-increased cAMP levels. We show that thyroid-stimulating blocking antibodies (TSBAbs), which block TSH or TSAb activity and are found in hypothyroid patients with idiopathic myxedema, continue to inhibit TSH-stimulated cAMP levels when threonine-40 is mutated to asparagine or alanine, suggesting that TSBAbs interact with different TSH receptor epitopes than the TSAb autoantibodies in Graves' patients. This is confirmed by the demonstration that these TSBAbs interact with high affinity TSH-binding sites previously identified at tyrosine-385 or at residues 295-306 of the extracellular domain of the TSH receptor. This is evidenced by a loss in the ability of TSBAbs to inhibit TSAb activity when these residues are mutated or deleted, respectively. Since the TSAb and TSBAb epitopes are in regions of the extracellular domain of the TSH receptor that have no homology in gonadotropin receptors, these data explain at least in part the organ-specific nature of TSH receptor autoantibodies in autoimmune thyroid disease. Data are additionally provided which indicate that residues 30-37 and 42-45, which flank the TSAb epitope at threonine-40, appear to be ligand interaction sites more important for high affinity TSH binding than for the ability of TSH to increase cAMP levels and that cysteine-41 is critical for TSH receptor conformation and expression on the surface of the cell. Thus, despite unchanged maximal values for TSH-increased cAMP levels, substitution of residues 42-45 or deletion of residues 30-37 results in receptors, which, by comparison to wild-type constructs, exhibit significantly worsened Kd values for TSH binding than EC50 values for TSH- or TSAb-increased cAMP activity.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of thyroid stimulating antibody (TSAb) in the thyroid function of patients with post-partum hypothyroidism.

We investigated the association between thyroid function and the biological activities of thyroid stimulating antibodies (TSAb) and thyroid stimulation blocking antibodies (TSBAb) in patients with post-partum hypothyroidism. A prospective study. We studied 25 patients with post-partum hypothyroidism who visited our thyroid clinic during the period from 1985 to 1990. We measured TSH binding inhibitory immunoglobulin (TBII) and TSAb activity at the initial presentation of each of the 25 patients. Women found to have elevated TSAb activity were followed up. Upon finding negative TSAb activity along with positive TBII activity in the serum at the initial presentation, we measured TSBAb activity. Women found to have elevated levels of TSBAb at the initial presentation were also followed up. Elevated TBII activity was found in six of the 25 patients, as was high TSAb activity (205-2651%, normal 55.0-145.0%) in five of these six and in one other patient at the initial presentation. Markedly elevated TSBAb activity (89%) was found in one TBII positive patient. We were able to follow up serially five TSAb positive patients and the TSBAb positive patient over periods ranging from 11.5 to 26.5 months post-partum. The maximal value of TSAb activity was observed at the initial presentation in all TSAb positive patients, following which the activities gradually decreased. One of these patients developed Graves' hyperthyroidism associated with high TSAb activity (1223%) at 10.5 months post-partum. One of the other patients was restored to euthyroid with elevated TSAb activity (279%), but thereafter developed hypothyroidism in conjunction with the disappearance of TSAb activity at 26.5 months post-partum. In the other two patients, normalization of thyroid function was observed with elevated TSAb activity. Thereafter, thyroid function remained within the normal range even with the disappearance of TSAb activity. In the other patient, normalization of thyroid function was observed at 11.5 months post-partum, 3 months after the disappearance of TSAb activity. In the TSBAb positive patient, TSBAb activity decreased to 21% by 17.5 months post-partum associated with normalization of thyroid function. The present study demonstrates the presence of elevated levels of TSAb activity in some patients with post-partum hypothyroidism. In these patients, Graves' hyperthyroidism may be induced by TSAb activity, and hypothyroidism may reoccur with the disappearance of the TSAb activity. Furthermore, post-partum hypothyroidism may be due to increased TSBAb activity in some patients.

Different binding of stimulatory-type and blocking-type TSH receptor antibody with guinea-pig testis membrane

A receptor assay using [125I]bTSH-binding to guinea-pig testis membrane was developed. Unlabelled hCG and FSH inhibited [125I]bTSH binding. In patients with Graves' disease and in untreated hyperthyroid patients, almost all long-acting thyroid stimulators and thyroid-stimulating antibodies, respectively did not inhibit [125I]bTSH binding, which on the other hand was inhibited by thyroid stimulation blocking antibodies in patients with primary hypothyroidism. When the inhibitory effect on the binding of [125I]hCG and 125I-synthetic alpha-subunit peptide (alpha 26-46) of hCG to testis membrane was examined, bTSH resulted in a significant inhibition. However, all three kinds of TSH receptor antibodies had no inhibitory effect. This study demonstrated 1. interaction of alpha-subunit of TSH and hCG with the testicular receptor; 2. binding of thyroid stimulation-blocking antibody and lack of binding of thyroid-stimulating antibody to the testicular TSH receptor in spite of binding of these TSH receptor antibodies to the thyroidal TSH receptor, and 3. lack of binding of thyroid-stimulating antibody and thyroid stimulation-blocking antibody to the testicular gonadotropin receptor.

Immunoglobulins from Graves' disease patients interact with different sites on TSH receptor/LH-CG receptor chimeras than either TSH or immunoglobulins from idiopathic myxedema patients

To examine the identity of binding sites for thyrotropin (TSH) and thyroid stimulating antibodies (TSAbs) associated with Graves' disease, we constructed eight human TSH receptor/rat LH-CG receptor chimeras. Substitution of amino acid residues 8–165 of the TSH receptor with the corresponding LH-CG receptor segment (Mc1+2) results in a chimera which retains high affinity TSH binding and the cAMP response to TSH but loses both the cAMP response to Graves' IgG and Graves' IgG inhibition of TSH binding. Two of three IgGs from idiopathic myxedema patients which contain thyroid stimulation blocking antibodies (TSBAbs) still, however, react with this chimera. Chimeras which substitute residues 90–165 (Mc2) and 261–370 (Mc4) retain the ability to interact with TSH, Graves' IgG, and idiopathic myxedema IgG. The data thus suggest that residues 8–165 contain an epitope specific for TSAbs and that TSH receptor determinants important for the activities of TSAbs and TSH are not identical. Further, binding sites for TSBAbs in idiopathic myxedema may be different from receptor binding sites for both Graves' IgG TSAb as well as TSH and may be different in individual patients.

The Incidence of Thyroid Stimulating Blocking Antibodies during the Hypothyroid Phase in Patients with Subacute Thyroiditis

The etiology of subacute (de Quervain's) thyroiditis (SAT) is uncertain, although it probably represents a nonspecific inflammatory response by the thyroid to a variety of viruses. It has been suggested that nonimmune processes are involved in SAT patients who have negative autoantibody titers. The disease has a variable course; although it is self-limited in most cases, some patients develop transient hypothyroidism, and others do not during the recovery period. The present study was performed to evaluate the occurrence of TSH receptor antibody (TRAb), measured by RRA (TSH binding inhibitor), TRAb measured by stimulation assay (thyroid-stimulating antibody), and TRAb measured by blocking assay [TSH-blocking antibody (TSH-BAb)] activity in 68 patients with SAT who had negative autoantibody titers. The patients were divided into 2 groups: group I, 31 patients who developed hypothyroidism during the recovery period; and group II, 37 patients who remained euthyroid during recovery. Positive immunoglobulin activity occurred in about 20% of group I patients during follow-up, but in only 3% of group II patients. About 20% of group I patients developed positive TSH-BAb activity and were hypothyroid, requiring exogenous hormone therapy for 1.2-3.5 yr, whereas hypothyroidism was relatively transient in group I patients who had negative TSH-BAb activity (2-6 months). Although increased TSH-BAb activity may account for hypothyroidism in some patients with SAT, the precise mechanism for the development of transient hypothyroidism in SAT remains enigmatic.

Thyroid stimulating activity of rabbit antibodies toward the human thyrotropin receptor peptide

We have produced antibodies against a peptide corresponding to the unique N-terminal segment (amino acid residues 29–57) in the extracellular domain of the human thyrotropin (TSH) receptor by immunizing it to rabbits, and evaluated for their thyroid stimulating antibody (TSAb), thyroid stimulation blocking antibody (TSBAb) and TSH-binding inhibitor immunoglobulin (TBII) activities. Antibody raised in rabbit B showed significant TSAb activity but not TSBAb activity. In contrast, antibody raised in rabbit A lacked TSAb activity but possessed TSBAb activity. None of these antibodies had TBII activity. These results indicate that TSH receptor antibody can successfully mimic the action of TSH and also suggest that the N-terminal region of TSH receptor is substantially associated with both TSAb and TSBAb activities, but not parallel to TBII activity.