High-level intrathymic thyrotrophin receptor expression in thyroiditis-prone mice protects against the spontaneous generation of pathogenic thyrotrophin receptor autoantibodies.

The thyrotrophin receptor (TSHR) A-subunit is the autoantigen targeted by pathogenic autoantibodies that cause Graves' hyperthyroidism, a common autoimmune disease in humans. Previously, we reported that pathogenic TSHR antibodies develop spontaneously in thyroiditis-susceptible non-obese diabetic (NOD).H2h4 mice bearing a human TSHR A-subunit transgene, which is expressed at low levels in both the thyroid and thymus (Lo-expressor transgene). The present study tested recent evidence that high intrathymic TSHR expression protects against the development of pathogenic TSHR antibodies in humans. By successive back-crossing, we transferred to the NOD.H2h4 background a human TSHR A-subunit transgene expressed at high levels in the thyroid and thymus (Hi-expressor transgene). In the sixth back-cross generation (> 98% NOD.H2h4 genome), only transgenic offspring produced spontaneously immunoglobulin (Ig)G class non-pathogenic human TSHR A-subunit antibodies. In contrast, both transgenic and non-transgenic offspring developed antibodies to thyroglobulin and thyroid peroxidase. However, non-pathogenic human TSHR antibody levels in Hi-expressor offspring were lower than in Lo-expressor transgenic mice. Moreover, pathogenic TSHR antibodies, detected by inhibition of TSH binding to the TSHR, only developed in back-cross offspring bearing the Lo-expressor, but not the Hi-expressor, transgene. High versus low expression human TSHR A-subunit in the NOD.H2h4 thymus was not explained by the transgene locations, namely chromosome 2 (127-147 Mb; Hi-expressor) and chromosome 1 (22.9-39.3 Mb; low expressor). Nevertheless, using thyroiditis-prone NOD.H2h4 mice and two transgenic lines, our data support the association from human studies that low intrathymic TSHR expression is associated with susceptibility to developing pathogenic TSHR antibodies, while high intrathymic TSHR expression is protective.

A novel method for measuring TBAb activity in TSAb- and TBAb-positive serum.

We reported a conversion assay in which thyroid blocking antibody (TBAb) function as thyroid stimulating antibody (TSAb). TBAb-bound porcine thyroid cells (PTC) were made by incubating TBAb(+) serum and PTC for 1 hour. When these TBAb-bound PTC were incubated 4 h with rabbit anti-human (h) IgG antibody (Ab), cAMP production was high, but when incubated with normal rabbit serum (NRS) cAMP production was low. TBAb-Mnoclonal Ab (MoAb) (KI-70) showed similar conversion. However, when TSAb-MoAb(M22) was assayed, anti-hIgG Ab-produced cAMP was lower than NRS-produced cAMP. When a mixture of M22 and KI-70 was assayed, anti-hIgG Ab-produced cAMP was higher than NRS. Thus, it is possible to determine existence of TBAb in TSAb(+)serum when anti-IgG Ab-produced cAMP is higher than NRS-produced cAMP. In this assay TBAb activity in TSAb(+)serum was scored as positive, gray zone and negative when the difference [anti-hIgG Ab-produced cAMP(%)-NRS-produced cAMP(%)] was >100%, 50-100% and <±50%, respectively. In TSAb(+)sera of Graves' patients with no treatment or anti-thyroid therapy, positive TBAb was 9% (3/33 )and 6.9% (5/72), and gray zone was 18 % (6/33) and 25% (18/72), respectively. A low prevelance of TBAb and low TBAb activity (<200% as cAMP) was found in these Graves' patients. A radioisotope treated Graves' patient showed existence of both TSAb and TBAb at 5 months (NRS, 800% cAMP and anti-IgGAb,1,350% cAMP), and highly positive TBAb (NRS, 180% cAMP and anti-hIgG Ab, 3,200% cAMP) at 30 months. This conversion assay is useful principally for TBAb determination but is also useful for TBAb determination in TSAb(+)serum.

A new small-molecule antagonist inhibits Graves' disease antibody activation of the TSH receptor.

CONTEXT: Graves' disease (GD) is caused by persistent, unregulated stimulation of thyrocytes by thyroid-stimulating antibodies (TSAbs) that activate the TSH receptor (TSHR). We previously reported the first small-molecule antagonist of human TSHR and showed that it inhibited receptor signaling stimulated by sera from four patients with GD. OBJECTIVE: Our objective was to develop a better TSHR antagonist and use it to determine whether inhibition of TSAb activation of TSHR is a general phenomenon. DESIGN: We aimed to chemically modify a previously reported small-molecule TSHR ligand to develop a better antagonist and determine whether it inhibits TSHR signaling by 30 GD sera. TSHR signaling was measured in two in vitro systems: model HEK-EM293 cells stably overexpressing human TSHRs and primary cultures of human thyrocytes. TSHR signaling was measured as cAMP production and by effects on thyroid peroxidase mRNA. RESULTS: We tested analogs of a previously reported small-molecule TSHR inverse agonist and selected the best NCGC00229600 for further study. In the model system, NCGC00229600 inhibited basal and TSH-stimulated cAMP production. NCGC00229600 inhibition of TSH signaling was competitive even though it did not compete for TSH binding; that is, NCGC00229600 is an allosteric inverse agonist. NCGC00229600 inhibited cAMP production by 39 ± 2.6% by all 30 GD sera tested. In primary cultures of human thyrocytes, NCGC00229600 inhibited TSHR-mediated basal and GD sera up-regulation of thyroperoxidase mRNA levels by 65 ± 2.0%. CONCLUSION: NCGC00229600, a small-molecule allosteric inverse agonist of TSHR, is a general antagonist of TSH receptor activation by TSAbs in GD patient sera.

Prevention of autoantibody-mediated Graves'-like hyperthyroidism in mice with IL-4, a Th2 cytokine.

Graves' hyperthyroidism has long been considered to be a Th2-type autoimmune disease because it is directly mediated by autoantibodies against the thyrotropin receptor (TSHR). However, several lines of evidence have recently challenged this concept. The present study evaluated the Th1/Th2 paradigm in Graves' disease using a recently established murine model involving injection of adenovirus expressing the TSHR (AdCMVTSHR). Coinjection with adenovirus expressing IL-4 (AdRGDCMVIL-4) decreased the ratio of Th1/Th2-type anti-TSHR Ab subclasses (IgG2a/IgG1) and suppressed the production of IFN-gamma by splenocytes in response to TSHR Ag. Importantly, immune deviation toward Th2 was accompanied by significant inhibition of thyroid-stimulating Ab production and reduction in hyperthyroidism. However, in a therapeutic setting, injection of AdRGDCMVIL-4 alone or in combination with AdCMVTSHR into hyperthyroid mice had no beneficial effect. In contrast, coinjection of adenoviruses expressing IL-12 and the TSHR promoted the differentiation of Th1-type anti-TSHR immune responses as demonstrated by augmented Ag-specific IFN-gamma secretion from splenocytes without changing disease incidence. Coinjection of adenoviral vectors expressing IL-4 or IL-12 had no effect on the titers of anti-TSHR Abs determined by ELISA or thyroid-stimulating hormone-binding inhibiting Ig assays, suggesting that Ab quality, not quantity, is responsible for disease induction. Our observations demonstrate the critical role of Th1 immune responses in a murine model of Graves' hyperthyroidism. These data may raise a cautionary note for therapeutic strategies aimed at reversing Th2-mediated autoimmune responses in Graves' disease in humans.

The influence of the exon 1 polymorphism of the cytotoxic T lymphocyte antigen 4 gene on thyroid antibody production in patients with newly diagnosed Graves' disease.

Increasing evidence supports the genetic susceptibility for thyroid antibody (TAb) production in patients with autoimmune thyroid disease, and recently, it has been shown that the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene is most likely a major TAb susceptibility gene. To assess the relationship between exon 1 CTLA-4 gene polymorphism and TAb production, we genotyped 67 patients with newly diagnosed Graves' disease. Free thyroid hormones and TAb were measured, including thyroglobulin antibodies (TgAb), thyroid peroxidase antibodies (TPOAb), and thyroid-stimulating antibodies (TSAb). AA genotype was found in 25 patients, AG genotype in 34 patients, and GG genotype in 8 patients. G allele carrying genotypes showed significantly higher frequency of positive TPOAb (p < 0.005) and TgAb (p < 0.05) compared to AA genotype. Furthermore, the median values of TPOAb were significantly higher in the group with G allele (p < 0.002). However, the median values of TgAb and TSAb did not differ significantly between both groups and similarly, CTLA-4 genotype showed no association with serum free thyroxine (T(4)) and Graves' ophthalmopathy. In conclusion, our findings suggest that G allele carrying genotype of the CTLA-4 gene influences higher production of TPOAb and TgAb, and therefore, support the hypothesis that CTLA-4 gene plays a major role in TAb production.

Induction of TSH-receptor antibodies in patients with toxic multinodular goitre by radioiodine treatment.

Previous studies have indicated pre-existing subclinical Graves' disease (GD) in many patients with the scintigraphic diagnosis of disseminated thyroid autonomy (DISA) or toxic multinodular goitre (TMG) type A. After radioiodine (RAI) treatment, an increase or the induction of TSH-receptor antibodies (TRAbs) in patients with GD or TMG has been repeatedly reported. In the present study, we investigated whether RAI could induce TRAbs in patients with TMG in whom pre-existing GD was excluded with highly sensitive TBII and TSAB assays. Therefore, TRAbs, anti-thyroperoxidase antibodies (anti-TPO-Abs) and anti-thyroglobulin antibodies (anti-TG-Abs) were determined in 43 consecutive patients at the nuclear medicine outpatient clinic with the scintigraphic diagnosis of toxic adenoma (TA; n = 20) or TMG type A (n = 11) or type B (n = 12) before and after RAI treatment. After RAI therapy, we detected TRAbs in 36 % (4 of 11) of patients with TMG type A only, whereas TRAbs were not detectable in patients with TMG type B or in patients with TA. Furthermore, 3 of the 4 patients with detectable TRAbs after RAI showed positive anti-TPO-Abs before RAI therapy. These findings provide further evidence for pre-existing GD in patients with TMG type A or DISA as previously suggested. Therefore, patients with TMG type A and high anti-TPO-Abs seem to be at increased risk of developing TRAbs or side-effects such as relapse of hyperthyroidism or thyroid associated ophthalmopathy. These patients therefore require more frequent evaluation after RAI treatment.

Genetic immunization of outbred mice with thyrotropin receptor cDNA provides a model of Graves' disease.

We performed genetic immunization of outbred NMRI mice, using a cDNA encoding the human thyrotropin receptor (TSHr). All mice produced antibodies capable of recognizing the recombinant receptor expressed at the surface of stably transfected Chinese hamster ovary (CHO) cells, and sera from most of the immunized mice blocked TSH-dependent stimulation of cAMP accumulation in cells expressing the TSHr. Five out of 29 female mice showed sign of hyperthyroidism including elevated total T4 and suppressed TSH levels. The serum of these mice contained thyroid-stimulating activity, as measured in a classic assay using CHO cells expressing recombinant TSHr. In contrast, only 1 male out of 30 had moderately elevated serum total T4 with undetectable TSH values. The hyperthyroid animals had goiters with extensive lymphocytic infiltration, characteristic of a Th2 immune response. In addition, these animals displayed ocular signs reminiscent of Graves' ophthalmopathy, including edema, deposit of amorphous material, and cellular infiltration of their extraocular muscles. Our results demonstrate that genetic immunization of outbred NMRI mice with the human TSHr provides the most convincing murine model of Graves' disease available to date.

Characterisation of the antibody response to the extracellular region of recombinant thyrotropin receptor.

Autoantibodies to the human thyrotropin receptor (TSH-R) are pathogenic in a number of autoimmune thyroid diseases including Graves' disease. We have characterised polyclonal antisera to TSH-R for antibodies which may mimic those present in autoimmune thyroid disease. For immunisations, recombinant extracellular region of human TSH-R which does not interact with its ligand TSH was used. The induced antibodies react with the full length membrane receptor in transfected mammalian cells by flow cytometry showing the presence of antibody capable of recognising the native functional receptor. The properties of the generated antibodies have been compared after two injections or following a multiple immunisation protocol with the receptor in adjuvant. High titre antisera were readily generated after the short injection protocol and further immunisations did not lead to any change in antibody titers. Analysis of the epitopes recognised using synthetic peptides confirmed previous observations that the immunodominant determinants localise to the amino and the carboxyl terminal part of the extracellular region of the receptor. Antisera from both rabbits contain TSH blocking antibody as assessed by inhibition of TSH mediated cAMP stimulation. There was an increase in TSH binding inhibitory immunoglobulin (TBII) activity with multiple injections. Furthermore, the increase in TBII activity was not related to spreading of the antibody response to new determinants on TSH-R. Our results support previous observations on the difficulties in reproducing, by adjuvant immunisation with recombinant TSH-R preparations, the fine specificity of antibodies to TSH-R present in autoimmune disorders such as Graves' disease or primary myxoedema.

Production of thyroid-stimulating antibodies in mice by immunization with T-cell epitopes of human thyrotropin receptor.

We examined whether mice, immunized with TSH receptor (TSH-R) peptides, which are known to be T-cell epitopes in patients with Graves' disease, would show thyroid-stimulating antibody (TSAb). We immunized DBA/1J mice with TSH-R peptide amino acids 132-150, 145-163, 158-176, and 172-186 and with a pool of these four peptides. The antibodies produced in these mice were evaluated by measurement of TSAb activity using Chinese hamster ovary cells expressing human TSH-R. Seven of 20 mice showed TSAb activity that could be partially blocked with TSH-R peptides. To assess the role of T-cell epitope-specific T-cells in the production of TSAb, we transferred a T-cell line developed from a TSAb-positive mouse to other syngeneic DBA/1J mice. Two of 4 recipient mice showed TSAb activities. These findings suggest that specific T-cell epitopes of TSH-R play a crucial role in the production of TSAb.

Isolation of Epstein-Barr-virus-transformed lymphocytes producing IgG class monoclonal antibodies using a magnetic cell separator (MACS): preparation of thyroid-stimulating IgG antibodies from patients with Graves' disease.

In autoimmune diseases, IgG class autoantibodies are generally considered to be more pathognomonic than IgM class ones. Although Epstein-Barr virus (EBV)-transformation of lymphocytes is a useful method to obtain human monoclonal autoantibodies, it tends to result predominantly in IgM-producing cells. We depleted IgM+ cells before EBV-transformation with a Magnetic Cell Separator (MACS) in order to increase the chance of acquisition of cells producing IgG class anti-thyrotropin (TSH) receptor antibodies (TRAb). As a result, we obtained four independent B cell clones producing IgG class monoclonal thyroid-stimulating antibodies (TSAb) from three patients with Graves' disease. None of these clones showed any TSH binding inhibitor immunoglobulin (TBII) activity, suggesting independence of TSAb-producing lymphocytes from those producing TBII.