Regulation of major histocompatibility class II gene expression in FRTL-5 thyrocytes: opposite effects of interferon and methimazole

Safety of long-term antithyroid drug treatment? A systematic review

Continued low-dose MMI treatment for longer than 12-18 months may be considered in patients not in remission. However, ATDs are not free from adverse effects. We undertook a systematic review to clarify safety of long-term ATD treatment. Medline and the Cochrane Library for trials published between 1950 and Nov 2018 were systematically searched. We included original studies containing data for long-term (> 18 months) ATD treatment. Two reviewers independently extracted data from included trials and any disagreement was adjudicated by consensus. Of 615 related articles found, 12 fulfilled the criteria. Six articles had data for adults, five for non-adults and one article had data for both groups. The sample sizes ranged between 20 and 249 individuals, and the mean duration of ATD treatment ranged between 2.1 and 14.2 years. Considering all data from 1660 patients treated with ATD for a mean duration of 5.8 years (around 10,000 patient-years), major complications occurred only in 14 patients: 7 severe agranulocytosis, 5 severe liver damage, one ANCA-associated glomerulonephritis and one vasculitis with small cutaneous ulcerations. Minor complications rates were between 2 and 36%, while more complications were in higher doses and in the children. The most reported AE was cutaneous reaction; the other adverse events were elevated liver enzymes, leukocytopenia, arthritis, arthralgia, myalgia, thrombocytopenia, fever, nausea and oral aphthous. Long-term ATD treatment is safe, especially in low dose and in adults, indicating that it should be considered as an earnest alternative treatment for GD.

Long-term Methimazole Therapy in Juvenile Graves' Disease: A Randomized Trial

BACKGROUND AND OBJECTIVES

Recent studies show that long-term (LT) antithyroid drugs reduce relapse of hyperthyroidism in patients with Graves' disease. Our objective was to evaluate the effectiveness and safety of LT methimazole treatment and to compare remission rates in Graves' disease patients after LT and short-term (ST) therapy.

METHODS

In this randomized, parallel group trial, 66 consecutive patients with untreated juvenile Graves' hyperthyroidism were enrolled. After a median 22 months of methimazole treatment, 56 patients were randomly assigned to either continue low-dose methimazole treatment (n = 24, LT group) or to discontinue treatment (n = 24, ST group). Twenty-four patients in LT group completed 96 to 120 months of methimazole treatment. Patients in both groups were managed for 48 months after discontinuation of treatment.

RESULTS

Except for 3 cases of cutaneous reactions, no other adverse events were observed throughout 120 months of methimazole therapy. Serum free thyroxine, triiodothyronine, thyrotropin, and thyrotropin receptor antibody remained normal, and the required daily dosage of methimazole was gradually decreased from 5.17 ± 1.05 mg at 22 months to 3.5 ± 1.3 mg between 96 and 120 months of treatment (P < .001). Hyperthyroidism was cured in 92% and 88% of LT patients and in 46% and 33% of ST patients, 1 and 4 years after methimazole withdrawal, respectively.

CONCLUSIONS

LT methimazole treatment of 96 to 120 months is safe and effective for treatment of juvenile Graves' disease. The four-year cure rate of hyperthyroidism with LT methimazole treatment is almost 3 times more than that of ST methimazole treatment.

Positive selection in coding regions and motif duplication in regulatory regions of bottlenose dolphin MHC class II genes

The vertebrate immune response is mediated through highly adaptive, quickly evolving cell surface receptors, the major histocompatibility complex (MHC). MHC molecules bind and present a diverse array of pathogenic molecules and trigger a cascade of defenses. Use of MHC variation as a marker for population health has also evolved quickly following advances in sequencing methods. We applied a combination of traditional and next generation sequencing methodology to characterize coding (peptide binding region) and regulatory (proximal promoter) sequence variation in MHC Class II DQA and DQB genes between estuarine and coastal populations of the bottlenose dolphin, Tursiops truncatus, an apex predator whose health status is indicative of anthropogenic impacts on the ecosystem. The coding regions had 10 alleles each at DQA and DQB; the promoters had 6 and 7 alleles at DQA and DQB, respectively with variation within key regulatory motifs. Positive selection was observed for the coding regions of both genes while both coding and promoter regions exhibited geographic differences in allele composition that likely indicates diversifying selection across habitats. Most notable was the discovery of a complete duplication of a 14-bp T-box motif in the DQA promoter. Four class II promoter regions (DQA, DQB, DRA, DRB) were characterized in species from four cetacean families (Delphinidae, Monodontidae, Lipotidae, and Physeteridae) and revealed substantial promoter structural diversity across this order. Peptide binding regions may not be the only source of adaptive potential within cetacean MHC for responding to pathogenic threats. These findings are the first analysis of cetacean MHC regulatory motifs, which may divulge unique immunogenetic strategies among cetaceans and reveal how MHC transcriptional control continues to evolve. The combined MHC regulatory and coding data provide new genetic context for distinct vulnerability profiles between coastal and estuarine populations, which are key concerns for health and risk management.

Long-Term Antithyroid Drug Treatment: A Systematic Review and Meta-Analysis

BACKGROUND

Several studies have reported inconsistent findings on the advantages and disadvantages of long-term treatment with antithyroid drugs (ATD). A systematic review and meta-analysis was undertaken to clarify the numerous aspects of long-term treatment with ATD.

METHODS

Medline and the Cochrane Library for trials published between 1950 and May 2016 were systematically searched. Studies containing data for long-term (>24 months) ATD treatment were included. Summary estimates of pooled prevalence, odds ratio, and weighted mean difference were calculated with a random effects model.

RESULTS

Of 587 related articles found, six fulfilled the inclusion criteria. Long-term ATD treatment induced a remission rate of 57% [confidence interval (CI) 45-68%], a rate that was higher in adults than in non-adults (61% vs. 53%). The rate of complications was 19.1% [CI 9.6-30.9%], of which only 1.5% were major complications. The annual remission rate for each year of treatment was 16% [CI 10-27%], which was higher in adults than non-adults (19% vs. 14%). However, it should be noted that this is not a true linear correlation, but a positive relationship can be suggested between time and remission rate. Meta-regression revealed that smoking had a significant lowering effect on remission rate.

CONCLUSIONS

Long-term ATD treatment is effective and safe, especially in adults, indicating that it should be considered as an alternative treatment for Graves' disease.

Propylthiouracil increases sodium/iodide symporter gene expression and iodide uptake in rat thyroid cells in the absence of TSH

BACKGROUND

Propylthiouracil (PTU) and methimazole (MMI) are drugs that are widely used to treat Graves' disease. Although both exert an antithyroid effect primarily by blocking thyroid peroxidase activity, their molecular structure and other actions are different. We hypothesized that PTU and MMI may have differential effects on thyroid-specific gene expression and function.

METHODS

The effects of PTU and MMI on thyroid-specific gene expression and function were examined in rat thyroid FRTL-5 cells using DNA microarray, reverse transcriptase (RT)-polymerase chain reaction (PCR), real-time PCR, Western blot, immunohistochemistry, and radioiodine uptake studies.

RESULTS

DNA microarray analysis showed a marked increase in sodium/iodide symporter (NIS) gene expression after PTU treatment, whereas MMI had no effect. RT-PCR and real-time PCR analysis revealed that PTU-induced NIS mRNA levels were comparable to those elicited by thyroid-stimulating hormone (TSH). PTU increased 5'-1880-bp and 5'-1052-bp activity of the rat NIS promoter. While PTU treatment also increased NIS protein levels, the size of the induced protein was smaller than that induced by TSH, and the protein localized predominantly in the cytoplasm rather than the plasma membrane. Accumulation of (125)I in FRTL-5 cells was increased by PTU stimulation, but this effect was weaker than that produced by TSH.

CONCLUSIONS

We found that PTU induces NIS expression and iodide uptake in rat thyroid FRTL-5 cells in the absence of TSH. Although PTU and MMI share similar antithyroid activity, their effects on other thyroid functions appear to be quite different, which could affect their therapeutic effectiveness.

Regulation of major histocompatibility complex gene expression in thyroid epithelial cells by methimazole and phenylmethimazole

Increased expression of major histocompatibility complex (MHC) class-I genes and aberrant expression of MHC class-II genes in thyroid epithelial cells (TECs) are associated with autoimmune thyroid diseases. Previous studies have shown that methimazole (MMI) reduces MHC class-I expression and inhibits interferon-gamma (IFN-gamma or IFNG as listed in the MGI Database)-induced expression of the MHC class-II genes in TECs. The action of MMI on the MHC class-I genes is transcriptional, but its mechanism has not been investigated previously. In the present study, we show that in Fisher rat thyroid cell line 5 cells, the ability of MMI and its novel derivative phenylmethimazole (C10) to decrease MHC class-I promoter activity is similar to TSH/cAMP suppression of MHC class-I and TSH receptor genes, and involves a 39 bp silencer containing a cAMP response element (CRE)-like site. Furthermore, we show that C10 decreases MHC class-I gene expression to a greater extent than MMI and at 10- to 50-fold lower concentrations. C10 also reduces the IFN-gamma-induced increase in the expression of MHC class-I and MHC class-II genes more effectively than MMI. Finally, we show that in comparison to MMI, C10 is a better inhibitor of specific protein-DNA complexes that are formed with a CRE-like element on the MHC class-II promoter. These data support the conclusion that the immunosuppressive mechanism by which MMI and C10 inhibit MHC gene expression mimics 'normal' hormonal suppression by TSH/cAMP.

Lack of effect of methimazole on dendritic cell (DC) function and DC-induced Graves' hyperthyroidism in mice

In addition to the biochemical inhibition of thyroid hormone synthesis, antithyroid drugs including methimazole (MMI) may have immunosuppressive effect through inhibition of major histocompatibility complex (MHC) class I and II expressions on non-professional (thyrocytes) and professional (macrophages and B cells) antigen presenting cells (APCs). Dendritic cells (DCs) are another professional APCs and very likely play the most important role in the primary immune response. Therefore, we focused in this study on evaluating the effect of MMI on DC function in mice. Bone marrow cells cultured with granulocyte macrophage colony stimulating factor and interleukin (IL)-4 expressed high levels of CD11c and moderate levels of MHC class II, both of which are widely used markers for DCs. In vitro incubation of this DC-containing cell population with 10(- 6)-10(- 4) M MMI for 2 days did not change basal- and maturation signal (adenoviral infection and lipopolysaccharide)-induced levels of the cell surface marker expressions such as MHC class I and II, CD86, CD40 and DEC205, and of proinflammatory cytokine IL-6 release. Further we found that treatment of the DC-containing cell population with MMI did not influence the incidence of Graves' hyperthyroidism and anti-thyrotropin receptor (TSHR) antibody titers in a mouse Graves' model we have recently established with DCs infected with adenovirus expressing the TSHR A subunit. Although we cannot completely exclude immunosuppressive effect of MMI on other immune cells, our data indicate that DCs do not appear to be the primary target for the immunosuppressive effect of MMI.

Long-term follow-up of patients with hyperthyroidism due to Graves' disease treated with methimazole. Comparison of usual treatment schedule with drug discontinuation vs continuous treatment with low methimazole doses: a retrospective study

Antithyroid drugs may be proposed as the firstline therapy for hyperthyroidism due to Graves' disease since some patients undergo prolonged remission after drug withdrawal. On the other hand, some studies, though controversial, indicated that methimazole (MMI) has some immunomodulating activity. We retrospectively analyzed 384 consecutive patients newly diagnosed with Graves' disease in the years 1990-2002 to ascertain whether long-term therapy with low doses of MMI may prevent relapse of thyrotoxicosis. Two hundred and forty-nine patients were included in our study. The date of reduction of MMI dose to 5 mg/day was considered time 0 for survival analysis. In 121 MMI was discontinued in less than 15 months after time 0 (group D), while in the remaining 128 a daily MMI 2.5-5 mg dose was maintained (group M). One hundred and thirty-five patients were excluded for inadequate response to MMI, relapse of thyrotoxicosis that could be related to an improper withdrawal or reduction of MMI, inadequate or too short followup, iodide contamination, steroid or interferon therapy, pregnancy or post-partum. D and M groups did not differ for clinical and hormonal parameters except age, which was lower in D (p=0.019). Age > vs < 35 yr was relevant in survival analysis; therefore patients were divided in 2 groups according to this age cut-off. In younger patients relapse of thyrotoxicosis occurred in 15 patients of group D 2.4-39.6 months (median 19.0) after time 0, and 8 M after 5.9-40.0 (21.3) months, while 14 D and 5 M maintained euthyroidism until the end of the observation after 31.8-95.3 (56.6) months and 30.4-62.1 (46.5) months, respectively. Survival analysis indicated that the risk of relapse was similar in group D and M. In older patients relapse of thyrotoxicosis occurred in 40 patients of group D after 8.2-65.8 (25.4) months and 29 M after 5.8-62.5 (22.4) months, while 52 D and 86 M maintained euthyroidism until the end of the observation, 20.1-168.0 (46.7) months and 24.1-117.4 (53.4) months respectively. Survival analysis indicated that the risk of relapse was increased in group D. Therefore long-term treatment with low doses of MMI seems to prevent relapse in Graves' disease in patients above 35 yr of age. This should be confirmed in a prospective study.

Antithyroid drugs inhibit thyroid hormone receptor-mediated transcription

CONTEXT

Methimazole (MMI) and propylthiouracil (PTU) are widely used as antithyroid drugs (ATDs) for the treatment of Graves' disease. Both MMI and PTU reduce thyroid hormone levels by several mechanisms, including inhibition of thyroid hormone synthesis and secretion. In addition, PTU decreases 5'-deiodination of T(4) in peripheral tissues. ATDs may also interfere with T(3) binding to nuclear thyroid hormone receptors (TRs). However, the effect of ATDs on the transcriptional activities of T(3) mediated by TRs has not been studied.

OBJECTIVE

The present study was undertaken to determine whether ATDs have an effect on the gene transcription regulated by T(3) and TRs in vitro.

METHODS

Transient gene expression experiments and GH secretion assays were performed. To elucidate possible mechanisms of the antagonistic action of ATDs, the interaction between TR and nuclear cofactors was examined.

RESULTS

In the transient gene expression experiments, both MMI and PTU significantly suppressed transcriptional activities mediated by the TR and T(3) in a dose-dependent manner. In mammalian two-hybrid assays, both drugs recruited one of the nuclear corepressors, nuclear receptor corepressor, to the TR in the absence of T(3). In addition, PTU dissociated nuclear coactivators, such as steroid receptor coactivator-1 and glucocorticoid receptor interacting protein-1, from the TR in the presence of T(3). Finally, MMI decreased the GH release that was stimulated by T(3).

CONCLUSIONS

ATDs inhibit T(3) action by recruitment of transcriptional corepressors and/or dissociation of coactivators. This is the first report to show that ATDs can modulate T(3) action at the transcriptional level.

Overexpression of CIITA in T cells aggravates Th2-mediated colitis in mice

The MHC class II transactivator (CIITA) is the master transcriptional regulator of genes involved in MHC class II restricted antigen presentation. Previously we suggested another role of CIITA in Th1/Th2 balance by demonstrating that forced expression of CIITA in murine T cells repressed Th1 immunity both in vitro and in vivo. However, the results were contradictory to the report that CIITA functioned to suppress the production of Th2 cytokine by CD4+ T cells in CIITA deficient mice. In this study, we investigated the influence of constitutive expression of CIITA in T cells on Th2 immune response in vivo using murine experimental colitis model. In the dextran sodium sulfate-induced acute colitis, a disease involving innate immunity, CIITA transgenic mice and wild type control mice showed similar progression of the disease. However, the development of oxazolone-induced colitis, a colitis mediated by predominantly Th2 immune response, was aggravated in CIITA-transgenic mice. And, CD4+ T cells from the mesenteric lymph node of CIITA-transgenic mice treated with oxazolone exhibited a high level of IL-4 secretion. Together, these data demonstrate that constitutive expression of CIITA in T cells skews immune response to Th2, resulting in aggravation of Th2-mediated colitis in vivo.

Methimazole upregulates T-cell-derived cytokines without improving the existing Th1/Th2 imbalance in Graves' disease

There is probably a systemic shift of cytokine production in patients with Graves' disease (GD) toward the Th2 cytokine response. Methimazole (MMI) is the first choice for patients with GD and presumably has some direct immunomodulatory action. The aim of this study was to evaluate the balance shift in Th1/Th2 cytokines in patients with GD after 1 yr of MMI treatment, when compared to the same balance in patients with newly diagnosed GD before treatment and in healthy controls. Peripheral blood mononuclear cells (PBMC) were isolated from 17 healthy volunteers, from 18 patients with newly diagnosed GD before treatment and from 15 euthyroid patients with GD after 1 yr of MMI treatment. The PBMC were activated with ionomycin and phorbol 12-myristate 13-acetate (PMA). The concentrations of Th1/Th2 related cytokines [interferon (IFN)-gamma, interleukin (IL)-12 vs IL-4, IL-10] in the culture supernatants were measured by ELISA. PBMC from patients with GD after treatment produced significantly more IFN-gamma and IL-4 than PBMC from patients with GD before treatment, but there were no significant differences in calculated ratios of Th1 against Th2 cytokines between these two groups. When compared to PBMC from healthy controls, PBMC from patients with GD after treatment produced significantly more IL-4 and significantly less IL-12. The calculated IL-12/IL-4 ratio after treatment was significantly lower than the same ratio from healthy controls. In conclusion, our results show no significant change in the ratio between Th1 and Th2 cytokines produced by PBMC from patients with GD after 1 yr of MMI treatment, when compared to the ratio before treatment. The ongoing prevalence of the Th2 immune response after treatment speaks against the immunomodulatory action of the drug on the systemic level.

Methimazole protects from experimental autoimmune uveitis (EAU) by inhibiting antigen presenting cell function and reducing antigen priming

Methimazole (methyl-mercapto-imidazole, MMI), a compound used clinically in therapy of Graves' thyroiditis, was found to inhibit development of several autoimmune diseases in animal models. It was suggested on the basis of in vitro data that inhibition is through down-regulation of interferon-gamma (IFN-gamma)-induced expression of major histocompatibility complex class I and class II molecules. Here, we investigate the effect of MMI on experimental autoimmune uveoretinitis (EAU) and study its mechanism(s). Treatment of EAU with MMI administered in drinking water inhibited induction of the disease and associated antigen (Ag)-specific proliferation and cytokine production by draining lymph node cells (LNCs). The treatment was protective only if administered during the first but not during the second week after immunization, suggesting an effect on the induction phase of EAU. It is interesting that MMI inhibited disease in IFN-gamma knockout mice, indicating that the in vivo protective effect is IFN-gamma-independent. Flow cytometric analysis of draining LNCs extracted 5 days after immunization showed that MMI partly to completely reversed the increase in Mac-1(+)/class I(+)/class II(+) cells induced by immunization and reduced the proportion of B7-1 and CD40-positive cells, suggesting a deficit in the Ag-presenting cell (APC) population. APC from untreated mice largely restored antigen-specific proliferation of MMI-treated LNCs. We suggest that MMI inhibits EAU at least in part by preventing the recruitment and/or maturation of APC, resulting in reduced generation of Ag-specific T cells.

Patterned variation in murine MHC promoters

To compare variation in regulatory and coding DNA, promoter sequences have been obtained from wild-derived mice and laboratory rats. The sequences are from the proximal promoter of the H2Aa, H2Ab, H2Eb, and H2K genes of 24 wild-derived inbred strains and a sample of the corresponding exon 2 sequences and of the RT1.Ba gene of six strains of laboratory rat. They reveal a high level of variation in the mouse MHC class II promoters (H2A and H2E), a low level in MHC class I (H2K), and none in the rat. The variation is pronounced in and around the cAMP response element, a major binding site for modulating promoter activity in response to external stimulation. This finding, together with the different levels of variation in MHC classes I and II, is suggestive of natural selection. However, selection operating via the MHC coding sequences must also contribute, as indicated by the minimal variation in both the MHC class II promoter and coding sequences of the rat. Furthermore CIITA (trans-activator of class II) of the mouse has been reported to have minimal variation in its promoter and none in its coding sequence. Taken together these data suggest that the regulatory and coding sequences undergo coselection. Each of the mouse class II promoters has a pattern of variation that appears to be basically dimorphic, with further variation added by recombination/mutation. The dimorphic allelic lineages are in marginally detectable linkage disequilibrium with the exon 2 sequences, particularly in H2Aa, thus lending further support to the coevolution hypothesis.

Antithyroid drugs inhibit in vivo HLA-DR expression in thyroid follicular cells in Graves' disease

Antithyroid drugs have been reported to reduce the expression of HLA-DR in thyrocytes in Graves' disease, but only circumstantial evidence has been provided about their in vivo immunologic effects. This present study was designed to examine the in vivo immunologic effect of antithyroid drugs on thyroid follicular cells. The study was conducted on 25 patients who had Graves' disease in remission or in activity and who were or were not receiving treatment (7 in overt thyrotoxicosis, 6 patients in remission, and 12 patients under medication). HLA-DR expression in thyroid biopsies was verified by immunohistochemistry. The follicular cells of all patients in overt thyrotoxicosis expressed HLA-DR whereas those of patients in remission were negative for HLA-DR. HLA-DR was also not expressed in all patients under medication, but this did not correlate with the clinical evolution after thyroid drug withdrawal. In conclusion, antithyroid drugs inhibit follicular cell HLA-DR expression in Graves' disease, when thyrotoxicosis is controlled. This suggests that additional mechanisms not involving HLA-DR play a role in thyroid autoimmune disease.

Graves' disease: a host defense mechanism gone awry

In this report we summarize evidence to support a model for the development of Graves' disease. The model suggests that Graves' disease is initiated by an insult to the thyrocyte in an individual with a normal immune system. The insult, infectious or otherwise, causes double strand DNA or RNA to enter the cytoplasm of the cell. This causes abnormal expression of major histocompatibility (MHC) class I as a dominant feature, but also aberrant expression of MHC class II, as well as changes in genes or gene products needed for the thyrocyte to become an antigen presenting cell (APC). These include increased expression of proteasome processing proteins (LMP2), transporters of antigen peptides (TAP), invariant chain (Ii), HLA-DM, and the co-stimulatory molecule, B7, as well as STAT and NF-kappaB activation. A critical factor in these changes is the loss of normal negative regulation of MHC class I, class II, and thyrotropin receptor (TSHR) gene expression, which is necessary to maintain self-tolerance during the normal changes in gene expression involved in hormonally-increased growth and function of the cell. Self-tolerance to the TSHR is maintained in normals because there is a population of CD8- cells which normally suppresses a population of CD4+ cells that can interact with the TSHR if thyrocytes become APCs. This is a host self-defense mechanism that we hypothesize leads to autoimmune disease in persons, for example, with a specific viral infection, a genetic predisposition, or even, possibly, a TSHR polymorphism. The model is suggested to be important to explain the development of other autoimmune diseases including systemic lupus or diabetes.

Role of peroxiredoxins in regulating intracellular hydrogen peroxide and hydrogen peroxide-induced apoptosis in thyroid cells

Peroxiredoxins (Prxs) play an important role in regulating cellular differentiation and proliferation in several types of mammalian cells. One mechanism for this action involves modulation of hydrogen peroxide (H(2)O(2))-mediated cellular responses. This report examines the expression of Prx I and Prx II in thyroid cells and their roles in eliminating H(2)O(2) produced in response to thyrotropin (TSH). Prx I and Prx II are constitutively expressed in FRTL-5 thyroid cells. Prx I expression, but not Prx II expression, is stimulated by exposure to TSH and H(2)O(2). In addition, methimazole induces a high level of Prx I mRNA and protein in these cells. Overexpression of Prx I and Prx II enhances the elimination of H(2)O(2) produced by TSH in FRTL-5 cells. Treatment with 500 micrometer H(2)O(2) causes apoptosis in FRTL-5 cells as evidenced by standard assays of apoptosis (i.e. terminal deoxynucleotidyl transferase deoxyuridine triphosphate-biotin nick end labeling, BAX expression, and poly(ADP-ribose) polymerase cleavage. Overexpression of Prx I and Prx II reduces the amount of H(2)O(2)-induced apoptosis measured by these assays. These results suggest that Prx I and Prx II are involved in the removal of H(2)O(2) in thyroid cells and can protect these cells from undergoing apoptosis. These proteins are likely to be involved in the normal physiological response to TSH-induced production of H(2)O(2) in thyroid cells.

Transcriptional regulation of the MHC II gene DRA in untransformed human thyrocytes

MHC class II molecules are heterodimeric, polymorphic transmembrane glycoproteins physiologically expressed on cells of the immune system and pathologically expressed on the affected target cells of autoimmunity. Their function is to present processed peptides to antigen-specific CD4(+) T cells. To understand the molecular mechanism of the regulation of class II genes in autoimmune target cell thyrocytes, we investigated the transcriptional regulation of DRA on untransformed, differentiated human thyroid cells following IFN-gamma stimulation, which is potentially relevant to the inappropriate class II expression found in Graves' disease. Data from this study show that IFN-gamma enhances a promoter Y box binding protein and induces an X box binding protein in untransformed thyrocytes, but not in SV-40-transfected thyrocytes. Initial characterization of the proteins has indicated that the Y box binding protein is approximately 132 kDa in size while the X box binding protein binds to the X2 region and is approximately 116 kDa. The X box binding protein may correspond to poly(ADP-ribose) polymerase, a recently described component of the X2 box binding protein, X2BP. In addition, the signal transducer and activator of transcription 1alpha protein (STAT1alpha) is also induced by IFN-gamma in these cells. These results further suggest that there are differences in class II gene regulation between differentiated cells and transformed cell lines.

Hypothyroidism in transgenic mice expressing IFN-gamma in the thyroid

IFN-gamma has been implicated with contradictory results in the pathogenetic process of autoimmune (Hashimoto's) thyroiditis, the most common cause of hypothyroidism in adults. To test whether the local production of IFN-gamma can lead to thyroid dysfunction, we have generated transgenic mice that express constitutively IFN-gamma in the thyroid follicular cells. This expression resulted in severe hypothyroidism, with growth retardation and disruption of the thyroid architecture. The hypothyroidism derived from a profound inhibition of the expression of the sodium iodide symporter gene. Taken together, these results indicate a direct role of IFN-gamma in the thyroid dysfunction that occurs in autoimmune thyroiditis.

Differential effects of acute and chronic exposure to interferon-gamma on cyclic adenosine 3',5'-monophosphate response element-regulated gene expression

TSH stimulates proliferation and maintains differentiated function in thyroid follicular cells. The mitogenic activity and the stimulatory effects of TSH on thyroid-specific gene expression are impaired by interferon-gamma (IFNgamma); however, the mechanisms for these effects have not been elucidated in detail. We examined the effects of IFNgamma on acute responses to TSH in rat thyroid cells. IFNgamma did not impair TSH-stimulated p70/p85 ribosomal protein S6 kinase (p70/p85s6k) activity or cAMP response element (CRE)-regulated gene expression, although it inhibited DNA synthesis and thyroglobulin expression, effects measured over a more prolonged time course than those on kinase activity and reporter gene expression. Unexpectedly, when cells were chronically exposed to IFNgamma, CRE-lacZ promoter activity was decreased, whereas other cAMP-mediated signals, such as p70/p85s6k activity and CRE-binding protein phosphorylation, were unaffected. Activating protein-1-regulated promoters were also impaired by IFNgamma treatment, but with kinetics that differed from those of CRE-regulated promoters. Neither acute nor chronic treatment with interleukin-1beta impaired cAMP signaling, indicating that the effects of IFNgamma are specific. These studies identify CRE- and activating protein-1-regulated promoters as targets of IFNgamma in thyroid cells and fibroblasts. IFNgamma-mediated inhibition of these promoters, in addition to those containing thyroid-specific transcription factor-1-binding sites, may contribute to the profound effects of IFNgamma on thyroid cells.

The effect of methimazole, iodine and splenocytes on thyroid transplants in BB/Wor rats

BACKGROUND

BB/Wor rats develop spontaneous autoimmune insulin-requiring diabetes mellitus and lymphocytic thyroiditis (LT). Our investigations examined the effect of the thyroid-specific agents, iodine and methimazole (MMI) on thyroid graft survival in BB/Wor rats, compared the intrathyroidal cytokine mRNA expression of endogenous and engrafted thyroids, and ascertained whether unfractionated splenocytes could protect thyroid grafts from lymphocytic infiltration.

METHODS

In study 1, 0.025% iodine water-treated LT-prone NB line BB/Wor rats were randomized to receive one of the following treatments: (1) 1.0 x 10(8) splenocytes, IV from LT-resistant WA line BB/Wor rats, (2) WA rat thyroid transplants, (3) both, or (4) neither (controls). In study 2, after thyroid transplantation, LT-prone BB/Wor rats were randomized to receive (1) WA splenocytes, (2) 0.025% iodine water, (3) 0.05% MMI water or, (4) tap water (controls). The incidence of LT was determined by microscopic inspection after hematoxylin and eosin staining. Lymphocytic infiltrates were characterized by immunohistochemistry. Cytokine mRNA was detected by RT-PCR.

RESULTS

Grafts from MMI-treated rats had a significantly lower incidence of lymphocytic infiltration (MMI: 2/5; Tap: 5/5; I 5/5, P<0.05, chi2). IL-10 mRNA was expressed in 77% (7/9) endogenous thyroids and 20% (1/5) of the transplanted WA thyroids (P<0.05, chi2) from iodine-treated rats with LT. There was no difference in IL-12 mRNA expression. Lymphocytic infiltration occurred in 100% of the splenocyte-treated graft recipients. Both endogenous and engrafted thyroids contained CD4 and C8 T cells with scattered IgG staining.

CONCLUSION

Target organ-specific interventions that suppress antigen presentation may have an adjunctive role in transplantation tolerance. The differential expression of IL-10 may indicate preferential Th2 lymphocyte activation in the endogenous tissues.

Nicotinamide potentiates TSHR and MHC class II promoter activity in FRTL-5 cells

Here we show that nicotinamide modulates the promoter activity of rat thyrotropin (TSHR) and major histocompatibility complex (MHC) class II genes in rat FRTL-5 thyroid cells, and have identified a novel mechanism for its action. TSHR and MHC class II, are potentiated through reduced expression of a common repressor of these two genes, TSEP-1 (TSHR suppressor element binding protein-1)/YB-1. Thus we show that TSHR mRNA is increased and TSHR promoter activity was concentration-dependently activated from 0 to 40 mM nicotinamide. The promoter lengths of TSHR and MHC class II containing TSEP/YB-1 binding sites were enhanced by 40 mM nicotinamide, but not the ones deleted of these binding sites. TSEP-1/YB-1 binding to the recognition sites in both TSHR and MHC class II promoters was reduced in nicotinamide-treated FRTL-5 nuclear extracts. Nicotinamide reduced the expression of TSEP-1/YB-1 mRNA and TSEP-1/YB-1 protein in the nucleus.

Thyrotropin receptor epitopes recognized by graves' autoantibodies developing under immunosuppressive therapy

Abnormal modulation of the immune system is a prerequisite for the expression of Graves' disease. Thus, when hyperthyroidism developed in a renal transplant recipient under long term immunosuppression with cyclosporine A and prednisone, we carefully evaluated the basis for her hyperthyroidism and her state of immunosuppression. Immunosuppression was confirmed by finding markedly deficient lymphocyte responses to common mitogens. Lymphocyte phenotype frequencies were those previously found in Graves', i.e. elevated frequencies of CD3/DR, CD5/26, and CD3/25 lymphocytes. There was also reversal of the CD4/CD8 ratio due to increased CD8 frequency; this is not a typical finding in autoimmune hyperthyroidism, but has been seen in the intrathyroidal lymphocyte populations of some Graves' patients and is associated with other forms of autoimmunity. The patient's serum contained a broad spectrum of TSH receptor autoantibodies (TSHRAbs) characteristic of Graves' disease. To determine whether these were an unusual population of autoantibodies, we determined their functional epitopes before and for nearly 1 yr after radioiodine therapy. Stimulating TSHRAbs that increase cAMP levels were human receptor (TSHR) specific and consistently recognized functional epitopes located on TSHR residues 90-165. Stimulating TSHRAbs that increased arachidonate release and inositol phosphate levels recognized residues 25-90, as did TSH binding inhibitory Igs present in the patient. These data demonstrate that Graves' disease with a wide array of TSHRAbs can develop in a patient despite adequate immunosuppression. More importantly, they show that the cAMP-stimulating TSHRAb associated with disease expression in this patient had a homogeneous subtype dependent on TSHR residues 90-165. As persistence of this type of TSHRAb over time has been associated with resistance to methimazole therapy in Graves' patients, we speculate that the development and persistence of TSHRAb with this homogeneous epitope may be linked to resistance to immunosuppressive therapy.

Regulation of HLA-DR and costimulatory B7 molecules in human thyroid carcinoma cells: differential binding of transcription factors to the HLA-DRalpha promoter

The consequence of autoantigen presentation by thyroid cells is dependent on the magnitude of expression of both HLA class II antigens (mainly HLA-DR) and costimulatory molecules, such as B7 (CD80 and CD86). Autoimmune thyrocytes are induced to express HLA-DR by interferon-gamma (IFN-gamma). The costimulatory signal leading to autoantibody production or cytotoxic T-cell immune response could be provided by antigen presenting cells (APCs) attracted to the thyroid by the primary autoimmune stimulus. Malignant thyrocytes can express HLA-DR antigens either constitutively, as a result of a nonimmunologic stimulus, or on induction with IFN-gamma after triggering of an immune response. However, their ability to express B7 molecules, which may determine enhanced antitumoral immune response mainly in the absence of intrathyroidal macrophages, has not yet been studied. The regulation of HLA-DR gene expression in APCs, such as B cells, is mediated by a series of short DNA consensus sequences located in the promoter, termed the W, X, and Y boxes, which bind several known transcription factors. We have previously characterized the expression of HLA-DR in four human thyroid carcinoma cell lines and found differences between constitutive and high- or moderate-induced expression of the protein and mRNA. Evaluation of B7 expression on the surface of thyroid cancer cells and understanding the mechanisms of HLA-DR gene expression may help in designing efficient immune response to thyroid tumors. Using the electrophoretic mobility shift assay (EMSA), we have demonstrated differences between the four thyroid cell lines in the binding of transcription factors to each of the three boxes. The binding to the promoter in each of the cell lines resulted in a single band, probably representing a complex of proteins formed via protein-protein interactions. Using flow cytometry we have shown that the B7 molecule was absent in the four thyroid cell lines and could not be induced by IFN-gamma. The absence of surface B7 molecules from the malignant thyroid cells may lead to either suppression of antitumoral cytotoxic T cell response or demand the cooperation of infiltrating APCs to favor immune response. Differences previously found in HLA-DR expression in the four human malignant thyroid cell lines may be explained by the variation in the binding of transcription factors to the boxes in the HLA-DRalpha promoter. The binding patterns of nuclear proteins derived from the four thyroid cell lines or from the B lymphocyte cell line--Raji--to each of the boxes or to the whole promoter exhibit similarities, thus suggesting similar DNA-protein interactions.

Major histocompatibility class II HLA-DR alpha gene expression in thyrocytes: counter regulation by the class II transactivator and the thyroid Y box protein

Aberrant expression of major histocompatibility complex (MHC) class II proteins on thyrocytes, which is associated with autoimmune thyroid disease, is mimicked by gamma-interferon (gamma-IFN). To define elements and factors that regulate class II gene expression in thyrocytes and that might be involved in aberrant expression, we have studied gamma-IFN-induced HLA-DR alpha gene expression in rat FRTL-5 thyroid cells. The present report shows that class II expression in FRTL-5 thyrocytes is positively regulated by the class II transactivator (CIITA), and that CIITA mimics the action of gamma-IFN. Thus, as is the case for gamma-IFN, several distinct and highly conserved elements on the 5'-flanking region of the HLA-DR alpha gene, the S, X1, X2, and Y boxes between -137 to -65 bp, are required for class II gene expression induced by pCIITA transfection in FRTL-5 thyroid cells. CIITA and gamma-IFN do not cause additive increases in HLA-DR alpha gene expression in FRTL-5 cells, consistent with the possibility that CIITA is an intermediate factor in the gamma-IFN pathway to increased class II gene expression. Additionally, gamma-IFN treatment of FRTL-5 cells induces an endogenous CIITA transcript; pCIITA transfection mimics the ability of gamma-IFN treatment of FRTL-5 thyroid cells to increase the formation of a specific and novel protein/DNA complex containing CBP, a coactivator of CRE binding proteins important for cAMP-induced gene expression; and the action of both gamma-IFN and CIITA to increase class II gene expression and increase complex formation is reduced by cotransfection of a thyroid Y box protein, which suppresses MHC class I gene expression in FRTL-5 thyroid cells and is a homolog of human YB-1, which suppresses MHC class II expression in human glioma cells. We conclude that CIITA and TSH receptor suppressor element binding protein-1 are components of the gamma-IFN-regulated transduction system which, respectively, increase or decrease class II gene expression in thyrocytes and may, therefore, be involved in aberrant class II expression associated with autoimmune thyroid disease.