Iodine and IFN-γ Synergistically Enhance Intercellular Adhesion Molecule 1 Expression on NOD.H2h4 Mouse Thyrocytes

Severe Autoimmune Thyroiditis in Transgenic NOD.H2h4 Mice Expressing Interleukin-4 in the Thyroid

Background: Hashimoto's thyroiditis is a common autoimmune thyroid disorder characterized by thyroid lymphocytic infiltrates and autoreactive antibodies against thyroglobulin (TgAbs) and thyroperoxidase. Final evolution of the disease can lead to hypothyroidism with destruction of the thyroid architecture. Interleukin-4 (IL-4) is involved in the humoral immune response and B cell activation required in autoimmune thyroiditis (AT) progression. We used our mouse model overexpressing IL-4 by thyrocytes (Thyr-IL4) to study the impact of a local IL-4 expression in AT using transgenic nonobese diabetic (NOD.H2^h4) derived animals treated with iodide-supplemented water to increase the incidence of spontaneous AT (SAT). Methods: Thyr-IL4 NOD.H2^h4 and nonpathogenic C57BL/6 animals aged 8 weeks were exposed to 0.05% sodium iodide (NaI) in their drinking water for 8 and 16 weeks. Circulating TgAbs and expression of intrathyroidal cytokines were quantified. Thyroid inflammation was assessed by classical histological analyses, including identification of some immune cell populations. The most sensitive parameter to evaluate the thyroid function, serum thyrotropin (TSH), was also measured at the end of the treatment. Results: Relative to wild-type (WT) animals, Thyr-IL4 NOD.H2^h4 mice developed severe accelerated SAT with elevated serum TgAbs and numerous thyroid infiltrates mainly composed of CD4⁺/CD8⁺ T cells, B lymphocytes, and monocytes/macrophages. Thyroid expression of T helper (Th) Th1/Th2 cytokines was also enhanced, as well as IL-17. In contrast, excessive iodide supply did not induce TgAbs in WT and Thyr-IL4 SAT-resistant C57BL/6 animals. However, moderate leukocyte infiltrations in transgenic thyroids were evident compared to WT, but associated with a limited number of T and B cells and a different cytokine profile from Thyr-IL4 NOD.H2^h4 mice. Finally, and despite their diverse immune responses, both transgenic strains presented marked thyroid enlargement and elevated serum TSH at the end of the treatment in contrast to their WT littermates. Conclusions: These findings demonstrated that ectopic expression of IL-4 from thyrocytes enhanced the severity of accelerated SAT in disease-prone Thyr-IL4 NOD.H2^h4 animals and promoted thyroid leukocyte infiltration in SAT-resistant transgenic C57BL/6 mice. Moreover, impaired thyroid function emerged in both transgenic strains during the progression of the disease.

Oxidative stress as a key feature of autoimmune thyroiditis: an update

INTRODUCTION

Oxidative stress has been proposed as one of the factors concurring in the pathophysiology of autoimmune thyroid diseases. Reactive oxygen species are the main expression of oxidative stress in biological systems, and their production can overcome antioxidant defenses ultimately leading to cell damage, apoptosis, and death. The present review was aimed at describing the state of the art of the relationships between oxidative stress and autoimmune thyroiditis. The most used biomarkers of oxidative stress and their correlation with thyroid function are reported.

EVIDENCE ACQUISITION

We conducted a search of the literature in the English language starting from 2000, using the following search terms: "Hashimoto thyroiditis," "autoimmune thyroiditis," "hypothyroidism," "hyperthyroidism," "oxidative stress," "oxidants," "antioxidant," "advanced glycation end products." Both clinical studies and animal models were evaluated.

EVIDENCE SYNTHESIS

Data form clinical studies clearly indicate that the balance between oxidants and antioxidants is shifted towards the oxidative side in patients with autoimmune thyroiditis, suggesting that oxidative stress may be a key event in the pathophysiology of the disease, irrespective of thyroid function. Studies in animal models, such as the NOD.H2h4 mouse, confirm that thyroidal accumulation of ROS plays a role in the initiation and progression of autoimmune thyroiditis.

CONCLUSIONS

Oxidant/antioxidant imbalance represent a key feature of thyroid autoimmunity. Oxidative stress parameters could be used as biochemical markers of chronic inflammation, to better predict the disease evolution along its natural history. Dietary habits and antioxidant supplements may provide protection from autoimmunity, opening new perspectives in the development of more tailored therapies.

The catalytic role of iodine excess in loss of homeostasis in autoimmune thyroiditis

PURPOSE OF REVIEW

To review the latest developments concerning the role of iodine in the pathophysiology of autoimmune thyroiditis.

RECENT FINDINGS

Recent studies have provided evidence that in areas with excess iodine intake, increased incidence of autoimmune thyroiditis marked by high titers of thyroid peroxidase and thyroglobulin antibodies has occurred. Investigations in the NOD.H2h4 mouse, a strain prone to AIT, showed that they are better adapted to the Wolff-Chaikoff effect.

SUMMARY

To provide an overview of the studies conducted during the last few years implicating iodine in the development and manifestation of autoimmune thyroiditis.

Thyroid autoantibodies and the effect on pregnancy outcomes

Thyroid antibody positivity is relatively common in women. While many epidemiological studies have investigated the links between thyroid antibodies and pregnancy complications, evidence regarding the effect of Levothyroxine treatment of euthyroid pregnant women with autoimmune thyroid disease on pregnancy outcome is limited. The objective of this paper is to provide a review on the impact of treatment of euthyroid thyroid antibody-positive pregnant women on adverse pregnancy outcome. This systematic review was conducted with a prospective protocol. PubMed, Science direct, Google scholar, Embase and the Cochrane Library databases were searched through January 2014 to identify studies that met pre-stated inclusion criteria. The search was limited to English manuscripts. We found that there is inadequate data regarding both the adverse effect of thyroid antibody positivity in euthyroid women on pregnancy outcomes and the effects Levothyroxine on these women. It seems that the results of most studies indicate adverse effects of thyroid antibody positivity in euthyroid women on pregnancy outcomes. Further randomised clinical trials are needed to investigate the effects of treating pregnant euthyroid women with positive thyroid antibodies on the maternal and early/late neonatal outcomes.

New Murine Model of Early Onset Autoimmune Thyroid Disease/Hypothyroidism and Autoimmune Exocrinopathy of the Salivary Gland

Sixty to seventy percent of IFN-γ(-/-) NOD.H-2h4 mice given sodium iodide (NaI)-supplemented water develop a slow onset autoimmune thyroid disease, characterized by thyrocyte epithelial cell (TEC) hyperplasia and proliferation (H/P). TEC H/P develops much earlier in CD28(-/-) mice and nearly 100% (both sexes) have severe TEC H/P at 4 mo of age. Without NaI supplementation, 50% of 5- to 6-mo-old CD28(-/-)IFN-γ(-/-) mice develop severe TEC H/P, and 2-3 wk of NaI is sufficient for optimal development of severe TEC H/P. Mice with severe TEC H/P are hypothyroid, and normalization of serum thyroxine levels does not reduce TEC H/P. Activated CD4(+) T cells are sufficient to transfer TEC H/P to SCID recipients. Thyroids of mice with TEC H/P have infiltrating T cells and expanded numbers of proliferating thyrocytes that highly express CD40. CD40 facilitates, but is not required for, development of severe TEC H/P, as CD40(-/-)IFN-γ(-/-)CD28(-/-) mice develop severe TEC H/P. Accelerated development of TEC H/P in IFN-γ(-/-)CD28(-/-) mice is a result of reduced regulatory T cell (Treg) numbers, as CD28(-/-) mice have significantly fewer Tregs, and transfer of CD28(+) Tregs inhibits TEC H/P. Essentially all female IFN-γ(-/-)CD28(-/-) NOD.H-2h4 mice have substantial lymphocytic infiltration of salivary glands and reduced salivary flow by 6 mo of age, thereby providing an excellent new model of autoimmune exocrinopathy of the salivary gland. This is one of very few models where autoimmune thyroid disease and hypothyroidism develop in most mice by 4 mo of age. This model will be useful for studying the effects of hypothyroidism on multiple organ systems.

Exacerbation of Autoimmune Thyroiditis by CTLA-4 Blockade: A Role for IFNγ-Induced Indoleamine 2, 3-Dioxygenase

BACKGROUND

Cytotoxic T-lymphocyte associated protein 4 (CTLA-4) is a negative regulator of immune responses that suppresses the activity of effector T cells and contributes to the maintenance of self tolerance. When blocked therapeutically, CTLA-4 leads to an overall activation of T cells that has been exploited for cancer control, a control associated however with a variety of immune-related side effects such as autoimmune thyroiditis. To investigate the mechanism(s) underlying this form of thyroiditis, we used the NOD-H2(h4) mouse, a model that develops thyroiditis at very high incidence after addition of iodine to the drinking water.

METHODS

NOD-H2(h4) mice were started on drinking water supplemented with 0.05% sodium iodide when 8 weeks old and then injected with a hamster monoclonal antibody against mouse CTLA-4, polyclonal hamster immunoglobulins, or phosphate buffered saline when 11 weeks old. One month later (15 weeks of age), mice were sacrificed to assess thyroiditis, general immune responses in blood and spleen, and expression of indoleamine 2, 3-dioxygenase (IDO) in the thyroid and in isolated antigen-presenting cells after stimulation with interferon gamma. The study also analyzed IDO expression in four autopsy cases of metastatic melanoma who had received treatment with a CTLA-4 blocking antibody, and six surgical pathology Hashimoto thyroiditis controls.

RESULTS

CTLA-4 blockade worsened autoimmune thyroiditis, as assessed by a greater incidence, a more aggressive mononuclear cell infiltration in thyroids, and higher thyroglobulin antibody levels when compared to the control groups. CTLA-4 blockade also expanded the proportion of splenic CD4+ effector T cells, as well as the production of interleukin (IL)-2, interferon gamma, IL-10, and IL-13 cytokines. Interestingly, CTLA-4 blockade induced a strong expression of IDO in mouse and human thyroid glands, an expression that could represent a counter-regulatory mechanism to protect against the inflammatory environment.

CONCLUSIONS

This study shows that CTLA-4 blockade exacerbates the iodine-accelerated form of thyroiditis typical of the NOD-H2(h4) mouse. The study could also have implications for cancer patients who develop thyroiditis as an immune-related adverse event after CTLA-4 blockade.

2,3',4,4',5-Pentachlorobiphenyl Induces Inflammatory Responses in the Thyroid Through JNK and Aryl Hydrocarbon Receptor-Mediated Pathway

Polychlorinated biphenyls (PCBs) are durable and widely distributed environmental contaminants that can compromise the normal functions of multiple organs and systems; one important mechanism is the induction of inflammatory disorders. In this study, we explored the influences of 2,3',4,4',5-pentachlorobiphenyl (PCB118) on inflammatory responses and its underlying mechanisms in the thyroid. Wistar rats were administered PCB118 intraperitoneally at 0, 10, 100, and 1000 μg/kg/d, 5 days a week for 13 weeks; rat thyroid FRTL-5 cells were treated with PCB118 (0, 0.25, 2.5, and 25 nM) for indicated time. Results revealed that PCB118 promoted the generation of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule-1 (ICAM-1) in a time- and dose-related manner and decreased sodium/iodide symporter (NIS) protein expression. Moreover, stimulation with PCB118 resulted in the upregulation of the aryl hydrocarbon receptor (AhR)-responsive gene cytochrome P450 1A1 in FRTL-5 cells; whereas pretreatment with the AhR inhibitor α-naphthoflavone or AhR small interfering RNA (siRNA) suppressed AhR, CYP1A1, IL-6, and ICAM-1 and restored NIS expression. In vivo and in vitro studies also suggested that the c-Jun N-terminal kinase (JNK) pathway was activated on PCB118 exposure, and the experiments using siRNA for JNK partially blocked PCB118-induced upregulation of IL-6 and ICAM-1 and downregulation of NIS. Altogether, PCB118 stimulates production of IL-6, TNF-α, and ICAM-1 in the thyroid through AhR and JNK activations and subsequently interferes with NIS expression, resulting in the disruption of thyroid structure and function.

The Role of Iodine and Selenium in Autoimmune Thyroiditis

Iodine and selenium (Se) are both essential elements to thyroid hormone economy, while they represent key players in the development of autoimmune thyroiditis.Chronic high iodine intake has been associated in various studies with increased frequency of autoimmune thyroiditis. In susceptible individuals, iodine excess increases intra-thyroid infiltrating Th17 cells and inhibits T regulatory (TREG) cells development, while it triggers an abnormal expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in thyrocytes, thus inducing apoptosis and parenchymal destruction. As was shown in a mouse model, high iodine supply leads to changes in the immunogenicity of the thyroglobulin molecule, upregulation of vascular intercellular adhesion molecule-1 (ICAM-1), and reactive oxygen species (ROS) generation in the thyrocytes. Serum Se levels were found decreased in Hashimoto thyroiditis and especially in Graves' disease as well as in thyroid-associated ophthalmopathy patients, the levels being related to the pathogenesis and outcome. Selenium is strongly involved, via the variable selenoproteins, in antioxidant, redox, and anti-inflammatory processes. Selenium enhances CD4+/CD25 FOXP3 and T regulatory cells activity while suppressing cytokine secretion, thus preventing apoptosis of the follicular cells and providing protection from thyroiditis. Selenium supplementation may be useful in autoimmune thyroid diseases, though, while usually well-tolerated, it should not be universally recommended, and it is also likely to be helpful for those with low Se status and autoimmunity. Broadly speaking, the achievement and maintenance of "selenostasis" as well as adequate urinary iodine excretion are mandatory to control disease, while, putatively, they may additionally be critical to preventing disease.

Genes and environment as predisposing factors in autoimmunity: acceleration of spontaneous thyroiditis by dietary iodide in NOD.H2(h4) mice

In the field of autoimmune thyroiditis, NOD.H2(h4) mice have attracted significant and increasing attention since they not only develop spontaneous disease but they present thyroiditis with accelerated incidence and severity if they ingest iodide through their drinking water. This animal model highlights the interplay between genetic and dietary factors in the triggering of autoimmune disease and offers new opportunities to study immunoregulatory parameters influenced by both genes and environment. Here, we review experimental findings with this mouse model of thyroiditis.

NOD.H-2h4 mice: an important and underutilized animal model of autoimmune thyroiditis and Sjogren's syndrome

NOD.H-2h4 mice express the K haplotype on the NOD genetic background. They spontaneously develop thyroiditis and Sjogren's syndrome, but they do not develop diabetes. Although autoimmune thyroid diseases and Sjogren's syndrome are highly prevalent autoimmune diseases in humans, there has been relatively little emphasis on the use of animal models of these diseases for understanding basic mechanisms involved in development and therapy of chronic organ-specific autoimmune diseases. The goal of this review is to highlight some of the advantages of NOD.H-2h4 mice for studying basic mechanisms involved in development of autoimmunity. NOD.H-2h4 mice are one of relatively few animal models that develop organ-specific autoimmune diseases spontaneously, i.e., without a requirement for immunization with antigen and adjuvant, and in both sexes in a relatively short period of time. Thyroiditis and Sjogren's syndrome in NOD.H-2h4 mice are chronic autoimmune diseases that develop relatively early in life and persist for the life of the animal. Because the animals do not become clinically ill, the NOD.H-2h4 mouse provides an excellent model to test therapeutic protocols over a long period of time. The availability of several mutant mice on this background provides a means to address the impact of particular cells and molecules on the autoimmune diseases. Moreover, to our knowledge, this is the only animal model in which the presence or absence of a single cytokine, IFN-γ, is sufficient to completely inhibit one autoimmune thyroid disease, with a completely distinct autoimmune thyroid disease developing when it is absent.

Iodine Supplementation: Usage "with a Grain of Salt"

Iodine supplementation through salt iodization is a worldwide, effective strategy for preventing iodine deficiency-related problems. Its safety and efficacy profile has been extensively investigated, and benefits far outweigh the potential iodine-induced risks. Moreover, iodine supplementation during pregnancy in order to avoid brain damage in the newborn is considered a mainstay of preventive medicine. Exposure to high amounts of iodine is actually well tolerated in most cases and can be unrecognized. Nevertheless, at-risk individuals may develop thyroid dysfunction even when they are exposed to increases in iodine intake universally considered as safe. Iodine-induced thyroid disorders include thyroid autoimmunity, thyrotoxicosis, iodine-induced goiter, and hypothyroidism. Moreover, a relationship between iodine intake and histotype distribution of differentiated thyroid cancer has been observed, with a progressive shift from follicular to papillary thyroid cancer. To date, evaluating iodine status in a clinical setting has limitations, and assessing the actual risk for each individual can be challenging, since it is influenced by personal history, genetics, and environmental factors. In conclusion, iodine supplementation programs need to be continued and strengthened, but iodine should be used "with a grain of salt," because a growing number of susceptible individuals will be exposed to the risk of developing iodine-induced thyroid disorders.

Iodine excess as an environmental risk factor for autoimmune thyroid disease

The global effort to prevent iodine deficiency disorders through iodine supplementation, such as universal salt iodization, has achieved impressive progress during the last few decades. However, iodine excess, due to extensive environmental iodine exposure in addition to poor monitoring, is currently a more frequent occurrence than iodine deficiency. Iodine excess is a precipitating environmental factor in the development of autoimmune thyroid disease. Excessive amounts of iodide have been linked to the development of autoimmune thyroiditis in humans and animals, while intrathyroidal depletion of iodine prevents disease in animal strains susceptible to severe thyroiditis. Although the mechanisms by which iodide induces thyroiditis are still unclear, several mechanisms have been proposed: (1) excess iodine induces the production of cytokines and chemokines that can recruit immunocompetent cells to the thyroid; (2) processing excess iodine in thyroid epithelial cells may result in elevated levels of oxidative stress, leading to harmful lipid oxidation and thyroid tissue injuries; and (3) iodine incorporation in the protein chain of thyroglobulin may augment the antigenicity of this molecule. This review will summarize the current knowledge regarding excess iodide as an environmental toxicant and relate it to the development of autoimmune thyroid disease.

Enhanced iodine supplementation alters the immune process in a transgenic mouse model for autoimmune thyroiditis

BACKGROUND

The impact of excessive iodine intake on the development of autoimmune thyroiditis (AIT) is still under debate. Transgenic, antibody-devoid TAZ10 mice spontaneously develop AIT due to autoreactive thyroperoxidase-specific T cells. In this model, development of AIT is determined by a T cell infiltration of the thyroid gland leading to an elevation of serum thyrotropin (TSH) levels and significant weight gain. In the present study we investigated the impact of moderate and high iodine supplementation on the course of disease in these mice, which are immunologically prone to AIT.

METHODS

In addition to normal nutrition, mice were supplemented for 20 weeks with 2.5 μg versus 5 μg iodine per milliliter drinking water, which corresponds to a human daily iodine supplementation of 150 μg, 315 μg, and 615 μg iodine. AIT-defining parameters (weight gain, elevation of serum TSH levels, cellular infiltration of the thyroid) and immunologic effects were analyzed.

RESULTS

No significant differences were displayed when comparing weight and serum TSH levels in the iodine-supplemented versus control groups. Increased thyroid infiltrates with CD8⁺ T cells were detected by fluorescein-activated cell sorter (FACS) and immunofluorescence staining in mice supplemented with elevated iodine amounts (315 μg and 615 μg iodine per day, respectively). Immunologic monitoring revealed selective changes in immune cell frequencies (CD8⁺ and regulatory T cells, natural killer [NK] cells) and cytokine production (interferon-γ, interleukin-1α, and interleukin-17), however, without affecting the overall immune balance.

CONCLUSION

Our results demonstrate that elevated iodine supplementation has no physical impact on the course of disease in transgenic, antibody-devoid TAZ10 mice, which are immunologically prone to AIT.

Prevalence and risk factors of subclinical thyroid disease

Subclinical thyroid disease is defined biochemically by an abnormal thyrotropin (TSH) level and normal serum-free thyroxine level. The prevalence of this condition varies according to the reference range for TSH and geographic or demographic factors. Recently, several studies, including our community-based cohort studies, have reported on the incidence of subclinical thyroid disease in Korea. Using these studies, we reviewed the prevalence and risk factors of subclinical thyroid disease, focusing on subclinical hypothyroidism.

Significance of correlation between interferon-γ and soluble intercellular adhesion molecule-1 and interleukin-17 in hepatitis B virus-related cirrhosis

BACKGROUND AND OBJECTIVE

Hepatitis B virus (HBV)-related cirrhosis is known to be associated with chronic hepatic inflammation. The present study aimed to examine the correlation between inflammatory mediators INF-γ, IL-17, and sICAM-1 in HBV cirrhotic patients.

METHODS

The levels of sICAM-1, interleukin-17, and IFN-γ were measured with enzyme-linked immunosorbent assays in 120 cirrhotic patients with HBV and 270 sex- and age-matched healthy controls. Total bilirubin (TB) was measured and the association between TB and IFN-γ, sICAM-1, interleukin-17 were analyzed. The levels of these cytokines in serum and the association between IFN-γ and sICAM-1 as well as interleukin-17 were investigated. Relationships between these cytokines and Child-Pugh classes were analyzed in patients.

RESULTS

Age and sex were similar, but TB values were significantly different between the two groups (P<0.001). Serum levels of sICAM-1, interleukin-17, and IFN-γ were significantly higher in cirrhotic patients with HBV than in controls (P<0.001 for both). TB levels were positively correlated with IFN-γ, interleukin-17 and sICAM-1 levels. Significantly positive correlations were also found between IFN-γ and interleukin-17 as well as sICAM-1 (r=0.817 and r=0.561, respectively, P<0.01). There were significant differences between the studied cytokines (sICAM-1, interleukin-17, and IFN-γ) and Child-Pugh classes (P<0.01).

CONCLUSIONS

The increased IFN-γ level was correlated with both IL-17 and sICAM-1, and it may primarily play a role as cytokines trigger in liver injury. Both IL-17 and sICAM-1 may synergistically contribute to liver damage.

Excess dietary iodine differentially affects thyroid gene expression in diabetes, thyroiditis-prone versus -resistant BioBreeding (BB) rats

SCOPE

To identify genes involved in the susceptibility to iodine-induced autoimmune thyroiditis.

METHODS AND RESULTS

Diabetes, thyroiditis-prone (BBdp) and -resistant (BBc) rats were fed either a control or a high-iodine diet for 9 wk. Excess iodine intake increased the incidence of insulitis and thyroiditis in BBdp rats. BBdp rats fed the high-iodine diet that did not develop thyroiditis had higher mRNA levels of Fabp4, Cidec, perilipin, Pparγ and Slc36a2 than BBdp rats fed the control diet and BBc rats fed either the control or the high-iodine diet. BBdp rats fed the high-iodine diet that did develop thyroiditis had higher mRNA levels of Cidec, Icam1, Ifitm1, and Slpi than BBdp rats fed the control diet and BBc rats fed either the control or the high-iodine diet. BBdp rats that did develop thyroiditis had lower mRNA levels of Fabp4, perilipin and Slc36a2 but higher mRNA levels of Icam1, Ifitm1 and Slpi than BBdp that did not develop thyroiditis. Excess dietary iodine also increased the protein levels of Fabp4, Cidec and perilipin in BBdp rats.

CONCLUSION

Differential expression of thyroid genes in BBdp versus BBc rats caused by excess dietary iodine may be implicated in autoimmune thyroiditis and insulitis pathogenesis.

Invariant NKT Cell Lines Derived from the NOD·H2 Mouse Enhance Autoimmune Thyroiditis

To study the role of invariant Natural Killer T cell ( iNKT) cells in autoimmune thyroiditis, we derived two iNKT cell lines from the spleens of NOD· H2^h4 mice, a strain that develops spontaneous autoimmune thyroiditis exacerbated by excess dietary iodine. The two lines were CD1d-restricted and expressed CD4⁺, DX5⁺, and the Vα4Jα281 gene segment, of the T-cell receptor α locus. Upon stimulation with α-galactosyl-ceramide (α-GalCer), both lines rapidly produced IL-2, IL-4, IFN-γ, IL-10, and TNF-α. Strikingly, a similar cytokine response was also induced by thyroglobulin, one of the most abundant protein in the thyroid gland and a major autoantigen in human autoimmune thyroiditis. Transfer of the iNKT cell lines to syngeneic hosts enhanced autoimmune thyroiditis. Intraperitoneal injections of α-GalCer in iodine primed mice also induced thyroid disease. This paper reports for the first time that iNKT cells respond to thyroglobulin and enhance autoimmune thyroiditis in iodine fed NOD·H2^h4 mice.

Iodide-induced chemokines and genes related to immunological function in cultured human thyroid follicles in the presence of thyrotropin

BACKGROUND

It is well known that iodide exacerbates thyroid function in subclinical hypothyroid patients with autoimmune thyroiditis. To investigate the immunological mechanism of iodine-induced thyroid dysfunction, we studied the effect of iodide in cultured human thyroid follicles, which respond to physiological concentrations of human thyrotropin (TSH) (0.3-10 microU/mL) and maintain the Wolff-Chaikoff effect.

MATERIALS AND METHODS

Thyroid follicles obtained from Graves' patients at subtotal thyroidectomy were precultured in medium containing 0.5% fetal calf serum and 10(-8) M iodide for 5 days, and then cultured with the medium containing bovine TSH (30 microU/mL) and low (10(-8)M) or high (10(-5)M) concentrations of iodide. After 3-72 hours of culture, the effect of iodide on thyroid cell mRNA expression was analyzed by microarray and reverse transcriptase-polymerase chain reaction.

RESULTS

After 48 hours of culture, iodide nearly doubled the mRNA expression levels of the immunity-associated genes (intercellular adhesion molecule-1, transforming growth factor beta 1-induced protein, early growth response gene 1, guanylate-binding protein 1, and annexin A1) and decreased the mRNA expression of sodium-iodide symporter to less than 20%. Further, the mRNA expression levels of chemokines (CCL2, CXCL8, and CXCL14) increased nearly twofold, whereas their receptors did not show any significant response. Real-time polymerase chain reaction analyses confirmed that iodide increased the mRNA expression levels of these genes in a time- and concentration-dependent manner. Immunohistochemical studies revealed that the chemokines were expressed mainly in the thyroid follicular cells in addition to the immune cells. The iodide-induced increase in CCL2 was greater in thyroid follicles obtained from thyroid gland that had been moderately infiltrated with the immunocompetent cells.

CONCLUSION

We have demonstrated that iodide stimulates thyroid follicular cells to produce chemokines, particularly CCL2, CXCL8, and CXCL14. These chemokines and intercellular adhesion molecule-1 would attract immunocompetent cells into thyroid gland. These in vitro findings suggest that iodide at high concentrations may induce thyroid dysfunction through not only biochemical but also immunological mechanisms, particularly in patients with autoimmune thyroid disorders.

Environmental triggers of autoimmune thyroiditis

Autoimmune thyroiditis is among the most prevalent of all the autoimmunities. Autoimmune thyroiditis is multifactorial with contributions from genetic and environmental factors. Much information has been published about the genetic predisposition to autoimmune thyroiditis both in experimental animals and humans. There is, in contrast, very little data on environmental agents that can serve as the trigger for autoimmunity in a genetically predisposed host. The best-established environmental factor is excess dietary iodine. Increased iodine consumption is strongly implicated as a trigger for thyroiditis, but only in genetically susceptible individuals. However, excess iodine is not the only environmental agent implicated as a trigger leading to autoimmune thyroiditis. There are a wide variety of other synthetic chemicals that affect the thyroid gland or have the ability to promote immune dysfunction in the host. These chemicals are released into the environment by design, such as in pesticides, or as a by-product of industry. Candidate pollutants include polyaromatic hydrocarbons, polybrominated biphenols, and polychlorinated biphenols, among others. Infections are also reputed to trigger autoimmunity and may act alone or in concert with environmental chemicals. We have utilized a unique animal model, the NOD.H2(h4) mouse to explore the influence of iodine and other environmental factors on autoimmune thyroiditis.

Navigating the passage between Charybdis and Scylla: recognizing the achievements of Noel Rose

This special edition of the Journal of Autoimmunity is dedicated to celebrate the enormous contributions of Dr. Noel Rose, a physician-scientist, someone that can be readily anointed as a gifted scientist who laid down the foundation and fundamental concepts of human autoimmunity. Dr. Rose performed a series of landmark studies that extend back more than 50 years and whose work is the cornerstone of the commonly used term "from the bench to the bedside." The studies included not only characterization of a normal immune response but, more importantly, defining the nature of not only the antigen, but also the aberrant response that results in organ, tissue specific reactions and immunopathology. These pioneering studies contributed to the biochemical nature of antigens, dissection of the immune repertoire, the recognition of the importance of genetics and environment, and the distinctions between a normal and an autoimmune response. Hence, this volume has been coined "Navigating the Passage Between Charybdis and Scylla: Recognizing the Achievements of Noel Rose."

Influence of iodide excess and interferon-gamma on human primary thyroid cell proliferation, thyroglobulin secretion, and intracellular adhesion molecule-1 and human leukocyte antigen-DR expression

BACKGROUND

The effect of iodide on thyroid cell proliferation and function in vivo or in cultured thyroid cells has been previously reported and is still controversial. The aim of this study was to clarify these conflicting results by examining if prolonged high iodide exposition with or without interferon (IFN)-gamma has an effect on human primary thyroid cell proliferation, thyroglobulin (Tg) production, and intercellular adhesion molecule-1 (ICAM-1) and human leukocyte antigen (HLA)-DR expression.

METHODS

Primary human thyroid cells were used. Cells were cultured in Coon's modified Ham's F-12 medium supplemented with 5% fetal calf serum in monolayer conditions to induce proliferation and were aggregated for molecular expression and Tg production analysis. HLA-DR and ICAM-1 expression were measured by flow cytometry and Tg by immunometric assay.

RESULTS

Potassium iodide (KI) was more potent in arresting primary human thyroid cell proliferation as compared to sodium iodide and the effect was mediated by its action at G0/G1 and G2/M phases of the cell cycle. There were no signs of apoptosis or necrosis. An excess of KI alone did not change the expression of HLA-DR and Tg production, but gradually increased ICAM-1. Low-dose IFN-gamma and excess KI in combination transiently inhibited HLA-DR expression, while ICAM-1 was expressed at a higher level than with IFN-gamma alone. Tg production was moderately increased with low-dose IFN-gamma. However, a combination of high-dose KI with low-dose IFN-gamma significantly decreased Tg secretion, compared with IFN-gamma alone.

CONCLUSIONS

Augmented ICAM-1 in the presence of iodide excess and low-dose IFN-gamma could induce secretion of proinflammatory cytokines and lymphocytic infiltration in the thyroid gland. Decreased Tg production in the presence of KI excess and IFN-gamma could explain the development of hypothyroidism after adding iodide in a diet of subjects that already have lymphocytic infiltration and/or mild inflammation in the thyroid gland.

Intracellular adhesion molecule-1 up-regulation on thyrocytes by iodine of non-obese diabetic.H2(h4) mice is reactive oxygen species-dependent

Intracellular adhesion molecule-1 (ICAM-1) expression on the thyroid follicular cells of non-obese diabetic (NOD).H2(h4) mice is enhanced by iodide treatment, which correlates with autoimmune thyroid disease in genetically susceptible NOD.H2(h4) mice. The current study examines the mechanism of iodine-enhanced up-regulation of ICAM-1 on the surface of thyroid cells. We hypothesized that the up-regulation of ICAM-1 is due to a transient increase in production of reactive oxygen species (ROS). ROS may initiate signalling of the ICAM-1 gene promoter, enhancing up-regulated ICAM-1 protein on the cell surface. Single-cell suspensions of thyroid follicular cells from thyroiditis-susceptible NOD.H2(h4) or non-susceptible BALB/c mice were treated in vitro with sodium iodide. Extracellular and intracellular ROS were assessed by luminol-derived chemiluminescence and flow cytometry assays respectively. Our results demonstrate that thyroid follicular cells of NOD.H2(h4) generate higher levels of ROS compared with cells from non-susceptible strains of mice. Expression of a subunit protein of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, p67(phox), was analysed by Western blot immunoassay. A constitutive expression of the p67(phox) subunit protein was observed in NOD.H2(h4) mice prior to iodine treatment. No such expression was found in BALB/c mice. Treatment of NOD.H2(h4) thyroid cells with diphenyleneiodium, an inhibitor of NADPH oxidase, reduced generation of ROS and of ICAM-1 protein expression. Thus, thyrocytes from NOD.H2(h4) mice produce enhanced levels of ROS that may be mediated by NADPH oxidase. Consequently, in NOD.H2(h4) mice the ROS-induced signal for ICAM-1 up-regulation may contribute to mononuclear cellular infiltration of the thyroid gland and the progression of autoimmune thyroid disease.

Contrasting roles of IFN-gamma in murine models of autoimmune thyroid diseases

Interferon-gamma (IFN-gamma), a prototypic proinflammatory cytokine produced by several different cell types, including the Th1 subset of CD4(+) T cells, plays an important role in inflammation and autoimmune diseases. This review focuses on the varied and often contrasting roles of IFN-gamma in three murine models of autoimmune thyroid disease, experimentally induced autoimmune thyroiditis, the model of iodine-induced spontaneous autoimmune thyroiditis in NOD.H-2h4 mice and several different murine models of Graves' disease.

Thyroid autoimmunity in the current iodine environment

Iodine is essential for thyroid function. Thyroid disorders related to iodine deficiency decreased progressively with the continuous iodine prophylaxis and the increased iodine intake. An adverse effect resulting from iodine prophylaxis may be the induction of thyroid autoimmunity. Although experiments performed in animal models suggest that iodine could initiate or exacerbate thyroid autoimmunity, the role of iodine in humans remains controversial. Several observational studies in areas with adequate or high iodine intake suggest that there is an increase in the incidence of thyroid autoimmune disease. Moreover, intervention studies suggest that increased iodine intake may enhance thyroid autoimmunity too. However, not all studies generated the same findings, probably because of genetic, racial, and environmental differences. It seems that autoimmune exacerbation is a transient phenomenon. Studies have shown that in persons presenting thyroid antibodies, the levels of these antibodies progressively decrease when the majority of them react against a nonspecific pattern of thyroglobulin (Tg) epitopes. However, in a small number of these persons, the anti-Tg antibodies are similar to those in patients with patent thyroid autoimmune disease, reacting against specific immunodominant Tg epitopes, and their levels persist. One possible attractive explanation is that enhanced iodine intake increases the antigenicity of Tg through the incorporation of iodine into its molecule and the formation of iodinated Tg epitopes or even the generation of noniodinated pathogenetic Tg epitopes that are normally cryptic.