Iodination of human thyroglobulin (Tg) alters its immunoreactivity. I. Iodination alters multiple epitopes of human Tg

Exploring Salivary Iodine Concentration as a Biomarker for Iodine Status and Thyroid Nodules in Females From Different Water Iodine Areas: a Cross-sectional Study

BACKGROUND

It is unclear whether salivary iodine concentration (SIC) can assess iodine status in females from different water iodine regions.

OBJECTIVES

Through a cross-sectional study, we explored the feasibility of SIC as a biomarker to assess iodine status in females and develop optimal cutoff values.

METHODS

A total of 1991 females were analyzed in this cross-sectional study from the coastal iodine-deficient areas (CIDAs), inland iodine-deficient areas (IIDAs), iodine-adequate areas (IAAs), iodine-excess areas (IEAs), and iodine extra-high areas (IEHAs). SIC, spot urine iodine concentration (SUIC), and daily total iodine intake (TII) were assessed, and ultrasonography was performed in all subjects.

RESULTS

There was a positive correlation between SIC and SUIC (r = 0.67; 95% CI: 0.64, 0.69; P < 0.001), and TII (r = 0.47; 95% CI: 0.43, 0.50; P < 0.001). The prevalence of thyroid nodules (TN) showed an upward trend with SIC increasing (Z = -2.83; P-trend = 0.005). The area under the receiver-operating characteristic (ROC) curve for SIC to assess iodine deficiency was 0.62 (95% CI: 0.60, 0.65; P < 0.001) and 0.75 (95% CI: 0.73, 0.77; P < 0.001) for iodine excess. The cutoff values were as follows: SIC < 93.32 μg/L, iodine deficiency; 93.32-224.60 μg/L, iodine adequacy; and >224.60 μg/L, iodine excess. When SIC > 224.60 μg/L, the odds ratio (OR) for UIC > 300 μg/L, excessive TII, and the prevalence of TN were 6.44, 3.68, and 1.27 (95% CI: 4.98, 8.31; 2.83, 4.79; and 1.02, 1.56, respectively; P < 0.05); when SIC < 93.32 μg/L, the OR for UIC < 100 μg/L and insufficient TII were 2.34 and 1.94 (95% CI: 1.73, 3.14 and 1.33, 2.83, respectively; P < 0.05).

CONCLUSIONS

Using SIC as a biomarker, females in CIDA exhibited mild iodine deficiency, those in IIDA and IAA demonstrated moderate iodine deficiency, and those in IEA and IEHA exhibited an excess of iodine, consistent with SUIC to assess iodine status. SIC can be used as a good biomarker to evaluate the iodine status in population.

Thyroidal and Extrathyroidal Requirements for Iodine and Selenium: A Combined Evolutionary and (Patho)Physiological Approach

Iodide is an antioxidant, oxidant and thyroid hormone constituent. Selenoproteins are needed for triiodothyronine synthesis, its deactivation and iodine release. They also protect thyroidal and extrathyroidal tissues from hydrogen peroxide used in the ‘peroxidase partner system’. This system produces thyroid hormone and reactive iodine in exocrine glands to kill microbes. Exocrine glands recycle iodine and with high urinary clearance require constant dietary supply, unlike the thyroid. Disbalanced iodine-selenium explains relations between thyroid autoimmune disease (TAD) and cancer of thyroid and exocrine organs, notably stomach, breast, and prostate. Seafood is iodine unconstrained, but selenium constrained. Terrestrial food contains little iodine while selenium ranges from highly deficient to highly toxic. Iodine vs. TAD is U-shaped, but only low selenium relates to TAD. Oxidative stress from low selenium, and infection from disbalanced iodine-selenium, may generate cancer of thyroid and exocrine glands. Traditional Japanese diet resembles our ancient seashore-based diet and relates to aforementioned diseases. Adequate iodine might be in the milligram range but is toxic at low selenium. Optimal selenoprotein-P at 105 µg selenium/day agrees with Japanese intakes. Selenium upper limit may remain at 300–400 µg/day. Seafood combines iodine, selenium and other critical nutrients. It brings us back to the seashore diet that made us what we currently still are.

The relationship of different levels of high iodine and goiter in school children: a meta-analysis

Background

Over the past decade, the phenomenon of high urine iodine (HUI) and high water iodine (HWI) has become more common. But the risk of goiter caused by different levels of HUI and HWI remains unclear.

Objectives

To explore the risk of goiter development caused by HUI and HWI, and compare the risk of goiter development from different levels of high iodine.

Methods

The Medline, Cochrane library, Embase, China National Knowledge Infrastructure and Wan fang databases were searched for relevant population-based studies investigating the link between high iodine levels and goiter development in mainland China. Three reviewers extracted data from the included studies independently, assessing the prevalence of goiter development due to high iodine.

Results

Taking 100 μg/L ≤ UIC < 300 μg/L (UIC = urinary iodine concentration) as the reference group, the odds ratio (OR) regarding high iodine levels and goiter formation was 1.74 (95% CI 1.50, 2.01, P < 0.001), if the water iodine concentration (WIC) was greater than 100 μg/L, the OR between goiter development and WIC was 4.74 (95% CI 1.15, 19.46, P = 0.001). The Linear trend analysis of HUI and goiter showed that the prevalence of goiter increased with the increase of UIC (χ² = 734.605, P < 0.001).

Conclusions

When the UIC ≥ 300 μg/L or the WIC ≥ 100 μg/L, the risk of goiter will increase. The higher the UIC, the greater the risk of goiter development. In order to improve the public thyroid health, we should adhere to the monitoring of urinary iodine and water iodine, and keep them at an appropriate level.

Trial registration

PROSPEROCR, CRD42020197620. Registered 8 August 2020, https://www.crd.york.ac.uk/PROSPERO/.

Iodoprophylaxis and thyroid autoimmunity: an update

Adequate iodine intake is necessary for normal thyroid function. Iodine deficiency is associated with serious complications, but also iodine excess can lead to thyroid dysfunction, and iodine supplementation aimed to prevent iodine deficiency disorders has been associated with development of thyroid autoimmunity. The epidemiology of thyroid diseases has undergone profound changes since the implementation of iodoprophylaxis, notably by means of iodine-enriched salt, specifically resulting in decreased prevalence of goiter and neonatal hypothyroidism, improved cognitive function development in infancy, and reduced incidence of more aggressive forms of thyroid cancer. The main question we address with this review is the clinical relevance of the possible effect on autoimmunity exerted by the use of iodine-enriched salt to correct iodine deficiency. In animal models, exogenous iodine is able to trigger or exacerbate thyroid autoimmunity, but it is still not clear whether the observed immunological changes are due to a direct effect of iodine on immune response, or whether they represent a secondary response to a toxic effect of iodine on thyroid tissue. Previous iodine status of a population seems to influence the functional thyroid response to increased iodine intake and possibly the development of thyroid autoimmunity. Moreover, the prevalence of thyroid antibodies, regarded as hallmark of autoimmune thyroid disease, varies between populations under the influence of genetic and environmental factors, and the presence of thyroid antibodies does not always coincide with the presence of thyroid disease or its future development. In addition, the incidence of autoimmune diseases shows a general increasing trend in the last decades. For all these reasons, available data are quite heterogeneous and difficult to analyze and compare. In conclusion, available data from long-term population surveys show that a higher than adequate population iodine intake due to a poorly controlled program of iodine prophylaxis could induce thyroid dysfunction, including thyroid autoimmunity mostly represented by euthyroid or subclinical hypothyroid autoimmune thyroiditis. Close monitoring iodine prophylaxis is therefore advised to ensure that effects of both iodine deficiency and iodine excess are avoided.

Incidence and Clinical Implications of Autoimmune Thyroiditis in the Development of Acne in Young Patients

Autoimmune thyroiditis (AIT) is on the rise among the population, and is frequently associated with patients with acne vulgaris, especially females aged between 18–55 years old. The connection between the two is not fully elucidated. In this study, 236 patients diagnosed with acne in the dermatological office of the private Pelican Hospital and in few private dermatological offices from Oradea, Romania, during January 2018–December 2020, aged between 12 and 55 years old, were endocrinologically investigated to determine AIT and its influence on the severity of the acne. The values for the thyroid antibodies and thyroid-stimulating hormone (TSH) were determined for all of the subjects. The frequency of AIT in the study group was 72% and was associated with severe acne (p < 0.001). Patients with AIT with normal or hypofunction had more frequent severe acne than those with hyperfunction (p < 0.001, p = 0.002). The TSH and anti thyroidperoxidase (TPO) values did not influence the severity of the acne (p = 0.494; p = 0.111), while the anti-TG values were associated with severe acne (p = 0.007). The risk analysis indicated that raised values of anti-TPO (2.91 times greater) correlated with high anti-thyroglobulin (TG) values (4.36 times greater) doubled the risk of developing severe acne in patients. In acne evolution, the existence of AIT involves significant modifications.

Incidence and Clinical Implications of Autoimmune Thyroiditis in the Development of Acne in Young Patients

Autoimmune thyroiditis (AIT) is on the rise among the population, and is frequently associated with patients with acne vulgaris, especially females aged between 18–55 years old. The connection between the two is not fully elucidated. In this study, 236 patients diagnosed with acne in the dermatological office of the private Pelican Hospital and in few private dermatological offices from Oradea, Romania, during January 2018–December 2020, aged between 12 and 55 years old, were endocrinologically investigated to determine AIT and its influence on the severity of the acne. The values for the thyroid antibodies and thyroid-stimulating hormone (TSH) were determined for all of the subjects. The frequency of AIT in the study group was 72% and was associated with severe acne (p < 0.001). Patients with AIT with normal or hypofunction had more frequent severe acne than those with hyperfunction (p < 0.001, p = 0.002). The TSH and anti thyroidperoxidase (TPO) values did not influence the severity of the acne (p = 0.494; p = 0.111), while the anti-TG values were associated with severe acne (p = 0.007). The risk analysis indicated that raised values of anti-TPO (2.91 times greater) correlated with high anti-thyroglobulin (TG) values (4.36 times greater) doubled the risk of developing severe acne in patients. In acne evolution, the existence of AIT involves significant modifications.

Thiocyanate in excess develops goiter followed by auto immune thyroid diseases even after effective salt iodization in a rural community of north east India

PURPOSE

Salt iodization in Manipur of north-east India failed to prevent endemic goiter, therefore an in depth study carried out to evaluate thyroid functions of goitrous subjects in a randomly selected region.

METHODS

Goiter survey conducted in children and women of reproductive ages by palpation followed by measurement of urinary iodine, thiocyanate and house-hold salt iodine to evaluate iodine nutritional status and consumption pattern of bamboo-shoots (BS). In all grade-2 goitrous subjects, free thyroxine, triiodothyronine, TSH, TPO and Tg antibodies, thyroid volume and echogenecity by ultrasonography and cytomorphology of thyroid by FNAC studied.

RESULTS

Study population was 2486 children and 1506 women, goiter prevalence was 12.59% and 16.27% respectively; median urinary iodine and mean thiocyanate were 166 µg/l and 0.729 ± 0.408 mg/dl while salt iodine was ≥30 ppm. Serum thyroid hormones and TSH profiles of all grade-2 goitrous subjects showed 16.21% were subclinically hypothyroid, 2.16% overt hypothyroid, 4.86% subclinically hyperthyroid and 6.48% overt hyperthyroid, serum TPO- and Tg-antibodies found positive in 41.62%. Ultrasonographic results showed 24% had enlarged thyroid and 86.4% hypoechoic. Cytomorphological studies showed prevalence of colloid goiter (41.08%), lymphocytic thyroiditis (37.83%), Hashimoto's thyroiditis (8.10%), autoimmune thyroiditis (4.32%), sub-acute thyroiditis (2.16%) and 1.62% each papillary, medullary carcinoma, simple diffused hyperplasia and adenomoid nodular goiter.

CONCLUSIONS

Grade-2 goitrous individuals in this mild goiter endemic region were affected by hypo- and hyperthyroidism with hypoechoic thyroid and thyroiditis. Thiocyanate that originates from BS even in presence of adequate iodine developed goiter and led goitrous population towards such diseases.

Immunoglobulin Preparations Can Mislead Clinical Decision-Making in Follow-Up of Differentiated Thyroid Cancer

OBJECTIVE

Intravenous and subcutaneous immunoglobulins are commonly used for immune substitution or as immune modulators in a variety of inflammatory and autoimmune disorders. Exogenous thyroid-specific thyroglobulin (Tg) antibodies present in the donor plasma may interfere with the interpretation of measurements of Tg autoantibodies (Tg-Abs) in the recipient's plasma and potentially trigger an immune response in the recipient's immune cells. Levels of antibodies causing bioassay interferences or those leading to clinically relevant changes in patient outcomes are not known. Tg is used as a biomarker in the long-term surveillance of patients with differentiated thyroid cancer (DTC) following total thyroidectomy and radioactive iodine ablation. However, the presence of Tg-Abs in the circulation interferes with Tg measurements. Assessment of levels of Tg-Abs is thus recommended as a part of standard follow-up of DTC together with Tg testing.

METHODS

To understand the potential mechanisms and pathophysiologic significance of possible interferences associated with administration immunoglobulin preparations and Tg measurement, we overview the current knowledge on interactions between Tg autoimmunity and immunoglobulin preparations and illustrate diagnostic challenges and perspectives for follow-up of patients with DTC treated with exogenous immunoglobulins.

RESULTS

In patients with DTC treated with immunoglobulin preparations, monitoring of thyroid cancer using Tg and Tg-Abs is challenging due to possible analytical interferences through passive transfer of exogenous antibodies from immunoglobulin preparations.

CONCLUSION

Analytical interferences must be suspected when a discrepancy exists between clinical examination and diagnostic tests. Collaboration between endocrinologists, biologists, and pharmacologists is fundamental to avoid misdiagnosis and unnecessary medical or radiologic procedures.

ABBREVIATIONS

CT = computed tomography; DTC = differentiated thyroid cancer; FNAB = fine-needle aspiration biopsy; HAb = heterophile antibody; IMA = immunometric assay; IVIg = intravenous immunoglobulin; RAI = radioactive iodine; RIA = radioimmunoassay; SCIg = subcutaneous immunoglobulin; Tg = thyroglobulin; Tg-Ab = thyroglobulin autoantibody; Tg-MS = thyroglobulin mass spectrometry; TPO-Ab = thyroid peroxidase autoantibody; TSHR-Ab = thyrotropin receptor autoantibody.

Genome-Wide Analysis Identifies Two Susceptibility Loci for Positive Thyroid Peroxidase and Thyroglobulin Antibodies

INTRODUCTION

Thyroid peroxidase (TPO) and thyroglobulin (Tg) are main components of the thyroid gland and play an essential role in thyroid hormone synthesis. The development of antibodies to thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) is the major diagnostic hallmark and early indicator of autoimmune thyroid disease. TPOAb and TgAb are under strong genetic influence; however, genetic factors that determine thyroid antibody positivity are largely unknown.

MATERIALS AND METHODS

To identify novel loci associated with TPOAb and/or TgAb positivity, we performed a genome-wide meta-analysis in a total of 2613 individuals from Croatia. Participants with elevated plasma TPOAb and/or TgAb were defined as cases (N = 619) and those with TPOAb and TgAb within reference values were defined as controls (N = 1994).

RESULTS

We identified 2 novel loci, of which 1 is located within the YES1 gene (rs77284350, P = 1.50 × 10-8), and the other resides within the IRF8 gene (rs16939945, P = 5.04 × 10-8).

CONCLUSIONS

Although the observed variants were associated with TPOAb and TgAb positivity for the first time, both YES1 and IRF8 were previously linked to susceptibility to other autoimmune diseases, and represent plausible biological candidates. This study adds to the knowledge of genetics underlying thyroid antibodies and provides a good basis for further research.

The antigenic link between thyroid autoimmunity and breast cancer

The association between breast cancer and benign thyroid disorders, in particular thyroid autoimmunity, has been debated for decades. Autoantibodies to thyroid peroxidase, the hallmark of thyroid autoimmunity, have a higher prevalence among patients with breast cancer compared with the general population. Furthermore a correlation between their positivity and a better prognosis of breast cancer was found in several independent small-scale studies, even if such observation was not confirmed in a subsequent retrospective study conducted on the largest patient cohort to date. The thyroid and mammary glands present several biological similarities, therefore the hypothesis of an immune response to shared thyroid/breast antigens could in part explain the association between thyroid autoimmunity and breast cancer. The sodium iodide symporter is expressed in both glands, however it seems unlikely to be the key common antigen, considering that autoantibodies targeting it are rare. Instead thyroid peroxidase, one of the major thyroid autoantigens, is also expressed in breast tissue and therefore represents the main antigenic link between thyroid autoimmunity and breast cancer. Furthermore lactoperoxidase, an enzyme of the same family that shares structural similarities with thyroid peroxidase, is expressed in neoplastic breast cells and is responsible for the cross-reactivity with some autoantibodies to thyroid peroxidase. Novel strategies for the diagnosis and treatment of breast cancer might take advantage of the antigenic link between thyroid and breast tissues.

Thyroid Autoantibodies Display both "Original Antigenic Sin" and Epitope Spreading

Evidence for original antigenic sin in spontaneous thyroid autoimmunity is revealed by autoantibody interactions with immunodominant regions on thyroid autoantigens, thyroglobulin (Tg), thyroid peroxidase (TPO), and the thyrotropin receptor (TSHR) A-subunit. In contrast, antibodies induced by immunization of rabbits or mice recognize diverse epitopes. Recognition of immunodominant regions persists despite fluctuations in autoantibody levels following treatment or over time. The enhancement of spontaneously arising pathogenic TSHR antibodies in transgenic human thyrotropin receptor/NOD.H2^h4 mice by injecting a non-pathogenic form of TSHR A-subunit protein also provides evidence for original antigenic sin. From other studies, antigen presentation by B cells, not dendritic cells, is likely responsible for original antigenic sin. Recognition of restricted epitopes on the large glycosylated thyroid autoantigens (60-kDa A-subunit, 100-kDa TPO, and 600-kDa Tg) facilitates exploring the amino acid locations in the immunodominant regions. Epitope spreading has also been revealed by autoantibodies in thyroid autoimmunity. In humans, and in mice that spontaneously develop autoimmunity to all three thyroid autoantigens, autoantibodies develop first to Tg and later to TPO and the TSHR A-subunit. The pattern of intermolecular epitope spreading is related in part to the thyroidal content of Tg, TPO and TSHR A-subunit and to the molecular sizes of these proteins. Importantly, the epitope spreading pattern provides a rationale for future antigen-specific manipulation to block the development of all thyroid autoantibodies by inducing tolerance to Tg, first in the autoantigen cascade. Because of its abundance, Tg may be the autoantigen of choice to explore antigen-specific treatment, preventing the development of pathogenic TSHR antibodies.

Idiopathic Low Ovarian Reserve Is Associated with More Frequent Positive Thyroid Peroxidase Antibodies

BACKGROUND

While screening of thyroid peroxidase antibody (TPOAb) has been recommended in women with primary ovarian insufficiency, the relationship between thyroid autoimmunity (TAI) and ovarian reserve remains undetermined. Because the TAI prevalence was reported to be different between different ethnic/racial groups, this study aimed to investigate the TAI prevalence in Chinese women with variable ovarian reserve.

METHODS

This is a cross-sectional study conducted in a university infertility clinic between October 2013 and March 2016. Among patients at their first entry to the infertility clinic, a total of 1044 patients with available results of anti-Müllerian hormone (AMH), thyrotropin (TSH), TPOAb, and thyroglobulin antibody (TgAb) were enrolled. The TSH levels and the prevalence of positive TPOAb and positive TgAb were compared between patients with low, normal, and high ovarian reserve categorized with age-specific AMH levels.

RESULTS

For the whole study population, the TSH levels, TPOAb positivity, and TgAb positivity were comparable between patients with variable ovarian reserve. However, after patients with known causes compromising ovarian reserve (iatrogenic or genetic) were excluded, only TPOAb positivity became significantly different between patients with low (22.7%), normal (14.0%), and high ovarian reserve (10.3%; p = 0.012). The TPOAb levels were not significantly correlated to AMH levels (Spearman's ρ = -0.027; p = 0.413). For the infertile subgroup, TPOAb positivity was significantly associated with idiopathic low ovarian reserve in unexplained infertility (low ovarian reserve: 28.6%; normal: 15.7%; high: 9.5%; p = 0.020).

CONCLUSIONS

Idiopathic low ovarian reserve was associated with more frequent positive TPOAb rather than thyroid function or TgAb positivity in Chinese women.

A post-publication analysis of the idealized upper reference value of 2.5 mIU/L for TSH: Time to support the thyroid axis with magnesium and iron especially in the setting of reproduction medicine

Laboratory medicine approaches the evaluation of thyroid function mostly through the single determination of the blood level of thyroid stimulating hormone (TSH). Some authors have suggested an upper reference value for TSH of 2.5 mIU/L. This suggestion has not been confirmed by recent clinical studies. These studies have delivered a clinically valid reference range going from 0.3 to 3.5 mIU/L. These values are valid for both for the general population as well as in the setting of fertility and pregnancy. Current biochemical evidence about the elements required to maintain thyroid function shows that these not only include dietary iodine but also magnesium, iron, selenium and coenzyme Q10. Iron is important for the synthesis of thyroid peroxidase; magnesium-ATP contributes to the active process of iodine uptake; iodine has to be sufficiently present in the diet; selenium acts through selenoproteins to protect the thyroid cell during hormone synthesis and in deiodination of thyroxine; coenzyme Q10 influences thyroid vascularity. As a consequence, good clinical practice requires additional biochemical information on the blood levels of magnesium, selenium, coenzyme Q10 as well as iron status. Since these elements are also important for the maintenance of reproductive function, we postulate that they constitute the connecting link between both endocrine systems.

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.

Monitoring the effects of iodine prophylaxis in the adult population of southern Italy with deficient and sufficient iodine intake levels: a cross-sectional, epidemiological study

I prophylaxis is the most effective strategy to eradicate I deficiency disorders, but it has been shown to affect the thyroid disease pattern. In this study, we assessed the frequency of thyroid disorders in an adult population living in two areas of southern Italy after implementing I prophylaxis. To this aim, a cross-sectional, population-based study including 489 subjects from an I-deficient rural and an I-sufficient urban area of southern Italy was conducted. Thyroid ultrasound was performed on all participants, and urine and blood samples were collected from each subject. The levels of thyroid-stimulating hormone (TSH), thyroglobulin (TgAb) and thyroperoxidase antibodies (TPOAb), urinary I excretion (UIE), and thyroid volume and echogenicity were evaluated. We found that the median UIE was higher in the urban than in the rural area (P=0·004), whereas the prevalence of subjects affected by goitre was higher in the rural compared with the urban area (P=0·003). Positive TgAb rather than TPOAb were more frequent in subjects from the urban area compared with the rural area (P=0·009). The hypoechoic pattern at thyroid ultrasound (HT-US) was similar between the two areas, but TgAb were significantly higher (P=0·01) in HT-US subjects from the urban area. The frequency of elevated TSH did not differ between the two screened populations, and no changes were found for TgAb positivity in subjects with high TSH in the urban compared with the rural area. Our findings support that the small risks of I supplementation are far outweighed by the substantial benefits of correcting I deficiency, although continued monitoring of populations is necessary.

The Prevalence, Incidence and Natural Course of Positive Antithyroperoxidase Antibodies in a Population-Based Study: Tehran Thyroid Study

OBJECTIVE

Thyroid peroxidase antibody (TPOAb), the most common antibody frequently measured in population surveys is a protein expressed in the thyroid gland. We conducted the present study to analyze the prevalence and incidence of thyroid auto immunity and natural course of TPOAb in a population based study.

MATERIAL AND METHODS

This prospective study was conducted within the framework of the Tehran Thyroid Study (TTS) on 5783 (2376 men and 3407 women) individuals aged ≥ 20 years who had thyroid function tests at baseline and were followed up for median 9.1 year with TPOAb measurements at approximately every 3 years.

RESULTS

The mean age of total population at baseline was 40.04±14.32. At baseline, of the 5783 participants, 742 (12.8%) were TPOAb positive, with higher prevalence among women than in men (16.0 vs. 8.5%, p = 0.001). The prevalence of TPOAb positivity in the total population was 11.9, 14.9 and 13.6% in the young, middle age and elderly respectively. The total incidence rate (95%CI) of TPOAb positivity in the total population (5020) was 7.1 (6.36-7.98) per 1000 person-years of follow-up, with higher incidence of TPOAb positivity among young participants, i.e. 8.5 (7.5-9.7) per 1000 person-years. Sex specific incidence rate demonstrated that TPOAb positivity was higher in women, 9.3 (8.2-10.7) per 1000 person-years. The Cox's proportional hazard model analysis showed that the hazard ratio of developing TPOAb positivity was higher in women than men (P<0.0001) and tended to increase slightly with serum TSH levels (P<0.0001) but declined with increasing age (P<0.0001) in the total population. Our findings demonstrate that individuals, who became TPOAb positive in each phase, had significant elevation of TSH levels at the phase of seroconversion, compared to baseline values.

CONCLUSION

Gender, age and elevated serum TSH were found to be risk factors for developing TPOAb positivity. Furthermore, compared to baseline a significant elevation of TSH levels during seroconversion phase was observed in TPOAb positive individuals.

Insights into the posttranslational structural heterogeneity of thyroglobulin and its role in the development, diagnosis, and management of benign and malignant thyroid diseases

Thyroglobulin (Tg) is the major glycoprotein produced by the thyroid gland, where it serves as a template for thyroid hormone synthesis and as an intraglandular store of iodine. Measurement of Tg levels in serum is of great practical importance in the follow-up of differentiated thyroid carcinoma (DTC), a setting in which elevated levels after total thyroidectomy are indicative of residual or recurrent disease. The most recent methods for serum Tg measurement are monoclonal antibody-based and are highly sensitive. However, major challenges remain regarding the interpretation of the results obtained with these immunometric methods, particularly in patients with endogenous antithyroglobulin antibodies or in the presence of heterophile antibodies, which may produce falsely low or high Tg values, respectively. The increased prevalence of antithyroglobulin antibodies in patients with DTC, as compared with the general population, raises the very pertinent possibility that tumor Tg may be more immunogenic. This inference makes sense, as the tumor microenvironment (tumor cells plus normal host cells) is characterized by several changes that could induce posttranslational modification of many proteins, including Tg. Attempts to understand the structure of Tg have been made for several decades, but findings have generally been incomplete due to technical hindrances to analysis of such a large protein (660 kDa). This review article will explore the complex structure of Tg and the potential role of its marked heterogeneity in our understanding of normal thyroid biology and neoplastic processes.

Various Possible Toxicants Involved in Thyroid Dysfunction: A Review

About 300 million people across the world suffer from thyroid gland dysfunction. Environmental factors play an important role in causation of autoimmune thyroid diseases in susceptible individuals. Genetics contributes to 70% of the risk. In order to reduce the risk, we need to understand the association of environmental agents with thyroid dysfunction. These factors are especially relevant for those at increased risk due to positive family history. The ideal study to see the impact of a thyroid toxicant consists of directly measuring the degree of exposure to toxicant in an individual with his thyroid status. Knowledge of various factors influencing thyroid dysfunction can help in interpreting the results of such studies in a better way. This article is an attempt to highlight the various possible toxicants affecting thyroid function so that adequate measures can be undertaken to control excessive exposure in future to reduce the prevalence of thyroid disorders.

Iodine nutrition and thyroid diseases in Chengdu, China: an epidemiological study

OBJECTIVE

To assess the iodine nutritional status and investigate the prevalence of thyroid diseases in a community population in Chengdu, China.

METHODS

Eighty school-age children were randomly selected for measurements of urinary iodine concentration. A total of 1500 residents over the age of 18 who had lived in Chengdu for more than 5 years were selected by stratified cluster sampling. Serum thyroid hormone concentrations and thyroid autoantibodies were measured, and thyroid ultrasonography was performed.

RESULTS

The median urine iodine concentration was 184 µg/l in school-age children. The prevalence of clinical hyperthyroidism, subclinical hyperthyroidism, clinical hypothyroidism and subclinical hypothyroidism was 0.97%, 1.95%, 0.90% and 5.55%, respectively. The prevalence of thyroid autoantibodies and thyroid nodules was 15.82% and 16.87%, respectively. The prevalence of clinical hyper- and hypothyroidism was greater in females than in males (P < 0.05). The prevalence of subclinical hyper- and hypothyroidism, thyroid nodules and thyroid autoantibodies increased significantly with age (P < 0.05). The rate of new abnormal TSH was 9.37%, and the average serum Thyroid Stimulating Hormone (TSH) concentrations increased with age. When TSH >0.71 mU/l, the prevalence of positive TPOAb and/or TgAb increased significantly with rising concentrations of TSH (P < 0.05); however, the prevalence of thyroid nodules did not increase with escalating concentrations of TSH (P = 0.09).

CONCLUSION

Subclinical thyroid diseases, especially subclinical hypothyroidism and thyroid nodules, are common in an iodine sufficient area. Females and the elderly might benefit from routine screening for thyroid diseases, followed by appropriate detection and treatment.

Breaking tolerance to thyroid antigens: changing concepts in thyroid autoimmunity

Thyroid autoimmunity involves loss of tolerance to thyroid proteins in genetically susceptible individuals in association with environmental factors. In central tolerance, intrathymic autoantigen presentation deletes immature T cells with high affinity for autoantigen-derived peptides. Regulatory T cells provide an alternative mechanism to silence autoimmune T cells in the periphery. The TSH receptor (TSHR), thyroid peroxidase (TPO), and thyroglobulin (Tg) have unusual properties ("immunogenicity") that contribute to breaking tolerance, including size, abundance, membrane association, glycosylation, and polymorphisms. Insight into loss of tolerance to thyroid proteins comes from spontaneous and induced animal models: 1) intrathymic expression controls self-tolerance to the TSHR, not TPO or Tg; 2) regulatory T cells are not involved in TSHR self-tolerance and instead control the balance between Graves' disease and thyroiditis; 3) breaking TSHR tolerance involves contributions from major histocompatibility complex molecules (humans and induced mouse models), TSHR polymorphism(s) (humans), and alternative splicing (mice); 4) loss of tolerance to Tg before TPO indicates that greater Tg immunogenicity vs TPO dominates central tolerance expectations; 5) tolerance is induced by thyroid autoantigen administration before autoimmunity is established; 6) interferon-α therapy for hepatitis C infection enhances thyroid autoimmunity in patients with intact immunity; Graves' disease developing after T-cell depletion reflects reconstitution autoimmunity; and 7) most environmental factors (including excess iodine) "reveal," but do not induce, thyroid autoimmunity. Micro-organisms likely exert their effects via bystander stimulation. Finally, no single mechanism explains the loss of tolerance to thyroid proteins. The goal of inducing self-tolerance to prevent autoimmune thyroid disease will require accurate prediction of at-risk individuals together with an antigen-specific, not blanket, therapeutic approach.

Thyroglobulin autoantibodies: is there any added value in the detection of thyroid autoimmunity in women consulting for fertility treatment?

BACKGROUND

Thyroid autoimmunity (TAI) is frequent in infertile women, but to what extent thyroglobulin autoantibodies (Tg-Abs) contribute to TAI is unclear in the literature. The aims of the present study were to determine the prevalence of TAI in women consulting for fertility problems and to investigate the impact of isolated Tg-Abs, isolated thyroid peroxidase autoantibodies (TPO-Abs), and the presence of both autoantibody types on thyroid function. Furthermore, thyroid function was compared between women with and without TAI and between infertile and fertile women.

METHODS

A cross-sectional data analysis nested within an ongoing prospective cohort study was performed in order to determine the prevalence of TAI in unselected women consulting our tertiary referral center for reproductive medicine (CRM). The women underwent a determination of serum thyrotropin (TSH), free thyroxine (FT4), TPO-Abs, and Tg-Abs. The cause of infertility, age, body-mass index (BMI), and smoking habits were recorded.

RESULTS

The prevalence of TAI was 16% (163/992). In 8% of cases, both types of autoantibodies were present, in 5% isolated positive Tg-Abs were found, and 4% had isolated positive TPO-Abs (p=0.025 and p=0.003 respectively). The prevalence of TAI was significantly higher in infertile women as compared to that in fertile controls (19% vs. 13%; p=0.047). The median serum TSH level was significantly higher in the women with TAI and with isolated positive Tg-Abs compared to that in women without TAI (1.83 [1.44] and 1.90 [0.85] vs. 1.47 [0.94] mIU/L; p<0.001 respectively). The median FT4, age, BMI, and smoking habits were comparable between the study groups.

CONCLUSIONS

The prevalence of TAI was higher in infertile women as compared to fertile women consulting our CRM. Five percent of the women had isolated positive Tg-Abs and a significantly higher serum TSH compared to that in women without TAI.

Idiopathic chronic urticaria and thyroid autoimmunity: Experience of a single center

Urticaria is one of the most frequent dermatosis, being its prevalence in general population estimated about 20%. This prospective case-control study was aimed at determining the prevalence of thyroid autoimmune disorders in a cohort of patients with chronic urticaria (CU), all living within an area with mild-to-moderate iodine deficiency. Fifty four consecutive patients affected by CU were recruited and compared to 108 healthy controls. Assessment of the thyroid function included measurement of serum concentrations of TSH, FT3, FT4, anti-thyreoglobulin (anti-TG) and anti-peroxidase (anti-TPO) antibodies. Ultrasound scan of the thyroid gland was performed in all subjects using a 7.5 MHz linear transducer. All subjects were followed up for 6 months. The prevalence of thyroid antibodies was significantly higher in our cohort of patients with CU than in controls (22% vs. 6.5 %). Hashimoto's thyroiditis was also more frequent in patients than controls (18.5% vs. 1.8%). These frequencies do not differ from those previously reported by some other authors and confirm the association between CU and thyroid autoimmunity also in the area of iodine deficiency. However, presence of antibodies or thyroiditis does not seem to influence clinical course of CU. These results suggest that screening for thyroid function may be useful in all the patients with CU.

A cautious iodization programme bringing iodine intake to a low recommended level is associated with an increase in the prevalence of thyroid autoantibodies in the population

Autoantibodies against the thyroid gland with thyroid peroxidase antibody (TPO-Ab) and thyroglobulin antibody (Tg-Ab) as the most common can often be demonstrated in serum. The effect of public iodization programmes on antibody prevalence is uncertain.

AIM

To measure the concentrations of thyroid autoantibodies in the Danish population before and after mandatory iodization of salt.

METHODS

Two identical cross-sectional population studies were performed before (Cohort 1 (C1), year 1997-1998, n = 4649, median urinary iodine 61 μg/l) and 4-5 years after (Cohort 2 (C2), year 2004-2005, n = 3570, median urinary iodine 101 μg/l) mandatory iodine fortification of salt was implemented in Denmark. Blood tests were analysed for TPO-Ab and Tg-Ab using sensitive assays.

RESULTS

Antibodies were more frequent in C2 than in C1: TPO-Ab > 30 U/ml, C1 vs C2: 14·3 vs 23·8% (P < 0·001) and Tg-Ab > 20 U/ml, C1 vs C2: 13·7 vs 19·9% (P < 0·001). The C2 vs C1 effect was confirmed in multivariate regression models (C1 reference): TPO-Ab: OR (95% CI): 1·80 (1·59-2·04) and Tg-Ab: 1·49 (1·31-1·69). The increase in the frequency of thyroid antibodies was most pronounced in young women and especially observed at low concentrations of antibodies.

CONCLUSION

The prevalence of both TPO-Ab and Tg-Ab was higher 4-5 years after a cautious iodine fortification of salt was introduced in Denmark. The increase was most pronounced in young women and in the low concentrations of antibody. Further studies are needed to evaluate the long-term effects of increased iodine intake on thyroid autoimmunity in the population.

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.

Antithyroperoxidase and antithyroglobulin antibodies in a five-year follow-up survey of populations with different iodine intakes

OBJECTIVE

In a follow-up study, we determined the prevalence, incidence, and natural course of positive antithyroperoxidase antibodies (TPOAbs) and antithyroglobulin antibodies (TgAbs) in the general population and examined the influences of iodine intake.

DESIGN

The study was conducted in Panshan, Zhangwu, and Huanghua, regions with mildly deficient, more than adequate, and excessive iodine intake, respectively. Of the 3761 unselected subjects who were enrolled at baseline, 3018 participated in the 5-yr follow-up study. Serum TSH, TPOAb, and TgAb levels were measured.

RESULTS

Among subjects in Panshan, Zhangwu, and Huanghua, the prevalence of positive TPOAbs was 11.23, 11.83 and 12.02%, respectively, whereas 11.23, 11.17, and 11.26% of subjects were TgAb positive, respectively. In the older population (> or =45 yr), TgAb-positive individuals were more frequent in Huanghua than Panshan and Zhangwu (P < 0.05). The 5-yr cumulative incidence of positive TPOAb was 2.08, 3.84, and 2.84% in Panshan, Zhangwu, and Huanghua, respectively, whereas 2.91, 3.64, and 5.07% of subjects were TgAb positive, respectively (P < 0.05), corresponding to the increase in iodine intake. Subjects who were TPOAb and/or TgAb positive at baseline developed thyroid dysfunctions more frequently than those without antibodies (14.44 vs. 3.31%, P < 0.01); their incidence of elevated TSH levels was 1.32, 8.46, and 15.38% in Panshan, Zhangwu, and Huanghua, respectively (P < 0.05).

CONCLUSIONS

Subjects who were TPOAb and TgAb positive at baseline developed thyroid dysfunctions more frequently than seronegative subjects. High iodine intake was a risk factor for developing hypothyroidism in antibody-positive subjects. A constant exposure to excessive iodine intake increased the incidence of positive TgAb.

Recognition of thyroglobulin by T cells: the role of iodine

Among known autoantigens, thyroglobulin (Tg) is unique in its capacity to store iodine, an element provided in our daily diet. Evolutionary pressure has sculpted Tg into a large molecular scaffolding to allow organification of iodide and its incorporation into thyroid hormones. The increase in molecular size and the posttranslational modification by iodine had to exact immunological consequences. Over the last 15 years, numerous Tg peptides-targets of thyroiditogenic T cells-have been mapped, raising questions regarding the mechanisms that maintain or abrogate immune tolerance against this large autoantigen. This review summarizes the work in this area and discusses the role iodine may play in these processes.

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.

Induction of goitrous hypothyroidism by dietary iodide in SJL mice

Prolonged intake of large amounts of iodide has been reported to increase the incidence of goiter and/or hypothyroidism in humans as well as animals prone to spontaneous autoimmune thyroiditis. In the current study, we investigated the role of dietary iodide on the development of hypothyroidism, as well as thyroiditis, in strains of mice that do not develop spontaneous autoimmune thyroiditis. Intake of 0.05% NaI via drinking water for 10 wk induced hypothyroidism in SJL/J mice as indicated by elevated TSH and depressed total T(4) values in serum and formation of colloidal goiter with an inactive flattened thyroid epithelium. Hypothyroidism did not appear to have an autoimmune basis because only focal mononuclear cell infiltrates were found intrathyroidally, and antithyroglobulin antibodies or increased organification of iodide were not detected. These phenomena were not observed in similarly treated CBA/J mice, suggesting polymorphisms in genes controlling events downstream of iodide uptake by thyrocytes. Interestingly, RT-PCR analysis indicated that unlike CBA/J, SJL/J mice could not down-regulate Na/I symporter gene expression during the NaI treatment. No significant temporal or strain differences were observed regarding the expression of thyroglobulin, pendrin, thyroid peroxidase, and DUOX1 and DUOX2 genes after NaI intake. Our results point to the generation of a mouse model for the study of iodine-induced hypothyroidism, which does not seem to have an autoimmune basis.

Modifying effects of iodine on the immunogenicity of thyroglobulin peptides

We have previously shown that iodotyrosyl formation within thyroglobulin (Tg) generates neoantigenic determinants that are immunopathogenic. In the current study, we have examined iodination effects on three tyrosyl-containing Tg peptides that are immunogenic in their non-iodinated form. We found that iodotyrosyl formation can enhance (p179, a.a. 179-194), suppress (p2540, a.a. 2540-2554), or not alter (p2529, a.a. 2529-2545) the immunogenic profiles of these peptides at the T-cell level. On the other hand, iodination did not alter the MHC-restriction profile of p2529 and p2540 (A(k)-binders) or p179 (A(k)- and E(k)-binder) and did not significantly influence the pathogenicity of these determinants. At the B-cell level, addition of an iodine atom on Y192 in p179 generated a neoantigenic determinant, but analogous effects were not discernible in p2529 or p2540. Our results demonstrate that iodotyrosyl formation can exert variable effects on the immunogenic behavior of Tg epitopes which may not always result in enhanced pathology. These findings also suggest that variations in the iodine content of Tg may significantly alter the hierarchy of antigenic determinants, to which the immune system may or may not be tolerant.

Depletion of CD4+CD25+ regulatory T cells exacerbates sodium iodide-induced experimental autoimmune thyroiditis in human leucocyte antigen DR3 (DRB1*0301) transgenic class II-knock-out non-obese diabetic mice

Both genetic and environmental factors contribute to autoimmune disease development. Previously, we evaluated genetic factors in a humanized mouse model of Hashimoto's thyroiditis (HT) by immunizing human leucocyte antigen DR3 (HLA-DR3) and HLA-DQ8 transgenic class II-knock-out non-obese diabetic (NOD) mice. DR3+ mice were susceptible to experimental autoimmune thyroiditis (EAT) induction by both mouse thyroglobulin (mTg) and human (h) Tg, while DQ8+ mice were weakly susceptible only to hTg. As one environmental factor associated with HT and tested in non-transgenic models is increased sodium iodide (NaI) intake, we examined the susceptibility of DR3+ and/or DQ8+ mice to NaI-induced disease. Mice were treated for 8 weeks with NaI in the drinking water. At 0 x 05% NaI, 23% of DR3+, 0% of DQ8+ and 20% of DR3+DQ8+ mice had thyroid destruction. No spleen cell proliferation to mTg was observed. Most mice had undetectable anti-mTg antibodies, but those with low antibody levels usually had thyroiditis. At 0.3% NaI, a higher percentage of DR3+ and DR3+DQ8+ mice developed destructive thyroiditis, but it was not statistically significant. However, when DR3+ mice had been depleted of CD4+CD25+ regulatory T cells prior to NaI treatment, destructive thyroiditis (68%) and serum anti-mTg antibodies were exacerbated further. The presence of DQ8 molecules does not alter the susceptibility of DR3+DQ8+ mice to NaI-induced thyroiditis, similar to earlier findings with mTg-induced EAT. Susceptibility of DR3+ mice to NaI-induced EAT, in both the presence and absence of regulatory T cells, demonstrates the usefulness of HLA class II transgenic mice in evaluating the roles of environmental factors and immune dysregulation in autoimmune thyroid disease.

Iodination of tyrosyls in thyroglobulin generates neoantigenic determinants that cause thyroiditis

Thyroglobulin (Tg) is unique in its ability to incorporate and store available iodine in the form of iodotyrosyl residues. Iodination of Tg has been known to increase its immunopathogenicity in experimental animals, presumably through the formation of iodine-containing neoantigenic determinants that can elicit an autoimmune response, but defined pathogenic Tg peptides carrying iodotyrosyls have not yet been identified. We report in this study that a systematic, algorithm-based search of mouse Tg has delineated three iodotyrosyl-containing peptides that activate autoreactive T cells and cause experimental autoimmune thyroiditis in normal CBA/J mice. These peptides (aa 117-132, 304-318, and 1931-1945) were not immunogenic in their native form, and iodination of tyrosyls facilitated either peptide binding to MHC or T cell recognition of the peptide. These results demonstrate that iodotyrosyl formation in normal Tg confers pathogenic potential to certain peptides that may otherwise remain innocuous and undetectable by conventional mapping methods.

Is hepatitis C virus a risk factor for thyroid autoimmunity?

The role of hepatitis C virus (HCV) in inducing thyroid autoimmunity is still under discussion and to assess the prevalence of thyroid autoantibodies and thyroid disease in the general population and to analyse the role of HCV in inducing thyroid autoimmunity. We studied 697 subjects residing in Arsita (a small town in central Italy). Thyroid autoantibodies and nonorgan-specific autoantibodies (NOSAs) were tested in each subject, who were also screened for anti-HCV antibodies; all subjects found positive to HCV-RNA were considered as being HCV-infected. Thyroid function tests were performed in all subjects positive for thyroid autoantibody. Seventy-one subjects were found HCV-positive; four of these (5.6%) were positive for at least one thyroid autoantibody, as opposed to 7 (4.9%) of the 142 sex- and age-matched controls of the same population (P = n.s.). Thyroid dysfunction was found in 2/4 HCV-positive, and in 1/7 HCV-negative subjects with thyroid autoantibodies (P = n.s.). NOSAs were significantly more common in HCV-positive than in HCV-negative subjects (P < 0.0001). Hence HCV per se is not responsible for thyroid autoimmune dysfunction, whereas HCV does seem to induce NOSAs. It should be taken into account, however, that the phenotypic expression of autoimmune diseases is obviously influenced by a number of risk factors, including genetic predisposition, female sex and infectious agents, that could trigger the onset of the disease.

Natural course of autoimmune thyroiditis after elimination of iodine deficiency in northwestern Greece

We have previously reported the elimination of iodine deficiency and increasing prevalence of autoimmune thyroiditis (AIT) among schoolchildren in northwestern Greece. This study followed up 29 children (12-18 years old) with AIT for 5 years to track its course in the postiodination era. At diagnosis, thyroid peroxidase autoantibodies (TPOAbs) were positive in 25 children (86%) and became positive in all children during follow-up. Thyroglobulin autoantibodies (TgAbs) were positive in 17 children at diagnosis (59%) and became positive in 3 more children (69%). Both antibody types increased by the end of the observation period (p < 0.005). Regarding thyroid function, 7 children (24%) at diagnosis had subclinical hypothyroidism that persisted and 4 more children developed subclinical hypothyroidism during the study period (38%). Only 5 of these children (45%) had positive TgAbs. There was an increase in thyrotropin (TSH) so that at the end of the study all children had TSH greater than 2.5 mU/L but none developed overt hypothyroidism. Thyroid hypoechogenicity that increased over time was seen in all children, especially in those with subclinical hypothyroidism. In conclusion, both antibody types increased in frequency and level, but TPOAbs were the predominant autoimmunity marker predictive of impending thyroid failure in children with AIT, as was thyroid hypoechogenicity on ultrasound.

Iodination of murine thyroglobulin enhances autoimmune reactivity in the NOD.H2 mouse

Autoimmune thyroiditis in humans has been linked to excess iodine intake. A causative relationship between dietary iodine and thyroiditis has been clearly established in animal models of thyroiditis, including the NOD.H2(h4) mouse strain, which develops enhanced thyroiditis spontaneously after supplementation of drinking water with sodium iodide. To assess the mechanisms by which iodine may contribute to disease pathogenesis, we have purified hypoiodinated thyroglobulin (Lo-I Tg) from the thyroids of mice fed methimazole and potassium perchlorate. This preparation contained only a trace of iodine and was poorly reactive to monoclonal antibody 42C3, which has been shown previously to distinguish hypoiodinated from normal Tg. A cloned T cell line 2D11 from a diseased NOD.H2(h4) mouse proliferated in response to normal Tg, but not to Lo-I Tg. Serum antibodies from NOD.H2(h4) mice with thyroiditis were poorly reactive to Lo-I Tg. To determine that these changes were due specifically to iodine content, Lo-I Tg was reiodinated in vitro. Reiodination of Lo-I Tg partially re-established the reactivity of NOD.H2(h4) serum antibodies. The data demonstrate that the reactivity of thyroglobulin-specific antibodies and certain T cells are dependent on the iodine content of thyroglobulin. These findings suggest that iodine contributes to autoimmune thyroiditis in the NOD.H2(h4) mouse by directly enhancing the antigenicity of thyroglobulin.

Development of severe thyroid-associated ophthalmopathy in a patient with disseminated thyroid cancer treated with recombinant human thyrotropin/radioiodine and retinoic acid

We present a case in which a patient with disseminated well-differentiated papillary thyroid cancer developed severe thyroid-associated ophthalmopathy. Eight years after initial surgery and ablative radioiodine therapy the patient was found to have multiple pulmonary metastases. The metastases showed poor uptake of radioiodine. An attempt was made to use 13-cis-retinoic acid in order to achieve a redifferentiation of the thyroid cancer cells before recombinant human thyrotropin (rhTSH) stimulated radioiodine therapy. The treatment did not improve the uptake of radioiodine. However, approximately 2 weeks after completion of the treatment the patient experienced discomfort in her eyes and then over the next months she developed a severe ophthalmopathy. The analyses of TSH receptor antibodies and S-thyroglobulin simultaneously showed a pronounced increase. An association between therapy given and severe ophthalmopathy cannot be excluded.

Thyroglobulin autoantibodies in iodized subjects: relationship between epitope specificities and longitudinal antibody activity

INTRODUCTION

We previously reported a high thyroglobulin autoantibodies (TgAb) prevalence in healthy Sri Lankans after iodine supplementation. In the present study 58 TgAb-positive schoolgirls were followed up after 5 years of continued iodination. The objectives were: (1) to observe the longitudinal profile of TgAb epitope specificities and (2) to examine the relationship between these specificities and the course of thyroid autoimmunity in this population.

METHODS

Paired subjects' sera (at onset and at 5-year follow-up) were tested for TgAb, thyroid peroxidase antibody (TPOAb), and TgAb epitope-specificity. Epitope reactivity was determined by employing a panel of 10 murine monoclonal antibodies (Tg-mAbs) directed against 6 Tg antigenic clusters (I-VI) in competitive enzyme-linked immunosorbent assay (ELISA) reactions with test sera.

RESULTS

The overall pattern of epitope recognition in individual subject's sera remained preserved over the time period. Nine subjects showed restricted specificities while majority of the subjects were broadly heterogeneous. At follow-up, median TgAb concentration in the restricted group was higher than in the unrestricted (1650 versus 110 kIU/L; p < 0.005). Epitope specificity was a stronger determinant of TgAb persistence than the height of the initial TgAb response or the TPOAb status of subjects.

CONCLUSION

Tg epitope reactivity pattern in iodised populations may identify subjects at greater risk of developing autoimmune thyroid disease (AITD).

The thyroglobulin gene: the third locus for autoimmune thyroid disease or a false dawn?

Genetic studies have identified the HLA and CTLA4 regions as susceptibility loci for the development of common autoimmune thyroid diseases (AITDs), including Graves' disease and autoimmune hypothyroidism. Despite numerous studies, the identification of a third locus has remained elusive. Genetic-linkage studies have implicated chromosome 8q24 as a susceptibility locus for AITD. The gene encoding thyroglobulin (Tg), which encodes a major thyroid autoantigen, maps to this region, and a recent study has reported the association of several exonic single-nucleotide polymorphisms (SNPs) with disease. Although these preliminary data are potentially exciting, caution needs to be exercised, and replication of the data sought before Tg can be designated as the third locus for AITD.

Why measure thyroglobulin autoantibodies rather than thyroid peroxidase autoantibodies?

Autoantibodies to thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) are of immunoglobulin G (IgG) class and have high affinities for their respective autoantigens. Both autoantibodies are markers of thyroid autoimmunity and they can be measured by a variety of assays. From the clinical perspective, TgAb are less prevalent than TPOAb and less useful than TPOAb for prediction of thyroid dysfunction. Moreover, TgAb interfere with Tg measurements to monitor metastases in thyroid cancer. However, increasing evidence suggests that these TgAb provide a surrogate for Tg. In terms of disease pathogenesis, Tg has been suggested to play a role in Graves' ophthalmopathy. Pending further studies, TgAb epitopes could distinguish between individuals who are euthyroid or who have clinical disease. A final, intriguing reason for measuring and characterizing TgAb is the interest these autoantibodies have rekindled in their autoantigen. It is conceivable that Tg polymorphisms, combined with the explosive mix of iodine, TPO and H2O2 necessary for thyroid hormone synthesis, inadvertently provide the trigger for the autoimmune thyroid response.

Antigenicity and immunogenicity of the C-terminal peptide of human thyroglobulin

Thyroglobulin (Tg) is cleaved into several peptides during thyroid hormone synthesis, an oxidative process. P40, an iodinated C-terminal peptide from human Tg, has a molecular weight of about 40 kDa and contains two hormonogenic sites. P40 is the smallest peptide that is still recognized by monoclonal antibodies from mice immunized with human Tg directed against its immunodominant region. Since P40 also contains several T-cell epitopes, it is a good candidate for studying the primary events involved in the process of hormone synthesis leading to thyroid autoimmunity. The present results show that P40 is recognized by Tg antibodies from patients with thyroid disorders and induces Tg antibodies in CBA mice. P40 may therefore be involved in the autoimmune process, thus providing a useful tool for diagnostic and therapeutic purposes.

Thyroid peroxidase and thyroglobulin autoantibodies in a large survey of populations with mild and moderate iodine deficiency

BACKGROUND AND AIMS

Autoimmune thyroiditis is one of the most common autoimmune disorders. Autoantibodies against the thyroid gland, with thyroid peroxidase antibody (TPO-Ab) and thyroglobulin antibody (Tg-Ab) as the most common autoantibodies, can often be demonstrated in serum in population surveys. In the present study we evaluated if TPO-Ab and Tg-Ab tend to develop in parallel or whether one or the other may be more prevalent in subsets of the population.

METHODS

In a cross-sectional comparative study, performed in two areas of Denmark with mild and moderate iodine deficiency, 4649 randomly selected subjects in age groups between 18 and 65 years were examined. Blood tests were analysed for TPO-Ab and Tg-Ab using assays based on the radioimmunoassay (RIA) technique. The participants answered questionnaires, were clinically examined and had urine samples collected.

RESULTS

The overall prevalence rate of thyroid autoantibodies (TPO-Ab and/or Tg-Ab) was 18.8%. The prevalence rates of TPO-Ab and Tg-Ab were similar (13.1 vs. 13.0%). Both antibodies were more frequent in females than in males, and in females the prevalence rates increased with age. In the age group 60-65 years thyroid antibodies were more frequently measured in sera from moderate than from mild iodine-deficient area (P = 0.02), whereas no differences were seen in younger subjects. In 38.8% of participants with thyroid autoantibodies in serum, both antibodies were present. In sera with both TPO-Ab and Tg-Ab present the concentrations of the antibodies were generally higher than in sera with only one type of antibody present.

CONCLUSION

The prevalence rates of TPO-Ab and Tg-Ab were similar in this large population survey. The results suggest that TPO-Ab and Tg-Ab predominantly develop due to a general alteration in the immune system, whereas specific antigenic mechanisms are probably of less importance. However, further studies are needed to clarify the mechanisms involved in the development of thyroid autoantibodies.

Defining thyrotropin-dependent and -independent steps of thyroid hormone synthesis by using thyrotropin receptor-null mice

The thyrotropin (TSH) receptor (TSHR) is a member of the heterotrimeric G protein-coupled family of receptors whose main function is to regulate thyroid cell proliferation as well as thyroid hormone synthesis and release. In this study, we generated a TSHR knockout (TSHR-KO) mouse by homologous recombination for use as a model to study TSHR function. TSHR-KO mice presented with developmental and growth delays and were profoundly hypothyroid, with no detectable thyroid hormone and elevated TSH. Heterozygotes were apparently unaffected. Knockout mice died within 1 week of weaning unless fed a diet supplemented with thyroid powder. Mature mice were fertile on the thyroid-supplemented diet. Thyroid glands of TSHR-KO mice produced uniodinated thyroglobulin, but the ability to concentrate and organify iodide could be restored to TSHR-KO thyroids when cultured in the presence of the adenylate cyclase agonist forskolin. Consistent with this observation was the lack of detectable sodium-iodide symporter expression in TSHR-KO thyroid glands. Hence, by using the TSHR-KO mouse, we provided in vivo evidence, demonstrating that TSHR expression was required for expression of sodium-iodide symporter but was not required for thyroglobulin expression, suggesting that the thyroid hormone synthetic pathway of the mouse could be dissociated into TSHR-dependent and -independent steps.

Enhanced iodination of thyroglobulin facilitates processing and presentation of a cryptic pathogenic peptide

Increased iodine intake has been associated with the development of experimental autoimmune thyroiditis (EAT), but the biological basis for this association remains poorly understood. One hypothesis has been that enhanced incorporation of iodine in thyroglobulin (Tg) promotes the generation of pathogenic T cell determinants. In this study we sought to test this by using the pathogenic nondominant A(s)-binding Tg peptides p2495 and p2694 as model Ags. SJL mice challenged with highly iodinated Tg (I-Tg) developed EAT of higher severity than Tg-primed controls, and lymph node cells (LNC) from I-Tg-primed hosts showed a higher proliferation in response to I-Tg in vitro than Tg-primed LNC reacting to Tg. Interestingly, I-Tg-primed LNC proliferated strongly in vitro against p2495, but not p2694, indicating efficient and selective priming with p2495 following processing of I-Tg in vivo. Tg-primed LNC did not respond to either peptide. Similarly, the p2495-specific, IL-2-secreting T cell hybridoma clone 5E8 was activated when I-Tg-pulsed, but not Tg-pulsed, splenocytes were used as APC, whereas the p2694-specific T cell hybridoma clone 6E10 remained unresponsive to splenic APC pulsed with Tg or I-Tg. The selective in vitro generation of p2495 was observed in macrophages or dendritic cells, but not in B cells, suggesting differential processing of I-Tg among various APC. These data demonstrate that enhanced iodination of Tg facilitates the selective processing and presentation of a cryptic pathogenic peptide in vivo or in vitro and suggest a mechanism that can at least in part account for the association of high iodine intake and the development of EAT.

Iodine: an environmental trigger of thyroiditis

Like most autoimmune diseases of humans, chronic lymphocytic (Hashimoto's) thyroiditis results from the combination of a genetic predisposition and an environmental trigger. A body of clinical and epidemiologic evidence points to excessive ingestion of iodine as an environmental agent. In genetically determined thyroiditis in animals, iodine enrichment has been shown to increase the incidence and severity of disease. Its mechanism of action is still uncertain. Using a new animal model of autoimmune thyroiditis, the NOD.H2(h4) mouse, we have been able to show that iodine enhances disease in a dose-dependent manner. Immunochemical studies suggest that iodine incorporation in the thyroglobulin may augment the antigenicity of this molecule by increasing the affinity of its determinants for the T-cell receptor or the MHC-presenting molecule either altering antigen processing or by affecting antigen presentation.

Serum thyroglobulin measurement. Utility in clinical practice

Serum thyroglobulin measurement has greatly facilitated the clinical management of patients with differentiated thyroid cancer and a variety of other thyroid disorders. Thyroglobulin autoantibodies remain a significant obstacle to the clinical use of thyroglobulin measurement. The interpretation of any given thyroglobulin value requires the careful synthesis of all pertinent clinical and laboratory data available to the clinician. The diagnostic use of rhTSH-stimulated thyroglobulin levels has greatly facilitated the follow-up of low-risk patients with thyroid cancer. Although the measurement of thyroglobulin mRNA from peripheral blood is likely to affect the future management of these patients, it is expected that serum thyroglobulin measurement will continue to have a principal role in the care of patients with differentiated thyroid cancer.