HCV E2 protein binds directly to thyroid cells and induces IL-8 production: a new mechanism for HCV induced thyroid autoimmunity

Clinical and molecular impact of concurrent thyroid autoimmune disease and thyroid cancer: From the bench to bedside

The recent incorporation of immune checkpoint inhibitors targeting the PD-1 (programmed cell death receptor 1) and CTLA-4 (cytotoxic T lymphocyte antigen 4) pathways into the therapeutic armamentarium of cancer has increased the need to understand the correlation between the immune system, autoimmunity, and malignant neoplasms. Both autoimmune thyroid diseases and thyroid cancer are common clinical conditions. The molecular pathology of autoimmune thyroid diseases is characterized by the important impact of the PD-1/PD-L1 axis, an important inhibitory pathway involved in the regulation of T-cell responses. Insufficient inhibitory pathways may prone the thyroid tissue to a self-destructive immune response that leads to hypothyroidism. On the other hand, the PD-1/PD-L1 axis and other co-inhibitory pathways are the cornerstones of the immune escape mechanisms in thyroid cancer, which is a mechanism through which the immune response fails to recognize and eradicate thyroid tumor cells. This common mechanism raises the idea that thyroid autoimmunity and thyroid cancer may be opposite sides of the same coin, meaning that both conditions share similar molecular signatures. When associated with thyroid autoimmunity, thyroid cancer may have a less aggressive presentation, even though the molecular explanation of this clinical consequence is unclear. More studies are warranted to elucidate the molecular link between thyroid autoimmune disease and thyroid cancer. The prognostic impact that thyroid autoimmune disease, especially chronic lymphocytic thyroiditis, may exert on thyroid cancer raises important insights that can help physicians to better individualize the management of patients with thyroid cancer.

Human T-cell leukemia virus type 1 is associated with dysthyroidism in the French Amazon

Background

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus known to cause two major diseases: adult T-cell leukemia/lymphoma and a progressive neuromyelopathy-tropical spastic paraparesis. Many viruses may be involved in the pathogenesis of thyroiditis; however, few studies have focused on the role of HTLV-1. We aimed to investigate the association between HTLV-1 and biological thyroid dysfunction.

Methods

We included 357 patients with a positive HTLV-1 serology and thyroid-stimulating hormone assay data between 2012 and 2021 in a hospital in French Guiana; we compared the prevalence of hypothyroidism and hyperthyroidism in this group with that in an HTLV-1-negative control group (722 persons) matched for sex and age.

Results

The prevalence of hypothyroidism and hyperthyroidism in patients with HTLV-1 infection was significantly higher than that in the control group (11% versus 3.2% and 11.3% versus 2.3%, respectively; p < 0.001).

Conclusion

Our study shows, for the first time, the association between HTLV-1 and dysthyroidism in a large sample, suggesting that thyroid function exploration should be systematically implemented in this population as this may have an impact on therapeutic management.

The interplay between thyroid and liver: implications for clinical practice

A complex relationship exists between thyroid and liver in health and disease. Liver plays an essential physiological role in thyroid hormone activation and inactivation, transport, and metabolism. Conversely, thyroid hormones affect activities of hepatocytes and hepatic metabolism. Serum liver enzyme abnormalities observed in hypothyroidism may be related to impaired lipid metabolism, hepatic steatosis or hypothyroidism-induced myopathy. Severe hypothyroidism may have biochemical and clinical features, such as hyperammonemia and ascites, mimicking those of liver failure. Liver function tests are frequently abnormal also in hyperthyroidism, due to oxidative stress, cholestasis, or enhanced osteoblastic activity. Antithyroid drug-associated hepatotoxicity is a rare event, likely related mainly to an idiosyncratic mechanism, ranging from a mild hepatocellular damage to liver failure. Propylthiouracil-induced liver damage is usually more severe than that caused by methimazole. On the other hand, thyroid abnormalities can be found in liver diseases, such as chronic hepatitis C, liver cirrhosis, hepatocellular carcinoma, and cholangiocarcinoma. In particular, autoimmune thyroid diseases are frequently found in patients with hepatitis C virus infection. These patients, especially if thyroid autoimmunity preexists, are at risk of hypothyroidism or, less frequently, thyrotoxicosis, during and after treatment with interpheron-alpha alone or in combination with ribavirin, commonly used before the introduction of new antiviral drugs. The present review summarizes both liver abnormalities related to thyroid disorders and their treatment, and thyroid abnormalities related to liver diseases and their treatment.

Hepatitis C Virus Infection of Human Thyrocytes: Metabolic, Hormonal, and Immunological Implications

CONTEXT

Hepatitis C virus (HCV) infection is a prevalent disease worldwide. Thyroid dysfunction is one of the most common extrahepatic manifestations of HCV infection. We hypothesized that HCV can directly infect human thyrocytes thereby causing thyroid dysfunction.

SETTING

Human thyrocytes in primary cell culture, ML-1 human thyroid cell line, and Huh7.5 human hepatocyte cell line were infected with HCV using the Huh7.5JFH1 cell line that releases infectious HCV virions. After infection, the release of new virions, production of proinflammatory cytokines, and expression of miR-122 were evaluated. Ribonucleic acid (RNA) extracted from HCV-infected cells and mock-infected cells was subjected to RNA sequencing and transcriptomic analysis. Ingenuity pathway analysis was used to detect up- and down-regulated pathways.

RESULTS

Human thyrocytes express major HCV entry factors including CD81, occludin, claudin-1, and scavenger receptor class B1. Viral infection of thyroid cells was confirmed by detection of HCV core protein in supernatants and negative-sense HCV RNA in cell lysates. HCV infection of thyrocytes induced the production of the chemokine CXCL-8 and the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and significantly increased the expression of miR-122. Moreover, HCV infection of thyrocytes decreased expression of the thyroid peroxidase and thyroglobulin genes and increased expression of the deiodinase 2 gene. The top upregulated pathways in HCV-infected thyrocytes were immune pathways and metabolic pathways, while infected hepatocytes upregulated lipid and glucose metabolism pathways as previously reported.

CONCLUSIONS

HCV infection may induce thyroid dysfunction by different mechanisms including direct infection of thyrocytes leading to activation of inflammatory pathways and upregulation of miR-122. These findings support a general mechanism for viral induction of autoimmunity through direct infection of target tissues.

Graves' disease: Epidemiology, genetic and environmental risk factors and viruses

Graves' disease (GD) is the most common cause of hyperthyroidism in developed Countries. It is more common between 30 and 60 years; 5-10 times more frequent in women. The genetic predisposition accounts for 79% of the risk for GD, while environmental factors for 21%. About 70% of genes associated with autoimmune thyroid disorders (AITD) are implicated in T-cell function. Among GD endogenous factors, estrogens, X-inactivation and microchimerism are important. Among environmental risk factors, smoking, iodine excess, selenium and vitamin D deficiency, and the occupational exposure to Agent Orange have been associated with GD. Many studies showed that HCV is associated with thyroid autoimmunity and hypothyroidism, in patients with chronic HCV hepatitis (CHC); a significant link has been shown also between HCV-related mixed cryoglobulinemia and risk for GD. Moreover, IFN-α-treated CHC patients develop GD more frequently. Novel studies are needed about possible risk factors to reduce the occurence of GD in West Countries.

Cytokines and serum amyloid A in the pathogenesis of hepatitis C virus infection

Expression of the acute phase protein serum amyloid A (SAA) is dependent on the release of the pro-inflammatory cytokines IL-1, IL-6 and TNF-α during infection and inflammation. Hepatitis C virus (HCV) upregulates SAA-inducing cytokines. In line with this, a segment of chronically infected individuals display increased circulating levels of SAA. SAA has even been proposed to be a potential biomarker to evaluate treatment efficiency and the course of disease. SAA possesses antiviral activity against HCV via direct interaction with the viral particle, but might also divert infectivity through its function as an apolipoprotein. On the other hand, SAA shares inflammatory and angiogenic activity with chemotactic cytokines by activating the G protein-coupled receptor, formyl peptide receptor 2. These latter properties might promote chronic inflammation and hepatic injury. Indeed, up to 80 % of infected individuals develop chronic disease because they cannot completely clear the infection, due to diversion of the immune response. In this review, we summarize the interconnection between SAA and cytokines in the context of HCV infection and highlight the dual role SAA could play in this disease. Nevertheless, more research is needed to establish whether the balance between those opposing activities can be tilted in favor of the host defense.

Bystander activation and autoimmunity

The interaction over time of genetic, epigenetic and environmental factors (i.e., autoimmune ecology) increases or decreases the liability an individual would have to develop an autoimmune disease (AD) depending on the misbalance between risk and protective effects. Pathogens have been the most common antecedent events studied, but multiple other environmental factors including xenobiotic chemicals, drugs, vaccines, and nutritional factors have been implicated into the development of ADs. Three main mechanisms have been offered to explain the development of autoimmunity: molecular mimicry, epitope spreading, and bystander activation. The latter is characterized by auto-reactive B and T cells that undergo activation in an antigen-independent manner, influencing the development and course of autoimmunity. Activation occurs due to a combination of an inflammatory milieu, co-signaling ligands, and interactions with neighboring cells. In this review, we will discuss the studies performed seeking to define the role of bystander activation in systemic and organ-specific ADs. In all cases, we are cognizant of individual differences between hosts and the variable latency time for clinical expression of disease, all of which have made our understanding of the etiology of loss of immune tolerance difficult and enigmatic.

The role of viral infections in the development of autoimmune diseases

The exact aetiology of most autoimmune diseases remains unknown, nonetheless, several factors contributing to the induction or exacerbation of autoimmune reactions have been suggested. These include the genetic profile and lifestyle of the affected individual in addition to environmental triggers such as bacterial, parasitic, fungal and viral infections. Infections caused by viruses usually trigger a potent immune response that is necessary for the containment of the infection; however, in some cases, a failure in the regulation of this immune response may lead to harmful immune reactions directed against the host's antigens. The autoimmune attack can be carried out by different arms and components of the immune system and through different possible mechanisms including molecular mimicry, bystander activation, and epitope spreading among others. In this review, we examine the data available for the involvement of viral infections in triggering or exacerbating autoimmune diseases in addition to discussing the mechanisms by which these viral infections and the immune pathways they trigger possibly contribute to the development of autoimmunity.

Non-specific impairment of Lung Function on Spirometery in Patients with Chronic Hepatitis-C

Objectives:

To document frequency of non-specific impairment of lung functions (NILF) in patients of HCV and to compare according to gender, genotype, liver fibrosis score and smoking status.

Methods:

Patients of chronic hepatitis C were included after informed consent. Demographic data was recorded, and they underwent baseline investigations, fibroscan, abdominal ultrasound and PFT. Patients were segregated on basis of gender, fibroscan stages and smoking status. NILF was labelled if any two of three criteria are fulfilled (a) FVC < 80% of Predicted, (b) FEV1 < 80% Predicted, (c) FEV1/FVC ≥ 70.

Results:

Two hundred thirty four patients were of chronic HCV who fulfilled the selection criteria were inducted in study. These included 49.6% males and 50.4% females. There were 15.0% smokers, 16.2% were ex-smokers while 68.8% were never smokers. NILF was present in 130 (55.6%) out of which 61.5% were female and 38.5% were male (p <0.001), its presence in smokers was 56.2% and in never smokers was 55.3% (p=0.507). Presence of NILF increased with Fibroscan stages from F1 to F4 (p <0.001).

Conclusions:

NILF pattern on spirometry with normal chest radiograph is common among HCV patients. It was found more common in females and frequency increased progressively with fibro scan stages.

Endocrine disorders associated with hepatitis C virus chronic infection

The term "HCV syndrome" encompasses several organ- and systemic pathophysiological states, which often recognize autoimmunity or neoplastic evolution in their pathophysiology, as well as chronic HCV infection as trigger. The clinical features of HCV patients are heterogenous, and may include endocrine or metabolic disorders, namely autoimmune thyroiditis, type 2 diabetes mellitus, and erectile/sexual dysfunctions. In this review, we summarize current knowledge on the endocrine/metabolic diseases associated with chronic HCV infection, focusing on the main concepts emerged in the recent literature in this field. The application of this knowledge in everyday clinical practice may be relevant, in order to reinforce a holistic vision of the patient with chronic HCV infection, stimulating in turn a multi-disciplinary approach, thus increasing the probability of early diagnosis, more effective treatments, and a better prognostic outcome.

Seasonality of month of birth in children and adolescents with autoimmune thyroiditis: a continuing conundrum

Background The aim of this study was to analyze the seasonal birth month pattern in young patients with autoimmune thyroiditis and compare it with youth controls. Methods Medical records of a total of 298 children and adolescents of Greek origin, with a diagnosis of Hashimoto thyroiditis (HT) before the age of 21 years that were born from 1987 to 2010 were retrospectively reviewed. In addition, 298 consecutive subjects that were born from 1988 to 2012 and evaluated in a tertiary unit for any reason, served as controls, provided that they had no personal or family history of thyroid or any other autoimmune disease. Results Significant differences were found between children and adolescents with HT and healthy controls in the yearly pattern of month of birth distribution (p=0.029). During month-by-month analysis, it was shown that the highest and lowest predispositions to HT were among those born in spring (March) (odds ratio [OR] 2.34, p=0.005), and autumn (November) (OR 0.49, p=0.035), respectively. A binary logistic regression model also revealed that season of birth and sex were the only factors that remained related to HT disease, even after adjustment for confounding factors such as year of birth and age (p<0.001, Nagelkerke r-square 0.151). Conclusions This study suggests that the effect of certain seasonal factors during fetal development, reflected by the seasonal differences in birth pattern, in children and adolescents with autoimmune thyroiditis could contribute to long-term programming of an autoimmune response against the thyroid gland. Further studies are needed to demonstrate a clear cause and effect relationship between month of birth and HT.

[Chronic HCV infection: An internist's opinion (Part 2)]

Hepatitis C virus (HCV) infection results in not only chronic hepatitis and subsequent complications as liver cirrhosis and hepatocellular carcinoma, but also in a significant number of other diseases, the so-called extrahepatic manifestations of chronic HCV infection. In addition to lymphoproliferative and autoimmune disorders discussed in Part 1 of this review, many other diseases turned to be associated with chronic HCV infection. Part 2 of this review is dedicated to the analysis of the relationship of chronic HCV-infection to the development of some endocrine diseases, such as thyroiditis and diabetes mellitus, and cardiovascular disorders. It also provides the characteristics of the currently available antiviral agents and considers whether they may be used in patents with extrahepatic manifestations of chronic HCV infection.

Oncogenic mutations in KEAP1 disturbing inhibitory Nrf2-Keap1 interaction: Activation of antioxidative pathway in papillary thyroid carcinoma

BACKGROUND

Nuclear factor erythroid 2-like 2 (NFE2L2) encodes Nrf2, transcription factor of antioxidative genes. In the presence of reactive oxygen species, Keap1 (Kelch-ECH-associating protein-1) inhibitor complex undergoes conformational changes disrupting Keap1-Nrf2 binding and Nrf2 translocates into nucleus. We evaluated the presence of mutations in NFE2L2 and KEAP1 in papillary thyroid carcinomas (PTCs) and correlated them with clinical presentation.

METHODS

Coding regions of NFE2L2 and KEAP1 were sequenced in 131 patients with PTC. Clinical and histopathological features were analyzed. Immunohistochemical analysis of Nrf2 expression was performed in mutated carcinomas.

RESULTS

Although no mutations were found in NFE2L2, missense mutations in KEAP1 were observed in 6 patients with PTC (4.6%). Immunohistochemistry showed increased Nrf2 expression in nuclei of all mutated carcinomas, which presented poor prognostic features in histopathology.

CONCLUSION

We identified mutations in KEAP1 associated with Nrf2 overexpression in PTC. Mutations favored disruption of inhibitory interaction Nrf2-Keap1 to enable increased antioxidant Nrf2 activity, possibly with prognostic consequences.

Chronic urticaria and thyroid autoimmunity: a perplexing association

Chronic urticaria has long been thought to be associated with autoimmune conditions, in particular autoimmune thyroid disease (AITD). We detail an unusual case of a 49-year-old patient presenting with urticaria distributed on both shins and hands, with no known associated triggers, and subsequently diagnosed with AITD. The urticaria resolved upon treatment of the AITD. We also summarize the currently postulated pathophysiological links between the two diseases. This case highlights that physicians should have a low threshold for investigating autoimmune conditions in cases of chronic urticaria, with particular attention given to AITD.

Effect of Goiter Dispersion Formula on Serum Cytokines in Hyperthyroidism Patients with Neurologic Manifestations of Graves' Disease: A Randomized Trial on 80 Cases

PURPOSE

This study is aimed to explore the combined use of goiter dispersion formula and antithyroid drugs in the treatment of patients with neurologic manifestations of Graves' disease by examining its modulating effects on patients' cytokines.

METHODS

A total of 80 patients with Graves' disease were randomly divided into treatment and control groups. Patients of the treatment group received goiter dispersion formula and antithyroid drugs (methimazole or propylthiouracil), whereas those of the control group received antithyroid drug alone. FT3, FT4, and TSH contents were detected by chemiluminescence immunoassay at pre- and post-treatment; interleukin (IL)-2, IL-8, and IL-17 serum levels before and after the treatment were detected by radioimmunoassay; thyroid B-mode ultrasound and liver and renal function tests were performed in all patients of both groups. An additional cohort of 40 healthy subjects was recruited for baseline measurement.

RESULTS

All the enrolled patients completed the trial. The effective treatment rate was higher in the treatment group than in the control group, of which the difference was statistically significant (treatment group, 95%; control group, 75%, p < 0.01). For blood cytokine, before treatment, IL-2 was reduced whereas IL-8 and IL-17 were increased significantly in both groups of patients with Graves' disease comparing with those in healthy subjects (p < 0.01). For patients of the treatment group, after treatment, their IL-2 levels were increased (p < 0.01) with concomitant decreases in IL-8 and IL-17 levels (p < 0.05). There were no significant changes in blood cytokine levels before and after treatment in the control group.

CONCLUSIONS

Goiter dispersion formula significantly improved the treatment outcomes of antithyroid drug in hyperthyroidism patients with neurologic manifestations of Graves' disease by modulating IL-2, IL-8, and IL-17. The data supported the rationale for the use of goiter dispersion formula in Graves' disease treatment.

A preliminary analysis of hepatitis C virus in pancreatic islet cells

BACKGROUND

An association between hepatitis C virus (HCV) and type 2 diabetes (T2D) is supported by numerous epidemiologic studies. We hypothesized that HCV could infect human pancreatic islet cells in vitro.

METHODS

Measures of HCV RNA synthesis and protein production were used to evaluate HCV infection of pancreatic islets recovered from human donors.

RESULTS

Significant co-staining of insulin and the HCV entry factor CD81 was observed in pancreatic islets. Positive- and negative-sense HCV RNA were detected in HCV-exposed islets at days 1, 3, 7, and 14 post-infection. The HCV core and NS3 proteins were expressed and increased with time providing further evidence of viral replication. Interferon and an HCV polymerase inhibitor reduced viral replication in islet cells. In HCV-infected islets, TNFα levels were elevated at days 1, 3, and 7 post-infection, while IL-6 levels were elevated at day 1 but not days 3 or 7. Overall, the expression of miR-122 was low in islets compared to the Huh7.5 hepatocyte-derived cell line, although the relative expression of miR-122 increased in islet cells after viral infection (1, 6.63, and 5.83 at days 1, 3, and 7, respectively).

CONCLUSIONS

In this pilot study, viral infection was demonstrated in pancreatic islet cells from multiple donors using complementary measures of viral replication, thus providing evidence of in vitro infection. Altered cytokine expression may contribute to the development of insulin deficiency, and understanding the etiology of diabetes in individuals with HCV infection may facilitate the development of novel treatment modalities and prevention strategies. This in vitro system provides an important model for mechanistic studies of HCV-pancreas interactions and facilitates future studies of the potential impact of viral infection on islet cell function.

Liver diseases and thyroid functional status

The liver is closely related to the thyroid function. On one hand, many liver diseases can cause abnormal thyroid function, such as hepatitis B virus (HBV) infection, hepatitis C virus (HCV) infection, liver cirrhosis, and nonalcoholic fatty liver disease. Thyroid dysfunction is also commonly caused by interferon alpha treatment for anti-HBV or HCV therapy. On the other hand, thyroid diseases such as hyperthyroidism or hypothyroidism can result in abnormal liver function. In addition, liver injury can also be frequently caused by antithyroid drugs or levothyroxine of over conventional doses. The causal relationship between abnormal liver function and thyroid dysfunction remains unclear.

Thyroid Dysfunction in Non-Interferon Treated Hepatitis C Patients Residing in Hepatitis Endemic Area

Background

Association of thyroid dysfunction (TD) with interferon treatment of HCV is well known to clinicians. However, a few studies have highlighted the role of hepatitis C virus per se in the development of TD. The aim of this study was to know the prevalence of TD in non-interferon treated HCV infected patients referred for thyroid function testing.

Patients and Methods

Among 557 ELISA-positive HCV patients 446 (341 females, 105 males) were selected for this study. Serums FT₄, FT₃, and TSH were determined by radioimmunoassay method.

Results

TD was detected in 15.2% of patients: 9.0% hypothyroidism and 6.3% hyperthyroidism. In increasing order subclinical hypothyroidism, overt hypothyroidism, overt hyperthyroidism, and subclinical hyperthyroidism were found in 4.7%, 4.3%, 3.6%, and 2.7% patients, respectively. Overall TD was more common in female than in male HCV patients but the difference was not significant (16.1% versus 12.4%; p = 0.648). Hyperthyroidism and subclinical hypothyroidism were slightly more common in female and overall hypothyroidism and overt hypothyroidism in male patients but the difference was not statistically significant (p > 0.05). The incidence of TD was relatively high in patients above 36 years (median age) but the difference was not statistically significant either collectively or in gender base groups (p > 0.05).

Conclusion

Prior to interferon treatment, HCV infection itself causes biochemical thyroid dysfunction in 15.2% of local HCV patients.

Hepatitis C Virus E2 Protein Induces Upregulation of IL-8 Pathways and Production of Heat Shock Proteins in Human Thyroid Cells

CONTEXT

Thyroiditis is one of the most common extrahepatic manifestations of hepatitis C virus (HCV) infection. By binding to surface cell receptor CD81, HCV envelope glycoprotein E2 mediates entry of HCV into cells. Studies have shown that different viral proteins may individually induce host responses to infection. We hypothesized that HCV E2 protein binding to CD81 expressed on thyroid cells activates a cascade of inflammatory responses that can trigger autoimmune thyroiditis in susceptible individuals.

SETTING

Human thyroid cell lines ML-1 and human thyrocytes in primary cell culture were treated with HCV recombinant E2 protein. The expression of major proinflammatory cytokines was measured at the messenger RNA and protein levels. Next-generation transcriptome analysis was used to identify early changes in gene expression in thyroid cells induced by E2.

RESULTS

HCV envelope protein E2 induced strong inflammatory responses in human thyrocytes, resulting in production of interleukin (IL)-8, IL-6, and tumor necrosis factor-α. Furthermore, the E2 protein induced production of several heat shock proteins including HSP60, HSP70p12A, and HSP10, in human primary thyrocytes. In thyroid cell line ML-1, RNA sequencing identified upregulation of molecules involved in innate immune pathways with high levels of proinflammatory cytokines and chemokines and increased expression of costimulatory molecules, specifically CD40, known to be a major thyroid autoimmunity gene.

CONCLUSION

Our data support a key role for HCV envelope protein E2 in triggering thyroid autoimmunity through activation of cytokine pathways by bystander mechanisms.

Thyroid Involvement in Hepatitis C Virus-Infected Patients with/without Mixed Cryoglobulinemia

Thyroid involvement is a common condition that can be recorded during the natural course of different systemic rheumatic diseases, including the mixed cryoglobulinemia (MC) syndrome or cryoglobulinemic vasculitis. MC is triggered by hepatitis C virus (HCV) chronic infection in the majority of cases; it represents the prototype of autoimmune-lymphoproliferative disorders complicating a significant proportion of patients with chronic HCV infection. HCV is both hepato- and lymphotropic virus responsible for a great number of autoimmune/lymphoproliferative and/or neoplastic disorders. The complex of HCV-related hepatic and extrahepatic manifestations, including MC and thyroid involvement, may be termed "HCV syndrome." Here, we describe the prevalence and clinico-serological characteristics of thyroid involvement, mainly autoimmune thyroiditis and papillary thyroid cancer, in patients with HCV syndrome with or without cryoglobulinemic vasculitis.

Molecular mimicry and autoimmune thyroid disease

Hypothesized 40 years ago, molecular mimicry has been thereafter demonstrated as an extremely common mechanism by which microbes elude immune response and modulate biosynthetic/metabolic pathways of the host. In genetically predisposed persons and under particular conditions, molecular mimicry between microbial and human antigens can turn a defensive immune response into autoimmunity. Such triggering role and its pathogenetic importance have been investigated and demonstrated for many autoimmune diseases. However, this is not the case for autoimmune thyroid disease, which appears relatively neglected by this field of research. Here we review the available literature on the possible role of molecular mimicry as a trigger of autoimmune thyroid disease. Additionally, we present the results of in silico search for amino acid sequence homologies between some microbial proteins and thyroid autoantigens, and the potential pathogenetic relevance of such homologies. Relevance stems from the overlap with known autoepitopes and the occurrence of specific HLA-DR binding motifs. Bioinformatics data published by our group support and explain the triggering role of Borrelia, Yersinia, Clostridium botulinum, Rickettsia prowazekii and Helicobacter pylori. Our new data suggest the potential pathogenic importance of Toxoplasma gondii, some Bifidobacteria and Lactobacilli, Candida albicans, Treponema pallidum and hepatitis C virus in autoimmune thyroid disease, indicating specific molecular targets for future research. Additionally, the consistency between in silico prediction of cross-reactivity and experimental results shows the reliability and usefulness of bioinformatics tools to precisely identify candidate molecules for in vitro and/or in vivo experiments, or at least narrow down their number.

Hepatitis C virus infection and thyroid autoimmune disorders: A model of interactions between the host and the environment

The hepatitis C virus (HCV) infection is an important public health problem and it is associated with hepatic and extrahepatic manifestations. Autoimmune thyroid diseases are common in HCV infected patients and the standard interferon-based treatment is associated with an increase of the immune-mediated thyroid damage. Recent evidence in the literature analyzed critical points of the mechanisms of thyroid damage, focusing on the balance between the two sides of the interaction: The environment (virus infection with potential cross-reaction) and the host (susceptibility genes with consistent immune response). The spectrum of antiviral treatment for chronic HCV infection is rapidly expanding for the development of dual o triple therapy. The availability of interferon-free combined treatment with direct antiviral agents for HCV is very promising, in order to ameliorate the patient compliance and to reduce the development of thyroid autoimmunity.

Thyroid Peroxidase Antibodies in Non-Interferon Treated Hepatitis C Patients in Pakistan

Objective. Interferon therapy of HCV infected patients is associated with development of thyroid dysfunctions. Patients with pretreatment presence of antithyroid peroxidase (TPO-Ab) are at greater risk. This study, probably the first in Pakistan, was planned to determine TPO-Ab in sera of treatment-naive local HCV patients. Setting. Centre for Nuclear Medicine (CENUM), Mayo Hospital, Lahore. Patients and Methods. During July to December 2012, 190 patients (140 females, 50 males) newly diagnosed for HCV infection were selected for this study. Their age range was 15–55 years (mean: 35.3 ± 9.1 years). 262 age matched healthy subjects (211 females and 50 males) were recruited as control. Serum-free thyroxin (FT₄) and thyroid stimulating hormone (TSH) were detected by radioimmunoassay techniques. Serum TPO-Ab titer was determined by ELISA method using commercial kits. Results. Serum FT₄ and TSH levels in HCV patients and controls were within normal range. Between two groups there was no significant difference in mean value of FT₄ (16.0 ± 3.0 versus 16.2 ± 3.9; P = 0.619) but mean TSH value was significantly lower in HCV patients (1.5 ± 0.8 versus 1.8 ± 0.9; P = 0.003). Among HCV patients 51 (26.8%) were TPO-Ab positive and among control subjects 18 (6.9%) were TPO-Ab positive. The difference was statistically significant (P < 0.001). Further analysis showed that among HCV patients 39 (27.8%) females and 12 (24.0%) males were TPO-Ab positive, respectively, and difference was not statistically significant (P = 0.873). Moreover, TPO-Ab positive patients were older and had significantly higher serum TSH as compared to TPO-Ab negative HCV patients. Conclusion. Independent of patient's gender and increasing with advancing age, about one-fourth of local untreated HCV patients are TPO-Ab positive and are at greater risk of developing thyroid disorders during and after interferon treatment.

Autoimmune reactions in the course of the hepatitis C virus (HCV) infection

The immune response to the presence of the virus, both specific and non-specific, plays a decisive role in the natural history of the infection, and influences the intensity of lesions in the liver. Despite the great progress which we were able to observe over the last several years, many issues still require clarification.

The problem of autoimmune reactions during hepatitis C virus (HCV) infection includes at least two issues. First, the risk of exacerbating reactions against the organism’s own tissues that existed before the treatment. There is also an increased risk of the development of de novo autoimmune reactions, triggered mostly by interferon α. Hepatitis C virus infection predisposes to the development of diseases characterised as being certainly or probably immune-mediated.

Currently the situation has changed due to introducing non-interferon therapies for HCV treatment, which eliminate the risk associated with immunotherapy in patients with autoimmune diseases, yet the therapies are not widely available.

Hashimoto's thyroiditis and papillary thyroid cancer: are they immunologically linked?

Hashimoto's thyroiditis (HT) is the most common autoimmune disease in humans frequently leading to hypothyroidism. HT is characterized by a cellular immune response with lymphatic infiltration of the thyroid gland by T and B cells, as well as by a humoral immune response leading to specific antibody production. The synchronous appearance of HT and papillary thyroid cancer (PTC) indicates an immunological link between the two entities. Three different pathomechanisms may be postulated, including preexisting autoimmunity leading to malignancy due to inflammation, immunity towards preexisiting tumor cells leading to specific autoimmunity, and immune tolerance leading to malignancy despite (auto)immunity. In this article we review data describing these potential mechanisms that might lead to the synchronous appearance of HT and PTC.

Extrahepatic immune related manifestations in chronic hepatitis C virus infection

The association of chronic hepatitis C with immune related syndromes has been frequently reported. There is a great range of clinical manifestations affecting various systems and organs such as the skin, the kidneys, the central and peripheral nervous system, the musculoskeletal system and the endocrine glands. Despite the high prevalence of immune related syndromes in patients with chronic hepatitis C, the exact pathogenesis is not always clear. They have been often associated with mixed cryoglobulinemia, a common finding in chronic hepatitis C, cross reaction with viral antigens, or the direct effect of virus on the affected tissues. The aim of this review is to analyze the reported hepatitis C virus immune mediated syndromes, their prevalence and clinical manifestations and to discuss the most supported theories regarding their pathogenesis.

Autoimmune and neoplastic thyroid diseases associated with hepatitis C chronic infection

Frequently, patients with hepatitis C virus (HCV) chronic infection have high levels of serum anti-thyroperoxidase and/or anti-thyroglobulin autoantibodies, ultrasonographic signs of chronic autoimmune thyroiditis, and subclinical hypothyroidism, in female gender versus healthy controls, or hepatitis B virus infected patients. In patients with "HCV-associated mixed cryoglobulinemia" (MC + HCV), a higher prevalence of thyroid autoimmune disorders was shown not only compared to controls, but also versus HCV patients without cryoglobulinemia. Patients with MC + HCV or HCV chronic infection show a higher prevalence of papillary thyroid cancer than controls, in particular in patients with autoimmune thyroiditis. Patients with HCV chronic infection, or with MC + HCV, in presence of autoimmune thyroiditis, show higher serum levels of T-helper (Th)1 (C-X-C motif) ligand 10 (CXCL10) chemokine, but normal levels of Th2 (C-C motif) ligand 2 chemokine, than patients without thyroiditis. HCV thyroid infection could act by upregulating CXCL10 gene expression and secretion in thyrocytes recruiting Th1 lymphocytes that secrete interferon-γ and tumor necrosis factor-α. These cytokines might induce a further CXCL10 secretion by thyrocytes, thus perpetuating the immune cascade, which may lead to the appearance of autoimmune thyroid disorders in genetically predisposed subjects. A careful monitoring of thyroid function, particularly where nodules occur, is recommended in HCV patients.

CXCL8 in thyroid disease: from basic notions to potential applications in clinical practice

CXCL8 was the first chemokine shown to be secreted by thyrocytes. Experimental data suggest that CXCL8 plays a role in thyroid homeostasis but its role in thyroid diseases remains poorly investigated. Clinical studies measuring the serum levels of CXCL8 in patients with autoimmune-thyroid-diseases reported conflicting results. Solid evidences support a role of CXCL8 as a tumor-promoting agent in several human cancers. Studies in thyroid cancer are still in their initial stage, but promising. Several evidences indicate that thyroid cancer may share with other human malignancies some of the effects of CXCL8 and highlight the possibility of using CXCL8 as a marker of aggressiveness. Basic and clinical evidences in favor or against a role for CXCL8 in thyroid diseases are discussed.

Hepatitis C virus infection of a thyroid cell line: implications for pathogenesis of hepatitis C virus and thyroiditis

BACKGROUND

Autoimmune and non-autoimmune thyroiditis frequently occur in persons with hepatitis C virus (HCV) infection. Treatment with interferon alpha (IFNα) is also associated with significant risk for the development of thyroiditis. To explore HCV-thyroid interactions at a cellular level, we evaluated whether a human thyroid cell line (ML1) could be infected productively with HCV in vitro.

METHODS AND RESULTS

ML1 cells showed robust surface expression of the major HCV receptor CD81. Using a highly sensitive, strand-specific reverse transcription polymerase chain reaction assay, positive-sense and negative-sense HCV RNA were detected in ML1 cell lysates at days 3, 7, and 14 postinfection with HCV. HCV core protein was expressed at high levels in ML1 supernatants at days 1, 3, 5, 7, and 14 postinfection. The nonstructural protein NS5A was also detected in ML1 cell lysates by Western blotting. HCV entry into ML1 cells was shown to be dependent on the HCV entry factors CD81 and SR-B1/CLA1, while IFNα inhibited HCV replication in ML1 cells in a dose-dependent manner. Supernatants from HCV-infected ML1 cells were able to infect fresh ML1 cells productively, suggesting that infectious virions could be transferred from infected to naïve thyroid cells in vivo. Additionally, HCV infection of ML1 cells led to increased expression of the pro-inflammatory cytokine IL-8.

CONCLUSIONS

For the first time, we have demonstrated that HCV can infect human thyroid cells in vitro. These findings strongly suggest that HCV infection of thyrocytes may play a role in the association between chronic HCV infection and thyroid autoimmunity. Furthermore, the thyroid may serve as an extrahepatic reservoir for HCV viral replication, thus contributing to the persistence of viral infection and to the development of thyroid autoimmunity.

Genetic analysis of interferon induced thyroiditis (IIT): evidence for a key role for MHC and apoptosis related genes and pathways

Autoimmune thyroid diseases (AITD) have become increasingly recognized as a complication of interferon-alpha (IFNα) therapy in patients with chronic Hepatitis C virus (HCV) infection. Interferon-induced thyroiditis (IIT) can manifest as clinical thyroiditis in approximately 15% of HCV patients receiving IFNα and subclinical thyroiditis in up to 40% of patients, possibly resulting in either dose reduction or discontinuation of IFNα treatment. However, the exact mechanisms that lead to the development of IIT are unknown and may include IFNα-mediated immune-recruitment as well as direct toxic effects on thyroid follicular cells. We hypothesized that IIT develops in genetically predisposed individuals whose threshold for developing thyroiditis is lowered by IFNα. Therefore, our aim was to identify the susceptibility genes for IIT. We used a genomic convergence approach combining genetic association data with transcriptome analysis of genes upregulated by IFNα. Integrating results of genetic association, transcriptome data, pathway, and haplotype analyses enabled the identification of 3 putative loci, SP100/110/140 (2q37.1), HLA (6p21.3), and TAP1 (6p21.3) that may be involved in the pathogenesis of IIT. Immune-regulation and apoptosis emerged as the predominant mechanisms underlying the etiology of IIT.

Autoimmune thyroid disorders in hepatitis C virus infection: Effect of interferon therapy

The hepatitis C virus infection represents an important public health problem and is associated with various hepatic and extrahepatic manifestations. Symptoms outside of the liver can occur in multiple organ systems, including hematologic, renal, dermatologic, endocrine, and rheumatologic systems. Among these different organ systems, special attention has focused on the endocrine system because it affects almost every organ in the body. Among the endocrine disorders, thyroid problems are the most common and the thyroid is one of the principal target organs for extrahepatic manifestations in HCV infected patients. In addition, research data suggest that interferon treatment may be associated with immune-mediated thyroid lesions. However, case reports suggest that the response of thyroid extrahepatic manifestations to interferon in patients with chronic HCV is greatly different. The objective of this study was to summarize currently available data on thyroid conditions associated with chronic HCV infection. Moreover, we investigate the incidence of the development of immune mediated thyroid disorders during interferon therapy in these patients.

Hepatitis C virus infection and autoimmune diseases

Hepatitis C virus (HCV) infection is associated with a number of extrahepatic disorders. The most studied conditions associated with HCV are type II mixed cryoglobulinemia and B cell lymphoma. However, many reports suggest that HCV might also be associated with a number of autoimmune disorders, both organ-specific and not organ-specific. Although concomitant treatment of HCV infection is a confounding factor when ascertaining the actual role of HCV in inducing autoimmune disease, a considerable amount of experimental data indicates that HCV is able to subvert the immune system and consequently induce autoimmunity. In the present review, we report a series of observations which associate chronic HCV infection with the onset of autoimmune disorders.

Thyroid autoantibodies and dysfunction do not impact the treatment efficacy of peginterferon and ribavirin combination therapy in chronic hepatitis C

AIMS

Thyroid disorders, such as the emergence of thyroid autoantibodies (TAs) and thyroid dysfunction (TD), are not uncommon in chronic hepatitis C (CHC) patients. The study aimed to investigate the impact of TAs and dysfunction on the treatment response to pegylated interferon-α plus ribavirin (PegIFN/RBV) combination therapy in CHC patients. The association between interleukin-28B (IL-28B) genetic variants and occurrence of TAs and dysfunction was also analyzed.

METHODS

A total of 449 treatment-naive Taiwanese CHC patients with euthyroid status were consecutively enrolled. They received PegIFN/RBV combination therapy with current recommendation. TAs, TD, and IL-28B genetic variants were measured before treatment. Monitoring of TD was done at 3-month intervals during treatment, at end of treatment, and at end of follow-up (EOF).

RESULTS

The development of TAs was detected in 42 (9.4%) patients before treatment, and the incidence of TD during or at EOF was 20%. Of 287 patients with IL-28B rs8099917 TT genotype, 29 (10.1%) had TAs before treatment, whereas the patients with other genotypes did not have TAs (P = 0.04). There was no significant difference of TD incidence during treatment or at EOF between the patients with different IL-28B genotypes. There was also no significant difference of sustained virologic response according to the presence of TAs, TD, or different manifestations of TD.

CONCLUSION

Taiwanese CHC patients with rs8099917 TT genotype had a higher incidence of TAs. The development of TAs and TD did not impact the treatment efficacy of PegIFN/RBV combination therapy.

Hepatitis C virus-host interactions: Etiopathogenesis and therapeutic strategies

Hepatitis C virus (HCV) is a significant health problem facing the world. This virus infects more than 170 million people worldwide and is considered the major cause of both acute and chronic hepatitis. Persons become infected mainly through parenteral exposure to infected material by blood transfusions or injections with nonsterile needles. Although the sexual behavior is considered as a high risk factor for HCV infection, the transmission of HCV infection through sexual means, is less frequently. Currently, the available treatment for patients with chronic HCV infection is interferon based therapies alone or in combination with ribavirin and protease inhibitors. Although a sustained virological response of patients to the applied therapy, a great portion of patients did not show any response. HCV infection is mostly associated with progressive liver diseases including fibrosis, cirrhosis and hepatocellular carcinoma. Although the focus of many patients and clinicians is sometimes limited to that problem, the natural history of HCV infection (HCV) is also associated with the development of several extrahepatic manifestations including dermatologic, rheumatologic, neurologic, and nephrologic complications, diabetes, arterial hypertension, autoantibodies and cryglobulins. Despite the notion that HCV-mediated extrahepatic manifestations are credible, the mechanism of their modulation is not fully described in detail. Therefore, the understanding of the molecular mechanisms of HCV-induced alteration of intracellular signal transduction pathways, during the course of HCV infection, may offer novel therapeutic targets for HCV-associated both hepatic and extrahepatic manifestations. This review will elaborate the etiopathogenesis of HCV-host interactions and summarize the current knowledge of HCV-associated diseases and their possible therapeutic strategies.

Cutting edge: the etiology of autoimmune thyroid diseases

Significant progress has been made in our understanding of the mechanisms leading to autoimmune thyroid diseases (AITD). For the first time, we are beginning to unravel these mechanisms at the molecular level. AITD, including Graves' disease (GD) and Hashimoto's thyroiditis (HT), are common autoimmune diseases affecting the thyroid. They have a complex etiology that involves genetic and environmental influences. Seven genes have been shown to contribute to the etiology of AITD. The first AITD gene discovered, HLA-DR3, is associated with both GD and HT. More recently, this association was dissected at the molecular level when it was shown that substitution of the neutral amino acids Ala or Gln with arginine at position beta 74 in the HLA-DR peptide binding pocket is the specific sequence change causing AITD. Non-MHC genes that confer susceptibility to AITD can be classified into two groups: (1) immune-regulatory genes (e.g., CD40, CTLA-4, and PTPN22); (2) thyroid-specific genes-thyroglobulin and TSH receptor genes. These genes interact with environmental factors, such as infection, likely through epigenetic mechanisms to trigger disease. In this review, we summarize the latest findings on disease susceptibility and modulation by environmental factors.

Novel variant of thyroglobulin promoter triggers thyroid autoimmunity through an epigenetic interferon alpha-modulated mechanism

Autoimmune thyroid diseases (AITD) arise from complex interactions between genetic, epigenetic, and environmental factors. Whole genome linkage scans and association studies have established thyroglobulin (TG) as a major AITD susceptibility gene. However, the causative TG variants and the pathogenic mechanisms are unknown. Here, we describe a genetic/epigenetic mechanism by which a newly identified TG promoter single-nucleotide polymorphism (SNP) variant predisposes to AITD. Sequencing analyses followed by case control and family-based association studies identified an SNP (-1623A→G) that was associated with AITD in the Caucasian population (p = 0.006). We show that the nucleotide substitution introduced by SNP (-1623A/G) modified a binding site for interferon regulatory factor-1 (IRF-1), a major interferon-induced transcription factor. Using chromatin immunoprecipitation, we demonstrated that IRF-1 binds to the 5' TG promoter motif, and the transcription factor binding correlates with active chromatin structure and is marked by enrichment of mono-methylated Lys-4 residue of histone H3, a signature of active transcriptional enhancers. Using reporter mutations and siRNA approaches, we demonstrate that the disease-associated allele (G) conferred increased TG promoter activity through IRF-1 binding. Finally, treatment of thyroid cells with interferon α, a known trigger of AITD, increased TG promoter activity only when it interacted with the disease-associated variant through IRF-1 binding. These results reveal a new mechanism of interaction between environmental (IFNα) and genetic (TG) factors to trigger AITD.

Urticaria and thyroid autoimmunity

BACKGROUND

Chronic urticaria is a common clinical condition whose etiology, in about 75% of cases, is unknown and is therefore called chronic idiopathic urticaria (CIU). A link between CIU and autoimmune thyroid diseases was proposed several decades ago. Here we review this topic.

SUMMARY

Several studies have been performed to determine if and to what degree there is an association between CIU and autoimmune thyroid diseases, particularly autoimmune thyroiditis. Many of these studies were not well controlled, however. Approximately one-fourth of CIU patients have serological evidence of thyroid autoimmunity, suggesting that these two disorders are associated. The mechanisms for the apparent association between CIU and serological evidence of thyroid autoimmunity are not clear. There are no data regarding the correlations between CIU and histological features of autoimmune thyroiditis or hypothyroidism. Despite this, there are anecdotal reports regarding L-thyroxine administration in patients with CIU.

CONCLUSIONS

Screening for thyroid autoimmunity is probably useful in patients with CIU. More solid evidence, based on still lacking well-conducted controlled studies, is desirable to determine if there is a therapeutic role for L-thyroxine treatment in ameliorating the skin manifestations of urticaria.

IFN-α mediates the development of autoimmunity both by direct tissue toxicity and through immune cell recruitment mechanisms

IFN-α is known to play a key role in autoimmunity, but the mechanisms are uncertain. Although the induction of autoimmunity by IFN-α is consistent with primarily immunomodulatory effects, the high frequency of nonautoimmune inflammation suggests other mechanisms. We used thyroiditis as a model to dissect these possibilities. IFN-α treatment of cultured thyrocytes increased expression of thyroid differentiation markers, thyroglobulin, thyroid-stimulating hormone receptor, thyroid peroxidase, and sodium iodide transporter. RNAseq analysis demonstrated that pathways of Ag presentation, pattern recognition receptors, and cytokines/chemokines were also stimulated. These changes were associated with markedly increased nonapoptotic thyroid cell death, suggesting direct toxicity. To corroborate these in vitro findings, we created transgenic mice with thyroid-specific overexpression of IFN-α under control of the thyroglobulin promoter. Transgenic mice developed marked inflammatory thyroid destruction associated with immune cell infiltration of thyroid and surrounding tissues leading to profound hypothyroidism, findings consistent with our in vitro results. In addition, transgenic mice thyroids showed upregulation of pathways similar to those observed in cultured thyrocytes. In particular, expression of granzyme B, CXCL10, a subset of the tripartite motif-containing family, and other genes involved in recruitment of bystander cytotoxic immune responses were increased. Pathways associated with apoptosis and autophagy were not induced. Taken together, our data demonstrate that the induction of tissue inflammation and autoimmunity by IFN-α involves direct tissue toxic effects as well as provocation of destructive bystander immune responses.

The natural history of interferon-α induced thyroiditis in chronic hepatitis c patients: a long term study

BACKGROUND

Autoimmune thyroid disease is a common complication of patients with chronic hepatitis C undergoing combination pegylated interferon-α and ribavirin treatment. A small proportion develops interferon-induced thyroiditis of which the long term natural history is unknown and how it compares with de novo thyroiditis. The aim of the study is to determine the natural history of thyroid disease including antibody profile in this particular setting 36 months from the completion of therapy.

METHODS

A cohort of 18 hepatitis C patients (mean age 45 ± 8 years (standard deviation)) who developed exclusively thyroiditis in this setting was followed every 12 months after the completion of therapy for 36 months. Investigations included thyrotropin, free tetra-iodothyronine, free tri-iodothyronine levels and thyroid autoantibodies.

RESULTS

None of the patients developed any long term thyroid disease. Two patients had a prolonged hypothyroid phase of the thyroiditis early after the completion of treatment but recovered fully. The remaining 16 patients remained euthyroid. Similarly, thyroid autoantibodies all declined and returned to reference range.

CONCLUSIONS

The long term natural history in this small series of interferon induced thyroiditis was benign. If a larger series confirms a similar outcome then there is no long term residual effect on thyroid function and follow-up testing would not be warranted.

Environmental triggers of thyroiditis: hepatitis C and interferon-α

Autoimmune thyroid diseases (AITD) are postulated to develop as a result of a complex interplay between several genetic and environmental influences. The pathogenesis of AITD is still not clearly defined. However, among the implicated triggers (e.g. iodine, infections, medications), more recent data confirmed strong associations of AITD with the hepatitis C virus (HCV) infection and interferon-α (IFNα) therapy. Moreover, it is likely that HCV and IFN act in synergism to trigger AITD in patients. Indeed, approximately 40% of HCV patients develop either clinical or subclinical disease while receiving IFNα. Interferon induced thyroiditis (IIT) can manifest as non-autoimmune thyroiditis (presenting as destructive thyroiditis, or non-autoimmune hypothyroidism), or autoimmune thyroiditis [presenting with clinical features of Graves' disease (GD) or Hashimoto's thyroiditis (HT)]. Although not yet clearly understood, it is thought that IFNα can induce thyroiditis via both immune stimulatory and direct toxic effects on the thyroid. In view of the high frequency of IIT, routine screening and surveillance of HCV patients receiving IFNα is recommended to avoid the complications, such as cardiac arrhythmias, associated with thyrotoxicosis. In summary, IIT is a common clinical problem that can be readily diagnosed with routine thyroid function screening of HCV patients receiving IFN. The treatment of IIT consists of the standard therapy for differing clinical manifestations of IIT such as GD, HT, or destructive thyroiditis. However, anti-thyroid medications are not recommended in this setting since they can potentially be hepatotoxic.

Viral infection in induction of Hashimoto's thyroiditis: a key player or just a bystander?

PURPOSE OF REVIEW

Viral infection activates both the innate and adaptive immunity and is implicated as a trigger of autoimmune diseases including Hashimoto's thyroiditis. This review summarizes our knowledge respecting the role of viral infection in the cause of Hashimoto's thyroiditis.

RECENT FINDINGS

Components of several viruses such as hepatitis C virus, human parvovirus B19, coxsackie virus and herpes virus are detected in the thyroid of Hashimoto's thyroiditis patients. Bystander activation of autoreactive T cells may be involved in triggering intrathyroidal inflammation. Signaling molecules associated with antiviral responses including Toll-like receptors may participate in Hashimoto's thyroiditis induction. However, studies have provided insufficient direct evidence for the viral hypothesis in Hashimoto's thyroiditis.

SUMMARY

Despite interesting circumstantial evidence, whether viral infection is responsible for Hashimoto's thyroiditis remains unclear. Studies addressing this issue are required to substantiate a contribution from viral infection to Hashimoto's thyroiditis and, consequently, the prospect for developing preventive modalities for Hashimoto's thyroiditis.

Hepatitis C and interferon induced thyroiditis

Autoimmune thyroid diseases (AITDs) are complex diseases that develop as a result of interactions between genetic, epigenetic, and environmental factors. Significant progress has been made in our understanding of the genetic and environmental triggers contributing to AITD. The major environmental triggers of AITD include iodine, smoking, medications, pregnancy, and possibly stress. In this review we will focus on two well-documented environmental triggers of AITD, hepatitis C virus (HCV) infection and interferon alpha (IFNa) therapy. Chronic HCV infection has been shown to be associated with increased incidence of clinical and subclinical autoimmune thyroiditis (i.e. the presence of thyroid antibodies in euthyroid subjects). Moreover, IFNa therapy of chronic HCV infection is associated with subclinical or clinical thyroiditis in up to 40% of cases which can be autoimmune, or non-autoimmune thyroiditis. In some cases interferon induced thyroiditis (IIT) in chronic HCV patients may result in severe symptomatology necessitating discontinuation of therapy. While the epidemiology and clinical presentation of HCV and interferon induced thyroiditis have been well characterized, the mechanisms causing these conditions are still poorly understood.

Hepatitis C virus and autoimmunity

Hepatitis C virus infection is associated with several extrahepatic manifestations. About 60% of patients infected with HCV develop at least one extrahepatic manifestation. The majority of these diseases seem to be triggered through autoimmune mechanisms, such as autoantibody production, autoreactive T cells and complex autoimmune mechanisms leading to systemic autoimmune disorders. In this review we categorize these diseases into three groups according to the main pathogenetic process involved, in particular B-cell-mediated, T-cell-mediated and complex autoimmune systemic diseases.

Establishment and characterization of dengue virus type 2 nonstructural protein 1 specific T cell lines

Immunity against dengue viruses (DENV) infection may include cellular immune responses which involve in the immunopathology of DENV infection hosts. This study was to establish short-term dengue virus type 2 (DENV2) nonstructural protein 1 (NS1) specific T cells from splenocytes from BALB/c mice immunized with DENV2 NS1 in vitro, which may be used to identify immunopathologic mechanism of dengue. Nine DENV2 NS1 specific T cell lines were successfully established by using limiting dilution methods and maintained for 20 weeks by re-stimulated with DENV2 NS1, recombinant mouse IL-2 and antigen presenting cell weekly. Phenotypically, these cells were mainly composed of CD3(+)CD4(+) T cells. The culture supernatants of these cells contained large amounts of TNF-α and IFN-γ. Vascular tissue pathological change could be found in the mice adoptive transferred with DENV2 NS1 specific T cells. The results indicate that DENV2 NS1 specific T cells could be established and maintained with syngeneic T cell growth factors in vitro. Meanwhile, DENV2 NS1 specific T cells might contribute to the immunopathology of vascular leakage of dengue.

Interferon induced thyroiditis

Interferon-alpha (IFNalpha) is used for the treatment of various disorders, most notable chronic hepatitis C virus (HCV) infection. One of the commonest side effects of IFNalpha therapy is thyroiditis, with up to 40% of HCV patients on IFNalpha developing clinical or subclinical disease. In some cases interferon induced thyroiditis (IIT) may result in severe symptomatology necessitating discontinuation of therapy. IIT can manifest as clinical autoimmune thyroiditis, presenting with symptoms of classical Hashimoto's thyroiditis or Graves' disease, or as non-autoimmune thyroiditis. Non-autoimmune thyroiditis can manifest as destructive thyroiditis, with early thyrotoxicosis and later hypothyroidism, or as non-autoimmune hypothyroidism. While the epidemiology and clinical presentation of IIT have been well characterized the mechanisms causing IIT are still poorly understood. It is likely that the hepatitis C virus (HCV) itself plays a role in the disease, as the association between HCV infection and thyroiditis is well established. It is believed that IFNalpha induces thyroiditis by both immune stimulatory effects and by direct effects on the thyroid. Early detection and therapy of this condition are important in order to avoid complications of thyroid disease such as cardiac arrhythmias.

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.

Incidence and nature of infectious disease in patients treated with anti-TNF agents

Tumor necrosis factor alpha (TNF-alpha) inhibitors offer a targeted therapeutic strategy that contrasts with the nonspecific immunosuppressive agents traditionally used to treat most inflammatory diseases. These biologic agents have had a significant impact in ameliorating the signs and symptoms of inflammatory rheumatoid disease and improving patient function. From the onset of clinical trials, a central concern of cytokine blockade has been a potential increase in susceptibility to infections. Not surprisingly, a variety of infections have been reported in association with the use of TNF-alpha inhibitor agents. In particular, there is evidence suggesting an increased rate of granulomatous infections in patients treated with monoclonal TNF-alpha inhibitors. This review provides the incidence and nature of infections in patients treated with TNF-alpha inhibitor agents and reminds the clinician of the required vigilance in monitoring patients.