Expression of immunoregulatory molecules by thyrocytes protects nonobese diabetic-H2h4 mice from developing autoimmune thyroiditis

Alteration in kynurenine pathway metabolites in young women with autoimmune thyroiditis

The kynurenine pathway (KP) of tryptophan degradation includes several compounds that reveal immunomodulatory properties. The present study aimed to investigate the alteration in KP metabolites in young women with autoimmune thyroiditis (AIT) and their associations with thyroid function. The thyroid function tests, antithyroid antibodies measurement and ultrasonography of the thyroid gland have been performed in 57 young women with AIT and 38 age-matched healthy controls. The serum levels of tryptophan, kynurenine (KYN) and its metabolites were determined, and the activity of KP enzymes was calculated indirectly as product-to-substrate ratios. KP was activated and dysregulated in AIT, along with significantly elevated levels of KYN and anthranilic acid (AA), at the expense of the reduction of kynurenic acid (KYNA), which was reflected by the increase in the AA/KYNA ratio (p < 0.001). In univariate and multiple regression analyses, peripheral deiodinase (SPINA-GD) activity in AIT was positively associated with KYNA, AA, and quinolinic acid (QA). The merger of AA, AA/KYNA ratio, QA and SPINA-GD exhibited the highest sensitivity and specificity to predict AIT (p < 0.001) in receiver operating characteristic (ROC) analysis. In conclusion, the serum KYN metabolite profile is dysregulated in young women with AIT and could serve as a new predictor of AIT risk.

The Kynurenine Pathway-New Linkage between Innate and Adaptive Immunity in Autoimmune Endocrinopathies

The kynurenine pathway (KP) is highly regulated in the immune system, where it promotes immunosuppression in response to infection or inflammation. Indoleamine 2,3-dioxygenase 1 (IDO1), the main enzyme of KP, has a broad spectrum of activity on immune cells regulation, controlling the balance between stimulation and suppression of the immune system at sites of local inflammation, relevant to a wide range of autoimmune and inflammatory diseases. Various autoimmune diseases, among them endocrinopathies, have been identified to date, but despite significant progress in their diagnosis and treatment, they are still associated with significant complications, morbidity, and mortality. The precise cellular and molecular mechanisms leading to the onset and development of autoimmune disease remain poorly clarified so far. In breaking of tolerance, the cells of the innate immunity provide a decisive microenvironment that regulates immune cells' differentiation, leading to activation of adaptive immunity. The current review provided a comprehensive presentation of the known role of IDO1 and KP activation in the regulation of the innate and adaptive arms of the immune system. Significant attention has been paid to the immunoregulatory role of IDO1 in the most prevalent, organ-specific autoimmune endocrinopathies-type 1 diabetes mellitus (T1DM) and autoimmune thyroiditis.

CD8+ T cells: The past and future of immune regulation

Regulation of the adaptive immune response is critical for health. Regulatory activity can be found in multiple components of the immune system, however, the focus on particular components of the immune regulatory network has left many aspects of this critical immune component understudied. Here we review the evidence for activities of CD8+ T cells in immune homeostasis and regulation of autoimmune reactivity. The heterogeneous nature of identified CD8+ cell types are examined, and common phenotypes associated with functional activities are defined. The varying types of antigen signal crucial for CD8+ T cell regulatory activity are identified and the implications of these activation pathways for control of adaptive responses is considered. Finally, the promising capacity for transgenic antigen receptor directed cytotoxicity as a mechanism for modulation of autoimmunity is detailed.

[Biochemical and immunological markers of autoimmune thyroiditis]

Correlations between biochemical and immunological markers of programmed cell death (apoptosis), and the functional state of the thyroid gland (hyperthyroidism, euthyroidism, hypothyroidism) have been investigated in autoimmune thyroiditis (AT) (also known as chronic autoimmune thyroiditis). Annexin V, TRAIL and TNF-a, as well as DNA-hydrolyzing antibodies were used as the main markers. Increased levels of TRAIL were found in the serum of AT patients (hyperthyroidism>hypothyroidism>euthyroidism) compared with healthy individuals. The highest frequency of antibodies to denatured DNA (Abs-dDNA) had the highest frequency in AT patients (97%) compared with healthy controls. Among these patients, 75% had hyperthyroidism, 85% had hypothyroidism, and 84.7% had euthyroidism. Abs hydrolyzing activity demonstrated correlation dependence with symptoms of the thyroid dysfunction.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Postnatal expression of BRAFV600E does not induce thyroid cancer in mouse models of thyroid papillary carcinoma

The mutant BRAF (BRAF(V600E)) is the most common genetic alteration in papillary thyroid carcinomas (PTCs). The oncogenicity of this mutation has been shown by some genetically engineered mouse models. However, in these mice, BRAF(V600E) is expressed in all the thyroid cells from the fetal periods, and suppresses thyroid function, thereby leading to TSH elevation, which by itself promotes thyroid tumorigenesis. To overcome these problems, we exploited 2 different approaches, both of which allowed temporally and spatially restricted expression of BRAF(V600E) in the thyroid glands. First, we generated conditional transgenic mice harboring the loxP-neo(R)-loxP-BRAF(V600E)-internal ribosome entry site-green fluorescent protein sequence [Tg(LNL-BRAF(V600E))]. The double transgenic mice (LNL-BRAF(V600E);TPO-Cre) were derived from a high expressor line of Tg(LNL-BRAF(V600E)) mice and TPO-Cre mice; the latter expresses Cre DNA recombinase under the control of thyroid-specific thyroid peroxidase (TPO) promoter and developed PTC-like lesions in early life under normal serum TSH levels due to mosaic recombination. In contrast, injection of adenovirus expressing Cre under the control of another thyroid-specific thyroglobulin (Tg) promoter (Ad-TgP-Cre) into the thyroids of LNL-BRAF(V600E) mice did not induce tumor formation despite detection of BRAF(V600E) and pERK in a small fraction of thyroid cells. Second, postnatal expression of BRAF(V600E) in a small number of thyroid cells was also achieved by injecting the lentivirus expressing loxP-green fluorescent protein-loxP-BRAF(V600E) into the thyroids of TPO-Cre mice; however, no tumor development was again observed. These results suggest that BRAF(V600E) does not appear to induce PTC-like lesions when expressed in a fraction of thyroid cells postnatally under normal TSH concentrations.

TRAIL and DR5 promote thyroid follicular cell apoptosis in iodine excess-induced experimental autoimmune thyroiditis in NOD mice

Death receptor-mediated apoptosis has been implicated in target organ destruction in patients with chronic autoimmune thyroiditis. Several apoptosis signaling pathways, such as Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), have been shown to be active in thyroid cells and may be involved in destructive thyroiditis. Thyroid toxicity of iodide excess has been demonstrated in animals fed with an iodide-rich diet, but its pathogenic role remains unclear. The effects of excessive iodine on TRAIL and its death receptor expression in thyroid were investigated. Experimental autoimmune thyroiditis (EAT) was induced by excessive iodine and thyroglobulin (Tg) in non-obese diabetic mice. The expression of TRAIL and its death receptor DR5 was detected by immunofluorescence staining. Following administration of excessive iodine alone, Tg, and excessive iodine combined with Tg, TRAIL-positive cells appear not only in follicular cells but also in lymphocytes infiltrated in the thyroid, whereas DR5-positive cells appear only in follicular cells. Large numbers of CD3-positive cells and a few CD22-positive cells were detected in thyroid. A great amount of follicular cells were labeled specifically by terminal deoxynucleotide transferase-mediated deoxynucleotide triphosphate nick-end labeling assay. Taken together, our results suggest that excessive iodine could induce TRAIL and DR5 abnormal expression in thyroid. TRAIL band with DR5 to promote follicular cells apoptosis thus mediate thyroid destruction in EAT.

Dynamic changes of CD4+CD25 + regulatory T cells in NOD.H-2h4 mice with iodine-induced autoimmune thyroiditis

Iodine is an essential trace element for thyroid hormone synthesis and metabolism, either low or high intake may lead to thyroid disease, but the pathogenetic mechanisms by which iodine interacts with the thyroid autoimmune are poorly understood. We investigated the dynamic changes of CD4(+)CD25(+) regulatory T cells in NOD.H-2(h4) mice with iodine-induced autoimmune thyroiditis (AIT), and explore potential immune mechanism of AIT induced by iodine. NOD.H-2(h4) mice were randomly divided into two groups, and received plain water or water containing 0.005% sodium iodide. Eight weeks after iodine provision, the incidences of thyroiditis, relative weights of thyroids, and serum thyroglobulin antibody titers in the iodine-supplied groups were significantly increased compared to the control groups (p < 0.05). The AIT mice had fewer CD4(+)CD25(+)Foxp3(+) T cells and reduced Foxp3 mRNA expression in splenocytes compared with the controls (p < 0.01), and maintained relatively low levels during the development of thyroiditis. The changes described above aggravated gradually with the extension of iodine treatment. These data suggest that CD4(+)CD25(+) regulatory T cells may be involved in the pathogenesis and development of AIT induced by iodine.

The effect of regulatory T-cell depletion on the spectrum of organ-specific autoimmune diseases in nonobese diabetic mice at different ages

The nonobese diabetic (NOD) mouse spontaneously develops several autoimmune diseases, including type 1 diabetes and to a lesser extent thyroiditis and sialitis. Imbalance between effector T cells (Teffs) and regulatory T cells (Tregs) has recently been proposed as a mechanism for the disease pathogenesis in NOD mice, but previous studies have shown the various outcomes by different timing and methods of Treg-depletion. This study was, therefore, designed to compare the consequences of Treg-depletion by the same method (anti-CD25 antibody) on the spectrum of organ-specific autoimmune diseases in NOD mice of different ages. Treg-depletion by anti-CD25 antibody at 10 days of age accelerated development of all three diseases we examined (insulitis/diabetes, thyroiditis, and sialitis); Treg-depletion at 4 weeks of age accelerated only diabetes but not thyroiditis or sialitis; and Treg-depletion at 12 weeks of age hastened only development of thyroiditis and exhibited little influence on diabetes or sialitis. Increased levels of insulin autoantibodies (IAA) were, however, observed in mice depleted of Tregs at 10 days of age, not in those at 4 weeks. Thus, the consequences of Treg-depletion on the spectrum of organ-specific autoimmune diseases depend on the timing of anti-CD25 antibody injection in NOD mice. Aging gradually tips balance between Teffs and Tregs toward Teff-dominance for diabetes, but this balance for thyroiditis and sialitis likely alters more intricately. Our data also suggest that the levels of IAA are not necessarily correlated with diabetes development.

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.

Manipulation of indoleamine 2,3 dioxygenase; a novel therapeutic target for treatment of diseases

BACKGROUND

The discovery of indoleamine 2,3-dioxygenase (IDO) as a modulator for the maintenance of fetomaternal immuno-privileged state has been heralded as a significant step in further defining the role of IDO in immunobiology. IDO is an IFN-inducible, intracellular enzyme that catalyzes the initial and rate-limiting step in the degradation of the essential amino acid, tryptophan. It has been suggested that IDO has the capacity to regulate the immune system via two discrete mechanisms; firstly the deprivation of tryptophan, which is essential for T cell proliferation and via the cytotoxic effects of tryptophan metabolites on T(H)1 cell survival.

METHODS

The sources of information used to prepare the paper are published work on Pubmed/Medline. In this review, we examine the therapeutic role of modulating IDO activity a variety of disease states including tumour tolerance, chronic infection, transplant rejection, autoimmunity and asthma. We propose that IDO represents a novel therapeutic target for the treatment of these diseases. We also explore the diverse strategies which are being employed, either to augment or to inhibit IDO activity in order to modify various disease processes. The limitations associated with these strategies are also scrutinized.

Function and dysfunction of dendritic cells in autoimmune rheumatic diseases

Dendritic cells (DC) have been implicated both in initiation of immunity and in immune tolerance. The mechanisms whereby tolerogenic DC may induce and maintain peripheral tolerance include the generation or expansion of regulatory T cells (Treg) and the promotion of T-cell anergy or deletion. A wide spectrum of hematopoietic growth factors and cytokines are endowed with the ability to differentiate tolerogenic DC both in vitro and in vivo. Based on this knowledge, therapeutic vaccination with cytokine-modulated tolerogenic DC has been applied to animal models of autoimmune disorders. This article will review the current experimental evidence underpinning DC dysfunction in rheumatic autoimmune diseases and will discuss how the manipulation of DC and Treg number and function may control undesired T-cell responses.