Interferon gamma and iodide increase the inducibility of the 72 kD heat shock protein in cultured human thyroid epithelial cells

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.

Genes regulated by thyrotropin and iodide in cultured human thyroid follicles: analysis by cDNA microarray

Thyrotropin (TSH) regulates a number of genes in thyrocytes, leading to iodide uptake, de novo synthesis and release of thyroid hormones, and cell proliferation, accompanied by increased blood flow. At higher doses of iodide, however, the TSH-induced increases in thyroid hormone release and blood flow are downregulated, and high iodide intake occasionally worsens autoimmune thyroiditis. To elucidate the genes involved in such effects, we cultured human thyrocytes and examined genes modulated by TSH and iodide, using a cDNA microarray study, which can analyze 2400 genes in each run. When thyroid follicles were cultured with TSH for 2 days, more than 100 genes were upregulated. These genes included those for enzymes involved in carbohydrate and lipid metabolism, adenylate and guanylate cyclases, and enzyme involved in cell proliferation. When thyroid follicles were cultured with high iodide concentrations (10(-5) M) for 24 hours, more than 100 genes were upregulated. Interesting genes were interleukin-8, IFP53, 90-kd heat shock protein, osteopontin, and intercellular adhesion molecule-1. These results were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) followed by Southern blot hybridization. In summary, TSH upregulated a number of genes regulating thyroid functions. It is intriguing that thyroid follicles cultured with a high iodide concentration (10(-5) M) increased the expression levels of genes capable of modulating lymphocyte functions, even though immunocompetent cells were extensively removed by the present experimental culture conditions. Although we have analyzed only approximately 6%-8% of all human genes, the cDNA microarray study is a powerful tool to elucidate the effects of TSH and iodide on thyroid function.

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.

Costimulatory effects of interferon-gamma and interleukin-1beta or tumor necrosis factor alpha on the synthesis of Abeta1-40 and Abeta1-42 by human astrocytes

Chronic inflammation and astrocytosis are characteristic histopathological features of Alzheimer's Disease (AD). Astrocytes are one of the predominant cell types in the brain. In AD they are activated and produce inflammatory components such as complement components, acute phase proteins, and cytokines. In this study we analyzed the effect of cytokines on the production of amyloid beta (Abeta) in the astrocytoma cell line U373 and in primary human astrocytes isolated postmortem from healthy aged persons as well as from patients with AD. Astrocytes did not produce Abeta in the absence of stimuli or following stimulation with IL-1beta, TNFalpha, IL-6, and TGF-beta1. Neither did combinations of TNFalpha and IL-1beta, IL-6 or TGF-beta1, or the coadministration of IFNgamma and IL-6 or TGF-beta1 induce Abeta production. In contrast, pronounced production of Abeta1-40 and Abeta1-42 was observed when primary astrocytes or astrocytoma cells were stimulated with combinations of IFNgamma and TNFalpha or IFNgamma and IL-1beta. Induction of Abeta production was accompanied by decreased glycosylation of APP as well as by increased secretion of APPsbeta. Our results suggest that astrocytes may be an important source of Abeta in the presence of certain combinations of inflammatory cytokines. IFNgamma in combination with TNFalpha or IL-1beta seems to trigger Abeta production by supporting beta-secretase cleavage of the immature APP molecule.

The effect of iodine administration on the development of thyroid autoimmunity in patients with nontoxic goiter

OBJECTIVE

Previous studies, mostly performed in iodine-deficient areas, have suggested that the administration of iodine to patients with endemic goiter may be associated with the development of thyroid autoantibodies (ThAbs); however, this has not been a consistent finding. In this study, we evaluated the effect of iodine on thyroid function and on the development of indices of autoimmunity (ThAbs and lymphocytic infiltration) in an iodine replete area.

METHODS

Iodized oil (1 mL) was administered intramuscularly to 40 euthyroid patients with nontoxic goiter, adequate iodine intake, and absent or normal levels of ThAbs. Blood and urinary samples were taken at time 0, 3, 6, and 12 months after iodine administration. Thyroid volume was evaluated and fine-needle aspiration (FNA) was performed at 0, 6, and 12 months.

RESULTS

Seven patients developed abnormal levels of ThAbs at some time between 3 and 12 months after iodine administration (p = 0.017). Mean anti-thyroglobulin (Tg) antibody levels increased at 6 months without reaching abnormal levels, but did not reach statistical significance (p = 0.062). Lymphocytic infiltration was detected in FNA smears in 10 cases before and in 27 cases after treatment (p = 0.0003). Triiodothyronine (T3) decreased at 12 months of follow-up, while thyroxine (T4) and thyrotropin (TSH) levels did not change significantly. A decrease in the mean levels of thyroglobulin as well as a small reduction in goiter size was observed at 6 and 12 months.

CONCLUSION

The administration of iodized oil to patients with small nontoxic goiter in an iodine-replete area was accompanied by the development of abnormal levels of ThAbs in some cases and by an increase in thyroid lymphocytic infiltration.

Randomized, double blind, placebo-controlled trial of low dose iodide in endemic goiter

Iodine (I) is essential for normal thyroid function, and the majority of subjects tolerate a wide range of dietary levels. However, a subset of individuals upon exposure to normal or elevated levels of I develop thyroid dysfunction and autoimmunity. In this double blind trial, we evaluated efficacy and tolerability of low dose I in adults with euthyroid, diffuse, endemic goiter. Sixty-two subjects were randomly assigned I (0.2 mg/day) or placebo for 12 months. After termination of therapy, both groups were followed for a further 6 months. Thyroid sonography and determinations of thyroid-related hormones, urinary I excretion per 24 h, and thyroid antibodies were carried out at baseline and at 3, 6, 9, 12, 15, and 18 months. Markedly elevated urinary I values were found during therapy in subjects receiving I (32 at baseline vs. 213 micrograms/24 h at 12 months; P = 0.0001) compared to placebo (34 and 33 micrograms/24 h, respectively; P < 0.0001 vs. I). I substantially reduced thyroid volume (29 vs. 18 mL at 12 months; -38%; P = 0.0001), and at 18 months, the therapeutic effect was sustained. In the placebo group, no significant changes were observed. High microsomal and thyroglobulin autoantibody titers were present in 3 of 31 (9.7%) subjects receiving I, and I-induced hypo- and hyperthyroidism developed in 2 and 1, respectively. Fine needle biopsy revealed marked lymphocytic infiltration in all 3 cases. After withdrawal of I, thyroid dysfunctions spontaneously remitted, and antibody titers as well as lymphocytic infiltration decreased markedly. Follow-up of these 3 subjects for an additional 2 yr showed normalization of antibody titers in 2. Thus, among subjects with endemic goiter, low dose I successfully normalized thyroid volume and body I supplementation; nevertheless, reversible I-induced thyroid dysfunctions and autoimmunity were observed in nearly 10% of the subjects.

Heat shock protein 60 mRNA is not increased in Graves' disease thyroid tissue

Heat shock proteins (hsps) are highly conserved proteins which carry vital functions by assisting intracellular protein transport and degregation. Hsps of the 60-kD family have been shown to be strongly immunogenic and to be overexpressed in many autoimmune diseases. Hsp60 reactive T cells from thyroids from patients with Graveś disease have been isolated, but hsp60 expression in Graveś disease has not been investigated. We therefore investigated the expression of hsp60 mRNA in thyroids from patients with Graveś disease and from non autoimmune controls. Expression of hsp60 mRNA could be detected in all Graveś disease thyroids. This expression was not influenced by preoperative treatment with antithyroid drugs. Hsp60 mRNA was expressed in non autoimmune controls, too. There was no quantitative difference between autoimmune thyroids and controls, revealed by computer scanning of Northern blots. Our results demonstrate, that in contrast to some other autoimmune diseases hsp60 mRNA is not overexpressed in thyroids from patients with Graveś disease.

T cells from rejected human kidney allografts respond to heat shock protein 72

The immune response to heat shock proteins (hsps) is gaining more and more interest. Members of the 65 and the 70 kDa hsp families have been shown to be target molecules of the immune system in autoimmune diseases, in cancer immunity and recently in the rejection of rat heart allografts. It was therefore the aim of the present study to investigate whether T cells propagated from two rejected human renal allografts also recognised hsps. In vivo activated interleukin-2 (IL-2) receptor positive T cells were expanded from renal allografts, which had been removed because of irreversible rejection, by 1 week of culture in IL-2 only, followed by stimulation with OKT-3 in combination with IL-2. One T cell line was obtained from each graft. FACS analysis of the lines demonstrated that 51% and 53% of the cells were CD4+ and 45% and 42% CD8+; 4% and 5% were gamma delta + T cells. Both lines had a significant proliferative response when stimulated with recombinant human hsp 72. In contrast, hsp 65 did not induce stimulation. The lines also showed a proliferative response upon stimulation with epithelial kidney cells, purified and cultured from the respective rejected kidneys. These results demonstrate that T cells propagated from rejected human kidney allografts recognize hsp 72. This suggests that hsp-specific T cells may play a role in the rejection process of allograft kidneys.

Hyperthermia inhibits proliferation and stimulates the expression of differentiation markers in cultured thyroid carcinoma cells

In the last two decades hyperthermia has increasingly been used as adjuvant therapy for the treatment of malignant tumours. The effects of heat were therefore analysed on cultured thyroid epithelial cells from patients with thyroid cancer and from non-malignant control thyroids. Purified thyroid cells were subjected to heat treatment (42.5 degrees C; 90 min). After 24 h [3H]thymidine incorporation was assessed and the expression of heat shock protein 72 (hsp72), thyroglobulin, CD54 (ICAM-I) and MHC class-Il were analysed by immunofluorescence staining. Additionally mRNA analysis was performed by Northern blotting. Whereas hyperthermia inhibited the proliferation of thyroid cells, it significantly increased the expression of hsp72, thyroglobulin, CD54 and HLA-DR (P < 0.05). Our results suggest that hyperthermia may suppress growth while supporting differentiation and immune recognition in thyroid cancer. It may therefore be beneficial as a treatment for patients with thyroid carcinoma.

The potential immunological role of the thyroid cell in autoimmune thyroid disease

Over the last decade it has become evident that thyroid follicular cells express a number of immunologically active molecules in autoimmune thyroid disease that may endow them with the capacity to interact with cells of the classical immune system. Expression of major histocompatibility complex class II molecules is induced by gamma-interferon, but there is no evidence yet that thyroid follicular cells can concurrently express the costimulatory signals necessary for class II expression to result in T cell stimulation: in this situation, class II expression may have a protective role, inducing T cell anergy. Thyroid follicular cells also express a variety of cell surface proteins (in particular CD59) that may protect the cells from complement attack. On the other hand, the expression of adhesion molecules and cytokines by thyrocytes would seem to be harmful, as these are likely to exacerbate autoimmune injury. Further study of the immunological role of thyroid follicular cells will shed new light on the pathogenesis of Graves' disease and autoimmune hypothyroidism, and may lead to novel therapeutic approaches to these disorders.