Inflammatory cytokine regulation of Fas-mediated apoptosis in thyroid follicular cells

Wpływ suplementacji diety selenem na przebieg autoimmunologicznego zapalenia tarczycy – przegląd badań klinicznych przeprowadzonych w populacji europejskiej

Wiele obserwacji wskazuje na zależność między zmniejszonymi zasobami selenowymi organizmu a różnymi schorzeniami tarczycy, w tym także autoimmunologicznym zapaleniem tarczycy (AZT). W większości prac poświęconych temu zagadnieniu zmiana stężenia przeciwciał anty-TPO była główną miarą oceny skuteczności suplementacji selenem (Se) diety pacjentów z AZT. Stężenie przeciwciał anty-TPO ma wpływ na intensywność nacieków limfocytarnych w gruczole tarczowym i stopień jego uszkodzenia, dlatego zmniejszenie ich stężenia w wyniku zwiększonego spożycia Se może się przyczynić do skuteczniejszego leczenia AZT. W części prac omówionych w artykule ewaluacja immunoregulacyjnego działania Se w przebiegu AZT została rozpatrzona w odniesieniu do szerszego zakresu parametrów biochemicznych i immunologicznych (głównie dotyczy to zmian w wytwarzaniu cytokin i chemokin). Wielu autorów potwierdziło wpływ Se na zmniejszanie stężenia przeciwciał anty-TPO, jednak wyniki wszystkich prac nie są jednoznaczne. Przyczyną rozbieżności może być odmienny stopień wysycenia tarczycy Se i jodem w różnych grupach pacjentów, różny stopień zaawansowania choroby, różne dawki Se podawanego pacjentom, stosowanie lub niestosowanie jednoczesnej terapii L-tyroksyną oraz polimorfizmy pojedynczych nukleotydów (SNP) występujące w genach kodujących poszczególne selenobiałka.

Na podstawie dostępnej literatury można wnioskować, iż zagadnienie dotyczące roli Se w AZT jest nadal słabo poznane. Istnieje potrzeba kontynuowania badań oceniających wpływ suplementacji diety Se na przebieg tej choroby, które powinny obejmować poza anty-TPO inne parametry kliniczne. Dopiero wyniki tak szeroko ujętych badań mogą być pomocne w formułowaniu nowych wytycznych dotyczących wspomagania leczenia przez odpowiednią modyfikację diety z uwzględnieniem suplementacji Se.

Senescence and NFκB: A trojan horse in tumors?

The induction of senescence in tumor cells impairs transformation and promotes an anticancer immune response resulting from the production by senescent cells of cytokines and chemokines, an aspect known as "senescence-associated secretory phenotype" (SASP). Here we discuss recent findings regarding the role of NFκB in the modulation of the SASP and the consequent anticancer immune response.

Helicobacter pylori Infection and Autoimmune Thyroid Diseases: The Role of Virulent Strains

Aim: To verify a possible association between overall H. pylori and CagA+ H. pylori infection and autoimmune thyroid diseases (AITDs). Methods: Consecutive patients with AITDs admitted to one single centre of Endocrinology during one solar year were examined. The diagnoses were Hashimoto thyroiditis (HT) in 76, Graves’ Disease (GD) in 39, and aspecific thyroiditis (AT) in 44 patients. Controls were 136 individuals without AITDs. Median values of fT3, fT4, anti-thyreoglobulin (Tg) antibodies, IL-1β, IL-6, and TNF-α in patients were compared with those in controls. H. pylori infection and CagA status were determined serologically. Structural homology of some thyroid proteins with H. pylori antigens was investigated. Results: H. pylori infection prevalence was significantly increased in GD (66.6%) and HT (64.4%) patients, vs. 29.4% of controls and 34.0% of AT. CagA seropositivity was significantly more frequent in GD (46.1%) and HT (46.9%) infected patients, vs. infected controls (20%). fT3 and fT4 median values were significantly decreased in infected CagA+ GD patients vs. uninfected GD patients. IL-1β median values were increased in patients respect to controls, independently of the clinical form of AITD. Median values of IL-6, TNF-α and anti-Tg autoantibodies in CagA infected patients were significantly higher than those measured in infected CagA− and uninfected patients and in infected CagA+ controls. The examined thyroid proteins shared putative conserved domains with numerous bacterial antigens. Conclusions: Overall H. pylori and CagA+ H. pylori infection were associated with GD and HT, putatively through an increased inflammatory status and molecular mimicry.

S100A4 promotes the development of lipopolysaccharide-induced mouse endometritis

S100A4 is suggested to be a critical regulator of tumor metastasis, and implicated in progression of inflammation. The aim of this study is to investigate the expression and possible role of S100A4 in endometritis. Using a mouse model of endometritis induced by local injection of lipopolysaccharide (LPS), we found that infection induced recruitment of S100A4-positive cells in the endometrium of wild-type mice. Deficiency of S100A4 reduced uterine pathological reaction and mRNA expression of proinflammatory cytokine IL-1β and TNF-α (P < 0.01), suggesting S100A4 promoted the progression of endometritis. To further explore the potential mechanism, we examined the cellular proliferation and apoptosis in the endometrium. Western blot and immunohistochemical results showed that cell apoptosis in uterus during endometritis, marked by cleaved-Caspase 3 protein, was significantly cut down in S100a4-/- mice; cell proliferation, which was indicated by Ki-67, was also significantly decreased in the inflamed endometrial stroma of S100a4-/- mice. Overall, these results demonstrate that S100A4 promotes the development of LPS-induced endometritis, and it may be related to the process of cell proliferation and apoptosis during the inflammation.

Differential regulation of the production of reactive oxygen species in Th1 cytokine-treated thyroid cells

BACKGROUND

Th1 cytokines exert pleiotropic effects in Hashimoto's thyroiditis. Previous studies reported a downregulation of thyroperoxidase and dual oxidase (DUOX) protein and mRNA expression in thyroid cells treated with Th1 cytokines. Although this effect is partially mediated by intracellular reactive oxygen species (ROS) and reactive nitrogen species, the nature and the source of the ROS involved are currently unknown. The aim of this study was to examine further the nature and source of the ROS produced in response to Th1 cytokines.

METHODS

Two rat thyroid cell lines (PCCL3 and FRTL-5) and human thyrocytes were incubated with Th1 cytokines (interleukin [IL]-1α and interferon-γ) in the presence or absence of the Th2 cytokine IL-4, the nitric oxide synthase inhibitor N-nitroso-L-arginine methyl ester (L-NAME), or the synthetic antioxidant N-acetylcysteine. The nature and source of the intracellular and extracellular ROS produced were determined.

RESULTS

A rapid increase in intracellular ROS was observed in cells incubated with Th1 cytokines. This increase was not caused by extracellular hydrogen peroxide (H2O2) produced by DUOX because both DUOX expression and extracellular H2O2 synthesis were decreased by Th1 cytokines. Confocal colocalization experiments showed that the Th1 cytokine-triggered ROS were not produced from mitochondria. Electron paramagnetic resonance investigations of PCCL3 cells indicated that the highly reactive hydroxyl radical was not involved in the response to Th1 cytokines. NOX2 mRNA expression was significantly increased in PCCL3 cells incubated with Th1 cytokines, as was the expression of the protein in the thyroid of Hashimoto's thyroiditis patients. NOX4 expression was by contrast unaffected. These results suggest that at least superoxide could be produced after exposure of thyroid cells to Th1 cytokines. The effects of L-NAME and IL-4, both of which partially or totally reverse Th1 cytokine-induced effects, on ROS release were also analyzed. L-NAME and IL-4 significantly reduced the Th1 cytokine-induced surge of intracellular ROS in PCCL3 and human thyroid cells.

CONCLUSION

The data presented here reinforce the idea that ROS, other than extracellular H2O2 produced by DUOX, are released from NOX2 after exposure of thyroid cells to Th1 cytokines. ROS/reactive nitrogen species act as important, but as further explained, not exclusive intracellular mediators of Th1 cytokine-induced effects in thyroid cells.

Promotion and prevention of autoimmune disease by CD8+ T cells

Until recently, little was known about the importance of CD8+ T effectors in promoting and preventing autoimmune disease development. CD8+ T cells can oppose or promote autoimmune disease through activities as suppressor cells and as cytotoxic effectors. Studies in several distinct autoimmune models and data from patient samples are beginning to establish the importance of CD8+ T cells in these diseases and to define the mechanisms by which these cells influence autoimmunity. CD8+ effectors can promote disease via dysregulated secretion of inflammatory cytokines, skewed differentiation profiles and inappropriate apoptosis induction of target cells, and work to block disease by eliminating self-reactive cells and self-antigen sources, or as regulatory T cells. Defining the often major contribution of CD8+ T cells to autoimmune disease and identifying the mechanisms by which they alter the pathogenesis of disease is a rapidly expanding area of study and will add valuable information to our understanding of the kinetics, pathology and biology of autoimmune disease.

Hashimoto's Thyroiditis: From Genes to the Disease

Hashimoto's thyroiditis (HT) is the most prevalent autoimmune thyroid disorder. Intrathyroidal lymphocytic infiltration is followed by a gradual destruction of the thyroid gland which may lead to subclinical or overt hypothyroidism. Biochemical markers of the disease are thyroid peroxidase and/or thyroglobulin autoantibodies in the serum which are present with a higher prevalence in females than in males and increase with age. Although exact mechanisms of aetiology and pathogenesis of the disorder are not completely understood, a strong genetic susceptibility to the disease has been confirmed predominantly by family and twin studies. Several genes were shown to be associated with the disease occurrence, progression, and severity. Genes for human leukocyte antigen, cytotoxic T lymphocyte antigen-4, protein tyrosine phosphatase nonreceptor-type 22, thyroglobulin, vitamin D receptor, and cytokines are considered to be of utmost importance. Amongst endogenous factors for the disease development, the attention is focused predominantly on female sex, pregnancy with postpartum period and fetal microchimerism. Environmental factors influencing HT development are iodine intake, drugs, infections and different chemicals. Disturbed self-tolerance accompanied by the increased antigen presentation is a prerequisite for the HT occurrence, whereas proper interaction of thyroid cells, antigen presenting cells, and T cells are necessary for the initiation of thyroid autoimmunity. Secreted cytokines lead predominantly to T-helper type 1 (Th1) response as well as to Th 17 response which has only recently been implicated. Final outcome of HT is thyroid destruction which is mostly a consequence of the apoptotic processes combined with T-cell mediated cytotoxicity.

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.

Pulse modulated 900 MHz radiation induces hypothyroidism and apoptosis in thyroid cells: a light, electron microscopy and immunohistochemical study

PURPOSE

In the present study we investigated the possible histopathological effects of pulse modulated Radiofrequency (RF) fields on the thyroid gland using light microscopy, electron microscopy and immunohistochemical methods.

MATERIALS AND METHODS

Two months old male Wistar rats were exposed to a 900 MHz pulse-modulated RF radiation at a specific absorption rate (SAR) of 1.35 Watt/kg for 20 min/day for three weeks. The RF signals were pulse modulated by rectangular pulses with a repetition frequency of 217 Hz and a duty cycle of 1:8 (pulse width 0.576 ms). To assess thyroid endocrine disruption and estimate the degree of the pathology of the gland, we analysed structural alterations in follicular and colloidal diameters and areas, colloid content of the follicles, and height of the follicular epithelium. Apoptosis was confirmed by Transmission Electron Microscopy and assessing the activites of an initiator (caspase-9) and an effector (caspase-3) caspases that are important markers of cells undergoing apoptosis.

RESULTS

Morphological analyses revealed hypothyrophy of the gland in the 900 MHz RF exposure group. The results indicated that thyroid hormone secretion was inhibited by the RF radiation. In addition, we also observed formation of apoptotic bodies and increased caspase-3 and caspase-9 activities in thyroid cells of the rats that were exposed to modulated RF fields.

CONCLUSION

The overall findings indicated that whole body exposure to pulse-modulated RF radiation that is similar to that emitted by global system for mobile communications (GSM) mobile phones can cause pathological changes in the thyroid gland by altering the gland structure and enhancing caspase-dependent pathways of apoptosis.

Tunicamycin enhances TRAIL-induced apoptosis by inhibition of cyclin D1 and the subsequent downregulation of survivin

TNF-related apoptosis-inducing ligand (TRAIL) has been proposed as a promising cancer therapy that preferentially induces apoptosis in cancer cells, but not most normal tissues. However, many cancers are resistant to TRAIL by mechanisms that are poorly understood. In this study, we showed that tunicamycin, a naturally occurring antibiotic, was a potent enhancer of TRAIL-induced apoptosis through downregulation of survivin. The tunicamycin-mediated sensitization to TRAIL was efficiently reduced by forced expression of survivin, suggesting that the sensitization was mediated at least in part through inhibition of survivin expression. Tunicamycin also repressed expression of cyclin D1, a cell cycle regulator commonly overexpressed in thyroid carcinoma. Furthermore, silencing cyclin D1 by RNA interference reduced survivin expression and sensitized thyroid cancer cells to TRAIL; in contrast, forced expression of cyclin D1 attenuated tunicamycin-potentiated TRAIL-induced apoptosis via over-riding downregulation of survivin. Collectively, our results demonstrated that tunicamycin promoted TRAIL-induced apoptosis, at least in part, by inhibiting the expression of cyclin D1 and subsequent survivin. Of note, tunicamycin did not sensitize the differentiated thyroid epithelial cells to TRAIL-induced apoptosis. Thus, combined treatment with tunicamycin and TRAIL may offer an attractive strategy for safely treating resistant thyroid cancers.

Effect of type I interferon(s) on cell viability and apoptosis in primary human thyrocyte cultures

BACKGROUND

Interferon (IFN) therapy may induce a generalized activation of the immune system, hence triggering or exacerbating autoimmune disease. Apoptosis contributes to the development of hypothyroidism in autoimmune thyroiditis. IFN can affect all phases of the cell cycle and may induce apoptosis in several cell lines from varied histologies. To date, no data exist on the possible effect of type I IFN(s) on FAS/FASL system and cell apoptosis of human thyroid follicles. Therefore, we evaluated the effect of both IFN-alpha and -beta on apoptosis in primary human thyrocyte cultures and the potential role of the FAS/FASL pathway.

METHODS

Thyrocytes were cultured in monolayers and FAS, FASL, and Bcl-2 mRNA expression was determined by reverse transcriptase polymerase chain reaction after exposure to 10 mIU/mL bovine thyroid-stimulating hormone alone or in combination with increasing doses of IFN-alpha or -beta for 24, 48, and 72 hours. The percentage of apoptotic hypodiploid cells was evaluated by flow cytometry.

RESULTS

Thyroid-stimulating hormone significantly decreased FAS and increased Bcl-2 mRNA expression while reducing the percentage of hypodiploid cells. The concomitant addition of either IFN-alpha or -beta reduced cell viability and increased the number of hypodiloid cells, but only IFN-beta modulated the expression of FAS and Bcl-2 mRNA expression in a proapoptotic sense.

CONCLUSIONS

Both type I IFN(s) increase apoptosis in primary thyrocyte cultures, but only IFN-beta modulates FAS and Bcl-2 gene expression toward a proapoptotic pathway. Because apoptosis plays an important role in thyroid homeostasis and disease, this mechanism may contribute to the development and progression of type I IFN(s) therapy-associated thyroid disease.

A critical role for TRAIL in resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin (MTG)-sensitized splenocytes activated in vitro with MTG and IL-12. Thyroid lesions reach maximal severity 20 days after cell transfer, and usually resolve or progress to fibrosis by day 60 depending on the extent of thyroid damage at day 20. Our previous studies indicated that neutralization of TNF-alpha or FasL had no effect on G-EAT induction, but neutralization of TNF-alpha promoted, while neutralization of FasL inhibited, G-EAT resolution. TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily. This study was undertaken to define the role of endogenous TRAIL in G-EAT development and/or resolution. Neutralization of endogenous TRAIL had little effect on G-EAT induction, but significantly inhibited G-EAT resolution and increased thyroid fibrosis. This correlated with higher expression of pro-inflammatory cytokines and preferential expression of the pro-apoptotic molecule TRAIL, and anti-apoptotic molecules FLIP and Bcl-xL on inflammatory cells in thyroids of anti-TRAIL-treated recipients. The results suggest that endogenous TRAIL is not required for G-EAT development in recipients, but is critical for G-EAT resolution. Endogenous TRAIL might promote resolution, at least in part, through modulation of the balance between pro- and anti-inflammatory cytokines, and the expression pattern of pro- and anti-apoptotic molecules of thyroid epithelial cells (TECs) and inflammatory cells.

Cultured murine thyroid epithelial cells expressing transgenic Fas-associated death domain-like interleukin-1beta converting enzyme inhibitory protein are protected from fas-mediated apoptosis

The antiapoptotic molecule Fas-associated death domain-like IL-1beta-converting enzyme inhibitory protein (FLIP) inhibits Fas-mediated apoptosis by blocking activation of caspase-8. We previously showed that expression of transgenic FLIP on thyroid epithelial cells (TECs) of DBA/1 and CBA/J mice promoted earlier resolution of granulomatous experimental autoimmune thyroiditis in vivo. This study was undertaken to directly determine whether transgenic FLIP expressed on cultured TECs can protect TECs from Fas-mediated apoptosis in vitro. The results indicate that cultured TECs from DBA/1 and CBA/J mice can be sensitized in vitro by interferon-gamma and TNF-alpha to undergo Fas-mediated apoptosis. Transgenic overexpression of FLIP protected cultured TECs of FLIP transgene (Tg)+ DBA/1 and CBA/J mice from Fas-mediated apoptosis, and FLIP small interfering RNA transfection of cultured TECs of FLIP Tg+ DBA/1 and CBA/J mice abolished the protective effect. These in vitro results are consistent with our previous in vivo studies using DBA/1 and CBA/J FLIP Tg+ mice and provide direct support for the hypothesis that transgenic expression of FLIP promotes resolution of granulomatous experimental autoimmune thyroiditis by protecting TECs from apoptosis.

Interleukin-10 promotes resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin-sensitized splenocytes activated in vitro with mouse thyroglobulin and interleukin (IL)-12. Thyroid lesions reach maximal severity 20 days after cell transfer, and inflammation either resolves or progresses to fibrosis by day 60 depending on the extent of thyroid damage at day 20. Depletion of CD8(+) T cells inhibits G-EAT resolution. Our previous studies indicated that IL-10 was generally higher in G-EAT thyroids that resolved. Using both wild-type and IL-10(-/-) CBA/J mice, this study was undertaken to determine whether G-EAT resolution would be inhibited in the absence of IL-10. The results showed that either depletion of CD8(+) T cells or IL-10 deficiency increased fibrosis and inhibited resolution of inflammation. We also found a correlation between higher expression levels of proinflammatory cytokines and preferential expression levels of proapoptotic molecules, such as FasL and TRAIL, and antiapoptotic molecules, such as FLIP and Bcl-xL, in inflammatory cells from thyroids of both CD8-depleted and IL-10-deficient mice. Furthermore, many of the CD8(+) T cells were also IL-10(+). These results suggest that IL-10 plays an important role in G-EAT resolution and might promote resolution, at least in part, through its production in CD8(+) T cells. Further understanding of the mechanisms that promote the resolution of inflammation will facilitate the development of novel strategies for treating autoimmune diseases.

Expression of transgenic FLIP on thyroid epithelial cells inhibits induction and promotes resolution of granulomatous experimental autoimmune thyroiditis in CBA/J mice

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by transfer of thyroglobulin-primed in vitro activated splenocytes. Thyroid lesions reach maximal severity 20 d later, and inflammation resolves or progresses to fibrosis by d 60, depending on the extent of thyroid damage at d 20. Depletion of CD8+ T cells inhibits G-EAT resolution. We showed that expression of Fas-associated death domain-like IL-1beta-converting enzyme inhibitory protein (FLIP) transgene (Tg) on thyroid epithelial cells (TECs) of DBA/1 mice had no effect on G-EAT induction but promoted earlier resolution of G-EAT. However, when CBA/J wild-type donor cells were transferred to transgenic CBA/J mice expressing FLIP on TECs, they developed less severe G-EAT than FLIP Tg- littermates. Both strains expressed similar levels of the FLIP Tg, but endogenous FLIP was up-regulated to a greater extent on infiltrating T cells during G-EAT development in DBA/1 compared with CBA/J mice. After transient depletion of CD8+ T cells, FLIP Tg+ and Tg- CBA/J recipients both developed severe G-EAT at d 20. Thyroid lesions in CD8-depleted Tg+ recipients were resolving by d 60, whereas lesions in Tg- littermates did not resolve, and most were fibrotic. FLIP Tg+ recipients had increased apoptosis of CD3+ T cells compared with Tg- recipients. The results indicate that transgenic FLIP expressed on TECs in CBA/J mice promotes G-EAT resolution, but induction of G-EAT is inhibited unless CD8+ T cells are transiently depleted.

Microarray analysis of cytokine activation of apoptosis pathways in the thyroid

It has been suggested that Fas-mediated apoptosis plays an important role in the pathogenesis of autoimmune thyroid diseases. Our previous studies have demonstrated that normal primary thyroid epithelial cells are resistant to Fas-mediated apoptosis, but the resistance can be overcome by pretreatment with a combination of interferon-gamma (IFN-gamma) and IL-1beta. To understand the molecular mechanism responsible for the IFN-gamma/IL-1beta effects, we profiled changes in the transcription induced by these two cytokines in normal human thyroid cells, using cDNA microarrays. We found that IFN-gamma/IL-1beta showed a significant increase in apoptosis-related genes such as inducible nitric oxide synthase (iNOS), receptor-interacting protein 2 (RIP2), and caspases 10. These increases were confirmed by other methods, including real-time PCR and Western blot. Furthermore, the sensitization of primary thyroid epithelial cells to Fas-mediated apoptosis by IFN-gamma/IL-1beta was significantly blocked by a general caspase inhibitor, z-VAD, or by the combination of two specific individual caspase inhibitors. In addition, our results showed that IFN-gamma/IL-1beta enhance p38 MAPK phosphorylation and that SB 203580, a p38 MAPK inhibitor, can inhibit IFN-gamma/IL-1beta-induced p38 MAPK phosphorylation. SB 203580 also significantly prevented cytokine-induced iNOS expression and caspase activation and thus blocked Fas-mediated apoptosis of thyroid cells sensitized by IFN-gamma/IL-1beta. In conclusion, our data suggest that both p38 MAPK and iNOS are involved in IFN-gamma/IL-1beta-induced sensitization of the thyroid cells to Fas-mediated apoptosis via the activation of caspases 3, 7, and 10 and that this pathway may be further activated by BID. This hints that inflammatory cytokines regulate death-receptor-mediated apoptosis at multiple points in the process.

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

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

Murine FLIP transgene expressed on thyroid epithelial cells promotes resolution of granulomatous experimental autoimmune thyroiditis in DBA/1 mice

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin-sensitized splenocytes activated in vitro with mouse thyroglobulin and interleukin-12. In wild-type (WT) DBA/1 recipients of WT donor splenocytes, thyroid lesions reach maximal severity at day 20, with ongoing inflammation and extensive fibrosis at day 60. Our previous studies indicated the site of expression of FLIP and Fas ligand [thyroid epithelial cells (TECs) versus inflammatory cells] differed in mice when lesions would resolve or progress to fibrosis. To test the hypothesis that expression of FLIP by TECs would promote earlier G-EAT resolution in DBA/1 mice, transgenic (Tg) DBA/1 mice expressing FLIP on TECs were generated. In FLIP Tg(+) and Tg(-) littermate recipients of WT donor splenocytes, G-EAT severity was comparable at day 20, but fibrosis was decreased, and many lesions resolved by day 60 in Tg(+) but not Tg(-) recipients. FLIP and Fas ligand were primarily expressed by TECs in Tg(+) recipients and by inflammatory cells in Tg(-) recipients at day 60. Apoptosis of inflammatory cells was greater, and expression of proinflammatory cytokines was decreased in thyroids of Tg(+) compared with Tg(-) recipients. These results are consistent with the hypothesis that transgenic expression of FLIP on thyroid epithelial cells promotes earlier resolution of granulomatous experimental autoimmune thyroiditis.

A differential association of interferon-gamma high-producing allele T and low-producing allele A (+874 A/T) with Hashimoto's thyroiditis and Graves' disease

Cytokines play a crucial role in the pathogenesis of autoimmune thyroid disease. The aim of this study was to investigate the relationship of the single base change polymorphic variants identified in the first intron of interferon-gamma (IFN-gamma) (+874 T/A) with susceptibility to thyroid dysfunctions. A total of 340 subjects were included in the study comprising of 190 patients (104 patients with Hashimoto's thyroiditis, 26 with non-Hashimoto's hypothyroidism and 60 Graves' disease) and 150 controls. Genotyping was done by amplification refractory mutation system-polymerase chain reaction using a set of sequence-specific primers. Statistical analysis revealed a significant association between high IFN-gamma-producing genotype TT and Hashimoto's thyroiditis compared to controls (P value < 0.001). On the other hand, the frequency of genotype TT was decreased in patients with Graves' hyperthyroidism with a significant increase in low IFN-gamma-producing genotype AA among this group (P = 0.03). To conclude the results of the study suggest a differential association of high- and low-producing alleles of IFN-gamma gene with Hashimoto's thyroiditis and Graves' disease. The high IFN-gamma-producing allele T was observed to be associated with Hashimoto's thyroiditis in the present study where as in Graves' hyperthyroidism the association was observed to be stronger with the low producing allele A.

Expression of TPO and ThOXs in human thyrocytes is downregulated by IL-1alpha/IFN-gamma, an effect partially mediated by nitric oxide

Morphological and functional alterations in Hashimoto's thyroiditis (HT) are predominantly mediated by Th1 cytokines through apoptotic cell death. This ultimate step could be preceded by functional injuries in thyroid hormone synthesis. The action of two Th1 cytokines (IL-1alpha/IFN-gamma) on thyroperoxidase (TPO) and thyroid oxidase (ThOXs) expression was tested in human thyrocytes isolated from normal tissues, Graves' disease (GD) tissues, and autonomous toxic nodules. There was no evidence of cell death. Nitric oxide (NO) release was induced by cytokines but was absent when NG-nitro-L-arginine methyl ester (L-NAME) was coincubated. When thyrotropin (TSH)-incubated normal and GD thyrocytes were treated with IL-1alpha/IFN-gamma, TPO and ThOXs protein and mRNA expression dropped, a decrease partially prevented by L-NAME, suggesting that NO acts as a mediator of Th1 effects. In thyrocytes from autonomous toxic nodules, the high level of TPO and ThOXs protein expression was not influenced by TSH or by cytokines, a finding partially reproduced when normal thyrocytes were treated with increasing concentrations of TSH. In conclusion, incubation of normal or GD thyrocytes with Th1 cytokines induces a significant reduction in TSH-increased expression of both TPO and ThOXs, an effect partially mediated by NO. The thyroid cell function can therefore be severely affected in HT, even when cells remain viable. In autonomous toxic nodules, cells become partially insensitive to exogenous Th1 cytokines.

Death ligand tumor necrosis factor-related apoptosis-inducing ligand inhibits experimental autoimmune thyroiditis

The role of TNF-related apoptosis-inducing ligand (TRAIL) in autoimmune thyroiditis is unclear. We used experimental autoimmune thyroiditis to clarify the contribution of TRAIL to the development of autoimmune thyroiditis. CBA/J mice were immunized with murine thyroglobulin, and spleen cells from these mice were subsequently injected into irradiated recipient CBA/J mice. One week later, the recipient mice were treated with recombinant TRAIL or a control protein. Compared with control animals, TRAIL-treated mice developed a milder form of the disease with a significant decrease in mononuclear cell infiltration in the thyroid and less thyroid follicular destruction. Furthermore, the number of apoptotic thyrocytes and also thyroglobulin-specific T helper-1 cell responses in TRAIL-treated mice was lower than that in the control animals. This study suggests that exogenous TRAIL suppresses the development of autoimmune thyroiditis via altering the function of cells involved in the immune response. These findings may contribute toward a novel treatment autoimmune thyroiditis.

TGF-beta inhibits Fas-mediated apoptosis of a follicular dendritic cell line by down-regulating the expression of Fas and caspase-8: counteracting role of TGF-beta on TNF sensitization of Fas-mediated apoptosis

Follicular dendritic cells (FDC) constitute the framework of germinal center (GC) in secondary lymphoid follicles, and the integrity of FDC networks is critically affected by cytokines present in the GC. We have previously shown that TNF promotes Fas-mediated apoptosis of HK cells, an established FDC-like cell line, by up-regulating Fas expression. However, in the developing GC, FDC death is not a hallmark of GC despite the presence of TNF and FasL. In this study, we report that TGF-beta inhibits Fas-mediated apoptosis of HK cells by down-regulating the expression of surface Fas and caspase-8. The inhibitory effect of TGF-beta can be observed when HK cells were simultaneously treated with TNF and TGF-beta, indicating that TGF-beta counteracts the effect of TNF in sensitizing cells to Fas-mediated apoptosis. Furthermore, the deprivation of TGF-beta by injecting neutralizing TGF-beta Abs to the SRBC-immunized mice resulted in the sporadic appearance of FDC undergoing apoptosis in the lymphoid follicles, suggesting that TGF-beta functions as a naturally occurring inhibitor that rescues FDCs which are predisposed to apoptosis. Our study documents a novel function of TGF-beta in the maintenance of FDC networks.

Immune Selection and Emergence of Aggressive Tumor Variants as Negative Consequences of Fas-Mediated Cytotoxicity and Altered IFN-γ-Regulated Gene Expression

Antitumor responses can be induced in patients via active or adoptive immunotherapy, yet complete tumor eradication occurs infrequently. This paradox in tumor immunology led us to address two questions: (a) Does an antitumor response, which is intended to destroy the aberrant target population, also at the same time select for aggressive tumor variants (ATV) in vivo? (b) If this process does occur, what is the contribution of the perforin- or Fas-mediated effector mechanism in the immune selection of such ATV? Here, in an experimental mouse lung metastasis model, we showed that ATV generated either naturally in vivo or in vitro by anti-Fas selection resembled each other biologically and genetically as judged by enhanced tumor growth and genome-scale gene expression profiling, respectively. Furthermore, ATV that survived CTL adoptive immunotherapy displayed an even more profound loss of Fas expression and function as well as enhanced malignant proficiency in vivo. ATV, however, retained sensitivity to perforin-mediated lysis in vitro. Lastly, such ATV displayed a diminished responsiveness in their expression of IFN-gamma-regulated genes, including those mechanistically linked to Fas-mediated death (i.e., Fas and caspase-1). Overall, we showed that (a) immune selection did occur in vivo and played an important role in the emergence of ATV, (b) ATV bearing a Fas-resistant phenotype was a chief consequence of immune selection, and (c) an overall diminished responsiveness of IFN-gamma-regulated gene expression was characteristic of ATV. Thus, in this model, Fas-mediated cytotoxicity, in concert with IFN-gamma-regulated gene expression, mechanistically constituted significant determinants of immune selection of ATV in vivo.

Alpha-fodrin as a putative autoantigen in Graves' ophthalmopathy

Alpha-fodrin, an intracellular organ-specific cytoskeleton protein is a recently identified autoantigen associated with Sicca- and Sjogren's syndrome (SS). SS frequently affects patients with Graves' ophthalmopathy (GO). We have therefore cloned and expressed the human recombinant 120-kDa fodrin-fragment. A sequential purification procedure was applied to isolate the recombinant protein. Using sera from patients with SS, the antigenicity of the purified fodrin fragment was demonstrated by immunoblotting. Sera from 144 patients with GO and 1200 blood donors were screened for the presence of anti-alpha-fodrin IgA and IgG antibodies by a newly developed ELISA using the human alpha-fodrin fragment as an autoantigen. In contrast to controls (<1% IgA only, P < 0.001) and to subjects with various autoimmune diseases (P < 0.001), alpha-fodrin antibodies were detected in 22% of patients with GO (n = 32). IgA and IgG antibodies were present in 21 (15%) and 14 (10%) GO subjects, respectively. A total of 45 patients with GO (31%) had at least one fodrin- or SS-antibody. GO patients with SS showed SS- and high titres of alpha-fodrin-antibodies. In GO patients, fodrin antibodies correlated with TPO- (P < 0.05) and SS-A (P = 0.002) antibodies. Thus, for the first time, antibodies reactive with fodrin are reported in patients with GO.

Induction and Regulation of Fas-Mediated Apoptosis in Human Thyroid Epithelial Cells

Fas-mediated apoptosis has been proposed to play an important role in the pathogenesis of Hashimoto’s thyroiditis. Normal thyroid cells are resistant to Fas-mediated apoptosis in vitro but can be sensitized by the unique combination of interferon-γ and IL-1β cytokines. We sought to examine the mechanism of this sensitization and apoptosis signaling in primary human thyroid cells. Without the addition of cytokines, agonist anti-Fas antibody treatment of the thyroid cells resulted in the cleavage of proximal caspases, but this did not lead to the activation of caspase 7 and caspase 3. Apoptosis associated with the cleavage of caspases 7, 3, and Bid, and the activation of mitochondria in response to anti-Fas antibody occurred only after cytokine pretreatment. Cell surface expression of Fas, the cytoplasmic concentrations of procaspases 7, 8, and 10, and the proapoptotic molecule Bid were markedly enhanced by the presence of the cytokines. In contrast, P44/p42 MAPK (Erk) appeared to provide protection from Fas-mediated apoptosis because an MAPK kinase inhibitor (U0126) sensitized thyroid cells to anti-Fas antibody. In conclusion, Fas signaling is blocked in normal thyroid cells at a point after the activation of proximal caspases. Interferon-γ/IL-1β pretreatment sensitizes human thyroid cells to Fas-mediated apoptosis in a complex manner that overcomes this blockade through increased expression of cell surface Fas receptor, increases in proapoptotic molecules that result in mitochondrial activation, and late caspase cleavage. This process involves Bcl-2 family proteins and appears to be compatible with type II apoptosis regulation.

Tunicamycin preserves intercellular junctions, cytoarchitecture, and cell-substratum interactions in ATP-depleted epithelial cells

Pretreatment with the nucleoside antibiotic tunicamycin was found to protect cultured renal epithelial cells in the face of ATP-depletion, in large part by preserving junctional and cellular architecture. Tunicamycin pretreatment of Madin-Darby canine kidney cells not only preserved E-cadherin staining at the plasma membrane, but also inhibited ATP-depletion-mediated E-cadherin degradation. Electron microscopic analysis, together with the preservation of the staining patterns of the tight junction marker ZO-1, the apical/microvillar marker gp135, and basolateral marker Na/K-ATPase suggested that tunicamycin preserved the junctional complex and the polarized epithelial cell phenotype. Tunicamycin pretreatment also prevented reductions in the filamentous actin content of the cells, as well as preserving Golgi architecture. Moreover, a quantitative measure of cell adhesion demonstrated that tunicamycin pretreatment resulted in a fivefold increase in attachment of cells to the substratum (77% versus 16%). Thus, pretreatment with tunicamycin protects polarized epithelial cells from ischemic injury through the preservation of epithelial cell architecture, intercellular junctions, and cell-substratum interactions in the setting of intracellular ATP-depletion.

Unravelling the genetic complexity of autoimmune thyroid disease: HLA, CTLA-4 and beyond

The autoimmune thyroid diseases (AITDs) including Graves' disease (GD) and autoimmune hypothyroidism (AIH) are the commonest of the autoimmune conditions affecting 2-5% of the western population. Twin studies have clearly demonstrated that AITDs are caused by a combination of both environmental and genetic factors. Association of the HLA class II region with AITD has been documented for over 20 years now, but the primary aetiological variant in this region remains unknown. More recently the CTLA-4 gene region has been identified as the second locus conferring susceptibility to AITD. In contrast to HLA, a polymorphism of the CTLA-4 gene, which encodes an important negative regulator of the immune system, has been identified as a candidate for a primary determinant for AITD. A large number of candidate gene and genome wide linkage studies have been involved in the search for the elusive 'third' locus. The thyroglobulin (Tg) gene in humans maps to chromosome 8q, which has been linked in family studies to AITD. A number of association studies in humans and the mouse model for AITD are beginning to implicate the Tg gene although convincing evidence for a primary causative role is still needed. The establishment of large DNA disease resources along with more detailed genetic maps and the development of faster, more effective, high throughput genotyping and sequencing methods, provides some sense of optimism that novel loci will be identified in the near future and the complex aetiology of AITD will be further unraveled.

Intracellular regulation of Fas-induced apoptosis in human fibroblasts by extracellular factors and cycloheximide

Fibroblasts play an important role in reparative and inflammatory processes by synthesizing extracellular matrix components and releasing growth factors and cytokines. Fibroblast apoptosis has been observed at the termination phase of reparative or fibrotic responses, but its regulation in this context is poorly known. We investigated the susceptibility of human dermal fibroblasts (DF) to Fas-induced apoptosis and its regulation by extracellular factors potentially involved in immune-mediated inflammation and repair. DF expressed all components of the Fas apoptotic pathway: surface Fas, Fas-associated protein with death domain, and caspase-8 proteins. However, Fas activation resulted in caspase-8 activation and apoptosis only in the presence of cycloheximide (CHX). DF constitutively expressed Fas-associated death domain-like IL-1-converting enzyme-like inhibitory protein (FLIP) that was drastically down-regulated by CHX. Exogenous growth factors, cytokines, and adherence to the extracellular matrix shifted the balance of FLIP-caspase-8 proteins and modified the susceptibility of DF to Fas- or Fas-CHX-induced apoptosis. Short-term serum deprivation, suspension culture, and pretreatment with IFN-gamma or TNF-alpha increased, whereas long-term serum-free culture and pretreatment with TGF-beta or IL-10 decreased the apoptotic susceptibility of DF. Surface Fas expression was only modified by TNF-alpha and IFN-gamma, whereas all studied factors modified FLIP-caspase-8 protein expression, consistently with their pro- or antiapoptotic effects. Antisense FLIP oligonucleotides prevented resistance to Fas-induced apoptosis in DF. FLIP-caspase-8 balance seems tightly regulated in fibroblasts by extracellular factors that determine their susceptibility to Fas- or Fas-CHX-induced apoptosis. Th1 and Th regulatory cytokines display opposite effects on fibroblast apoptosis that suggest that their pro- or antifibrotic effects involve direct effects on fibroblast survival.

IFNgamma sensitization to TRAIL-induced apoptosis in human thyroid carcinoma cells by upregulating Bak expression

TRAIL preferentially induces apoptosis in tumor cells and virus-infected cells. Unlike other tumor necrosis factor family members, TRAIL does not kill cells from most normal tissues and has thus been proposed as a promising new cancer treatment. Our study demonstrated that IFNgamma combined with TRAIL can trigger apoptosis in vitro in several resistant thyroid tumor cell lines, such as thyroid anaplastic carcinoma cells (ARO cells), while either agent alone exerts only a minimal effect. We further tested this effect on a mouse thyroid tumor model, when in vivo tumor growth was also significantly inhibited by this combination. The mechanism of how IFNgamma sensitized thyroid carcinoma cells to TRAIL-induced apoptosis was investigated by screening global gene alterations in ARO cells treated with IFNgamma. Microarray data revealed that a proapoptotic gene, Bak, is markedly upregulated by IFNgamma, and this was confirmed by RNase protection assay. Western blot analysis also showed a significant increase in Bak at the protein level. Upregulation of Bak and sensitization for apoptosis by IFNgamma was blocked by overexpression of antisense Bak in ARO cells. Furthermore, overexpression of Bak sensitized ARO cell to TRAIL-induced apoptosis without the need for IFNgamma pretreatment. This suggests that Bak is a regulatory molecule involved in IFNgamma-facilitated TRAIL-mediated apoptosis in thyroid cancer cells.

Functional effects of TNF-alpha on a human follicular dendritic cell line: persistent NF-kappa B activation and sensitization for Fas-mediated apoptosis

Follicular dendritic cells (FDC) play crucial roles in germinal center (GC) formation and differentiation of GC B cells. FDC functions are influenced by cytokines produced in the GC. Among the GC cytokines, TNF is known to be essential for the formation and maintenance of the FDC network in the GC. We found that TNF is a mitogenic growth factor to an established FDC-like cell line, HK cells. Differing from most cell types which become desensitized to TNF action, HK cells exhibited persistent TNF signaling, as demonstrated by prolonged and biphasic NF-kappaB activation even after 3 days of TNF treatment. As a result, antiapoptotic genes including TNFR-associated factors 1 and 2, and cellular inhibitor of apoptosis proteins 1 and 2 were persistently induced by TNF, leading to the protection against TNF-mediated cell death. However, TNF pretreatment enhanced Fas-mediated apoptosis by up-regulating surface Fas expression in an NF-kappaB-dependent pathway. During the GC responses, proliferation followed by FDC death has not been documented. However, our in vitro results suggest that FDCs proliferate in response to TNF, and die by Fas-mediated apoptosis whose susceptibility is enhanced by TNF, representing a mode of action for TNF in the maintenance of FDC networks by regulating the survival or death of FDC.

Detection and characterization of RANK ligand and osteoprotegerin in the thyroid gland

Receptor activator of NF-kappaB (RANK) ligand (RANKL) and osteoprotegerin (OPG) play essential roles in bone metabolism and immune responses. RANKL activates RANK, which is expressed by osteoclasts and dendritic cells (DC), whereas OPG acts as its decoy receptor. The role of RANKL and OPG in thyroid physiology is unclear. Northern analysis revealed pronounced OPG mRNA levels in normal human thyroid. By contrast, RANKL mRNA levels were most abundant in lymph node and appendix, and low in the thyroid. In the human thyroid follicular cell line XTC and in primary human thyroid follicular cells, OPG mRNA levels and protein secretion were upregulated by interleukin (IL)-1beta (33-fold), tumor necrosis factor (TNF)-alpha (eightfold), and thyrotropin (TSH) (threefold). RANKL mRNA was stimulated in XTC by IL-1beta and TNF-alpha, but inhibited by TSH. Conditioned medium harvested from IL-1beta-treated XTC (containing high concentrations of OPG) inhibited RANKL-induced CD40 upregulation and cluster formation of DC. OPG mRNA levels were three times more abundant in surgical thyroid specimens of Graves' disease as compared to other thyroid diseases. Our data suggest that RANKL and OPG are produced in the thyroid gland by thyroid follicular cells, are regulated by cytokines and TSH, and are capable of modulating dendritic cell functions. Thus, these cytokines may represent important local immunoregulatory factors involved in the pathogenesis of autoimmune thyroid diseases.

IFN-gammaupregulates apoptosis-related molecules and enhances Fas-mediated apoptosis in human cholangiocarcinoma

Human cholangiocarcinoma is a malignancy with no effective therapy and a poor prognosis. Previously, we demonstrated that cultured human cholangiocarcinoma cell lines heterogeneously express Fas on their surface, resulting in 2 subpopulations, Fas-high and Fas-low cells. Fas-low cells are resistant to apoptosis induced by Fas antibody and the calmodulin antagonists tamoxifen and trifluoperazine and are tumorigenic in nude mice (Pan et al., Am J Pathol 1999;155:193-203). Here, we show that IFN-gamma enhances apoptosis in both Fas-high and Fas-low cells. IFN-gamma upregulates many apoptosis-related molecules, including Fas, caspase-3, caspase-4, caspase-7, caspase-8 and Bak, in both cell lines. Pretreatment with IFN-gamma facilitated Fas-mediated caspase cleavage, cytochrome c release and Bax translocation. The ability of IFN-gamma to inhibit tumorigenesis of Fas-low cells was demonstrated in nude mice. Intratumoral injection of IFN-gamma decreased tumor volumes by 78%. These findings indicate that IFN-gamma modulates the apoptotic pathway by upregulating apoptosis-related genes. This renders tumorigenic Fas-low cholangiocarcinoma cells nontumorigenic and sensitive to Fas apoptosis, thus representing a possible therapeutic modality.

Regulation of Apo2L/tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in thyroid carcinoma cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)/Apo2 ligand selectively kills neoplastic cells, including thyroid carcinoma cells (Mitsiades et al: Thyroid carcinoma cells are resistant to FAS-mediated apoptosis but sensitive to tumor necrosis factor-related apoptosis-inducing ligand. Cancer Res 2000, 60:4122-41299). We investigated the mechanisms regulating Apo2L/TRAIL-induced apoptosis in thyroid carcinoma cells, as well as the impact of insulin-like growth factor (IGF)-1, interferon-gamma, and TNF-alpha. We found that the emergence of resistance to Apo2L/TRAIL, after prolonged incubation with this cytokine, was associated with increased levels of FLICE inhibitory protein (FLIP), and was overcome by cycloheximide and bisindolylmaleimide, that specifically down-regulated FLIP expression, as well as by transfection of a FLIP anti-sense oligonucleotide. IGF-1 activated Akt; up-regulated the caspase inhibitors FLIP, cIAP-2, XIAP, and survivin; and attenuated Apo2L/TRAIL-induced apoptosis. This effect was inhibited by the IGF-1 receptor neutralizing antibody aIR3, the PI-3K inhibitor wortmannin, and the heat shock protein-90 chaperone inhibitor geldanamycin. Transfection of constitutively active Akt protected from TRAIL. Conversely, interferon-gamma and TNF-alpha had a sensitizing effect. We conclude that FLIP may negatively regulate Apo2L/TRAIL-induced apoptosis in thyroid carcinomas. Microenvironmental paracrine survival factors, such as IGF-1, up-regulate caspase inhibitors, including FLIP, and protect from Apo2L/TRAIL in a PI-3K/Akt-dependent manner. T helper-1 cytokines and compounds that selectively abrogate the IGF-1 signaling pathway may be helpful adjunct agents in Apo2L/TRAIL-based anti-cancer therapeutic regimens.

Differential expression of the Fas-Fas ligand system on cytokine-induced apoptotic cell death in mouse osteoblastic cells

Apoptotic signalling, particularly in the Fas-Fas ligand (FasL) system, was studied in a mouse osteoblastic cell line, MC3T3-E1. A combination of the cytokines tumour necrosis factor-alpha, interleukin-1beta and interferon-gamma activated the Fas-FasL-dependent cell-death system. The cytokines caused significant enhancement of Fas mRNA and Fas protein, and led to apoptotic cell death. Western blot demonstrated that FasL protein was continuously present in MC3T3-E1 cells, although the cytokines had no effect on the induction of FasL. Exogenous FasL caused a decrease in cell viability and a large increase in apoptotic cell death in cells pre-treated with cytokines, indicating that the Fas-FasL system has the potential to cause apoptosis in osteoblastic cells. Treatment with anti-Fas IgG (antagonistic antibody) inhibited the DNA fragmentation induced by cytokines in a dose-dependent manner, suggesting that cytokine-induced Fas may cause apoptotic cell death in MC3T3-E1 cells. Taken together, these findings show that cytokine-induced apoptotic cell death was mediated by the autocrine or paracrine Fas-FasL system in mouse osteoblastic cells, and suggest that cytokine-induced apoptosis could have an important role in localised bone destruction associated with inflammatory bone diseases such as periodontal disease.

Autoimmune thyroid disease: new models of cell death in autoimmunity

Autoimmunity to thyroid antigens leads to two distinct pathogenic processes with opposing clinical outcomes: hypothyroidism in Hashimoto's thyroiditis and hyperthyroidism in Graves' disease. The high frequency of these diseases and easy accessibility of the thyroid gland has allowed the identification of key pathogenic mechanisms in organ-specific autoimmune diseases. In early investigations, antibody- and T-cell-mediated death mechanisms were proposed as being responsible for autoimmune thyrocyte depletion. Later, studies on apoptosis have provided new insights into autoimmune target destruction, indicating the involvement of death receptors and cytokine-regulated apoptotic pathways in the pathogenesis of thyroid autoimmunity.

Inflammatory cytokine regulation of TRAIL-mediated apoptosis in thyroid epithelial cells

Death receptor-mediated apoptosis has been implicated in target organ destruction in chronic autoimmune thyroiditis. Depending on the circumstances, inflammatory cytokines such as IL-1, TNF and IFNgamma have been shown to contribute to either the induction, progression or inhibition of this disease. Here we demonstrate that the death ligand TRAIL can induce apoptosis in primary, normal, thyroid epithelial cells under physiologically relevant conditions, specifically, treatment with the combination of inflammatory cytokines IL-1beta and TNFalpha. In contrast, IFNgamma is capable of blocking TRAIL-induced apoptosis in these cells. This regulation of TRAIL-mediated apoptosis by inflammatory cytokines appears to be due to alterations of cell surface expression of TRAIL receptor DR5 and not DR4. We also show the in vivo presence of TRAIL and TRAIL receptors DR5 and DcR1 in both normal and inflamed thyroids. Our data suggests TRAIL-mediated apoptosis may contribute to target organ destruction in chronic autoimmune thyroiditis.

A unique combination of inflammatory cytokines enhances apoptosis of thyroid follicular cells and transforms nondestructive to destructive thyroiditis in experimental autoimmune thyroiditis

Treatment of cultured primary human thyroid cells with IFN-gamma and TNF-alpha uniquely allows the induction of Fas-mediated apoptosis. To investigate the role of this cytokine combination in vivo, CBA/J mice were immunized with thyroglobulin and then injected with IFN-gamma and TNF-alpha. Compared with control animals, mice treated with IFN-gamma and TNF-alpha showed significantly sustained lymphocytic infiltration in the thyroid, which was associated with the destruction of portions of the follicular architecture at wk 6 after initial immunization. Furthermore, the number of apoptotic thyroid follicular cells was increased only in the thyroids from mice treated with the IFN-gamma and TNF-alpha. We also analyzed the function of the Fas pathway in vivo in cytokine-treated mice by using an agonist anti-Fas Ab injected directly into the thyroid. Minimal apoptosis of thyroid epithelial cells was observed unless the mice were pretreated with IFN-gamma and TNF-alpha. These data demonstrate that this unique combination of inflammatory cytokines facilitates the apoptotic destruction of thyroid follicular cells in experimental autoimmune thyroiditis, in a manner similar to what is observed in Hashimoto's thyroiditis in humans.

Non-apoptotic signaling pathways activated by soluble Fas ligand in serum-starved human fibroblasts. Mitogen-activated protein kinases and NF-kappaB-dependent gene expression

Many Fas-expressing cells do not undergo cell death upon Fas stimulation. In the normal human diploid cell line GM6112, the addition of soluble Fas ligand (sFasL) leads to morphological signs of cell death in less than 1% of cells. Treatment of serum-starved GM6112 fibroblasts with sFasL resulted in a rapid and transient phosphorylation of ERK1/2 without a significant increase in JNK and p38 activities. Unless co-treated with the protein synthesis inhibitor anisomycin, sFasL did not show gene-inducing activity in cells maintained in complete medium. However, when cells were serum-starved for 4 days, treatment with sFasL alone induced interleukin-6 gene expression and, less strongly, interleukin-8 gene expression. Sensitization of the gene-inducing activity by serum starvation correlated with NF-kappaB activation by sFasL. Furthermore, we found that the expression of FADD and caspase-8 was significantly reduced in serum-starved cells, whereas the level of cFLIP remained unchanged. Transfection of GM6112 cells with the antisense caspase-8 expression construct sensitized cells toward sFasL-induced NF-kappaB-dependent reporter activation. Our results support the notion that a change in the ratio of cFLIP and caspase-8 may be responsible for turning on the Fas-activated NF-kappaB pathway, which otherwise is supplanted by the death-inducing pathway.

Effector lymphocytes in autoimmunity

Autoimmune diseases result from complex interactions among different T- and B-lymphocyte subpopulations that target a rapidly growing number of autoantigens on different cell types. The etiology of most spontaneous autoimmune disorders, and both the kinetics and hierarchy of the underlying autoimmune responses are poorly understood. However, important advances have been made in recent years in our understanding of how autoreactive lymphocytes cause tissue damage, including the discovery that granzyme B binds to a cell surface receptor on target cells. This review is an attempt to summarize recent developments in this area.

Thyrocyte targets and effectors of autoimmunity: a role for death receptors?

In Hashimoto's thyroiditis, thyrocytes die by apoptosis. Whether this is the result of impaired antiapoptotic gene expression or hyperexpression of proapoptotic signals or other mechanisms is not fully established. Following the suggestion that thyrocytes from Hashimoto's glands die by a fratricidal killing mediated by Fas/Fas ligand, we have investigated whether thyroid cells from different clinical conditions are able to kill Fas-expressing target cells. We have studied whether this effector ability was mediated by Fas/Fas ligand, perforin or other death receptors/ligands, i.e., tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/tumor necrosis factor-related apoptosis-inducing ligand receptor (TRAIL-R). We have confirmed that thyroid preparations can kill Fas-expressing HUT78 targets through apoptosis. Cell death was only partially dependent on Fas/Fas ligand but it was trypsin-sensitive. Blocking perforin did not affect Fas-expressing target killing while caspase inhibitors had a consistent although limited effect. Thyroid cells were not sensitive to TRAIL/TRAIL-R. We have also found that both thyrocytes and lymphocytes from Graves' disease thyroids were effective at killing autologous and heterologous Fas-expressing targets. Conversely, killing of these targets could be shown only with lymphocytes (but not with thyrocytes) from Hashimoto's glands. In Hashimoto's thyroiditis, thyrocytes were poorly functional while lymphocytes were able to operate as effectors. It is envisaged that thyrocyte death in Hashimoto's would result from autologous thyrocyte killing perpetrated by lymphocytes. Death receptors/ligands would appear to play a role. However, a caspase-independent mechanism may also coexist and contribute to cell death in Hashimoto's thyroiditis.