Expression and regulation of Fas and Fas ligand on thyrocytes and infiltrating cells during induction and resolution of granulomatous experimental autoimmune thyroiditis

Sphingosine kinase 2 restricts T cell immunopathology but permits viral persistence

Chronic viral infections are often established by the exploitation of immune-regulatory mechanisms that result in nonfunctional T cell responses. Viruses that establish persistent infections remain a serious threat to human health. Sphingosine kinase 2 (SphK2) generates sphingosine 1-phosphate, which is a molecule known to regulate multiple cellular processes. However, little is known about SphK2's role during the host immune responses to viral infection. Here, we demonstrate that SphK2 functions during lymphocytic choriomeningitis virus Cl 13 (LCMV Cl 13) infection to limit T cell immune pathology, which subsequently aids in the establishment of virus-induced immunosuppression and the resultant viral persistence. The infection of Sphk2-deficient (Sphk2-/-) mice with LCMV Cl 13 led to the development of nephropathy and mortality via T cell-mediated immunopathology. Following LCMV infection, Sphk2-/- CD4+ T cells displayed increased activity and proliferation, and these cells promoted overactive LCMV Cl 13-specific CD8+ T cell responses. Notably, oral instillation of an SphK2-selective inhibitor promoted protective T cell responses and accelerated the termination of LCMV Cl 13 persistence in mice. Thus, SphK2 is indicated as an immunotherapeutic target for the control of persistent viral infections.

Molecular Insights Into the Relationship Between Autoimmune Thyroid Diseases and Breast Cancer: A Critical Perspective on Autoimmunity and ER Stress

The etiopathologies behind autoimmune thyroid diseases (AITDs) unravel misbehavior of immune components leading to the corruption of immune homeostasis where thyroid autoantigens turn foe to the self. In AITDs lymphocytic infiltration in the thyroid shows up a deranged immune system charging the follicular cells of the thyroid gland (thyrocytes) leading to the condition of either hyperthyroidism or hypothyroidism. The inflammation in AITDs consistently associate with ER function due to which disturbances in the ER protein homeostasis leads to unfolded protein response (UPR) that promotes pathogenesis of autoimmunity. The roles of ER stress in the instantaneous downregulation of MHC class I molecules on thyrocytes and the relevance of IFN γ in the pathogenesis of AITD has been well-documented. Thyroglobulin being the major target of autoantibodies in most of the AITDs is because of its unusual processing in the ER. Autoimmune disorders display a conglomeration of ER stress-induced UPR activated molecules. Several epidemiological data highlight the preponderance of AITDs in women as well as its concurrence with breast cancer. Both being an active glandular system displaying endocrine activity, thyroid as well as breast tissue show various commonalities in the expression pattern of heterogenous molecules that not only participate in the normal functioning but at the same time share the blame during disease establishment. Studies on the development and progression of breast carcinoma display a deranged and uncontrolled immune response, which is meticulously exploited during tumor metastasis. The molecular crosstalks between AITDs and breast tumor microenvironment rely on active participation of immune cells. The induction of ER stress by Tunicamycin advocates to provide a model for cancer therapy by intervening glycosylation. Therefore, this review attempts to showcase the molecules that are involved in feeding up the relationship between breast carcinoma and AITDs.

Mechanisms and kinetics of proliferation and fibrosis development in a mouse model of thyrocyte hyperplasia

IFN-γ(-/-) NOD.H-2h4 mice develop autoimmune disease with extensive hyperplasia and proliferation of thyroid epithelial cells (TEC H/P) and fibrosis. Splenic T cells from donors with severe TEC H/P transfer TEC H/P to SCID recipients. The goal of this study was to determine what factors control TEC H/P development/progression by examining T cells, markers of apoptosis, senescence and proliferation in thyroids of SCID recipients over time. At 28days, T cell infiltration was maximal, thyrocytes were proliferating, and fibrosis was moderate. At days 60 and 90, thyroids were larger with more fibrosis. T cells, cytokines and thyrocyte proliferation decreased, and cell cycle inhibitor proteins, and anti-apoptotic molecules increased. T cells and thyrocytes had foci of phosphorylated histone protein H2A.X, indicative of cellular senescence, when TEC H/P progressed and thyrocyte proliferation declined. Some thyrocytes were regenerating at day 90, with irregularly shaped empty follicles and ciliated epithelium. Proliferating thyrocytes were thyroid transcription factor (TTF1)-positive, suggesting they derived from epithelial cells and not brachial cleft remnants.

Effect of transgenic overexpression of FLIP on lymphocytes on development and resolution of experimental autoimmune thyroiditis

In our previous studies, resolution of granulomatous experimental autoimmune thyroiditis (G-EAT) was promoted when thyroid epithelial cells were protected from Fas-mediated apoptosis due to transgenic overexpression of FLIP. We hypothesized that if FLIP were overexpressed on lymphocytes, CD4(+) effector cells would be protected from Fas-mediated apoptosis, and resolution would be delayed. To test this hypothesis, we generated transgenic (Tg) mice overexpressing FLIP under the CD2 promoter. Transgenic FLIP was expressed on CD4(+) and CD8(+) T cells and B cells. Transgenic overexpression of FLIP protected cultured splenocytes from Fas-mediated, but not irradiation-induced, apoptosis in vitro. Unexpectedly, Tg(+) donor cells transferred minimal G-EAT, which was partially overcome by depleting donor CD8(+) T cells. When Tg(+) and Tg(-) donors transferred equivalent disease, G-EAT resolution was delayed in FLIP transgenic mice. However, CD2-FLIP Tg(+) donors often transferred less severe G-EAT, even after depletion of CD8(+) T cells. This influenced the rate of G-EAT resolution, resulting in little difference in G-EAT resolution between groups. Tg(+) mice always had reduced anti-mouse thyroglobulin autoantibody responses, compared with Tg(-) littermates, presumably because of FLIP overexpression on B cells. These results suggest that effects of transgenic FLIP on a particular autoimmune disease vary, depending on what cells express the transgene and whether those cells are effector cells or if they function to modulate disease.

Comparison of sensitivity of Th1, Th2, and Th17 cells to Fas-mediated apoptosis

Following activation through the TCR, CD4+ T cells can differentiate into three major subsets: Th1, Th2, and Th17 cells. IL-17-secreting Th17 cells play an important role in the pathogenesis of several autoimmune diseases and in immune responses to pathogens, but little is known about the regulation of apoptosis in Th17 cells. In this study, the sensitivity of in vitro-polarized Th1, Th2, and Th17 cells to Fas-mediated apoptosis was compared directly by different methods. The order of sensitivity of T cell subsets to Fas-mediated apoptosis is: Th1 > Th17 > Th2. The greater sensitivity of Th17 cells to Fas-mediated apoptosis compared with Th2 cells correlated with their higher expression of FasL and comparable expression of the antiapoptotic molecule FLIP. The decreased sensitivity of Th17 compared with Th1 cells correlated with the higher expression of FLIP by Th17 cells. Transgenic overexpression of FLIP in T cells protected all three subsets from Fas-mediated apoptosis. These findings provide new knowledge for understanding how survival of different subsets of T cells is regulated.

The crystal structure of CD8 in complex with YTS156.7.7 Fab and interaction with other CD8 antibodies define the binding mode of CD8 alphabeta to MHC class I

The CD8alphabeta heterodimer interacts with class I pMHC on antigen-presenting cells as a co-receptor for TCR-mediated activation of cytotoxic T cells. To characterize this immunologically important interaction, we used monoclonal antibodies (mAbs) specific to either CD8alpha or CD8beta to probe the mechanism of CD8alphabeta binding to pMHCI. The YTS156.7 mAb inhibits this interaction and blocks T cell activation. To elucidate the molecular basis for this inhibition, the crystal structure of the CD8alphabeta immunoglobulin-like ectodomains were determined in complex with mAb YTS156.7 Fab at 2.7 A resolution. The YTS156.7 epitope on CD8beta was identified and implies that residues in the CDR1 and CDR2-equivalent loops of CD8beta are occluded upon binding to class I pMHC. To further characterize the pMHCI/CD8alphabeta interaction, binding of class I tetramers to CD8alphabeta on the surface of T cells was assessed in the presence of anti-CD8 mAbs. In contrast to YTS156.7, mAb YTS105.18, which is specific for CD8alpha, does not inhibit binding of CD8alphabeta to class I tetramers, indicating the YTS105.18 epitope is not occluded in the pMHCI/CD8alphabeta complex. Together, these data indicate a model for the pMHCI/CD8alphabeta interaction similar to that observed for CD8alphaalpha in the CD8alphaalpha/pMHCI complex, but in which CD8alpha occupies the lower orientation (membrane proximal to the antigen presenting cell), and CD8beta occupies the upper position (membrane distal). The implication of this molecular assembly for the function of CD8alphabeta in T cell activation is discussed.

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.

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.

Decreasing TNF-alpha results in less fibrosis and earlier resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced in DBA/1 mice by adoptive transfer of mouse thyroglobulin (MTg)-primed spleen cells. TNF-alpha is an important proinflammatory cytokine and apoptotic molecule involved in many autoimmune diseases. To study its role in G-EAT, anti-TNF-alpha mAb was given to recipient mice. Disease severity was comparable between mice with or without anti-TNF-alpha treatment at days 19-21, the time of maximal severity of G-EAT, suggesting TNF-alpha is not essential for development of thyroid inflammation. However, thyroid lesions resolved at day 48 in anti-TNF-alpha-treated mice, while thyroids of rat Ig-treated controls had fibrosis. These results suggested that reducing TNF-alpha contributed to resolution of inflammation and inhibited fibrosis. Gene and protein expression of inflammatory molecules was examined by RT-PCR and immunostaining, and apoptosis was detected using TUNEL staining and an apoptosis kit. Thyroids of anti-TNF-alpha-treated controls had reduced proinflammatory and profibrotic molecules, e.g., IFN-gamma, IL-1beta, IL-17, inducible NOS and MCP-1, at day 19 compared with thyroids of rat Ig-treated mice. There were more apoptotic thyrocytes in rat Ig-treated controls than in anti-TNF-alpha-treated mice. The site of expression of the anti-apoptotic molecule FLIP also differed between rat Ig-treated and anti-TNF-alpha-treated mice. FLIP was predominantly expressed by inflammatory cells of rat Ig-treated mice and by thyrocytes of anti-TNF-alpha-treated mice. These results suggest that anti-TNF-alpha may regulate expression of proinflammatory cytokines and apoptosis in thyroids, resulting in less inflammation, earlier resolution, and reduced fibrosis.

Cutting Edge: Fas Ligand (CD178) Cytoplasmic Tail Is a Positive Regulator of Fas Ligand-Mediated Cytotoxicity

The cytotoxic function of CD178 (Fas ligand (FasL)) is critical to the maintenance of peripheral tolerance and immune-mediated tissue pathology. The active site of FasL resides at the FasL extracellular region (FasL(Ext)) and it functions through binding/cross-linking Fas receptor on target cells. In this study, we report that FasL(Ext)-mediated cytotoxicity is regulated by the FasL cytoplasmic tail (FasL(Cyt)). Deleting the N-terminal 2-70 aa (delta70) or N-terminal 2-33 aa (delta33) reduced the cytotoxic strength as much as 30- to 100-fold. By contrast, change in the cytotoxic strength was not observed with FasL deleted of the proline-rich domains (45-74 aa, delta PRD) in the FasL(Cyt). Our study identifies a novel function of FasL(Cyt) and demonstrates that FasL(2-33), a sequence unique to FasL, is critically required for the optimal expression of FasL(Ext)-mediated cytotoxicity.

Fas ligand is required for resolution of granulomatous experimental autoimmune thyroiditis

We previously suggested that CD8(+) T cells promoted resolution of granulomatous experimental autoimmune thyroiditis (G-EAT) at least in part through regulation of Fas ligand (FasL) expression on thyroid epithelial cells. To directly evaluate the role of the Fas pathway in G-EAT resolution, Fas- and FasL-deficient mice on the NOD.H-2h4 background were used as recipients of activated G-EAT effector cells. When MTg-primed wild-type (WT) donor splenocytes were activated and transferred to WT recipients, thyroid lesions reached maximal severity on day 20 and resolved on day 50. Fas, FasL, and FLIP were up-regulated, and many apoptotic inflammatory cells were detected in recipient thyroids on day 20. Fas was predominantly expressed by inflammatory cells, and FasL and FLIP were mainly expressed by thyroid epithelial cells. After depletion of CD8(+) T cells, G-EAT resolution was delayed, FLIP and FasL were predominantly expressed by inflammatory cells, and few inflammatory cells were apoptotic. When WT donor splenocytes were transferred to gld recipients, disease severity on day 20 was similar to that in WT recipients, but resolution was delayed. As in CD8-depleted WT recipients, there were few apoptotic inflammatory cells, and FLIP and FasL were expressed primarily by inflammatory cells. These results indicated that the expression of functional FasL in recipient mice was critical for G-EAT resolution. WT cells induced minimal disease in lpr recipients. This was presumably because donor cells were eliminated by the increased FasL on lpr recipient cells, because donor cells were not eliminated, and the mice developed G-EAT if lpr recipients were given anti-FasL mAb.

Balance of proliferation and cell death between thyrocytes and myofibroblasts regulates thyroid fibrosis in granulomatous experimental autoimmune thyroiditis (G-EAT)

Severe granulomatous experimental autoimmune thyroiditis (G-EAT), which progresses to fibrosis, is induced in DBA/1 mice by adoptive transfer of mouse thyroglobulin-primed and -activated spleen cells. There is extensive destruction of thyrocytes and inflammatory cell infiltration including T cells, macrophages, neutrophils, and myofibroblasts (myofbs). Suppression of transforming growth factor-beta (TGF-beta) and deficiency of interferon-gamma (IFN-gamma) inhibit fibrosis, and inflammation eventually resolves. Thyrocyte destruction in wild-type (WT) mice was a result of apoptosis, as many deoxynucleotide triphosphate nick-end labeling + apoptotic thyrocytes were present in these thyroids. The balance of apoptosis and proliferation between thyrocytes and myofbs may be important factors determining the outcome of inflammation to fibrosis versus resolution. Apoptosis and proliferation in thyrocytes versus myofbs were evaluated by dual-staining of cell-proliferating marker (Ki-67) or in situ cell death and cytokeratin or alpha-smooth muscle actin and were analyzed by confocal microscopy. Apoptotic and antiapoptotic molecules in G-EAT thyroids were detected by immunostaining. In WT thyroids, which develop fibrosis, only a few myofbs were apoptotic, and many myofbs were Ki-67+, Fas-associated death domain protein-like interleukin-1beta-converting enzyme-like inhibitory protein (FLIP)+, and Bcl-XL+. In contrast, proliferation was predominant on thyrocytes of IFN-gamma-/- mice or anti-TGF-beta-treated WT mice. These results indicate that apoptosis of inflammatory cells and regeneration of thyrocytes in IFN-gamma-/- mice and anti-TGF-beta-treated WT mice may limit development of fibrosis, whereas excessive proliferation of myofbs and loss of thyrocytes in WT mice may contribute to fibrosis.

Novel Negative Regulator of Expression in Fas Ligand (CD178) Cytoplasmic Tail: Evidence for Translational Regulation and against Fas Ligand Retention in Secretory Lysosomes

Fas ligand ((FasL) CD178), a type II transmembrane protein, induces apoptosis of cells expressing the Fas receptor. It possesses a unique cytoplasmic tail (FasLCyt) of 80 aa. As a type II transmembrane protein, the early synthesis of FasLCyt could affect FasL translation by impacting FasL endoplasmic reticulum translocation and/or endoplasmic reticulum retention. Previous studies suggest that the proline-rich domain (aa 43-70) in FasLCyt (FasLPRD) inhibits FasL membrane expression by retaining FasL in the secretory lysosomes. This report shows that deletion of aa 2-33 of FasLCyt dramatically increased total FasL levels and FasL cell surface expression. This negative regulator of FasL expression is dominant despite the presence of FasLPRD. In addition, retention of proline-rich domain-containing FasL in the cytoplasm was not observed. Moreover, we demonstrated that FasLCyt regulates FasL expression by controlling the rate of de novo synthesis of FasL. Our study demonstrated a novel negative regulator of FasL expression in the FasLCyt region and its mechanism of action.

Mechanisms of spontaneous resolution versus fibrosis in granulomatous experimental autoimmune thyroiditis

When granulomatous experimental autoimmune thyroiditis (G-EAT) was induced in CBA/J or DBA/1 mice, thyroid lesions resolved in less severe (3+) G-EAT in wild-type mice or severe (5+) G-EAT in IFN-gamma(-/-) mice, but progressed to fibrosis in 5+ G-EAT in wild-type mice. To define the mechanisms leading to these distinct outcomes, the expression of inflammatory and apoptotic molecules and infiltrating cells was evaluated using immunohistochemistry, RT-PCR, and confocal microscopy. The ratio of CD4(+)/CD8(+) T cells in thyroid infiltrates was one factor that predicted G-EAT outcome. CD4(+) T cells outnumbered CD8(+) T cells when lesions progressed to fibrosis, while CD8(+) T cells outnumbered CD4(+) T cells in thyroids that resolved. Fas, Fas ligand, FLIP, TNF-alpha, inducible NO synthase, TGF-beta, and IFN-gamma were highly expressed by infiltrating cells when G-EAT progressed to fibrosis. The expression of active caspase-3 was low, possibly contributing to the persistence of CD4(+) T cells in fibrosis. In contrast, FLIP was mainly expressed by thyrocytes in resolving G-EAT, the expression of active caspase-3 was high, and resolution correlated with apoptosis of infiltrating cells. There was also relatively less expression of TGF-beta, IFN-gamma, TNF-alpha, and inducible NO synthase and higher expression of IL-10 in resolving G-EAT than in G-EAT that progressed to fibrosis. These differences were particularly striking when comparing IFN-gamma(-/-) vs wild-type mice. These results suggest that several opposing biological mechanisms contribute to the outcome of an ongoing autoimmune response. These include differential expression of pro- and antiapoptotic molecules, cytokines, and the ratio of CD4(+) vs CD8(+) T cells.

FLIP and FasL expression by inflammatory cells vs thyrocytes can be predictive of chronic inflammation or resolution of autoimmune thyroiditis

Spontaneous autoimmune thyroiditis (SAT) in NOD.H-2h4 mice is a model of chronic inflammation of the thyroid, while granulomatous experimental autoimmune thyroiditis (G-EAT) is a model with spontaneous resolution of inflammation. In chronic inflammation (SAT), Fas, FasL, and FLIP were upregulated and predominant in inflammatory cells. There were few apoptotic cells, and low expression of active caspase-8 and -3. In resolving G-EAT in CBA/J and NOD.H-2h4 mice, FasL and FLIP were predominantly expressed by thyrocytes. There were many apoptotic inflammatory cells, and increased expression of active caspase-8 and -3. Depletion of CD8+ T cells inhibited G-EAT resolution and resulted in chronic inflammation. FLIP was expressed predominantly by inflammatory cells, and apoptosis of inflammatory cells and expression of active caspase-3 was reduced as in chronic SAT. Thus, differences in expression of pro- or antiapoptotic molecules in SAT or G-EAT were apparently related to the acute vs chronic nature of the inflammatory response rather than the method of disease induction. Upregulation of FLIP by inflammatory cells may block Fas-mediated apoptosis, contributing to chronic inflammation, whereas increased FLIP expression by thyrocytes in resolving G-EAT may protect thyrocytes from apoptosis, and FasL expression by thyrocytes may induce apoptosis of inflammatory cells, contributing to resolution.

Fas ligand gene polymorphisms are not associated with Hashimoto's thyroiditis and Graves' disease

Hashimoto's thyroiditis and Graves' disease represent the two most common autoimmune thyroid disorders. Whereas in Hashimoto's thyroiditis FasL expression causes thyrocytes to undergo apoptosis, additional anti-apoptotic molecules appear to protect these cells in Graves' disease. Mutations of the FasL gene were observed in systemic lupus erythematosus. Given its functional relevance for the pathogenesis of thyroid autoimmunity we wondered whether variants of the FasL gene play a role in Hashimoto's thyroiditis and Graves' disease. We genotyped families with at least one offspring affected by Hashimoto's thyroiditis (n = 86) and Graves' disease (n = 90) for two FasL gene polymorphisms (C -843 T in the promoter, A IVS2nt-124 G in intron 2). Extended transmission disequilibrium (ETDT) and chi(2) testing were performed. Neither polymorphism alone nor the promoter/intron 2 haplotypes (p = 0.91) were associated with Hashimoto's thyroiditis. No association with Graves' disease was observed for the promoter polymorphism (p = 0.91) and the intron 2 "A" allele (57.1%; p = 0.36) or the promoter/intron 2 haplotypes (p = 0.31). Moreover, intron 2 genotyping revealed no difference between an additional 251 patients with Graves' disease and 197 healthy controls (p = 0.37). Italian and German families did not differ for the studied polymorphisms. In conclusion, our data do not suggest common genetic FasL variants to significantly contribute to the pathogenesis of either Hashimoto's thyroiditis or Graves' disease.

Inhibition of TGFbeta1 by anti-TGFbeta1 antibody or lisinopril reduces thyroid fibrosis in granulomatous experimental autoimmune thyroiditis

In this study, a murine model of granulomatous experimental autoimmune thyroiditis (G-EAT) was used to determine the role of TGFbeta1 in fibrosis initiated by an autoimmune inflammatory response. The fibrotic process was evaluated by staining thyroid tissue for collagen, alpha-smooth muscle actin, TGFbeta1, and angiotensin-converting enzyme (ACE), and measuring serum thyroxine in mice given anti-TGFbeta1 or the ACE inhibitor lisinopril. The role of particular inflammatory cells in fibrosis was tested by depletion experiments, and the cytokine profile in thyroids was examined by RT-PCR. Neutralization of TGFbeta1 by anti-TGFbeta1 or lisinopril resulted in less collagen deposition and less accumulation of myofibroblasts, and levels of active TGFbeta1 and ACE were reduced in thyroids of treated mice compared with those of untreated controls. Other profibrotic molecules, such as platelet-derived growth factor, monocyte chemotactic protein-1, and IL-13, were also reduced in thyroids of anti-TGFbeta1- and lisinopril-treated mice compared with those of controls. Confocal microscopy showed that CD4(+) T cells and macrophages expressed TGFbeta1. Fibrosis was reduced by injection of anti-CD4 mAb on day 12, when G-EAT was very severe (4-5+). Together, these results suggest a critical role for TGFbeta1 in fibrosis initiated by autoimmune-induced inflammation. Autoreactive CD4(+) T cells may contribute to thyroid fibrosis through production of TGFbeta1. This G-EAT model provides a new model to study how fibrosis associated with autoimmune damage can be inhibited.

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.