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

NOD.H-2h4 mice: an important and underutilized animal model of autoimmune thyroiditis and Sjogren's syndrome

NOD.H-2h4 mice express the K haplotype on the NOD genetic background. They spontaneously develop thyroiditis and Sjogren's syndrome, but they do not develop diabetes. Although autoimmune thyroid diseases and Sjogren's syndrome are highly prevalent autoimmune diseases in humans, there has been relatively little emphasis on the use of animal models of these diseases for understanding basic mechanisms involved in development and therapy of chronic organ-specific autoimmune diseases. The goal of this review is to highlight some of the advantages of NOD.H-2h4 mice for studying basic mechanisms involved in development of autoimmunity. NOD.H-2h4 mice are one of relatively few animal models that develop organ-specific autoimmune diseases spontaneously, i.e., without a requirement for immunization with antigen and adjuvant, and in both sexes in a relatively short period of time. Thyroiditis and Sjogren's syndrome in NOD.H-2h4 mice are chronic autoimmune diseases that develop relatively early in life and persist for the life of the animal. Because the animals do not become clinically ill, the NOD.H-2h4 mouse provides an excellent model to test therapeutic protocols over a long period of time. The availability of several mutant mice on this background provides a means to address the impact of particular cells and molecules on the autoimmune diseases. Moreover, to our knowledge, this is the only animal model in which the presence or absence of a single cytokine, IFN-γ, is sufficient to completely inhibit one autoimmune thyroid disease, with a completely distinct autoimmune thyroid disease developing when it is absent.

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.

Differential expression of Fas system apoptotic molecules in peripheral lymphocytes from patients with Graves' disease and Hashimoto's thyroiditis

OBJECTIVE

To examine whether the Fas system apoptotic molecules are differentially expressed in Graves' disease (GD) and Hashimoto's thyroiditis (HT), the two opposite phenotypes of autoimmune thyroid disease (AITD).

DESIGN

The expression of Fas and Fas ligand (FasL) on peripheral CD4 and CD8 lymphocytes, and non-lymphoid immune cells as well as their soluble forms in serum from untreated patients with GD and HT were evaluated.

METHODS

Flow cytometry was performed for the study of peripheral immune cells from 70 newly diagnosed patients with AITD (55 with HT and 15 with GD) and 20 controls. ELISA was used for the measurement of soluble Fas (sFas) in serum samples from a subgroup of 35 AITD patients.

RESULTS

An increase in the proportion of CD4 and CD8 cells expressing Fas was found in both GD and HT, albeit with some differences, when compared with controls. Importantly, in GD patients, the intensity of Fas expression on CD4 and CD8 lymphocytes was reduced and sFas levels in serum were simultaneously increased when compared with HT patients and controls.

CONCLUSIONS

The Fas system apoptotic molecules appear to be differentially expressed on peripheral lymphocytes in the two opposite phenotypes of AITD.

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.

No apparent damage in the thyroid of transgenic mice expressing antiapoptotic FLIP

FLIP is an antiapoptotic protein that has been demonstrated to play an important role in inflammation, cancer, and autoimmune diseases. However, it is not known whether increased expression of FLIP (FLICE inhibitory protein) in thyrocytes would alter the development of the thyroid and/or pathogenesis of thyroiditis. To examine the effects of overexpression of this antiapoptotic molecule on the thyroid, we have developed transgenic mouse lines that specifically express FLIP in thyrocytes. A DNA construct designed with an in-frame coding sequence for the E8 protein, a viral FLIP, was put under the control of the thyroglobulin (Tg) promoter (the Tg-FLIP transgene). In 8 of 12 resultant transgenic mouse lines, FLIP expression in thyrocytes driven by the Tg promoter was documented, and confirmed at RNA and protein levels. These Tg-FLIP transgenic mice were monitored for 1 year. Throughout the entire observation period, the transgenic mice remained alive and healthy without evidence of thyroid dysfunction. Adult mice were able to breed. Histologic examination of thyroids obtained at various time points did not reveal significant differences between transgenic mice and their control littermates. Therefore, transgenic mice with thyrocyte-specific expression of FLIP have normal thyroid development with no significant changes in thyroid cell death or proliferation.

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.

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.