CD4+ T Cell-Mediated Cytotoxicity Toward Thyrocytes: The Importance of Fas/Fas Ligand Interaction Inducing Apoptosis of Thyrocytes and the Inhibitory Effect of Thyroid-Stimulating Hormone

Abstract

SUMMARY:The accumulation of activated CD4 ϩ T cells and antigen (Ag)-dependent cellular interactions between thyrocytes and CD4 ϩ T cells have been determined in thyroid gland from patients with Graves' disease. The Fas/Fas ligand (FasL) interaction between antigen-presenting cells and T cells regulates the apoptosis of the former cells triggered by the latter cells. The inhibition of Fas-mediated apoptosis in thyrocytes could be a underlying mechanism of hyperplasia of thyrocytes in patients with Graves' disease. We investigated the potential role of Fas/FasL interaction between thyrocytes and CD4 ϩ T cells in the induction of Fas-mediated apoptosis of the former cells induced by the latter cells. The presence of only a few specific T cells responsive to a putative autoantigen has hampered the investigation of specific T cell activation toward antigen-presenting cells (APCs). Therefore, we used a superantigen, staphylococcal enterotoxin B (SEB), to examine specific T cell activation toward thyrocytes in vitro since it stimulates a large proportion of T cells with particular V␤ elements. Spontaneous apoptosis of thyrocytes in culture was not found even in the presence of various kinds of cytokines. In contrast, a clear induction of Fas-mediated apoptosis by anti-Fas IgM was determined in interferon-␥ (IFN-␥)-stimulated thyrocytes. In addition, a significant cytotoxicity of purified CD4 ϩ T cells toward IFN-␥-stimulated thyrocytes in the presence of SEB was induced, and the addition of anti-HLA-DR and -DQ monoclonal antibodies (mAbs) or blockade of the Fas/FasL interaction reduced this cytotoxicity. FasL expression of CD4 ϩ T cells cocultured with IFN-␥-stimulated thyrocytes in the presence of SEB was clearly induced. Furthermore, the addition of mAbs against CD54 and CD58 inhibited both cytotoxicity and FasL expression of CD4 ϩ T cells. The cytotoxicity of CD4 ϩ T cells toward IFN-␥-stimulated, SEB-pulsed thyrocytes was markedly inhibited when we used thyrocytes cultured with IFN-␥ in the presence of thyroid-stimulating hormone (TSH) as target cells. Our results suggest that 1) CD4 ϩ T cells were activated by thyrocytes expressing MHC class II molecules in an SEB-dependent manner and then expressed FasL. 2) These activated FasL ϩ CD4 ϩ T cells killed thyrocytes by interacting with Fas on thyrocytes and FasL on activated CD4 ϩ T cells. The presence of costimulating molecules such as CD54 and CD58 on thyrocytes was also necessary to generate activated FasL ϩ CD4 ϩ T cells. 3) Since the actions of thyroid stimulating antibody (TSAb) toward thyrocytes are similar to those of TSH, one goitrogenic activity of TSAb may, in part, be due to the inhibitory effect on Fas-mediated apoptosis of thyrocytes triggered by activated CD4 ϩ T cells. (Lab Invest 2000, 80:471-484).

Apoptosis and Autoimmune Disorders

“…Fas was also upregulated in the thyrocytes of patients with Graves' disease (Sera et al, 2000). The thyroid gland of Graves' disease patients contains TUNEL-positive thyrocytes and PCNA-positive thyrocytes, together with monocuclear cell infiltration (Sera et al, 2000). These data suggest that apoptosis and proliferation of thyrocytes may be abnormally accelerated, however, the proliferation of thyrocytes may outweigh their apoptosis, resulting in hyperplasia.…”

“…Giordano et al (1997) reported the constitutive expression of FasL (Fas ligand) on normal and Hashimoto's thyroiditis (HT) thyrocytes using immunohistochemistry, flow cytometry, and RT-PCR. The percentage of FasL-positive thyrocytes in Graves' thyroid was less than in normal thyroids (Sera et al, 2000). In contrast, another study was unable to detect FasL in thyrocytes (Xerri et al, 1997).…”

“…It has been demonstrated that there is increased expression of Fas in the thyrocytes of patients with Hashimoto's thyroiditis (Hammond et al, 1997). Fas was also upregulated in the thyrocytes of patients with Graves' disease (Sera et al, 2000). The thyroid gland of Graves' disease patients contains TUNEL-positive thyrocytes and PCNA-positive thyrocytes, together with monocuclear cell infiltration (Sera et al, 2000).…”

“…The Fas and TRAIL pathways are present and functional in the thyroid, and there is evidence suggesting their involvement in autoimmune diseases of the thyroid (Bretz et al, 1999;Kawakami et al 2000). Giordano et al (1997) reported the constitutive expression of FasL (Fas ligand) on normal and Hashimoto's thyroiditis (HT) thyrocytes using immunohistochemistry, flow cytometry, and RT-PCR.…”

Clinical and Therapeutic Implications of the Association between Chronic Urticaria and Autoimmune Thyroiditis

“…Various cytokines modulate hormone production by binding to specific receptors in endocrine tissues and vice versa, hormones bind to their own receptors on immune cells and are able to influence their function (27)(28)(29)(30). TSH has been shown to induce direct T cell, B cell and dendritic cell activation and the release of proinflammatory cytokines, leading to an inflammatory state that affects not only the thyroid gland, but other tissues as well, including the skin (28)(29)(30)(31)(32). This effect is amplified in the setting of autoimmune thyroiditis.…”