Induction of Rat Thyroid Cell MHC Class II Antigen by Thyrotropin and Y-Interferon*

Abstract

Major histocompatibility (MHC) class II antigen expression by thyroid epithelial cells has been widely implicated in the pathogenesis of autoimmune thyroid disease. We have examined rat MHC (RT1) class II antigen gene regulation in 1B-6 cells, cloned in our laboratory from the Fisher rat thyroid line FRT-L5. 1B-6 cells are TSH dependent for growth and proliferation, and are responsive to more than 5 microU/ml bovine TSH (bTSH) in terms of extracellular cAMP accumulation. Recombinant rat gamma interferon (gamma IF; 1-1000 U/ml) treatment for 5 days together with bTSH (10(3) microU/ml) was able to induce class II antigen expression in up to 90% of 1B-6 cells, as detected by a murine monoclonal antibody to rat MHC class II antigen (FITC-OX-6). Total cellular RNA was examined in Northern blot analyses using an HLA-DR alpha-chain-specific RNA probe, which shares 78% sequence homology with the rat RT1.D alpha-chain gene. A 1.4-kilobase mRNA transcript was detected in gamma IF-stimulated cells, but not in untreated cells. Dose-response studies of MHC class II gene expression, using a cytoplasmic RNA slot blot technique for alpha-chain mRNA levels and FITC-OX 6 monoclonal antibody for detection of MHC class II antigen expression, indicated 1B-6 sensitivity to gamma IF in the range of 10-100 U/ml (in the presence of 10(3) microU/ml bTSH) and to bTSH in the range of 10-100 microU/ml (in the presence of 10(2) U/ml gamma IF). These data demonstrate dual control of MHC class II antigen gene expression by gamma IF and bTSH in a differentiated rat thyroid cell. Clone 1B-6 represents a powerful means of analyzing reproducibly and in long term studies the regulation of thyroid cell MHC class II gene expression.

Hormonal regulation of major histocompatibility complex class I genes in rat thyroid FRTL-5 cells: thyroid-stimulating hormone induces a cAMP-mediated decrease in class I expression.

“…Although surface levels of class I in thyrocytes are normally low relative to lymphoid cells, TSH specifically triggers a further reduction in this level. The ability of TSH to decrease MHC class I gene and antigen expression is very different from its effect on class II gene and antigen expression in FRTL-5 cells (8). Thus, TSH alone has no effect on class II but is necessary for interferonmediated increases in class II gene expression.…”

“…In studies to be published elsewhere, we show that insulin, insulin-like growth factor 1, and hydrocortisone can also negatively regulate class I expression (31). We suggest that hormonal signals induce a reduction in class I expression that may be necessary to avoid immune responses to thyroid products (i.e., TPO and Tg), which are known autoantigens present in the sera of patients with autoimmune thyroid disease (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Continued examination of hormonal regulation of MHC class I expression in FRTL-5 cells should provide additional information concerning regulatory elements of MHC class I genes as well as serve as a model to better understand the development or progression of autoimmune Graves disease.…”

“…As a result, the roles of the major histocompatibility (MHC) class I and class II cell surface molecules in the etiology ofthese diseases have been examined extensively (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Both class I and class II molecules are glycoproteins that play pivotal roles in the induction and propagation of immune responses (11)(12)(13).…”

“…In Graves disease and autoimmune thyroiditis, both class I and class II cell surface levels have been shown to be elevated. Although there have been extensive studies on the factors regulating class II expression in thyrocytes, including the rat FRTL-5 thyroid cell model (5)(6)(7)(8)(9)(10), less attention has been focused on the patterns of expression of MHC class I molecules.…”

Nonimmune thyroid destruction results from transgenic overexpression of an allogeneic major histocompatibility complex class I protein.

“…The direct infection of cultured human pancreatic islet cells by reovirus (9) or of rat thyrocytes by simian virus 40 (3) causes upregulation of MHC class I expression. In endocrine autoimmunity, mononuclear cells infiltrate the target tissue and release cytokines such as gamma interferon and tumor necrosis factor, which may further upregulate MHC class I and induce MHC class II molecules in islet cells (6,(10)(11)(12)33) and thyrocytes (22,24,28,32). The overexpression of MHC class I molecules should thus enhance the immunogenic properties of endocrine cells (8,19).…”