Effects of rat gamma- and non-gamma-interferons on the expression of Ia antigen, growth, and differentiated functions of FRTL5 cells

The cytokine storm and thyroid hormone changes in COVID-19

BACKGROUND

COVID-19 is now a worldwide pandemic. Among the many extra-pulmonary manifestations of COVID-19, recent evidence suggested a possible occurrence of thyroid dysfunction.

PURPOSE

The Aim of the present review is to summarize available studies regarding thyroid function alterations in patients with COVID-19 and to overview the possible physio-pathological explanations.

CONCLUSIONS

The repercussions of the thyroid of COVID-19 seem to be related, in part, with the occurrence of a "cytokine storm" that would, in turn, induce a "non-thyroidal illness". Some specific cytokines and chemokines appear to have a direct role on the hypothalamus-pituitary-thyroid axis. On the other hand, some authors have observed an increased incidence of a destructive thyroiditis, either subacute or painless, in patients with COVID-19. The hypothesis of a direct infection of the thyroid by SARS-Cov-2 stems from the observation that its receptor, ACE2, is strongly expressed in thyroid tissue. Lastly, it is highly probable that some pharmaceutical agents largely used for the treatment of COVID-19 can act as confounding factors in the laboratory evaluation of thyroid function parameters.

Cytokines and Thyroid Autoimmunity

Cytokines may play important roles in the development and perpetuation of autoimmunity. In this paper are briefly reviewed selected data on the relationship between cytokines and thyroid autoimmune diseases (AITD), which represent a typical example of organ-specific autoimmune endocrinopathy. The availability of high efficiency T-cell cloning techniques recently allowed the phenotipic and functional characterization of T lymphocytes derived from thyroid infiltrates of patients with Graves' disease and Hashimoto's thyroiditis. A high prevalence of T cell clones with cytolytic potential and displaying increased γ-interferon production was observed in both diseases; in contrast, high tumor necrosis factor-α secretion was a peculiar characteristic of T-cell clones derived only from Hashimoto's infiltrates. The production of IL-4 by CD4 + T cell clones from AITD infiltrates was remarkably low, suggesting a quite homogeneous populations of Thl-type «inflammatory» T cells. This pattern of cytokine production by thyroid infiltrates may be important not only in triggering and/or maintaining thyroid autoimmune reaction, but could also modulate the expression of AITD by exerting direct functional effects on thyroid epithelial cells, as suggested by recent in vitro studies.

Differential effects of acute and chronic exposure to interferon-gamma on cyclic adenosine 3',5'-monophosphate response element-regulated gene expression

TSH stimulates proliferation and maintains differentiated function in thyroid follicular cells. The mitogenic activity and the stimulatory effects of TSH on thyroid-specific gene expression are impaired by interferon-gamma (IFNgamma); however, the mechanisms for these effects have not been elucidated in detail. We examined the effects of IFNgamma on acute responses to TSH in rat thyroid cells. IFNgamma did not impair TSH-stimulated p70/p85 ribosomal protein S6 kinase (p70/p85s6k) activity or cAMP response element (CRE)-regulated gene expression, although it inhibited DNA synthesis and thyroglobulin expression, effects measured over a more prolonged time course than those on kinase activity and reporter gene expression. Unexpectedly, when cells were chronically exposed to IFNgamma, CRE-lacZ promoter activity was decreased, whereas other cAMP-mediated signals, such as p70/p85s6k activity and CRE-binding protein phosphorylation, were unaffected. Activating protein-1-regulated promoters were also impaired by IFNgamma treatment, but with kinetics that differed from those of CRE-regulated promoters. Neither acute nor chronic treatment with interleukin-1beta impaired cAMP signaling, indicating that the effects of IFNgamma are specific. These studies identify CRE- and activating protein-1-regulated promoters as targets of IFNgamma in thyroid cells and fibroblasts. IFNgamma-mediated inhibition of these promoters, in addition to those containing thyroid-specific transcription factor-1-binding sites, may contribute to the profound effects of IFNgamma on thyroid cells.

Regulation of major histocompatibility class II gene expression in FRTL-5 thyrocytes: opposite effects of interferon and methimazole

Aberrant expression of major histocompatibility complex (MHC) class II antigens is associated with autoimmune thyroid disease; aberrant expression duplicating the autoimmune state can be induced by interferon-gamma (IFNgamma). We have studied IFNgamma-induced human leukocyte antigen (HLA)-DR alpha gene expression in rat FRTL-5 thyroid cells to identify the elements and factors important for aberrant expression. Using an HLA-DR alpha 5'-flanking region construct from -176 to +45 bp coupled to the chloramphenicol acetyltransferase reporter gene, we show that there is no basal class II gene expression in FRTL-5 thyroid cells, that IFNgamma can induce expression, and, as is the case for antigen-presenting cells from the immune system, that IFNgamma-induced expression requires several highly conserved elements on the 5'-flanking region, which, from 5' to 3', are the S, X1, X2, and Y boxes. Methimazole (MMI), a drug used to treat patients with Graves' disease and experimental thyroiditis in rats or mice, can suppress the IFNgamma-induced increase in HLA-DR alpha gene expression as a function of time and concentration; MMI simultaneously decreases IFNgamma-induced endogenous antigen presentation by the cell. Using gel shift assays and the HLA-DR alpha 5'-flanking region from -176 or -137 to +45 bp as radiolabeled probes, we observed the formation of a major protein-DNA complex with extracts from FRTL-5 cells untreated with IFNgamma, termed the basal or constitutive complex, and formation of an additional complex with a slightly faster mobility in extracts from cells treated with IFNgamma. MMI treatment of cells prevents IFNgamma from increasing the formation of this faster migrating complex. Formation of both complexes is specific, as evidenced in competition studies with unlabeled fragments between -137 and -38 bp from the start of transcription; nevertheless, they can be distinguished in such studies. Thus, high concentrations of double stranded oligonucleotides containing the sequence of the Y box, but not S, X1, or X2 box sequences, can prevent formation of the IFNgamma-increased faster migrating complex, but not the basal complex. Both complexes involve multiple proteins and can be distinguished by differences in their protein composition. Thus, using specific antisera, we show that two cAMP response element-binding proteins, activating transcription factor-1 and/or -2, are dominant proteins in the upper or basal complex. The upper or basal complex also includes c-Fos, Fra-2, Ets-2, and Oct-1. A dominant protein that distinguishes the IFNgamma-increased lower complex is CREB-binding protein (CBP), a coactivator of cAMP response element-binding proteins. We, therefore, show that aberrant expression of MHC class II in thyrocytes, induced by IFNgamma, is associated with the induction or increased formation of a novel protein-DNA complex and that its formation as well as aberrant class II expression are suppressed by MMI, a drug used to treat human and experimental autoimmune thyroid disease. Its component proteins differ from those in a major, basal, or constitutive protein-DNA complex formed with the class II 5'-flanking region in cells that are not treated with IFNgamma and that do not express the class II gene.

Iodide suppression of major histocompatibility class I gene expression in thyroid cells involves enhancer A and the transcription factor NF-kappa B

High concentrations of iodide can induce transient, clinical improvement in patients with autoimmune Graves' disease. Previous work has related this iodide action to the autoregulatory effect of iodide on the growth and function of the thyroid; more recently, we additionally related this to the ability of iodide to suppress major histocompatibility (MHC) class I RNA levels and antigen expression on thyrocytes. In this report, we describe a transcriptional mechanism involved in iodide suppression of class I gene expression, which is potentially relevant to the autoregulatory action of iodide. Transfection experiments in FRTL-5 cells show that iodide decreases class I promoter activity and that this effect can be ascribed to the ability of iodide to modulate the formation of two specific protein/DNA complexes with enhancer A, -180 to -170 bp, of the class 1 5'-flanking region. Thus, iodide decreases the formation of Mod-1, an enhancer A complex involving the p50 subunit of NF-kappa B and a c-fos family member, fra-2, which was previously shown to be important in the suppression of class I levels by hydrocortisone. Unlike hydrocortisone, iodide also increases the formation of a complex with enhancer A, which we show, in antibody shift experiments, is a heterodimer of the p50 and p65 subunits of NF-kappa B. The changes in these complexes are not duplicated by chloride and are related to the action of iodide on class I RNA levels by the following observations. First, FRTL-5 thyroid cells with an aged phenotype coincidentally lose the ability of iodide to decrease MHC class I RNA levels and to induce changes in either complex. Second, the effect of iodide on class I RNA levels and on enhancer A complex formation with Mod-1 and the p50/p65 heterodimer is inhibited by agents that block the inositol phosphate, Ca++, phospholipase A2, arachidonate signal transduction pathway: acetylsalicylate, indomethacin, and 5,8,11,14-eicosatetraynoic acid. Interestingly, iodide can also decrease formation of the Mod-1 complex and increase formation of the complex with the p50/p65 subunits of NF-kappa B when the NF-kappa B enhancer sequence from the Ig kappa light chain, rather than enhancer A, is used as probe; and both actions mimic the action of a phorbol ester. This suggests that iodide may regulate complex formation with NF-kappa B regulatory elements on multiple genes associated with growth and function, providing a potential mechanism relating the autoregulatory action of iodide on thyroid cells and its action on class I gene expression.

Major histocompatibility class II HLA-DR alpha gene expression in thyrocytes: counter regulation by the class II transactivator and the thyroid Y box protein

Aberrant expression of major histocompatibility complex (MHC) class II proteins on thyrocytes, which is associated with autoimmune thyroid disease, is mimicked by gamma-interferon (gamma-IFN). To define elements and factors that regulate class II gene expression in thyrocytes and that might be involved in aberrant expression, we have studied gamma-IFN-induced HLA-DR alpha gene expression in rat FRTL-5 thyroid cells. The present report shows that class II expression in FRTL-5 thyrocytes is positively regulated by the class II transactivator (CIITA), and that CIITA mimics the action of gamma-IFN. Thus, as is the case for gamma-IFN, several distinct and highly conserved elements on the 5'-flanking region of the HLA-DR alpha gene, the S, X1, X2, and Y boxes between -137 to -65 bp, are required for class II gene expression induced by pCIITA transfection in FRTL-5 thyroid cells. CIITA and gamma-IFN do not cause additive increases in HLA-DR alpha gene expression in FRTL-5 cells, consistent with the possibility that CIITA is an intermediate factor in the gamma-IFN pathway to increased class II gene expression. Additionally, gamma-IFN treatment of FRTL-5 cells induces an endogenous CIITA transcript; pCIITA transfection mimics the ability of gamma-IFN treatment of FRTL-5 thyroid cells to increase the formation of a specific and novel protein/DNA complex containing CBP, a coactivator of CRE binding proteins important for cAMP-induced gene expression; and the action of both gamma-IFN and CIITA to increase class II gene expression and increase complex formation is reduced by cotransfection of a thyroid Y box protein, which suppresses MHC class I gene expression in FRTL-5 thyroid cells and is a homolog of human YB-1, which suppresses MHC class II expression in human glioma cells. We conclude that CIITA and TSH receptor suppressor element binding protein-1 are components of the gamma-IFN-regulated transduction system which, respectively, increase or decrease class II gene expression in thyrocytes and may, therefore, be involved in aberrant class II expression associated with autoimmune thyroid disease.

Cytokines and thyroid function

Cytokines play a crucial role in autoimmune thyroid disease (ATD) through various mechanisms. They are produced in the thyroid by intrathyroidal inflammatory cells, in particular lymphocytes, as well as by the thyroid follicular cells (TFC) themselves and may thus act in a cascade to enhance the autoimmune process (Fig. 1). Cytokines upregulate the inflammatory reaction through stimulation of both T and B cells, resulting in antibody production and tissue injury. In addition, intrathyroidal cytokines induce immunological changes in TFC including enhancement of both major histocompatibility complex (MHC) class I and class II molecule expression, and upregulation of adhesion and complement regulatory molecule expression. Cytokines can also modulate both growth and function of TFC and have a role in extrathyroidal complications of ATD, most importantly thyroid-associated ophthalmopathy (TAO), where they induce fibroblast proliferation and enhance the production of glycosaminoglycans (GAG), resulting in proptosis and the other clinical features of the disease. In addition to these effects, exogenous administration of cytokines has been associated with impairment of thyroid function ranging from the appearance of autoantibodies alone to the development of frank thyroid dysfunction. Cytokines have also been implicated in subacute thyroiditis (SAT) and amiodarone-induced thyroid dysfunction, as well as in thyroid function abnormalities occurring in patients with non-thyroidal illnesses (NTI). Genetic variations in cytokine genes represent potential risk factors for ATD, and disease associations have been described for polymorphisms in IL-1ra and TNF beta genes. Recent experimental evidence suggests the possibility of novel cytokine-based therapeutic approaches for ATD and its complications, in particular TAO.

Hormonal modulation of major histocompatibility complex class I gene expression involves an enhancer A-binding complex consisting of Fra-2 and the p50 subunit of NF-kappa B

Hydrocortisone decreases major histocompatibility complex (MHC) class I gene expression in rat thyroid cells and counteracts increases induced by interferons. Using FRTL-5 cells transfected with class I promoter-reporter gene chimeras, we show that hydrocortisone action is transcriptional and mediated by an element located between 180 and 170 base pairs upstream of the start of transcription. Gel shift assays reveal that hydrocortisone causes the decrease of a specific protein-DNA complex; this same complex, referred to as Mod-1, is increased by interferon. Oligonucleotide competition assays reveal that the Mod-1 complex is associated with enhancer A of the class I gene, -180 to -170 base pairs (5'-GGGGAGTCCCC-3'), immediately upstream of the interferon response element. Antibodies to fra-2, a fos family member, and to the p50, but not the p65, subunit of NF-kappa B supershift the Mod-1 complex. We suggest that hydrocortisone decreases MHC class I gene expression by reducing the formation of Mod-1, which contains both p50 and fra-2; interferon reverses the hydrocortisone effect and increases Mod-1 formation. These observations are relevant to the molecular basis of hydrocortisone therapy in autoimmune thyroid disease and to the actions of interferon to exacerbate or induce autoimmune disease.

Induction in vitro of 72-kD heat shock protein in a continuous culture of rat thyroid cells, FRTL5

In Graves' disease and Hashimoto's thyroiditis, the presence of 72-kD heat shock protein (hsp-72) on thyrocytes has been reported. To clarify the significance of this phenomenon, we induced the antigen in thyroid cell culture in vitro. In the FRTL5 rat cell line, which had been heated at 42.5 degrees C or treated with sodium arsenite, expression of hsp-72 was examined with immunoperoxidase staining and immunoprecipitation of the metabolically labelled protein using a specific MoAb. In the cells cultured either with or without thyrotropin (TSH), heat and chemical stresses reproducibly and dose-dependently induced hsp-72 antigen, whereas unstimulated controls had no significant immunoreactivity. Unlike in Graves' retrocular fibroblasts, hydrogen peroxide was not an effective stress in FRTL5, and the induction was not suppressed by methylmercaptoimmidazole and propylthiouracil, nor enhanced by interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). These data could not support the hypotheses that suppression of thyroid autoimmunity by thionamides is due to their modulatory action on hsp-72 expression, or that presence of that antigen in the thyroid tissues affected by autoimmunity is secondary to cytokine secretion from infiltrating immunocytes. On the other hand, coculture experiments of stressed FRTL5 cells and syngeneic Fisher rat splenocytes suggest that aberrantly expressed hsp may activate part of the thyroid-infiltrating lymphocytes and thereby aggravate autoimmune processes. The induction and detection systems of hsp-72 using FRTL5 cells would facilitate future studies, possibly utilizing human materials as well, to explore possible relations between stress proteins and thyroid autoimmunity.

The role of interferon-gamma in lymphocytic thyroiditis: its functional and pathological effect on human thyrocytes in culture

Interferon-gamma (IFN-gamma) has been recognized to possess diverse non-immunological effects on epithelial cells such as cellular growth and differentiation. We have previously demonstrated that IFN-gamma suppressed thyroid-stimulating hormone (TSH)-stimulated thyroglobulin (TG) synthesis in human thyrocytes through inhibition of TG gene transcription. To define the pathological mechanism involved in the action of IFN-gamma, we studied the ultrastructural changes of human thyrocytes cultured in monolayer. Stimulation of the thyrocytes with TSH 10 mU/ml for 2 days resulted in marked increase in TG release into the medium. This was accompanied by elongation of microvilli, increase in follicles and acinar formation, increase in secretory granules and prominence of Golgi apparatus and rough-surfaced endoplasmic reticulum. Addition of IFN-gamma (500 U/ml) resulted in marked degeneration with shrinkage of the cell membrane, vacuolation of cytoplasm, swollen mitochondria and presence of lysosomal granules. Co-culturing the thyrocytes with the IFN-gamma and TSH resulted in suppression of the morphological responsiveness to TSH. There was also suppression of TSH-induced TG secretion. However, at 500 U/ml IFN-gamma did not cause lysis of the thyrocytes as estimated by the cellular DNA content. Furthermore, binucleated cells were frequently encountered in those wells that were treated with IFN-gamma for either 2 or 5 days. The findings suggest that IFN-gamma resulted in de-differentiation and degeneration of the thyrocytes, which subsequently regained the growth potential and showed attempts at regeneration. This may explain why most patients with lymphocytic thyroiditis recover from the acute injury and do not suffer from permanent hypothyroidism.

Molecular basis for the autoreactivity against thyroid stimulating hormone receptor

The present report identifies an important immunogenic region of the TSH receptor and determinants on the TSH receptor for the two types of autoantibodies seen in hyperthyroid Graves' disease and hypothyroid idiopathic myxedema, TSAbs and TSBAbs, respectively. The immunogenic domain with no important functional determinants, is contained within residues 303-382 and involves residues 352-366 in particular. There are determinants flanking the immunogenic domain on the C-terminal portion of the receptor which are the TSBAb and high affinity TSH binding sites: residues 295-306, 387-395, and tyrosine 385. Determinants on the N-terminal portion of the external domain, centered on residues 38-45, are TSAb interactions linked to low affinity TSH binding important for signal generation: threonine 40 and residues 30-33, 34-37, 42-45, 52-56, and 58-61. These determinants are conserved in human and rat receptors, are not present in gonadotropin receptors, and are each related to separate actions of TSH: binding vs. signal generation. They can, therefore, account for organ specific autoimmunity and the different disease expression effected by TSBAbs vs TSAbs, i.e. hypo- vs. hyperthyroidism, respectively. It is proposed that, in the thyroid, hormonal (TSH, insulin, hydrocortisone, IGF-I) suppression of class I genes might be one means of preserving self-tolerance in the face of the hormone action to increase the expression of tissue specific genes such as thyroglobulin and thyroid peroxidase. Inappropriately high class I expression in the thyroid, i.e. if induced by interferon, viruses, or some as yet unknown agent, would contribute to the generation of autoimmune disease. Thus, it would result in increased antigen presentation to the immune system, particularly those autoantigens increased by TSH and its cAMP signal such as thyroglobulin or thyroid peroxidase, or whose turnover is increased by TSH and its cAMP signal, such as the TSH receptor. In the case of the latter, peptide 352-366, known to be near a protease sensitive site on the receptor [41,49], would now act as a potent self-antigen and induce the formation of receptor autoantibodies. It is further proposed that methimazole and high doses of iodide are therapeutically effective agents in thyroid autoimmune disease because they, in part, decrease MHC class I gene expression. Speculation is presented which suggests that elimination of negative regulation of MHC class I and the TSH receptor is an important factor in the development of autoimmune thyroid disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Recruitment of T lymphocytes and induction of tumor necrosis factor in thyroid cancer by a local immunotherapy

To elucidate the mechanism of action for intratumoral injection of immunopotentiators, infiltrating mononuclear cells and tumor necrosis factor (TNF) were assayed by immunostaining tissue samples of differentiated thyroid cancer resected with or without presurgical local application of OK-432, a streptococcal preparation. Frozen sections of resected specimens were stained with monoclonal antibodies using either a conventional or a modified immunoperoxidase method. The tumors injected with OK-432 showed increased T lymphocyte infiltration and HLA-DR expression on cancer cells as compared to the non-injected controls. Among these T cells, the CD4+ subset was more numerous than the CD8+ population. In four out of the seven cases constituting the injected group, numerous TNF-positive cells were seen in clusters or lines as well as scattered, while none of the seven cases in the control group was associated with a considerable amount of these cells. In their morphology and distribution pattern, these TNF-positive cells appeared to be of macrophage lineage. Thus local injection of OK-432 in thyroid cancer was shown to recruit T lymphocytes of predominantly the CD4+ subset and to induce in situ production of TNF, a known potent tumoricidal cytokine. The present data warrant further studies in this direction besides wider clinical intratumoral application of the reagent.

Cholecalciferol metabolites attenuate cAMP production in rat thyroid cells (FRTL-5)

A rat thyroid cell line (FRTL-5) was used to study the effect of cholecalciferols on cAMP production. The active cholecalciferol metabolite, calcitriol, caused a reduction in basal and thyrotropin (TSH)-stimulated cAMP production. The inhibitory effects were demonstrated after 1 and 2 days, respectively. The maximum effect on both basal and TSH-stimulated cAMP production was observed after 3-4 days of treatment. The effect was detectable at 10(-10) and maximal at 10(-8) mol/l. Calcitriol was about 300 times more potent than calcidiol in attenuating cAMP production, whereas (24R)-hydroxycalcidiol in concentrations up to 3 x 10(-8) mol/l had no effect. After removal of added calcitriol the cAMP response to TSH returned to normal within 8 days. Calcitriol (10(-8) mol/l) also inhibited cell growth. Our results show that calcitriol at physiological concentrations inhibits both basal and TSH-stimulated cAMP production in rat thyroid cells. This indicates that calcitriol may modulate the effect of TSH on thyroid function and growth.

The microsomal/peroxidase antigen: modulation of its expression in thyroid cells

Evidence has accumulated in the last few years that the expression of the microsomal/peroxidase antigen (M/TPO-Ag) in thyroid cells is induced by TSH, through pathways which involve intracellular cAMP accumulation and protein synthesis. These data have been found true in any thyroid system studied so far, both in terms of immunologic and enzymatic activity of TPO. TSH and cAMP also increase the levels of the specific mRNA for TPO in thyroid cells from different species. Whether this phenomenon is due to a direct transcriptional regulation of the TPO gene, as shown in dog thyroid cells, or to posttranscriptional effects, as it would appear in FRTL-5 cells, remains to be clarified by future experiments. Thyroid stimulating antibody (TSAb) of Graves' disease also stimulates the expression of M/TPO-Ag. This finding gives further support to the relevance of TSAb in the pathogenesis of hyperthyroidism and explains the well known observation that the "microsomal" antigen is particularly abundant in glands of Graves' patients. The modulation of M/TPO-Ag surface expression by TSH can explain the decrease of circulating anti-MAb observed during L-thyroxine therapy in hypothyroid patients with Hashimoto's thyroiditis. Other agents, such as methimazole and sodium iodide, which influence thyroid cell function, do not directly interfere with the expression of M/TPO-Ag. Cytokines, such as gamma-interferon, interleukin-1, and interleukin-6 have been shown to inhibit the TSH-induced increase of TPO mRNA, but further investigations are required to elucidate the exact role of cytokines in the regulation of M/TPO-Ag expression.

Effects of recombinant human interferon gamma on human thyroid tissues from patients with Graves' disease and normal subjects transplanted into nude mice

We have attempted to determine whether interferon gamma (IFN gamma) would enhance, sustain or induce autoimmune thyroid disease (AITD) in xenotransplanted thyroid tissue from patients with Graves' disease or normal persons (actually paranodular tissue) in nude athymic mice, in the absence of an intact immune system. A dosage of 4000 U/mouse of human IFN gamma (hIFN gamma) was injected intraperitoneally daily for six consecutive weeks into the xenotransplanted mice. The parameters measured included the free T4 index, thyroid autoantibodies and TSH during the course of hIFN gamma injections. Thyroid epithelial cell (TEC) HLA-DR expression was measured in the thyroid tissue before xenotransplantation and at sacrifice; in addition, light and electron microscopic studies were carried out at those times. There were no significant differences in thyroid function between the control results and those obtained with hIFN gamma in either group of tissues. TEC HLA-DR expression was significantly increased by hIFN gamma in the normal group, but insignificantly in the Graves' group. In both light and electron microscopic observations, Graves' tissue (whether or not treated with hIFN gamma) was indistinguishable at sacrifice from normal thyroid tissue. The appearance had markedly altered from the same Graves' tissue examined at the time of the initial human surgery, which then showed the usual histological appearance of this disorder. We conclude that IFN gamma induced HLA-DR expression alone is not sufficient to sustain the ongoing process of AITD in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of long-term, high-dose bovine thyrotropin administration on human thyroid tissues from patients with graves' disease and normal subjects xenografted into nude mice

We have attempted to determine whether the administration of thyrotropin would have any different functional or histological effects on Graves' tissue as opposed to human normal thyroid tissue in an in vivo situation (i.e., after xenograft into nude athymic mice). A dosage of 0.03 units per mouse of bovine thyroid-stimulating hormone (b-TSH) was injected intraperitoneally daily for 6 consecutive weeks into xenografted mice. The parameters measured included the free T₄ index and thyroid autoantibodies during the course of b-TSH injections. Tritiated (³H)-thymidine incorporation into thyroid epithelial cells (TECs) and TEC HLA-DR expression were measured in the thyroid tissue at the time of human surgery and at sacrifice; in addition, light-microscopical observations were made at those times. Although there was a decline in free T₄ index values during the course of the study, there was light-microscopical evidence suggestive of hyperplasia in both types of xenografted thyroid tissue. The TSH appeared to result in thyrocyte down-regulation, possibly of receptor or postreceptor origin. The administration of the b-TSH seemed to induce TEC HLA-DR expression in this study. Because these results differ from the effects of TSH on TEC in vitro with respect to TEC HLA-DR expression, it may be postulated that there are other factors liberated in vivo in the nude mice that interact with the TEC and TSH and initiate the TEC HLA-DR expression. We conclude that there are no significant differences between the responses of Graves' tissue and the normal human thyroid tissue in these studies.

Intrathyroidal lymphocytes from non toxic multinodular goiter: no evidence for production of thyroid stimulating antibodies

Although an autoimmune pathogenesis for non toxic goiter has been suggested, reports concerning circulating antibodies to TSH receptor structures have been conflicting. Intra thyroid lymphocytes, capable of secreting IgG, have been shown to be involved in the pathogenesis of Graves' and Hashimoto's diseases; therefore, the ability of conditioned media obtained from intra thyroid lymphocyte culture, and of IgG purified from these media, to stimulate cAMP accumulation and [3H]-Thymidine (TdR) uptake in FRTL-5 cells was investigated. The activity of IgG produced "in vitro" was compared with that of circulating IgG. Thyroid tissue samples were obtained at surgery from 21 patients with non toxic multinodular goiter (MNG), 5 patients with active Graves' disease (GD), and from 10 normal subjects, undergoing neck surgery for non-thyroidal pathology. IgG purified from media of GD lymphocyte cultures stimulated both cAMP accumulation and [3H]-TdR in 5 out of 5 cases: all of the IgG purified from control or MNG lymphocyte culture media was not active in either assay. Circulating IgG did not affect cAMP accumulation or [3H]-TdR in any of the non toxic MNG cases: controls showed no changed at all. However, both activities represented were increased by GD IgG. Conditioned media from intra thyroid lymphocyte cultures significantly inhibited basal cAMP accumulation in 7 out of the 21 non toxic MNG samples and totally abolished the response in all GD patients. [3H]-TdR was not affected by IgG of any of the controls, but it had an inhibitory effect on 8 out of 21 non toxic MNG patients, and significantly stimulated [3H]-TdR in all GD patients. In conclusion, present data demonstrate that intra thyroid lymphocytes from non toxic MNG do not produce antibodies capable of mimicking TSH actions through the adenylate cyclase cascade. Conversely, soluble factors interacting in TSH-mediated functions of FRTL-5 cells are present in conditioned media of intra thyroid lymphocytes of GD and MNG thyroid lymphocytes of GD and MNG thyroid cultures.