Thyroid Cell Damage Research Articles

Hypothyroidism Induced by a TSH Receptor Peptide-Implications for Thyroid Autoimmunity.

Background: The "neutral" thyrotropin receptor autoantibodies (N-TSHR-Ab) directed at the TSHR ectodomain's hinge region have been shown to induce thyroid cell damage in vitro. During these earlier studies, we developed a mouse monoclonal antibody (MC1) specific for a peptide (amino acid 322-340) in the region (MC1-Mab) which was able to induce thyroid cell stress and apoptosis when administered invivo. Methods: In order to examine the effect of invivo generated N-TSHR-Abs, rather than an acutely administered monoclonal antibody, we immunized Balb/c mice with the hinge region peptide over 18 weeks. Serum TSHR antibodies, specific TSHR hinge region antibodies, serum thyroglobulin (TG) and anti-TG as well as thyroxine and thyrotropin (TSH) levels were examined to evaluate the response to the immunization. Histological examination of the thyroid glands and flow cytometry of spleen T cells, B cells and macrophages were also performed to explore the underlying mechanisms. Results: We found that TSHR-peptide immunized mice developed N-TSHR-Abs against the peptide which resulted in thyroid damage shown by thyroid follicular destruction with follicular cell apoptosis, M1 macrophage infiltration, thyroglobulin release, and induction of thyroglobulin antibodies. This resulted in hypothyroidism with increased TSH levels. Conclusion: This study demonstrated that endogenous neutral antibodies to the TSHR could induce thyroid cell damage from apoptosis and M1 macrophage infiltration and resulted in hypothyroidism.

Simultaneous Thyroid Autoimmunity: A Coexistence of Grave's Disease and Hashimoto's Thyroiditis

Introduction: Grave’s Disease (GD) and Hashimoto's Thyroiditis (HT) are two autoimmune diseases whose coexistence is rare. We report a case of a patient in whom both diseases manifested simultaneously. Case report: A 36- year-old woman presented with thyrotoxicosis. She had tachycardia with WHO grade 2 homogeneously non-pulsatile goiter, without exophthalmos. The evaluation revealed peripheral hyperthyroidism with positive anti-thyroid peroxidase (anti-TPO) antibodies and anti-thyroid-stimulating hormone receptor (anti-TSHR) antibodies. Cervical ultrasound revealed a goiter affecting the right lobe in the context of thyroiditis. Thyroid scintigraphy indicated a picture suggestive of Graves' disease in the left lobe and hypocaptating thyroiditis in the right lobe. The patient was treated with propranolol and Carbimazole, with alternating phases of hyperthyroidism and hypothyroidism. Discussion and Conclusion: Autoimmune thyroid diseases, GD and HT, are specific to the thyroid gland and are common in women. They share pathogenic features that could explain their association, including genetic and environmental factors leading to thyroid cell damage, T-cell-mediated autoimmunity, human leukocyte antigen binding, and the presence of autoantibodies such as anti-thyroid peroxidase antibodies in GD. Rare cases have demonstrated that HT can manifest after GD, and vice versa, leading to an alternation of hyperthyroidism and hypothyroidism in certain patients due to changes in the balance between various categories of antibodies. In the present case, the patient simultaneously presented both diseases.

Молекулярні механізми патогенезу автоімунного тиреоїдиту Хашимото (огляд літератури)

The purpose of the study was to systematize and analyze material of recent studies on molecular mechanisms of pathogenesis of autoimmune Hashimoto's thyroiditis. Materials and methods. Analytical and bibliosemantic methods were used in the study. Results and discussion. Autoimmune Hashimoto's thyroiditis is a chronic inflammatory disease of the thyroid gland of autoimmune genesis in which impaired tolerance to thyroid autoantigens results in chronic progressive lymphoid infiltration followed by gradual destruction of thyroid parenchyma. The disease is more often observed at the age of 45-65 years and is multifactorial – both genetic predisposition and environmental factors contribute to its development. The ratio of female to male patients is approximately 10-20:1, and in recent years, the prevalence of autoimmune Hashimoto's thyroiditis has increased more than tenfold. On morphological examination, the section of the thyroid is diffusely enlarged, the surface of the section is pale, yellow-brown in color, dense and nodular. Microscopic examination reveals numerous large mononuclear inflammatory infiltrates in the parenchyma, consisting of small lymphocytes and plasma cells, well-formed germinal centers. A twin method is used to assess the degree of contribution of genetic and environmental factors. Studies demonstrate significantly greater concordance in monozygotic twins than in dizygotic twins, confirming the important role of genetic factors in the etiology. Among the main immune mechanisms of damage are: direct action of CD8+ cytotoxic T cells on thyrocytes by binding through the Fas-receptor – Fas ligand system; the influence of cytokines, in particular – interferon γ, produced by TH1 cells and leading to macrophage activation with subsequent damage to follicles, antibody-dependent cell-mediated cytotoxicity, in which Fc fragments of antibodies previously bound to thyroid cells are binding sites to cells that commit killing, in particular – to the natural killer cells. In terms of thyroid cell damage, cytokines produced by the lymphocytic infiltrate play a key role. These include differentiation, signal transduction, and stimulation of other cells to release proinflammatory mediators or synthesize antibodies. Their ability to stimulate the thyroid cells themselves to release inflammatory mediators should be noted, thereby enhancing and perpetuating the autoimmune process. Researchers have identified other mechanisms, and the ratio of their contribution to the overall pathological process is a matter of debate and may vary from patient to patient. One explanation may be the multifactorial nature of the disease. In particular, different genetic mutations can lead to different disorders of intracellular and intercellular signaling, but the resulting factor will be one – immune autoaggression. Conclusion. The pathogenesis of autoimmune Hashimoto's thyroiditis is complex and multifaceted, involving both humoral and cellular immunity. The disease may be provoked both by mutations in the mechanisms of immune regulation, by mutations in the thyroid cells themselves, and by environmental factors

A Stem Cell Surge During Thyroid Regeneration.

BackgroundMany tissues, including the thyroid, contain resident (adult) stem cells that are responsible for regeneration and repair after injury. The mechanisms of thyroid regeneration and the role of thyroid stem cells and thyroid progenitor cells in this process are not well understood. We have now used a new mouse thyroid injury model to gain insight into this phenomenon.MethodsTamoxifen induced TPO-Cre mice (TPOCreER2) were crossed with inducible Diphtheria Toxin Receptor homozygous mice (ROSA26iDTR) to give rise to TPOCreER2/iDTR mice, allowing for the Cre-mediated expression of the DTR and rendering TPO expressing thyroid cells highly sensitive to diphtheria toxin (DT). This model of TPOCreER2/iDTR mice allowed us to study the repair/regeneration of thyroid follicles after diphtheria toxin induced thyroid damage by measuring serum thyroid hormones and cell fate.ResultsIn TPOCreER2/iDTR double transgenic mice we observed severe thyroid damage as early as 2 weeks after initiating intraperitoneal DT injections. There was marked thyroid tissue apoptosis and a ~50% drop in serum T4 levels (from 5.86 to 2.43 ug/dl) and a corresponding increase in serum TSH (from 0.18 to 8.39 ng/dl). In addition, there was a ~50% decrease in transcription of thyroid specific genes (thyroglobulin, TSH receptor, and sodium-iodide symporter). After suspending the DT administration, the thyroid rapidly recovered over a 4-week period during which we observed a transient surge in stem cell marker expression (including Oct4, Nanog, Sox2, and Rex1). In addition, cells immunostaining with stem cell markers Oct4 and Ssea-1 were found in clusters around new thyroid follicles in TPOCreER2/iDTR double transgenic mice. Furthermore, the presence of clusters of thyroid progenitor cells was also identified by Pax8 staining of thyroglobulin negative cells. This recovery of the injured gland was followed by a rapid and sequential restoration of thyroid function.ConclusionThese data demonstrate that a new model of thyroid cell damage induced by DT can be used to study the mobilization of resident adult stem cells. Furthermore, the model clearly demonstrates the involvement of both stem and progenitor cells in the in vivo regeneration of the thyroid after severe destruction.

Elevated blood Hsp60, its structural similarities and cross-reactivity with thyroid molecules, and its presence on the plasma membrane of oncocytes point to the chaperonin as an immunopathogenic factor in Hashimoto's thyroiditis

The role Hsp60 might play in various inflammatory and autoimmune diseases is under investigation, but little information exists pertaining to Hashimoto's thyroiditis (HT). With the aim to fill this gap, in the present work, we directed our attention to Hsp60 participation in HT pathogenesis. We found Hsp60 levels increased in the blood of HT patients compared to controls. The chaperonin was immunolocalized in thyroid tissue specimens from patients with HT, both in thyrocytes and oncocytes (Hurthle cells) with higher levels compared to controls (goiter). In oncocytes, we found Hsp60 not only in the cytoplasm but also on the plasma membrane, as shown by double immunofluorescence performed on fine needle aspiration cytology. By bioinformatics, we found regions in the Hsp60 molecule with remarkable structural similarity with the thyroglobulin (TG) and thyroid peroxidase (TPO) molecules, which supports the notion that autoantibodies against TG and TPO are likely to recognize Hsp60 on the plasma membrane of oncocytes. This was also supported by data obtained by ELISA, showing that anti-TG and anti-TPO antibodies cross-react with human recombinant Hsp60. Antibody-antigen (Hsp60) reaction on the cell surface could very well mediate thyroid cell damage and destruction, perpetuating inflammation. Experiments with recombinant Hsp60 did not show stimulation of cytokine production by peripheral blood mononuclear cells from HT patients. All together, these results led us to hypothesize that Hsp60 may be an active player in HT pathogenesis via an antibody-mediated immune mechanism.

Autoimmune Thyroid Disorders

Thyroid autoimmunity, as reflected by the presence in serum of autoantibodies directed against the thyroid autoantigens thyroglobulin (Tg) and thyroid peroxidase (TPO), is present in >10% of the US population over 12 years of age [1] and is the most common cause of endocrine dysfunction in iodine-sufficient populations [2]. The underlying mechanism is a failure of T-cell tolerance leading to lymphocytic infiltration of the thyroid gland [3] and to a complex sequence of humoral and cellular immune responses to thyroid antigens, presumably in response to an environmental trigger [4]. In chronic lymphocytic thyroiditis (CLT), the predominant immunologic mechanisms are T-cell- and cytokine-mediated thyroid cell damage and apoptotic cell death whereas in Graves' disease (GD) generation of thyrotropin (TSH) receptor autoantibodies leads to thyroid cell stimulation [5], but significant overlap exists. Seven susceptibility genes, in addition to the major histocompatibility gene (HLA-DR3), have now been identified [6]. Some of these genes affect the immune response in general (CD40, CTLA-4, and PTPN22), while others are thyroid specific (thyroglobulin, thyrotropin (TSH) receptor). Some are common to both CLT and GD, while others are specific for GD. In view of the importance of AITD as well as the diverse array of new information, it is only fitting that this special issue of the Journal of Thyroid Research is devoted entirely to this complex subject. Four of the papers we have selected are focused on clinical topics, including AITD in childhood, during pregnancy, in the postpartum period, and in patients with type 1 diabetes mellitus. The fifth paper addresses the potential role of NKT cells in an animal model of thyroiditis. We conclude this special edition with a discussion of thyroid autoimmunity in patients with papillary thyroid cancer (PTC). The association of AI and thyroid cancer was first reported by Dailey et al. [7]. In general, patients with AI appear more likely to have PTC than follicular thyroid cancer (FTC), but a lower frequency of extrathyroidal extension, nodal and distant metastases when compared with patients without AI. In some but not all series, patients with autoimmune thyroiditis (AT) and PTC have improved survival when compared to those with PTC alone, suggesting that thyroid autoimmunity might contribute to improved survival [8–10]. In contrast, other data suggest that AI might actually increase the risk to develop thyroid cancer [10–12]. Several theories have been proposed to explain how AI might increase the risk for thyroid malignancy. Thyrocyte apoptosis and proliferation are increased in AI suggesting that thyrocytes rapidly progressing through the cell cycle might accumulate increased DNA damage resulting in malignant transformation [13]. Russell et al. hypothesized that thyroid cells predestined to become cancers might secrete proinflammatory cytokines that affect immune cells [14]. They showed that thyrocytes of ret/PTC3 transgenic mice express increased levels of interleukins, tumor necrosis factor-α, and cyclooxygenase-2 [14] that could attract and/or activate cells of the immune system. Finally, the ret/PTC recombinant genes have been detected in samples of AI [15–17] suggesting that ret/PTC rearrangements might be present in AI and could be precursors to PTC. From these papers, it is clear that thyroid autoimmunity is a frequent problem in the population and that thyroid autoimmunity can lead to a variety of thyroid disorders including alterations in thyroid hormone synthesis and possibly even neoplasia. Focused research in this area is beginning to illuminate some of the molecular mechanisms that help to explain these associations. Rosalind Brown Gary L. Francis

Association of Duoxes with Thyroid Peroxidase and Its Regulation in Thyrocytes

Thyroid hormone synthesis requires H(2)O(2) produced by dual oxidases (Duoxes) and thyroperoxidase (TPO). Defects in this system lead to congenital hypothyroidism. H(2)O(2) damage to the thyrocytes may be a cause of cancer. The objective of the study was to investigate whether Duox and TPO, the H(2)O(2) producer and consumer, might constitute a complex in the plasma membrane of human thyroid cells, thus maximizing efficiency and minimizing leakage and damage. The interaction between Duox and TPO was studied by coimmunoprecipitation and Western blotting of plasma membranes from incubated follicles prepared from freshly resected human thyroid tissue from patients undergoing thyroidectomy, and COS-7 cells transiently transfected with the entire Duoxes or truncated [amino (NH2) or carboxyl (COOH) terminal]. The following results were reached: 1) Duox and TPO from membranes are coprecipitated, 2) this association is up-regulated through the Gq-phospholipase C-Ca(2+)-protein kinase C pathway and down-regulated through the Gs-cAMP-protein kinase A pathway, 3) H(2)O(2) increases the association of Duox1 and Duox2 to TPO in cells and in membranes, and 4) truncated NH(2)- or COOH-terminal Duox1 and Duox2 proteins show different binding abilities with TPO. Coimmunoprecipitations show that Duox and TPO locate closely in the plasma membranes of human thyrocytes, and this association can be modulated by H(2)O(2), optimizing working efficiency and minimizing H(2)O(2) spillage. This association could represent one part of a postulated pluriprotein complex involved in iodination. This suggests that defects in this association could impair thyroid hormone synthesis and lead to thyroid insufficiency and cell damage.

Relation of anti‐TPO autoantibody titre and T‐lymphocyte cytokine production patterns in Hashimoto's thyroiditis

Cytokines produced by cytotoxic T cells or autoantibodies lead to thyroid cell damage and/or cell death in Hashimoto's thyroiditis (HT). Anti-TPO autoantibodies (TPOAb) are the most frequently represented autoantibodies in the sera of patients with HT. Data describing the quantitative correlation between TPOAb titre and cytokine pattern are missing so far. To our knowledge this is the first study systematically evaluating the correlation of possible parameters of disease activity such as changes in CD4 and CD8 T-cell cytokine production and of TPOAb titre. Twenty-four consecutive patients (aged 29-58) with verified HT under levothyroxine therapy were included in the present study. The patients were divided into two groups. Group I: 12 HT patients with a high TPOAb titre (> 1000 U/ml), group II: 12 HT patients with a low TPOAb titre (< 100 U/ml). All patients underwent intracellular cytokine detection in CD4 and CD8 T cells of peripheral blood mononuclear cells (PBMC) by flow cytometry. Twelve healthy volunteers matched in sex and age consisted the control group (group III). T cells from patients with a high TPOAb titre (group I) had significantly higher percentages of cells producing IFN-gamma compared to healthy donors (group III). A detailed analysis of cytokine production patterns revealed that this was accompanied by an increased frequency of single IFN-gamma positive cells, i.e. cells not expressing other cytokines tested, such as IL-2, IL-4, IL-5, IL-6, IL-10, IL-13 or TNF-beta. Similarly, patients in group I also showed higher percentages of TNF-alpha positive cells than healthy donors (group III). In this case, cells expressing TNF-alpha alone as well as cells coexpressing TNF-alpha and IFN-gamma were found at significantly higher frequencies. On the other hand, cytokine production patterns of patients with a low TPOAb titre (group II) showed significant difference neither to patients of group I nor to healthy donors (group III). Taken together, we were able for the first time to demonstrate that high TPOAb titre correlates with increased frequencies of T cells producing Th/Tc1 cytokines, probably responsible for thyroid cell damage and/or death in Hashimoto's thyroiditis.

Recombinant thyroid peroxidase-specific Fab converted to immunoglobulin G (IgG) molecules: evidence for thyroid cell damage by IgG1, but not IgG4, autoantibodies.

A recombinant autoantibody Fab (SP1.4) to thyroid peroxidase (TPO), cloned from intrathyroidal B cell immunoglobulin genes, interacts with an epitope on TPO recognized by all patients with autoimmune thyroid disease. To compare the biological properties of IgG1 and IgG4 TPO autoantibodies, we converted Fab SP1.4 to full-length immunoglobulins. The SP1.4 heavy and kappa light chain variable region genes, spliced by overlap PCR to a mammalian signal peptide, were transferred to expression vectors for human IgG1, IgG4, and kappa L chains. Plasmids containing the IgG1 (or IgG4) heavy chain and the kappa L chain were cotransfected into SP2/0 mouse myeloma cells. Cells secreting TPO autoantibodies were cloned, and IgG1-SP and IgG4-SP were affinity purified from medium using protein G. Their subclass specificities were confirmed by enzyme-linked immunosorbent assay and fluorometry after binding to Chinese hamster ovary cells expressing cell surface TPO. Further confirmation of SP1.4 Fab conversion to full-length molecules was the ability of protein A to precipitate IgG1-SP and IgG4-SP complexed to [125I]TPO. IgG1-SP1.4, IgG4-SP1.4, and Fab SP1.4 had similar high affinities for TPO (Kd = approximately 2 x 10(-10) mol/L). Complexes of [125I]TPO and IgG1-SP (but not IgG4-SP) bound to peripheral blood mononuclear cells (PBMC), but not to a B cell line. Flow cytometry demonstrated Fc receptors Fc gamma RI, Fc gamma RII, and Fc gamma RIII on PBMC, but only Fc gamma RII on the B cell line. Together, these data indicate that IgG1-SP/TPO complexes bind to either Fc gamma RI on monocytes or RIII on natural killer cells. In assays for antibody-dependent cytotoxicity using PBMC, 51Cr release was higher for thyroid cells preincubated with IgG1-SP (13.4%) than with IgG4-SP (2.5%) or with culture medium alone (-0.7%). No specific 51Cr release was observed when either fibroblasts or Chinese hamster ovary cells expressing cell surface TPO were used as target cells. In conclusion, a human TPO-specific Fab converted to IgG1, but not IgG-4, can mediate cytotoxic effects on human thyroid cells in vitro. These observations support the clinical relevance of TPO autoantibody subclass distribution and emphasize the likelihood that, as opposed to being simple markers of thyroid damage, TPO autoantibodies may play a role in the induction of thyroid dysfunction in vivo.

Recombinant Thyroid Peroxidase-Specific Fab Converted to Immunoglobulin G (IgG) Molecules: Evidence for Thyroid Cell Damage by IgG1, but Not IgG4, Autoantibodies

Recombinant Thyroid Peroxidase-Specific Fab Converted to Immunoglobulin G (IgG) Molecules: Evidence for Thyroid Cell Damage by IgG1, but Not IgG4, Autoantibodies

Thyroid epithelial cells produce large amounts of the Alzheimer beta-amyloid precursor protein (APP) and generate potentially amyloidogenic APP fragments.

The Alzheimer beta-amyloid precursor protein (APP) is a transmembrane glycoprotein from which the amyloid beta-protein is proteolytically derived. The latter is a hydrophobic peptide that can aggregate and forms the core of the senile plaques found in the brains of patients suffering from Alzheimer's disease (AD). In view of the known association between familial AD and thyroid autoimmune disease, the expression pattern and cellular processing of APP in human thyroid cells were investigated. Cultured thyroid epithelial cells and homogenized thyroid tissue from normal and pathological thyroid samples were analyzed by immunoblotting using specific N- and C-terminal APP antibodies as well as by reverse transcription-polymerase chain reaction in which two sets of oligonucleotide primers were used. The results of these studies demonstrated that APP isoforms 770 and 751 were expressed in fresh thyroid extracts as well as in cultured thyroid epithelial cells, with APP 770 being the predominant form. Compared to other types of cells, such as lymphocytes and fibroblasts, thyroid epithelial cells produced larger amounts of APP. Most of the mature protein was cleaved within the amyloid beta region, as a result of which a large N-terminal APP fragment was released into the culture medium, whereas a C-terminal nonamyloidogenic fragment of 14 kilodaltons (kDa) was retained within the cell. Interestingly, thyroid epithelial cells also contained larger C-terminal APP fragments of 21, 35, and 41 kDa. From the sizes of these fragments it could be deduced that they contained the entire amyloid beta sequence and were thus potentially amyloidogenic. The 41-kDa fragment was unique to thyroid cells. These fragments may be released into the circulation after thyroid cell damage. Increased/altered thyroid APP expression in familiar AD may induce alterations in thyroid epithelial cells and cell damage, and thus explain the frequent occurrence of thyroid autoimmunity in this disease.

Serum interleukin-6 in amiodarone-induced thyrotoxicosis.

Amiodarone, an iodine-rich cardiac drug, may induce thyrotoxicosis (AIT), which can occur in patients with preexisting thyroid abnormalities and in subjects with apparently normal thyroid glands. The pathogenesis of AIT is often due to iodine-induced excessive thyroid hormone synthesis, especially in patients with underlying thyroid disease. In some instances, however, AIT may be related to a destructive process due to amiodarone-induced thyroiditis, resulting in thyroid cell damage and thyroid hormone release into the circulation. Another thyroid inflammatory process, subacute thyroiditis, has been recently reported to be associated with markedly increased serum interleukin-6 (IL-6) levels. To investigate the significance of serum IL-6 levels in AIT, we evaluated in a cross-sectional study the following subjects: 27 AIT patients, 15 with no apparent thyroid abnormalities (AIT-) and 12 with nodular goiter and/or thyroid autoimmune disease (AIT+); 14 euthyroid patients receiving chronic amiodarone therapy; 10 patients with amiodarone-induced hypothyroidism; 56 patients with spontaneous hyperthyroidism due to Graves' disease (n = 35) or toxic adenoma/nodular goiter (n = 21); 20 subjects with nontoxic goiter; and 50 healthy controls. Serum free thyroid hormone concentrations did not differ in patients with amiodarone-induced or spontaneous hyperthyroidism. Mean (+/- SE) serum IL-6 values were as follows: AIT-, 573.5 +/- 78.7 fmol/L (range, 149.4-1145.1); AIT+, 152.7 +/- 46.3 fmol/L (range, < 25-505.6); euthyroid patients receiving chronic amiodarone therapy, 51.4 +/- 10.0 fmol/L (range, < 25-122.5); amiodarone-induced hypothyroidism, 43.8 +/- 8.4 fmol/L (range, < 25-84.3); Graves' disease, 108.2 +/- 18.2 fmol/L (range, < 25-250); toxic adenoma/nodular goiter, 97.6 +/- 10.3 fmol/L (range, < 25-168.9); nontoxic goiter, 47.3 +/- 7.1 fmol/L (range, < 25-106.6); and controls, 37.8 +/- 6.2 fmol/L (range, < 25-99.4). Serum IL-6 values in AIT- patients were markedly higher (P < 0.0001) than those in all other groups. Values in AIT+, although slightly higher, did not significantly differ from those in patients with spontaneous hyperthyroidism. AIT- patients had low 24-h thyroidal radioiodine uptake (RAIU), whereas AIT+ had inappropriately low normal to high (9-58%) RAIU values in the presence of excess iodine. The presence of markedly elevated serum IL-6 concentrations and low thyroidal RAIU values in patients with AIT without underlying thyroid disease suggests the presence of amiodarone-induced thyroiditis as the etiology of thyrotoxicosis. Treatment of 2 such patients with prednisone was associated with a dramatic reduction and prompt normalization of IL-6 and thyroid hormone values.(ABSTRACT TRUNCATED AT 400 WORDS)

High Incidence of Thyroiditis and Anti-Thyroid Autoantibodies in NOD Mice

NOD mice develop spontaneous insulin-dependent diabetes mellitus (IDDM) associated with infiltration of pancreatic islets with mononuclear cells. Islet infiltration results in autoimmune destruction of insulin-secreting beta-cells. Because in humans and BB rats diabetes is often associated with autoimmune thyroid disease (ATD), the NOD mouse model was examined for evidence of thyroiditis and serum antibodies reactive with mouse thyroid membrane antigens (MTMAs). The incidence of thyroiditis was 77% in mice greater than 180 days old, 67% in mice 61-180 days old, 72% in mice 31-60 days old, 74% in mice 21-30 days old, 78% in mice 11-20 days old, and 90% in mice less than or equal to 10 days old. NOD mice less than or equal to 30 days old had less-severe thyroiditis than animals greater than 180 days old. There was no significant different in severity of thyroiditis between any of the other age-groups tested. The incidence of thyroiditis was not increased in diabetic compared with nondiabetic animals, nor was an association found between thyroiditis and sex. The high incidence of thyroiditis in the less than or equal to 30-day-old age-group indicates that infiltration of lymphocytes into the thyroid can precede initiation of insulitis in this model. Although both thyroiditis and insulitis in NOD mice began early (by the 1st and 2nd mo of life, respectively), no significant association between infiltration of these two organs was noted in individual mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathology of the thyroid in amiodarone-associated thyrotoxicosis.

Among 83 consecutive patients operated on for thyrotoxicosis at the Mayo Clinic between January 1, 1980 and May 1, 1986, four had a combination of pathologic findings that were similar and unexpected: involutional changes; degenerative and destructive follicular lesions; and zones of fibrosis. These four, but none of the remaining 79, were being treated with amiodarone for cardiac tachyarrhythmias; this drug is known to be taken up by the thyroid gland. Characteristically, small groups of involuted follicles exhibited varying degrees of damage ranging from degenerative changes in a few lining cells to total follicular destruction. Damaged follicular cells were swollen and featured granular or vacuolated cytoplasm. This type of cytoplasmic alteration has been reported to occur in pneumocytes and hepatocytes damaged by amiodarone. Therefore, the drug probably is the cause of the thyroid cell damage, and follicular disruption (with consequent release of iodothyronines into the circulation) is likely to be an important contributor to the associated thyrotoxicosis.

Cell-mediated immunity and immune complexes in thyroid disease

As shown diagrammatically in Figure 12, one might postulate that in vivo several immune mechanisms may play separate or associated roles in the pathogenesis of autoimmune thyroid disease. Although relatively little is known concerning the triggering of an autoimmune response, for the sake of simplicity one might say that the initiating reaction is some sort of breakdown in the control mechanism resulting in the proliferation of autoreactive T and B lymphocytes, i.e., a breakdown in immunological tolerance to self. Specifically sensitised B lymphocytes are involved in the production of antibody. The role of thyroid specific autoantibodies has not been firmly established and much evidence argues against their being primarily responsible for the thyroid lesions with the exception of thyrotoxicosis. Transfusion of large quantities of Hashimoto serum to Rhesus monkeys produces no thyroid alteration (Roitt and Doniach, 1960), and although thyroglobulin antibodies in high titre can cross the placenta, thyroiditis is rarely observed in babies of affected mothers (Parker and Beierwaters, 1961). Complement fixing thyroid microsomal antibody has proved to be cytotoxic to trypsinised thyroid cells in culture suggesting that slight surface injury to these cells may allow access of cytotoxic antibody resulting in cell death (Pulvertaft, Doniach and Roitt, 1961; Irvine, 1962). In vivo cytotoxic antibodies may play a secondary role in the potentiation of the disease following an initial damage to the gland (Roitt, Jones and Doniach, 1962). Morphological and immunological observations suggest that cell-mediated immune mechanisms may be involved in the pathogenesis of autoimmune thyroid disease. In vitro tests for CMI such as the migration inhibition test and lymphocyte transformation test suggest that patients with autoimmune thyroid disease possess circulating lymphocytes capable of recognising and responding to thyroid antigens. In vivo, such sensitised lymphocytes could cause thyroid cell damage either through a direct cytolytic action or via the release of lymphokines. A third mechanism which could be of pathogenic significance in vivo is that involving K cells and antibody. The presence of thyroid specific antigen-antibody complexes on the surface of a thyroid epithelial cell renders it highly susceptible to lysis by K cells. Whether in fact such complexes are freely available on the surface can only be speculative, although there is one report in the literature describing distinct electron-dense deposits in the follicular basement membrane of some follicles in Hashimoto thyroid glands resembling the antigen-antibody deposits of immune complex nephropathies. Similarly, the presence of antigen-antibody complexes in antibody excess in the circulation could result in the recruitment of large numbers of K cells with the specificity to destroy antigen-labelled target cells in the thyroid gland. The extent to which K-cell-mediated cytotoxic mechanisms as opposed to T-cell-mediated phenomena are involved in the production of thyroiditis is again speculative although it is of interest that the level of circulating K cells in Hashimoto patients is elevated, whereas the number of T cells appears to be within the normal range. Studies on the cytotoxic activity of lymphoid cells isolated from an infiltrated Hashimoto gland would be of considerable interest. Recently, Evans and Alexander (1972) have described mechanisms of immunologically specific killing of tumour cells by macrophages. Specific killing of tumour cells can be achieved by (i) macrophages from the peritoneal cavity of tumour-immunised mice, (ii) normal macrophages ‘armed’ in vitro by exposure to spleen cells from tumour-immunised mice and by (iii) normal macrophages ‘armed’ in vitro by exposure to the cell-free supernatant obtained when spleen cells from immunised mice are cultured with specific antigen. The role of macrophages in autoallergic thyroid cell damage has not so far been investigated but studies in this area are well merited. In view of the complexity of the immune system, it would seem unlikely that any one immune mechanism is solely responsible for the production of autoimmune lesions. It is more likely that several mechanisms play associated roles in the pathogenesis, the severity of the disease possibly being dependent on the extent to which one of these mechanisms predominates and this in turn may be related to the underlying triggering reaction. Although it is obviously essential in the first instance to characterise the basic mechanisms involved in the production of autoallergic tissue damage, a clear insight into the pathogenesis of thyroiditis cannot really be achieved until there is a better understanding of the nature of the autoimmune response.