Expression of intercellular adhesion molecule-1 (ICAM-1) on thyroid epithelial cells in Hashimoto's thyroiditis but not in Graves' disease or papillary thyroid cancer.

In order to study the possible role of antigen-independent adhesion systems in thyroid autoimmunity, we evaluated by indirect immunofluorescence the expression of lymphocyte functional antigen-1 (LFA-1) and its ligand ICAM-1 on mononuclear cell infiltrates (when present) and thyroid follicular cells of four patients with Hashimoto's thyroiditis, 30 with Graves' disease, five with papillary cancer, two with follicular adenoma, and two normal thyroid specimens. The expression of MHC class I and class II antigens was also evaluated. Most mononuclear infiltrates were LFA-1 positive, as expected. A positivity for ICAM-1 on follicular cells was observed in three out of four Hashimoto's thyroiditis specimens; such a phenomenon was totally absent in Graves' disease or any other pathological condition, or in normal tissue. MHC class II expression on thyrocytes was observed in all the patients with Hashimoto's thyroiditis, in 27 out of 30 with Graves' disease and in three out of five papillary cancer specimens.     

Fas-FasL in Hashimoto's Thyroiditis

Hashimoto's thyroiditis is a common chronic autoimmune disease characterized by the loss of thyroid follicular cells (thyrocytes) that are gradually replaced by lymphocytic infiltration and diffuse fibrosis. These morphological findings suggested that autoreactive T-cell clones were responsible for thyrocyte destruction and hypothyroidism through effector–target cytotoxic recognition. Later, autonomous interaction between thyrocyte Fas and FasL has been proposed as a major mechanism of thyrocyte depletion in Hashimoto's thyroiditis. Here, we analyze the possible role of Fas and FasL in the pathogenesis of Hashimoto's thyroiditis. We suggest that the Fas–FasL system dictates the outcome of the autoimmune response by acting on both immune and target cells.     

Fas ligand gene polymorphisms are not associated with Hashimoto's thyroiditis and Graves' disease

Hashimoto's thyroiditis and Graves' disease represent the two most common autoimmune thyroid disorders. Whereas in Hashimoto's thyroiditis FasL expression causes thyrocytes to undergo apoptosis, additional anti-apoptotic molecules appear to protect these cells in Graves' disease. Mutations of the FasL gene were observed in systemic lupus erythematosus. Given its functional relevance for the pathogenesis of thyroid autoimmunity we wondered whether variants of the FasL gene play a role in Hashimoto's thyroiditis and Graves' disease. We genotyped families with at least one offspring affected by Hashimoto's thyroiditis (n = 86) and Graves' disease (n = 90) for two FasL gene polymorphisms (C -843 T in the promoter, A IVS2nt-124 G in intron 2). Extended transmission disequilibrium (ETDT) and chi(2) testing were performed. Neither polymorphism alone nor the promoter/intron 2 haplotypes (p = 0.91) were associated with Hashimoto's thyroiditis. No association with Graves' disease was observed for the promoter polymorphism (p = 0.91) and the intron 2 "A" allele (57.1%; p = 0.36) or the promoter/intron 2 haplotypes (p = 0.31). Moreover, intron 2 genotyping revealed no difference between an additional 251 patients with Graves' disease and 197 healthy controls (p = 0.37). Italian and German families did not differ for the studied polymorphisms. In conclusion, our data do not suggest common genetic FasL variants to significantly contribute to the pathogenesis of either Hashimoto's thyroiditis or Graves' disease.     

Expression and function of multiple regulators of complement activation in autoimmune thyroid disease.

Membrane attack complexes of complement occur around thyroid follicles in Graves' disease and Hashimoto's thyroiditis. The lytic potential of such complexes is controlled by membrane-bound and fluid phase regulators and we have investigated the role of these in autoimmune thyroid disease. By immunohistochemical staining, clusterin and S-protein were found in all nine thyroid specimens from patients with Graves' disease and S-protein was found in one of two Hashimoto glands. CD46, CD55 and CD59 were found on thyroid cells in all specimens. CD46 and CD55 expression occurred on thyroid cells cultured in vitro and was increased significantly by culture with interleukin-1 (IL-1) and interferon-gamma (IFN-gamma), which are known to be released by the lymphocytic infiltrate in these conditions. Blocking CD55 had a weak and inconsistent effect on complement-mediated thyroid cell killing in vitro but, in four of five experiments, blocking CD46 enhanced killing. However, the effect of blocking CD59 was greater in all cases than blocking CD46 or CD55. Expression of these fluid phase and membrane-bound proteins may be important in determining the severity of thyroid damage produced by complement fixation in Graves' disease and Hashimoto's thyroiditis.     

Autoantibodies highly increased in patients with thyroid dysfunction

To evaluate the significance of antithyroid antibodie levels, five hundred and twenty-six patients with thyroid diseases and 292 health subjects from Yuci district, Shanxi province, China, were studied. Serum levels were determined for thyroid hormone receptor antibody （TRAb）, microsomal antibody （TMAb） and thyroglobulin antibody （TGAb）. Among patients, the percentages for nodular goiter and thyroid adenoma, Graves＇ disease, and Hashimoto＇s thyroiditis are 44.1%, 19.6% and 17.7%, respectively. The ratios of female to male were 2.0 to 15.6. Antibody-positive patients for TMAb, TGAb and TRAb were detectable as 94.6%, 76.3% and 20.4% for Hashimoto＇s thyroiditis, and 40.0%, 30.0% and 90.3% for Graves＇s disease. In conclusion, the high levels of the TRAb in Graves＇ disease, and those of the TGAbFFMAb in Hashimoto＇s thyroiditis and idiopathic hypothyroidism are meaningful for characterizing the epidemiological basis of the diseases and for using as prognostic indicators for the relapse in individual patients. Cellular ＆ Molecular Immunology.     

Ultrastructural localization of thyroid peroxidase, hydrogen peroxide-generating sites, and monoamine oxidase in benign and malignant thyroid diseases

Despite thyroid tissue heterogeneity, biochemical and morphological features have been associated with certain thyroid diseases. We analyzed the ultracytochemical localization of thyroperoxidase (TPO), TPO-associated hydrogen peroxide-generating sites (H(2)O(2) sites), and monoamine oxidase (MAO) in terms of morphology and biochemical TPO activity in abnormal thyroids. We examined 11 cases of nontoxic multinodular goiter, 5 cases of Hashimoto's thyroiditis, 1 case of oncocytic (Hürthle or oxyphilic cell) adenoma, 5 cases of Graves' disease, 4 cases of papillary carcinoma, and 4 cases of perinodular normal tissue. In the perinodular tissue, TPO was detected mainly in the nuclear envelope, rough endoplasmic reticulum (RER), and subapical vesicles, but not in the apical surface. In multinodular goiter, heterogeneous TPO reactivity ranging from almost null to strongly positive was detected in similar locations as in the perinodular tissue, and was absent in the microvilli. Follicular cells from Hashimoto's thyroiditis displayed TPO in the nuclear envelope and the scarce RER. Remarkably, oncocytic cells from both Hashimoto's thyroiditis and oncocytic adenoma, typically packed with mitochondria, displayed evident TPO reaction exclusively in mitochondrial cristae. In Graves' disease, the nuclear envelope, enlarged RER, and apical vesicles were strongly TPO positive, and microvilli also exhibited TPO activity. Papillary carcinoma cells were negative for TPO. The localization and characteristics of TPO activity in the H(2)O(2) sites were similar to that of TPO in all tissues. MAO was positive in mitochondria of perinodular tissues, multinodular goiter, and oncocytes and negative in Hashimoto's thyroiditis and Graves' disease. Interestingly, MAO was intensely positive in the nuclear envelope of papillary carcinoma but unreactive in mitochondria. Biochemical TPO activity was increased in multinodular goiter and Graves' disease. In conclusion, several changes in ultracytochemical characteristics of TPO, H(2)O(2) sites, and MAO were associated with thyroid disease. Nonmalignant oncocytic cells exhibited an unusual mitochondrial location of TPO and H(2)O(2) sites. The distribution of MAO in nuclear envelope of papillary carcinoma cells could be a further feature of malignancy.     

Control of target cell survival in thyroid autoimmunity by T helper cytokines via regulation of apoptotic proteins

After autoimmune inflammation, interactions between CD95 and its ligand (CD95L) mediate thyrocyte destruction in Hashimoto's thyroiditis (HT). Conversely, thyroid autoimmune processes that lead to Graves' disease (GD) result in autoantibody-mediated thyrotropin receptor stimulation without thyrocyte depletion. We found that GD thyrocytes expressed CD95 and CD95L in a similar manner to HT thyrocytes, but did not undergo CD95-induced apoptosis either in vivo or in vitro. This pattern was due to the differential production of TH1 and TH2 cytokines. Interferon gamma promoted caspase up-regulation and CD95-induced apoptosis in HT thyrocytes, whereas interleukin 4 and interleukin 10 protected GD thyrocytes by potent up-regulation of cFLIP and Bcl-xL, which prevented CD95-induced apoptosis in sensitized thyrocytes. Thus, modulation of apoptosis-related proteins by TH1 and TH2 cytokines controls thyrocyte survival in thyroid autoimmunity.     

Terminal complement complexes and C1/C1 inhibitor complexes in autoimmune thyroid disease.

The potential role of complement activation and the membrane attack complex in the pathogenesis of Graves' disease and Hashimoto's thyroiditis has been investigated by measuring serum concentrations of the C1r-C1s-C1 inhibitor complex (C1/C1-inh) and the terminal complement complex (TCC), and by studying the binding to thyroid tissue of monoclonal and polyclonal antibodies against TCC neoantigens. Serum C1/C1-inh and TCC concentrations were significantly increased in 29 patients with untreated Graves' disease compared with 47 healthy subjects (P less than 0.001 for both), and decreased significantly after carbimazole treatment in 18 of these patients for whom post-treatment samples were available (P less than 0.01 and P less than 0.02, respectively). The serum TCC concentration, but not that of C1/C1-inh, was also significantly increased in 15 patients with Hashimoto's thyroiditis compared with the 47 healthy subjects (P less than 0.001). TCCs were identified by immunohistochemical staining around the thyroid follicles in thyroidectomy specimens from patients with Graves' disease (six out of six) and Hashimoto's thyroiditis (two out of two); normal thyroid tissue from two subjects showed no staining. These results suggest a role for complement, in particular the membrane attack complex in the pathogenesis of autoimmune thyroid disease.     

Detection of interleukin-6 and interleukin-1 production in human thyroid epithelial cells by non-radioactive in situ hybridization and immunohistochemical methods.

Human endocrine thyroid epithelial cells have been described to produce cytokines in vitro. In order to determine whether they do so in vivo during thyroiditis, parallel studies on mRNA expression with a non-radioactive in situ hybridization technique and immunohistochemical detection for the protein were performed on frozen sections of thyroid samples from autoimmune thyroiditis (Graves' disease and Hashimoto's thyroiditis), non-toxic goitre and normal thyroid tissue. cDNA probes were sulphonated and their hybridization with mRNA was detected with a sulphonyl-specific monoclonal antibody. This signal was amplified and visualized with the alkaline phosphatase-anti-alkaline phosphatase (APAAP) system. The protein products were detected with immuno-purified rabbit F(ab')2 antibody fragments recognizing recombinant human cytokines, visualized by the immunoperoxidase technique. Each sample was studied at the two levels. Both interleukin-6 mRNA and protein were found in the endocrine cells. There was no obvious difference between autoimmune thyroiditis and non-toxic goitre. However, normal thyroid epithelial cells produced less interleukin-6. Interleukin-1 alpha mRNA and its protein were found in epithelial cells from Hashimoto's thyroiditis samples, but not in the others, except one Graves' disease sample, in which only mRNA was detected. Interleukin-1 beta was not detected in these cells, its mRNA was only found in one of the Graves' disease samples. These cytokines were also detected in some infiltrating cells.     

Intrathyroidal HLA-DR expression and T lymphocyte phenotypes in Graves'' thyrotoxicosis, Hashimoto''s thyroiditis and nodular colloid goitre.

Thyroid surgical biopsies from 21 individuals were examined by a double immunoenzymatic technique with respect to HLA-DR expression and lymphocytic infiltration. HLA-DR positive thyrocytes were observed in two examined Hashimoto goitres and in nine of 11 specimens from patients with Graves' disease. HLA-DR positive thyrocytes were localized to areas harbouring infiltrating lymphocytes, whereas regions with no lymphocytes only rarely expressed HLA-DR antigens. In two specimens of nodular goitre HLA-DR positive thyrocytes were observed in the vicinity of lymphocytic infiltration. Tissues from another three nodular goitres, from one follicular adenoma and from two normal individuals contained no HLA-DR positive thyrocytes and no or only a few lymphocytes. The lymphocytic infiltrates were dominated by cells with the Leu 3a helper/inducer phenotype irrespective of underlying disease, although most pronounced in Hashimoto's thyroiditis. The results indicate that HLA-DR antigens is expressed on thyrocytes in thyroid disorder. The extent of expression correlated with lymphocytic infiltration, which suggests that the two findings are related and of importance for the development of thyroid autoimmunity.     

Comparative study of angiogenesis in thyroid glands with Graves disease and Hashimoto's thyroiditis.

Angiogenesis entails the sprouting of new vessels from pre-existing vasculature. In adults, angiogenesis occurs in the thyroid gland during disease processes such as hyperplastic goiter, Graves disease, thyroiditis, and cancer. In the present study multiple morphologic characteristics of microvessels were measured in and compared between 18 cases of Graves disease, 29 cases of Hashimoto's thyroiditis, and 15 control cases. All histologic sections were immunostained for CD31. Quantification of microvessel density (MVD), major axis length, minor axis length, area, perimeter and shape factor was performed by image analysis. MVD was increased significantly in both forms of autoimmune thyroid disease. Significantly higher values were found in Graves disease in comparison to Hashimoto's thyroiditis. In contrast, major axis length, minor axis length, and area had significantly higher values in Hashimoto's thyroiditis than in Graves disease. The statistical analysis revealed MVD as the unique significant morphometric factor discriminating the two autoimmune entities.     

A differential association of interferon-gamma high-producing allele T and low-producing allele A (+874 A/T) with Hashimoto's thyroiditis and Graves' disease

Cytokines play a crucial role in the pathogenesis of autoimmune thyroid disease. The aim of this study was to investigate the relationship of the single base change polymorphic variants identified in the first intron of interferon-gamma (IFN-gamma) (+874 T/A) with susceptibility to thyroid dysfunctions. A total of 340 subjects were included in the study comprising of 190 patients (104 patients with Hashimoto's thyroiditis, 26 with non-Hashimoto's hypothyroidism and 60 Graves' disease) and 150 controls. Genotyping was done by amplification refractory mutation system-polymerase chain reaction using a set of sequence-specific primers. Statistical analysis revealed a significant association between high IFN-gamma-producing genotype TT and Hashimoto's thyroiditis compared to controls (P value < 0.001). On the other hand, the frequency of genotype TT was decreased in patients with Graves' hyperthyroidism with a significant increase in low IFN-gamma-producing genotype AA among this group (P = 0.03). To conclude the results of the study suggest a differential association of high- and low-producing alleles of IFN-gamma gene with Hashimoto's thyroiditis and Graves' disease. The high IFN-gamma-producing allele T was observed to be associated with Hashimoto's thyroiditis in the present study where as in Graves' hyperthyroidism the association was observed to be stronger with the low producing allele A.     

Expression of HIF-1alpha, VEGF and VEGF receptors in the carotid body of chronically hypoxic rat

We examined the protein expression and localization of HIF-1alpha, VEGF, VEGF receptors in the carotid body (CB) of rats breathing 10% inspired oxygen for up to 4 weeks. The immunoreactivity (IR) of HIF-1alpha was distributed numerously in the nuclei of glomus (type-I) and other cells since hypoxia for 1 day, but was faint and scattered in the normoxic CBs. Cytoplasmic staining of the VEGF was intense in glomus cells of the hypoxic but not the normoxic group. The IR levels of HIF-1alpha and VEGF reached plateau at 4 weeks, and the IRs of VEGFR-1 and VEGFR-2 were strongly positive in the hypoxic group. Yet, the expression of VEGFR-1-IR was mild, whereas the VEGFR-2-IR was intense in normoxic CBs, suggesting an upregulation of VEGFR-1 but not VEGFR-2 in hypoxia. Hence, HIF-1 may activate the expression of VEGF and VEGFR-1 in the CB and the expression of VEGF in the chemoreceptors may play a paracrine role in the vascular remodeling during chronic hypoxia.     

Heterogeneity of thyroid autoantigens identified by immunoblotting

Autoimmune thyroid disease in man is commonly associated with autoantibodies against thyroglobulin, microsomes, and the TSH receptor, and the character and specificity of these antithyroid antibodies have been extensively utilized in investigating these conditions. In the present study we have asked whether other thyroid-related antigens exist, against which autoantibodies may be directed. A crude thyroid extract was separated by polyacrylamide gel electrophoresis followed by immunoblotting with serum obtained from patients with Graves' disease or Hashimoto's thyroiditis. Antibodies in sera from patients with Graves' disease and Hashimoto's thyroiditis reacted with many antigenic determinants in immunoblots of the thyroid membrane preparation (2000g supernatant). These determinants were disease specific in that sera from normals and patients with Addison's disease and rheumatoid arthritis did not react, but there was no difference between the patterns of reactivity with Graves' disease or Hashimoto's thyroiditis sera. Thyroglobulin produced two predominant bands of reactivity at 320 and 200 kDa, whereas purified microsomal antigen produced a triplet of bands around 105 kDa, when these preparations were reacted with appropriate autoimmune sera. Nonetheless, some sera produced additional bands with the microsomal antigen blots, indicating that some of the antigens which were detected using crude thyroid membrane remained in the microsome preparation to produce multiple antibody binding reactivities. We were unable to inhibit any of the antibody binding with TSH. Purification of individual thyroid antigens on the basis of their molecular weights should standardize current antibody assays and permit more detailed evaluation of the cellular immune responses in Graves' disease and Hashimoto's thyroiditis.     

In vitro production of interferon-gamma by peripheral blood from patients with Graves'' disease, Hashimoto''s thyroiditis and rheumatoid arthritis.

The production of interferon-gamma (IFN-gamma) by peripheral blood mononuclear cells (PBMC), CD4 cells, or CD8 cells in response to interleukin-2 (IL-2) stimulation has been studied; the samples were obtained from 12 healthy control subjects, 19 patients with Graves' disease (10 hyperthyroid and nine euthyroid), 13 patients with Hashimoto's thyroiditis (four hypothyroid and nine euthyroid), and 15 patients with rheumatoid arthritis (11 active and four inactive). A dose of IL-2 (25 U/ml) was utilized to induce IFN-gamma by PBMC from all four groups. The incremental increase in IFN-gamma values (with IL-2 stimulation minus without stimulation) was significantly less in PBMC from patients with Graves' disease, Hashimoto's thyroiditis, and rheumatoid arthritis than that in PBMC from control subjects. The values from PBMC in patients with Graves' disease in a euthyroid state were below normal but greater than those from patients with Graves' disease in a hyperthyroid state. The incremental increase in IFN-gamma values from Graves' disease PBMC correlated with the serum TSH values (r = 0.622, P less than 0.01), but not with thyroid autoantibodies (anti-thyroid microsomal antibodies, anti-thyroid microsomal antibodies, nor TSH-binding inhibitory immunoglobulin activities). The incremental increase in IFN-gamma from PBMC from both control subjects and Graves' disease was correlated with that from CD4 cells (r = 0.711, P less than 0.01), but not with that from CD8 cells. The production of IFN-gamma in response to IL-2 from PBMC in Graves' disease correlated inversely with thyroid function, appearing to reflect the very effect of hyperthyroidism in this process. The precise explanation of these phenomena remains unclear. The decreased response of IFN-gamma to IL-2 stimulation by PBMC from patients with Graves' disease, Hashimoto's thyroiditis, and rheumatoid arthritis seems to be a non-specific phenomenon occurring in both organ specific autoimmune disease and systemic autoimmune disease. It may be due to a down-regulation in autoimmune disease of CD4 cells in response to IL-2, a decreased level of IL-2 cellular receptors or a decreased receptor affinity, associated increased soluble IL-2 receptors, or a defect of the intra-CD4 cellular IL-2 signal to produce or release IFN-gamma in the conditions studied.     

The expression and role in T cell adhesion of LFA-3 and ICAM-2 on human thyroid cells.

Thyroid follicular cells from patients with Graves' disease and Hashimoto's thyroiditis express intercellular adhesion molecule-1 (ICAM-1) and this is in part responsible for T cell adherence in vitro. To assess the potential role of other adhesion molecules in autoimmune thyroiditis, we investigated the expression and function of lymphocyte function-associated antigen-3 (LFA-3) and ICAM-2 on thyroid cells. Under basal culture conditions, a mean of 22.7% of Graves' thyroid cells (n = 8) expressed LFA-3 and this was enhanced by a mixture of T cell-derived cytokines and by IL-1, but not by TSH. LFA-3 was also demonstrated on Graves' (n = 4) and Hashimoto (n = 2) thyroid cells by immunohistochemical staining ex vivo. A small number of thyroid cells (mean 5.5%, n = 5) expressed ICAM-2 by flow cytometry but this was not altered by cytokines, and ICAM-2 could only be demonstrated on endothelial cells by immunohistochemical staining. It seems likely that contamination of primary thyroid cultures by such cells accounted for the small number of ICAM-2+ cells found using flow cytometry. Almost all of the cultured cells expressing LFA-3 or ICAM-2 also expressed ICAM-1, as assessed by dual staining. Blocking LFA-1, LFA-3, and ICAM-1 with monoclonal antibodies inhibited the adherence of T cells to thyroid follicular cells in assays of cell clustering; antibodies against ICAM-2 had no effect. These results show that two important adhesion receptor ligands, ICAM-1 and LFA-3, are expressed by thyroid cells in autoimmune thyroiditis and that these are likely to have functional importance in allowing T cells to bind to thyroid cell targets. This may play an important role in the initiation and maintenance of Graves' disease and Hashimoto's thyroiditis.     

凋亡相关因子参与自身免疫性甲状腺疾病发病的研究

目的:了解细胞凋亡相关蛋白Fas,FasL和Bcl-2表达在自身免疫性甲状腺疾病发病机制及病理变化中的作用及意义。方法:采用免疫组织化学方法,检测20例桥本甲状腺炎,20例Graves病以及20例甲状腺腺瘤(作为对照组)患者甲状腺标本中Fas、FasL和Bcl-2表达及分布。结果:Fas在所有的标本中表达,主要分布于甲状腺滤泡细胞表面和细胞质上。除3例甲状腺瘤标本外,其余均表达FasL。Bcl-2表达于15例桥本甲状腺炎、19例Graves病以及17例甲状腺瘤滤泡细胞上。在甲状腺瘤滤泡细胞上表达中等强度Fas,很少或是没有表达FasL。在桥本甲状腺炎中Fas和FasL免疫染色强阳性甲状腺滤泡细胞多分布于浸润淋巴滤泡附近,浸润淋巴细胞中Fas、FasL免疫染色相对较弱。在Graves病中,Fas表达强度与桥本甲状腺炎类似,但FasL表达却更弱。在Graves病和甲状腺瘤组织中,Bcl-2表达两者类似。但在桥本甲状腺炎组织中,分布于浸润淋巴细胞附近的甲状腺滤泡细胞以及生发中心的淋巴细胞上,Bcl-2表达很弱。结论:Fas、FasL和Bcl-2表达在桥本甲状腺炎和Graves病中相似。FasL高表达和Bcl-2低表达可能引起桥本甲状腺炎滤泡细胞凋亡。进一步证明3种凋亡相关因子在自身免疫性甲状腺疾病发病机制中的作用。在桥本甲状腺炎中,滤泡细胞凋亡并非由浸润淋巴细胞其FasL发挥作用直接杀伤,但是它们能分泌细胞因子促进滤泡细胞自身Fas、FasL表达,从而导致滤泡细胞凋亡。     

Expression of p63 in papillary thyroid carcinoma and in Hashimoto's thyroiditis: a pathobiologic link?

p63 proteins are p53 homologs that are postulated to regulate squamous stem cell commitment. An immunohistochemical survey of p63 expression in normal thyroid and in reactive, neoplastic, and inflammatory thyroid disorders was performed. Sections from routinely fixed and processed archival thyroidectomy specimens were pretreated with citric acid, pH 6.0, for antigen retrieval, then incubated overnight with anti-p63 monoclonal antibody 4A4. Slides were stained using a streptavidin-biotin kit and diaminobenzidine as a chromagen, and then were counterstained with hematoxylin. The results showed that p63 expression was negative in normal thyroid tissue, nodular goiters, and oncocytic follicular adenomas. Positivity was rare and weak in follicular adenomas. p63-positive foci were commonly found in Hashimoto's thyroiditis (1 or more foci in 78.8% of cases), but rare in Graves' disease. Twenty-seven of 33 papillary thyroid carcinomas (81.8%) displayed p63-positive foci. Staining was uncommon in follicular carcinomas and rare in medullary carcinomas. One case of insular carcinoma was p63-positive. All squamoid structures were p63-positive; p63-positive structures morphologically consistent with solid cell nests were also identified. Based on the results of this study, we conclude that p63 is commonly expressed in papillary thyroid carcinoma and in Hashimoto's thyroiditis. Given the debated association of papillary thyroid carcinoma with Hashimoto's thyroiditis, it is possible that p63 expression may be a potential pathobiologic link between the two disorders. The finding of p63 in benign squamoid nests supports a possible interrelationship between these structures and both Hashimoto's thyroiditis and papillary carcinoma. The high percentage of papillary carcinomas with p63-positive foci appears to distinguish papillary carcinoma from other neoplasms originating in the thyroid.