An update on the pathogenesis of Hashimoto's thyroiditis.

It is 70 years since Noel Rose embarked on his pioneering studies that lead to the discovery of autoimmune thyroiditis and the elucidation of Hashimoto's thyroiditis. This short review to honour his passing focuses on the developments in our understanding of the causes and pathogenesis of HT over the last five years. Recent genetic studies have reported heritability estimates for HT and associated diseases for the first time, and emphasised the complexity of the genetic factors involved, including monogenic forms of HT. Environmental factors continue to be elucidated, especially as a side effect of drugs which modulate the immune system therapeutically. Regarding pathogenetic mechanisms, multiple cytokine networks have been identified which involve the thyroid cells in a circuit of escalating proinflammatory effects, such as the expression of inflammasome components, and an array of different defects in T regulatory cells may underlie the loss of self-tolerance to thyroid autoantigens. Finally, a number of studies have revealed fresh insights into disease associations with HT which may have both pathological and clinical significance, the most intriguing of which is a possible direct role of the autoimmune process itself in causing some of the persistent symptoms reported by a minority of patients with levothyroxine-treated HT.

The Pathogenesis of Hashimoto's Thyroiditis: Further Developments in our Understanding.

Hashimoto's thyroiditis (HT) is part of a spectrum of thyroid autoimmune conditions and this review provides an update on the latest developments in the field. HT has a genetic predisposition with a number of immune-related and thyroid-specific genes conferring disease susceptibility. However, disentangling genes with protective and predisposing effect is a complex process that requires further work. The recent increase in the incidence of HT implicates environmental factors in disease pathogenesis including improved hygiene, increased dietary iodine intake, new treatment modalities and chemical agents. Additional unmodifiable predisposing factors include stress, climate, age and gender. Both cellular and humoral immunity play a role in HT pathogenesis. Defects in T regulatory cells and increased activation of follicular helper T cells may have a role in disease initiation/perpetuation. Infiltrating lymphocytes can be directly cytotoxic to thyroid follicular cells (TFC) or may affect cell viability/function indirectly through cytokine production, which alters TFC integrity and modulates their metabolic and immune function. Thyroid peroxidase and thyroglobulin antibodies are present in the majority of HT patients and help with management decisions. Antibodies against the sodium iodide symporter and pendrin are present in a minority with little known about their clinical relevance. In addition to immune cells, recent work has identified DNA fragments, generated following cell death, and micro RNA as potential factors in HT pathogenesis. Despite the large number of studies, the mechanistic pathways in HT are still not fully understood and further work is required to enhance our knowledge and identify novel preventative and therapeutic clinical targets.

The angiotensin-converting enzyme gene insertion/deletion polymorphism in Indian patients with vitiligo: a case-control study and meta-analysis.

BACKGROUND: Vitiligo is a common, acquired, idiopathic depigmenting skin disorder. Although the exact pathogenesis remains unknown, genetic susceptibility and autoimmune responses play a role in vitiligo development. Previous studies have suggested that the D allele of the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is associated with vitiligo in Indians and Koreans. Furthermore, significantly higher serum ACE levels have been demonstrated in patients with some autoimmune and autoinflammatory disorders. OBJECTIVES: The objectives were to investigate any association between the ACE I/D polymorphism and vitiligo susceptibility in an Indian population, and to compare serum ACE levels in patients with vitiligo and healthy subjects. METHODS: The ACE I/D genotypes of 79 patients with vitiligo and 100 normal individuals were determined by polymerase chain reaction amplification. A meta-analysis was done to compare the distribution of the ACE I/D alleles and genotypes in the current and three previous studies. Serum ACE levels were evaluated by enzyme-linked immunosorbent assay. RESULTS: A significant increase in the frequency of the ACE I/D D allele was evident in patients with vitiligo in both the case-control study [P=0·005; odds ratio (OR) 1·87; 95% confidence intervals (CI) 1·22-2·85] and the meta-analysis (P=0·044; OR 1·44; 95% CI 1·01-2·06). Serum ACE levels were significantly increased in patients with vitiligo compared with healthy subjects (P<0·0001). CONCLUSIONS: In agreement with earlier reports, the ACE I/D D allele is associated with vitiligo susceptibility in the Indian population. The significantly elevated serum ACE levels in our cohort of patients with vitiligo concur with those previously found in patients with some other autoimmune diseases.

Vitiligo patients from India (Mumbai) show differences in clinical, demographic and autoantibody profiles compared to patients in western countries.

BACKGROUND: Vitiligo is a common, idiopathic skin disorder characterized by depigmented skin due to the loss of cutaneous melanocytes. Several studies have reported the clinical and demographic characteristics of Indian vitiligo patients, however, none has characterized their antibody profiles. OBJECTIVE: To establish the clinical, demographic and serological details of a population of vitiligo patients from Mumbai, India, and to evaluate the data for any associations between clinical presentations and the occurrence of antibody responses. METHODS: Vitiligo patients (n = 79) were recruited to the study and their clinical and demographic details recorded. Serum antibodies, including those against melanocyte-specific antigens, thyroid antigens and keratinocytes, were evaluated. RESULTS: The prevalence of vitiligo was independent of sex, and non-segmental vitiligo was the most common form of the disease occurring in 65% of the patients. Patients with segmental vitiligo (mean age = 14.4 ± 4.6 years) presented at a younger age than those with non-segmental disease (mean age = 32.5 ± 17.8 years). Personal and family histories of other autoimmune diseases occurred in 3% and 8% of patients, respectively. Antibodies were detected against tyrosinase, tyrosine hydroxylase, thyroid peroxidase, thyroglobulin and keratinocytes at frequencies of 11%, 22%, 18%, 24% and 27%, respectively. Overall, antibodies were more common in patients with non-segmental vitiligo (50-67%) than in those with segmental disease (0-17%), and were detected more frequently in patients with shorter disease durations (<10 years). CONCLUSION: Our study provides novel information relative to the clinical details, demographic features and serological parameters of a population of vitiligo patients from Mumbai, India. Important distinctions from similar surveys conducted in European patients were evident such as an infrequency of family history, a low prevalence of clinical autoimmune disease, and an absence of particular antibody specificities. These differences may have a bearing on the pathogenesis and course of the disease in Indian patients.

Epitopes, avidity and IgG subclasses of tyrosine hydroxylase autoantibodies in vitiligo and alopecia areata patients.

BACKGROUND: We previously detected antibodies against tyrosine hydroxylase (TH) in 23% of patients with nonsegmental vitiligo and in 19% of patients with alopecia areata (AA). OBJECTIVES: To identify TH epitopes recognized by TH antibodies in patients with vitiligo and AA. METHODS: Recombinant plasmids containing defined fragments of TH cDNA were constructed. The cloned TH cDNA fragments were subsequently translated in vitro to produce a series of [(35) S]-labelled TH protein fragments which were then used in radioimmunoassays to analyse the immunoreactivity of sera from 18 TH antibody-positive patients with vitiligo and so initially define TH epitope domains. Further localization of TH epitopes was investigated by antibody absorption experiments using synthetic TH peptides and nonradiolabelled, in vitro-expressed TH protein fragments. Antibody binding to identified epitopes was confirmed in TH peptide enzyme-linked immunosorbent assays. RESULTS: Analysis of the results obtained indicated the presence of two major antibody-binding sites on TH between amino acids 1 and 14 (epitope 1-14) and between amino acids 61 and 80 (epitope 61-80). Of 18 patients with vitiligo and six with AA, 17 (94%) and five (83%), respectively, had antibodies against epitope 1-14. In addition, 11/18 (61%) vitiligo and 2/6 (33%) AA patient sera displayed immunoreactivity against epitope 61-80. CONCLUSIONS: Two major binding sites for human TH antibodies are located at the N-terminus of the protein. The humoral immune response to TH in vitiligo and AA is heterogeneous in nature in that patients may have antibodies to more than one TH epitope. TH antibodies from patients with vitiligo or AA can recognize identical epitopes.

Diseases associated with thyroid autoimmunity: explanations for the expanding spectrum.

Anyone who has been in an endocrine clinic will appreciate that associations exist between autoimmune thyroid disease (AITD) and other autoimmune disorders. However, the full extent of these associations is still not fully appreciated, and new associations are being uncovered which may shed new light on the pathogenic basis for these connections, and the underlying reasons for them are only now becoming understood. This review is based on the British Thyroid Association Pitt-Rivers Lecture 2010. The first section provides an update on studies which have detailed the strength of various autoimmune disease associations, the second section discusses the environmental and genetic factors which underlie these associations and the final section describes some recently identified, unexpected AITD associations. Unravelling these associations further will illuminate the pathogenesis of autoimmune diseases and offers the prospect of new therapeutic approaches.

Demonstration of autoantibodies against tyrosine hydroxylase in patients with alopecia areata.

BACKGROUND: There is strong evidence to suggest that alopecia areata (AA) is a tissue-specific, T cell-mediated autoimmune disease, which is usually characterized by patchy areas of hair loss on the scalp. Tyrosine hydroxylase (TH) is a known B-cell autoantigen in patients with autoimmune polyendocrine syndrome type 1 (APS1) associated with the presence of AA. In addition, melanocyte-specific proteins, gp100 and MelanA, are putative T-cell autoantigens in AA and so may also represent targets of the humoral immune response. OBJECTIVE: To analyse the sera of patients with AA for the presence of antibodies against TH and the melanocyte-specific proteins tyrosinase, tyrosinase-related protein (TRP)-1, TRP-2, gp100 and MelanA. METHODS: Radioimmunoassays were used to detect the relevant antibodies in sera from patients with AA (n = 32) and in sera from healthy individuals (n = 28). RESULTS: Of 32 patients with AA, six (19%) were positive for TH antibodies. A significant increase in the frequency of TH antibodies in the AA patient group was evident when compared with controls (P = 0·03). Only three of 32 (9%) patients exhibited antibody responses to tyrosinase, TRP-1, TRP-2 and gp100. No immunoreactivity against MelanA was detected in any patient with AA. CONCLUSION: Antibodies against TH can be present in patients with AA unrelated to APS1. Humoral immune responses against tyrosinase, TRP-1, TRP-2, gp100 and MelanA are not prevalent in patients with AA. Overall, a dominant melanocyte-specific B-cell autoantigen in AA has yet to be identified.

The genetics of autoimmune thyroid disease.

Recent studies have confirmed that polymorphisms in several genes confer susceptibility for the development of autoimmune thyroid disease, and that of these HLA-DR alleles, and the genes encoding CTLA-4, PTPN22, FCRL3, and probably the IL-2 receptor all have associations with other autoimmune disorders, indicating that they provide a lowering of the background threshold for the development of autoimmunity. Other factors (the TSHR and possibly Tg genes, HLA-C alleles, and environmental factors) determine that the type of disease which results from this background propensity specifically targets the thyroid. We also now appreciate much better how complex these disorders are in their pathogenesis: multiple genes influencing multiple immunological pathways are involved in pathogenesis, but are not involved in every patient. Any individual patient with thyroid autoimmunity has their own cluster of genetic (and environmental) susceptibility factors, only very partially shared with other patients who have the same diagnostic and clinical label. The interplay of forces that cause autoimmune thyroid disease in an individual patient are more subtle than previously imagined and there is at present no obvious upper limit on the number of genes which may be involved.

Free triiodothyronine has a distinct circadian rhythm that is delayed but parallels thyrotropin levels.

CONTEXT: TSH is known to have a circadian rhythm, but the relationship between this and any rhythm in T(4) and T(3) has not been clearly demonstrated. OBJECTIVE: With a view to optimizing thyroid hormone replacement therapy, we have used modern assays for free T(4) (FT4) and free T(3) (FT3) to investigate circadian rhythmicity. SETTING: The study was performed at a university hospital. DESIGN AND SUBJECTS: This was a cross-sectional study in 33 healthy individuals with 24-h blood sampling (TSH in 33 and FT4 and FT3 in 29 individuals) and cosinor analysis. RESULTS: Of the individuals, 100% showed a sinusoidal signal in TSH, for FT4 76%, and for FT3 86% (P < 0.05). For FT4 and FT3, the amplitude was low. For TSH the acrophase occurred at a clock time of 0240 h, and for FT3 approximately 90 minutes later at 0404 h. The group cosinor model predicts that TSH hormone levels remain above the mesor between 2020 and 0820 h, and for FT3 from 2200-1000 h. Cross correlation of FT3 with TSH showed that the peak correlation occurred with a delay of 0.5-2.5 h. When time-adjusted profiles of TSH and FT3 were compared, there was a strong correlation between FT3 and TSH levels (rho = 0.80; P < 0.0001). In contrast, cross correlation revealed no temporal relationship between FT4 and TSH. CONCLUSIONS: FT3 shows a circadian rhythm with a periodicity that lags behind TSH, suggesting that the periodic rhythm of FT3 is due to the proportion of T(3) derived from the thyroid. Optimizing thyroid hormone replacement may need to take these rhythms into account.

Autoimmune thyroid disease: further developments in our understanding.

The revolution in molecular techniques has allowed dissection of the autoimmune response in a way impossible to imagine 10 yr ago. There have been spectacular advances in our understanding of self-tolerance mechanisms and how these may fail, combined with a detailed comprehension of antigen presentation, functional T cell subsets, and TCR utilization in autoimmunity, albeit usually in animal models that resemble, but do not exactly duplicate, human diseases. More gradually, these findings are being translated to thyroid autoimmunity, where the major achievement of the last decade has been the molecular characterization of the three main thyroid autoantigens. This in turn has allowed epitope identification, although again the only clear data so far have come from animal models of EAT. Another advance has been the recognition that the thyrocyte is not a helpless target of autoaggression, being capable of expressing a wide array of immunologically active molecules, which may exacerbate or diminish the autoimmune response. In 1983, there was considerable excitement at the discovery of the first of these phenomena, namely MHC class II expression, but its possible role in autoantigen presentation remains to be defined. By analogy with pancreatic beta-cells, and based on our own data, we believe that class II-expressing thyrocytes have little, if any, such role and suspect that instead this may be a mechanism for inducing peripheral tolerance. Defining the contribution of thyrocytes to the intrathyroidal autoimmune response, whether from released cytokines or surface-bound molecules, will be crucial to our future understanding, as well as holding the promise that these thyroid-derived products might be therapeutic targets. Despite molecular developments in HLA analysis, there have been no really major improvements in our understanding of the immunogenetics of thyroid autoimmunity, equivalent to those made in type 1 diabetes mellitus. The available data suggest strongly that non-MHC genes play an important role in susceptibility, and novel approaches will be required to identify these. On the other hand, we know more about the importance of environmental and endogenous (most probably hormonal) factors in thyroid autoimmunity. Understanding the basic immunological changes in the postpartum period is still poor, however, as most studies to date have concentrated on epidemiology and clinical delineation. As PPTD undergoes spontaneous remission, elucidation of these mechanisms has clear implications for treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Techniques to quantify TSH receptor antibodies.

The presence of antibodies to TSH receptor (TSHR) is the hallmark of Graves disease (GD). These antibodies mimic the action of TSH, resulting in TSHR stimulation and hyperthyroidism, and have been associated with GD-associated extrathyroidal manifestations. TSH binding inhibition assays and bioassays for measurement of TSHR antibody levels have been used for clinical and research purposes. In the former, inhibition of TSH binding to purified or recombinant TSHR by a patient's immunoglobulins is measured by radioactive or chemiluminescent techniques. In the latter, cyclic AMP production is measured by use of radioimmunoassays or chemiluminescent methods in cells natively or artificially expressing TSHR. In this Review, the different techniques used for the detection of antibodies to TSHR are discussed, together with the clinical applications of antibody measurement, including diagnosis of GD and Graves ophthalmopathy. Prediction of relapse after medical treatment and the clinical course of Graves ophthalmopathy are also addressed.

Kappa/lambda immunoglobulin distribution in Graves' thyroid-stimulating antibodies. Simultaneous analysis of C lambda gene polymorphisms.

From patients with untreated Graves' disease 11 sera showing high cAMP release in the FRTL-5 cell assay were studied for relative proportions of kappa or lambda Ig molecules showing cAMP releasing activity. Immunoabsorption of gamma-globulins was performed using monoclonal murine anti-kappa or anti-lambda antibodies linked to cyanogen bromide-activated sepharose. Specific kappa- or lambda-adsorbed fractions were also eluted from immunoabsorbents using chaotrophic thiocyanate buffers and equilibrated with pH 7.4 low salt buffer by dialysis. Immunoabsorption and elution experiments showed that five Graves' sera contained predominant cAMP-releasing activity within lambda Ig fractions, whereas two Graves' sera showed predominant cAMP-releasing activity in kappa Ig fractions. Four sera showed cAMP release approximately equally divided between kappa and lambda Ig both after immunoabsorption and specific anti-kappa or anti-lambda eluates were studied. C lambda genotypes were examined by Southern blotting and restriction fragment length polymorphism analysis of Eco RI-digested genomic DNA from 158 patients with Graves' disease in parallel with 112 normal controls and 29 patients with autoimmune hypothyroidism. Notable shifts in proportions of 8/8 and 18/18 genotypes were present when Graves' patients were compared with normal controls. Allelic frequencies and ratios of genotype 8 to 18 were significantly different (P less than 0.05) when Graves' patients were compared either to normal controls or to patients with autoimmune hypothyroidism.

Thyroid-stimulating antibody activity between different immunoglobulin G subclasses.

To investigate the distribution of thyroid-stimulating antibody (TSAb) activity between IgG subclasses, sera from 11 patients with Graves disease (including the National Institute of Biological Standards and Control (NIBSC) Research Standard, long acting thyroid stimulator-B) were fractionated by chromatography on affinity columns of monoclonal IgG subclass antibodies or protein A to deplete all but a single subclass. The resulting fractions were 98% or more pure for a single subclass. In all 11 patients, TSAb activity appeared to be confined to the IgG1 fraction as determined by cAMP production on addition of the fractions to the FRTL-5 rat thyroid cell line. In all of eight specimens from seven patients so tested, the whole serum activity was recovered in the IgG1 fraction, after adjusting for the recovery of the isotype from the column. TSAb activity in one serum comprised both lambda and kappa light chains but was IgG1 restricted. This IgG subclass restriction was not found when the same fractions were tested for thyroglobulin, microsomal/thyroid peroxidase, or tetanus toxoid antibody activity. Together with previous results showing marked restriction of both light chain usage and isoelectric point of TSAb, these results support the idea that Graves' disease may be the result of an oligo- or possibly monoclonal response at the B cell level.

A genome-wide screen in 1119 relative pairs with autoimmune thyroid disease.

CONTEXT: Autoimmune thyroid diseases (AITD), comprising Graves' disease and autoimmune hypothyroidism, are characterized by loss of immunological self-tolerance to thyroid antigens. These are complex diseases arising from a combination of genetic and environmental factors. An understanding of the genetic susceptibility factors for AITD could help to target treatments more effectively and identify people at risk for these conditions. OBJECTIVE: The objective of this study was to identify regions of genetic linkage to AITD that could potentially harbor genetic susceptibility factors for these conditions. DESIGN: The study design was a genome-wide screen performed on affected relative pairs with AITD. SETTING: Patients were recruited through hospital endocrinology clinics. PARTICIPANTS: Some 1119 Caucasian relative pairs affected with AITD (Graves' disease or autoimmune hypothyroidism) were recruited into the study. INTERVENTION: Blood samples were obtained from each participant for DNA analysis, and clinical questionnaires were completed. MAIN OUTCOME MEASURE: The study aimed to identify regions of genetic linkage to AITD. RESULTS: Three regions of suggestive linkage were obtained on chromosomes 18p11 (maximum LOD score, 2.5), 2q36 (maximum LOD score, 2.2), and 11p15 (maximum LOD score, 2.0). No linkage to human leukocyte antigen was found. CONCLUSIONS: The absence of significant evidence of linkage at any one locus in such a large dataset argues that genetic susceptibility to AITD reflects a number of loci, each with a modest effect. Linkage analysis may be limited in defining such loci, and large-scale association studies may prove to be more useful in identifying genetic susceptibility factors for AITD.

Is there a need to redefine the upper normal limit of TSH?

Mild forms of hypothyroidism--subclinical hypothyroidism--have recently been discussed as being a risk factor for the development of overt thyroid dysfunction and for a number of clinical disorders. The diagnosis critically depends on the definition of the upper normal limit of serum TSH as, by definition, free thyroxine serum concentrations are normal. Cut-off levels of 4-5 mU TSH/l have been conventionally used to diagnose an elevated TSH serum concentration. Recent data from large population studies have suggested a much lower TSH cut-off with an upper limit of 2-2.5 mU/l but application of strict criteria for inclusion of subjects from the general population studies aiming at assessing TSH reference intervals (no personal or family history of thyroid disease, no thyroid antibodies and a normal thyroid on ultrasonography) did not result in an unequivocal upper limit of normal TSH at 2.0-2.5 mU/l. When summarizing the available evidence for lowered upper TSH cut-off values and their potential therapeutic implications there is presently insufficient justification to lower the upper normal limit of TSH and, for practical purposes, it is still recommended to maintain the TSH reference interval of 0.4-4.0 mU/l. Classifying subjects with a TSH value between 2 and 4 mU/l as abnormal, as well as intervening with thyroxine treatment in such subjects, is probably doing more harm than good.

Cloning and analysis of IgM anti-thyroglobulin autoantibodies from patients with Hashimoto's thyroiditis.

Hashimoto's thyroiditis is an autoimmune disease in which autoantibodies reactive to a number of thyroid antigens are made. In order to investigate the autoantibody repertoire in this disease, B cells from four patients with Hashimoto's thyroiditis were immortalised and, after limiting dilution, screened for reactivity to thyroid antigens. After a second limiting dilution, one anti-thyroglobulin IgM-secreting clone from three patients, and four clones from one patient, were analysed. The Ig heavy and light chain genes from each clone were amplified using the polymerase chain reaction and sequenced. The resulting heavy and light chain sequences were heterogeneous, although the four clones from one patient and the clone from a second patient shared a germline VH sequence. All antibodies had similar functional affinity, comparable to serum IgG from Hashimoto's patients. The cross-reactivity of the antibodies was analysed against bovine and rat thyroglobulin, histones, cardiolipin and human skeletal muscle. The antibodies were polyreactive, indicating that they are probably natural autoantibodies of unknown pathogenic significance.

Detection of tyrosinase autoantibodies in patients with vitiligo using 35S-labeled recombinant human tyrosinase in a radioimmunoassay.

Tyrosinase antibodies recently have been reported to occur frequently in patients with vitiligo. We describe the detection of tyrosinase antibodies in vitiligo patients using in vitro 35S-labeled human tyrosinase in a radioimmunoassay. Of 46 vitiligo sera examined in the assay, five (10.9%) were found to be positive for tyrosinase antibodies. In contrast, 20 control sera and sera from 10 patients with Hashimoto's thyroiditis were negative. Four of the sera positive in the radioimmunoassay were also positive in an ELISA using mushroom tyrosinase as antigen. Absorption studies indicated that pre-incubation with mushroom tyrosinase absorbed out the immunoreactivity of the positive sera in the radioimmunoassay, suggesting cross-reactivity, but this absorption was never complete, indicating that there are tyrosinase antibodies in human sera that do not react with the mushroom protein. There was no obvious association between the presence of tyrosinase antibodies and the age of the patients (range: 22-62 y), their duration of disease (range: 5-20 y), or the type of vitiligo (one segmental, one symmetrical/periorificial, three symmetrical), although the three patients with the highest antibody levels also had an associated autoimmune disorder (one with Graves' disease; two with autoimmune hypothyroidism). The results confirm that tyrosinase autoantibodies are present in the sera of vitiligo patients but at a low frequency. The technique described is sensitive and quantitative and allows the detection of conformational epitopes. It will be useful in longitudinal studies to determine the relation between the clinical features of vitiligo and tyrosinase antibody levels.

Identification of epitopes on tyrosinase which are recognized by autoantibodies from patients with vitiligo.

The identification of tyrosinase autoantibodies in some patients with vitiligo has previously been reported. In this study we have determined the B cell epitopes on tyrosinase which are recognized by these autoantibodies. Deletion derivatives of tyrosinase cDNA were constructed and then translated in vitro with the concomitant incorporation of [35S]methionine into the protein products. The 35S-labeled tyrosinase derivatives were subsequently used in radioimmunoassays to investigate the reactivity of sera from five vitiligo patients. The epitope regions identified were: three in a central region of tyrosinase (amino acids 240-255, 289-294, and 295-300) and two others towards the C-terminal end of the protein (amino acids 435-447 and 461-479). Computer analysis of the potential B cell epitopes on tyrosinase revealed that the epitope regions recognized by the vitiligo sera were located in areas predicted to be highly antigenic. In addition, the centrally located antigenic regions (amino acids 289-294 and 295-300) had amino acid sequence homology to both tyrosinase-related protein-1 and -2. Thus, the epitopes on tyrosinase recognized by vitiligo patient sera are heterogeneous and include a region with homology to two related proteins which may explain the cross-reactivity previously noted between these antigens.

The effects of hyperthyroidism on experimental autoimmune thyroiditis in the rat.

The effects of hyperthyroidism on experimental autoimmune thyroiditis were investigated in the rat. Rats were given T4 twice daily by sc injection in amounts sufficient to raise circulating hormone levels 10-fold 4 h after administration. Thyroiditis was induced by immunization with rat thyroglobulin (Tg) in complete Freund's adjuvant, and the severity of the disease was assessed by comparison with saline-treated controls. Thymic and splenic hypertrophy were found in T4-treated animals, whereas lymph node wt decreased. The levels of Tg antibodies did not differ between animals given saline and those given T4, but the expected sustained rise in control animals was not seen in those treated with T4; in addition, there was a significant decrease in the amount of Tg antibody produced by in vitro culture of lymph node lymphocytes from T4-treated rats. Continuous T4 administration lowered the number of T cells in the circulation, but the number of phenotypically identified helper cells remained the same. The most striking effects of T4 were to ameliorate the intensity of histologically defined thyroiditis and lower the response of lymph node T cells to the nonspecific mitogen, phytohemagglutinin. These results show that excessive T4 does not, as previously suggested, enhance the immune response in autoimmune thyroid disease: on the contrary, suppression is found with the dose and model we have used. In view of the magnitude of this effect, it is now important to identify the site of T4 action and investigate how this effect contributes to the autoimmune response in Graves' disease.