Nucleotide and amino acid homology between the human thyrotropin receptor and the HIV-1 Nef protein: identification and functional analysis

Role of genetic and non-genetic factors in the etiology of Graves' disease

In spite of the advancements in understanding the pathogenic mechanisms of Graves' disease (GD), its ultimate cause remains elusive. The majority of investigators agree that GD is likely a multifactorial disease, due to a complex interplay of genetic and non-genetic factors that lead to the loss of immune tolerance to thyroid antigens and to the initiation of a sustained autoimmune reaction. Twin and family studies support a role of genetic factors, among which the HLA complex, CD40, CTLA-4, PTPN22, FCRL3, thyroglobulin, and the TSH receptor may be involved. Among non-genetic factors, iodine, infections, psychological stress, gender, smoking, thyroid damage, vitamin D, selenium, immune modulating agents, and periods of immune reconstitution may contribute the development of the diseases. Here we review in detail the respective role of genetic and non-genetic factors in the etiology of GD, taking advantage of the great bulk of data generated especially over the past 30 years.

Postinfectious immunodeficiency and autoimmunity: pathogenic and clinical values and implications

Autoimmunity is still a mystery of clinical immunology and medicine as a whole. The etiology and pathogenesis of autoimmune disorders remain unclear and, thus, are assessed as a balance between hereditary predisposition, triggering factors and the appearance of autoantibodies and/or self-reactive T cells. Among the immunological armamentarium, molecular mimicry, based on self-reactive T- and B-cell activation by cross-reactive epitopes of infectious agents, is of special value. Hypotheses regarding the possible involvement of molecular mimicry in the development of postinfectious autoimmunity are currently very intriguing. They provide new approaches for identifying etiological agents that are associated with postinfectious autoimmunity, paired microbial- and tissue-linked epitopes targeted for autoimmune reaction determination, postinfectious autoimmunity pathogenesis recognition and specific prevention, and therapy for autoimmune disorder development.

Viruses and thyroiditis: an update

Viral infections are frequently cited as a major environmental factor involved in subacute thyroiditis and autoimmune thyroid diseases This review examines the data related to the role of viruses in the development of thyroiditis.

Our research has been focused on human data. We have reviewed virological data for each type of thyroiditis at different levels of evidence; epidemiological data, serological data or research on circulating viruses, direct evidence of thyroid tissue infection. Interpretation of epidemiological and serological data must be cautious as they don't prove that this pathogen is responsible for the disease. However, direct evidence of the presence of viruses or their components in the organ are available for retroviruses (HFV) and mumps in subacute thyroiditis, for retroviruses (HTLV-1, HFV, HIV and SV40) in Graves's disease and for HTLV-1, enterovirus, rubella, mumps virus, HSV, EBV and parvovirus in Hashimoto's thyroiditis. However, it remains to determine whether they are responsible for thyroid diseases or whether they are just innocent bystanders. Further studies are needed to clarify the relationship between viruses and thyroid diseases, in order to develop new strategies for prevention and/or treatment.

Infection, immunity, and hormones/endocrine interactions

Infections and stress, immune responses, and hormones are interconnected, ensuring immune competence to deal with immediate threat of overwhelming infection and metabolic collapse. Emergence of cytokines as key signal mediators and appreciation of autocrine-paracrine influences of hormones have helped explain how signals are transmitted and responses evoked. This has led to possibilities of creating therapies that might be used to enhance protective signals and dampen signals emanating from host and invading organism interaction that might otherwise be detrimental. Correcting certain metabolic abnormalities, such as hyperglycemia and metabolic acidosis, benefits the host by decreasing morbidity and mortality.

Virus-mediated modulation of the host endocrine signaling systems: clinical implications

Viruses, which are among the simplest infective pathogens, can produce characteristic endocrine manifestations in infected patients. In addition to the classic modification of the host endocrine system by either direct or indirect destruction of the endocrine organs and/or effects exerted by systemic production of inflammatory and/or stress mediators, recent progress in molecular virology and endocrinology has revealed that virus-encoded molecules might alter the host endocrine-signaling systems by affecting extracellular and/or intracellular signal transduction and hormone sensitivity of host target tissues. Here, we provide a brief overview of such viral-mediated modulation of host endocrine signaling systems. We propose that virus-encoded molecules and the signaling systems they influence are potential therapeutic targets for the treatment of disorders that are associated with some viral infections.

Characteristics of autoimmune thyroid disease occurring as a late complication of immune reconstitution in patients with advanced human immunodeficiency virus (HIV) disease

Experimental evidence from animal models has provided a framework for our current understanding of autoimmune disease pathogenesis and supports the importance of genetic predisposition, molecular mimicry, and immune dysregulation. However, only recently has evidence emerged to support the role of immune dysregulation in human organ-specific autoimmune disease. In the current study of the "late" manifestation of autoimmune thyroid disease (AITD) in a cohort of human immunodeficiency virus (HIV)-positive patients following highly active antiretroviral therapy (HAART), we discuss how immune dysregulation and factors associated with the immunopathology of HIV infection fit the current understanding of autoimmunity and provide a plausible basis for our clinical observations. De novo diagnoses of thyroid disease were identified between 1996 and 2002 in 7 HIV treatment centers (5/7 centers completed the study). Patients were diagnosed as clinical case entities and not discovered through thyroid function test screening. Paired plasma specimens were used to demonstrate sequential rise in thyroid antibodies. Seventeen patients were diagnosed with AITD (median age, 38 yr; 65% were of black African or black Caribbean ethnicity; and 82% were female). The median duration of immune reconstitution was 17 months. Graves disease (GD) was diagnosed in 15 of 17 patients. One patient developed hashithyrotoxicosis with atypically raised C-reactive protein, and another developed hypothyroidism. One GD patient had associated secondary hypoadrenalism. The estimated combined prevalence of GD for 4 treatment centers for female patients was 7/234 and for males was 2/1289. The denominator numbers were matched controls, from 4 centers able to provide data, who commenced HAART during the same time (January 1996 to July 2002) and who did not develop clinical AITD. The mean baseline pre-HAART CD4 count was 67 cells/mL, and the mean increase from nadir to AITD presentation was 355 cells/mL. AITD patients were more likely than controls (95% confidence interval, chi-square test) to be severely compromised at baseline (as defined by a CD4 count < 200 cells/mL or the presence of an acquired immunodeficiency syndrome [AIDS]-defining diagnosis), and to experience greater CD4 increments following HAART. AITD may be a late manifestation of immune reconstitution in HIV-positive patients taking HAART, and immune dysregulation may be an important factor.

Self-recognition and the role of fetal microchimerism

The course and severity of the autoimmune thyroid diseases (AITD) is known to be influenced by pregnancy as evidenced by disease suppression during pregnancy and initiation, or exacerbation, of disease postpartum. AITD is also known to affect both fertility and pregnancy outcome as evidenced by increased fetal loss. However, the precise mechanisms of this influence have not been fully understood. Here we have reviewed the mechanisms of self-recognition thought to be active in AITD and we have included recent information on the potential role of fetal microchimerism (exposure of paternal antigen to the mother during and after pregnancy).

Further evidence for a strong genetic influence on the development of autoimmune thyroid disease: the California twin study

To determine the heritable component of Graves' disease (GD) more precisely, a disease survey questionnaire completed by 13,726 California-born twin pairs over the age of 37 years was used as the foundation of this study. On the basis of this survey, each member of pairs reporting a past diagnosis of GD was then sought for an extensive telephone interview to seek diagnostic confirmation. Successful diagnostic evaluation occurred in 108 cases, of which 99 affected twin pairs form the basis of this report. The results indicate that the estimated pairwise concordance for is 17% in monozygotic (MZ) twins, and 1.9% in dizygotic (DZ) twins, which are in close agreement with a recent report from a Danish twin population. Moreover, the reported 3.9% occurrence of GD found in the first-degree relatives of affected twin pairs supports these findings. In contrast, only 0.45% of all twins, 0.27% of the spouses of twins, and approximately 0.16% of the first-degree relatives of unaffected twins were reported to have GD. Additionally, among the unaffected MZ twins of patients with GD, 17% reported having chronic thyroiditis and 10% other nonthyroid autoimmune conditions such as lupus erythematosus, pernicious anemia, or idiopathic thrombocytopenic purpura. Thus, a genetic predisposition appears to be shared for both thyroid and some nonthyroid autoimmune diseases. While it seems that GD is a strongly and nonspecifically heritable condition, the relatively low level of twin concordance indicates that this disease likely requires a nonheritable etiologic determinant(s) as well.

Evolutionary stable strategy: a test for theories of retroviral pathology which are based upon the concept of molecular mimicry

The genetic makeup of animal and plant populations is determined by established principles and concepts. Ecology and evolution provide a basic theoretical framework for understanding how genetic changes occur in populations. Whether these rules can be applied to host retroviral populations is unknown. Individuals infected with the human immunodeficiency virus (HIV) contain within their bodies a viral population. This population is known as a viral quasispecies. Located in the transmembrane protein of HIV-1 is the viral sequence Gly-Thr-Asp-Arg-Val. Previous immunological studies have shown that viral antibody is produced in response to this five-amino-acid sequence. Antibody to this viral sequence also crossreacts and binds to a related peptide sequence found on certain immune cells. This related sequence, Gly-Thr-Glu-Arg-Val, is found on immune cells bearing a structure known as the major histocompatibility complex (MHC). The viral transmembrane sequence, Gly-Thr-Asp-Arg-Val, can be substituted with alanine residues utilizing site-directed mutagenesis. This creates a viral clone devoid of the genetic similarity with the MHC. Chimpanzees progressing to AIDS contain both sequences of interest. Suppression of the chimpanzee quasispecies utilizing anti-retroviral drugs is proposed. This action serves to suppress the presence of the viruses containing the sequence Gly-Thr-Asp-Arg-Val. When viral load has been reduced significantly, a drug resistant, alanine altered clone is to be introduced in large numbers. The concept of evolutionary stable strategy predicts that a viable HIV clone with alanine residues can genetically dominate the viral population. Immune system recognition of the alanine sequence is likely to result in renewed antibody production. Antibodies to the alanine containing viral sequence should not recognize or bind to the MHC. Immunological parameters can then be measured to determine the physiological impact of eliminating a sequence responsible for molecular mimicry between virus and host.

The nature of autoantigens targeted in autoimmune endocrine diseases

Autoimmune endocrine diseases result from autoimmune processes involving autoreactive T cells and/or autoantibodies. Considerable progress has been made in elucidating the self- (auto-) antigens involved in these processes. These include tissue-specific membrane receptors, enzymes and secreted hormones. As discussed here by Yao-Hua Song and colleagues, diagnostic and therapeutic applications should now result from these discoveries.

Evidence for a retroviral trigger in Graves' disease

An apparently high frequency of Graves' disease encountered in New Orleans, Louisiana, prompted an investigation for a possible infectious agent that might be triggering the disease in genetically susceptible individuals. We studied 40 patients with Graves' disease, and compared them to the following groups of controls: age and gender matched healthy subjects; patients with multinodular goiter (non-autoimmune thyroid controls); patients with chronic lymphocytic thyroiditis (autoimmune thyroid disease controls) and additional organ or tissue specific autoimmune controls exclusive of thyroid autoimmunity, including patients with Type I diabetes and other endocrine autoimmune complex disorders. Serum antibodies against a prototypic strain of a human intracisternal A-type retroviral particle type 1 (HIAP-1) were detected by a sensitive and specific immunoblotting assay. In 87.5% (35/40) of the Graves' disease patients there was a positive reaction against several HIAP-1-associated proteins, predominantly 97 Kd and 80 Kd, with only 5 showing no reactivity to any. In contrast, 2% (2/105) of sera from normal controls showed positive reactivity. Furthermore, only 10% (1/10) of sera from multinodular goiter control patients and 10% (1/10) of Hashimoto's patients showed reactivity (p < 0.0005). Sera from 3 of 20 (15%) of Type I diabetic patients none of whom had Graves' disease, showed reactivity but there was no reactivity in 9 other patients with one or more of the endocrine autoimmune complex disorders, including Addison's disease, vitiligo, myasthenia gravis and pernicious anemia. In addition we studied two individuals with Graves' disease from each of two families residing outside Louisiana, all of whom were positive for these antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Infections and autoimmune endocrine disease

The literature examined in this review points to the possible involvement of infectious agents in the pathogenesis of autoimmune endocrine diseases, primarily autoimmune thyroid disease and diabetes mellitus. Various mechanisms have been proposed to explain induction of autoimmunity by infection but it seems that three possibilities may be important in individuals susceptible to developing autoimmune disease: molecular mimicry (perhaps to retroviruses); polyclonal T cell activation (by an endogenous superantigen or an infecting organism); and MHC class II antigen induction. It seems reasonable that all three mechanisms operate together or separately in different individuals. Data continue to accumulate in favour of infectious agents being important initiators of autoimmune disease.

A high prevalence of human T-lymphotropic virus type I carriers in patients with antithyroid antibodies

Human T-lymphotropic virus type I (HTLV-I) is a causative retrovirus of adult T-cell leukemia lymphoma and HTLV-I associated myelopathy/tropical spastic paraparesis. HTLV-I is also associated with some forms of pulmonary alveolitis, chronic arthropathy, polymyositis, and uveitis. In this study, the possible role of HTLV-I infection in the pathogenesis of autoimmune thyroid diseases with positive antithyroid antibody (ATA) to microsomal antigen or thyroglobulin was evaluated. In Fukuoka Prefecture or the northern part of Kyushu Island located in the southwestern part of Japan, the prevalence of patients with HTLV-I antibody was screened using the particle agglutination test and then was further confirmed either by the indirect immunofluorescence method or the western blot method. The observed prevalence in patients with thyroid disorders and the estimated prevalence calculated considering the sex- and age-specific prevalence among healthy blood donors (n = 16,008) were as follows: 19 (7.4%) vs 7.8 (3.0%) (p < 0.001) for ATA-positive chronic thyroiditis (n = 257), 21 (7.0%) vs 6.6 (2.2%) (p < 0.001) for ATA-positive Graves' disease (n = 298), 4 (4.3%) vs 2.1 (2.2%) (ns) for ATA-negative Graves' disease (n = 94), 1 (2.9%) vs 1.1 (3.1%) (ns) in ATA-negative hypothyroidism (n = 35), and 3 (1.8%) vs 5.0 (2.9%) (ns) for ATA-negative nodular goiter (n = 170). These findings thus suggest that HTLV-I infection may have some relationship to ATA-positive thyroid disorders.

Analysis of human immunodeficiency virus type 1 nef gene sequences present in vivo

The nef genes of the human immunodeficiency viruses type 1 and 2 (HIV-1 and HIV-2) and the related simian immunodeficiency viruses (SIVs) encode a protein (Nef) whose role in virus replication and cytopathicity remains uncertain. As an attempt to elucidate the function of nef, we characterized the nucleotide and corresponding protein sequences of naturally occurring nef genes obtained from several HIV-1-infected individuals. A consensus Nef sequence was derived and used to identify several features that were highly conserved among the Nef sequences. These features included a nearly invariant myristylation signal, regions of sequence polymorphism and variable duplication, a region with an acidic charge, a (Pxx)4 repeat sequence, and a potential protein kinase C phosphorylation site. Clustering of premature stop codons at position 124 was noted in 6 of the 54 Nef sequences. Further analysis revealed four stretches of residues that were highly conserved not only among the patient-derived HIV-1 Nef sequences, but also among the Nef sequences of HIV-2 and the SIVs, suggesting that Nef proteins expressed by these retroviruses are functionally equivalent. The "Nef-defining" sequences were used to evaluate the sequence alignments of known proteins reported to share sequence similarity with Nef sequences and to conduct additional computer-based searches for similar protein sequences. A gene encoding the consensus Nef sequence was also generated. This gene encodes a full-length Nef protein that should be a valuable tool in further studies of Nef function.

In vitro secretion of interleukin-1 beta and interferon-gamma by peripheral blood lymphomononuclear cells in diabetic patients

There is evidence that cytokines, in particular interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) might mediate beta cell destruction in type 1 diabetes. Therefore the secretion of these cytokines by peripheral blood lymphomononuclear cells (PBMNC) was investigated in basal conditions and 48 h after stimulation with T-cell mitogen phytohaemagglutinin (PHA) in 33 diabetic patients and in 10 normal controls. The patients were divided in 4 groups (Group 1, 10 controls; Group 2, 13 newly diagnosed type 1 diabetics, the onset had occurred from 5 days to 3 months before the study; Group 3, 10 Long Standing (LS) type 1 diabetics with duration of the disease between 2 years and 10 years; and Group 4, 10 type 2 diabetics). No difference was found among the 4 groups considered in IL-1 beta secretion by unstimulated cultures, although the percentage of TAC+ cells was significantly higher in type 1 newly diagnosed diabetic patients with respect to the LS, the type 2 diabetics and the controls. After PHA stimulation a significant increase of IL-1 beta was found in newly diagnosed type 1 diabetic patients in comparison with the control subjects, the LS and type 2 diabetic patients (P < 0.001). The supernatants of newly diagnosed type 1 diabetics also showed a significant reduction in IFN-gamma production both in basal (P < 0.01) and in stimulated conditions (P < 0.001) in comparison with the controls, the LS (P < 0.002 in basal, and P < 0.001 in stimulated conditions) and the type 2 diabetic patients (P < 0.001 both in basal and stimulated conditions).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunogenicity of a unique region of the human thyrotropin receptor

Clarifying the role of the TSH receptor protein in the autoimmune process may be the key to understanding the development of Graves' disease. In the present study we used a 16 amino acid peptide of the human TSH receptor (hTSHR) to immunize rabbits. A comparable, but theoretically less immunogenic, peptide was injected into other rabbits. The antibody response against these and other peptides, as well as against solubilized human thyroid membrane (TM) and guinea pig fat cell membrane (GPF) proteins, was tested using ELISA and Western blots. The GPF and TM binding pattern of rabbits' sera was compared to that of Graves' patients' sera. We have identified an area of antigenic cross-reactivity between GPF and TM; a 63 kD protein was present in both GPF and TM, and this protein uniformly bound IgG-s of the rabbits' postimmunization sera and one of eight Graves' patient's serum. We have shown that i) a theoretically immunogenic 16 amino acid peptide was indeed highly immunogenic in rabbits, ii) antibodies binding to GPF and TM were detected after immunization, and iii) the peak of thyroid stimulating immunoglobulin activity of sera was followed by a transient elevation of serum triiodothyronine levels. Further studies investigating the immunogenic epitopes of the hTSHR as well as characterizing the 63 kD protein are indicated.

Expression polymerase chain reaction for the in vitro synthesis and epitope mapping of autoantigen. Application to the human thyrotropin receptor

The clinical applicability of a newly described polymerase chain reaction directed protein expression system was assessed for the in vitro synthesis and partial epitope mapping of large radiolabeled human thyrotropin receptor (hTSH-R) protein segments. PCR amplification of targeted regions within the hTSH-R cDNA followed by in vitro transcription and translation permitted rapid synthesis of protein segments ranging in size from 18 to 62 kDa. Initial epitope mapping was directed at a 52 amino acid segment unique to the hTSH-R compared to otherwise homologous glycoprotein hormone receptors. Sera from Graves' disease patients known to have autoantibodies against the hTSH-R were used to immunoprecipitate two protein fragments differing only by the presence of the unique region in the larger fragment (E5) but not in the smaller fragment (E4). Dense precipitation bands were obtained using Graves' sera to immunoprecipitate E5 whereas little or no specific immunoprecipitation of E4 occurred. Normal sera gave only weak immunoprecipitation bands of E5. The technique provides significant advantages over conventional cloning methods and should have general applicability in the study of other protein targets of autoimmune disease.

Thyroid autoimmunity

Antigenic structure remains a major focus in thyroid immunology. The genes for three major thyroid antigens--thyroglobulin, thyroid peroxidase and the thyrotropin receptor--were sequenced in the late 1980's, and epitopes for antibody and T cells have been reported within the last year. In addition, new evidence for selective use of T-cell receptor V gene segments in human thyroid infiltrates may point the way to specific immunotherapy.

Graves' IgG recognizes linear epitopes in the human thyrotropin receptor

Twenty-nine peptides covering the full extracellular domain of the human thyrotropin receptor have been synthesized and tested for reactivity with Graves' patients' and normal sera in ELISA. Two peptides, amino acids 331-350 and the second extracellular loop of the transmembrane segment, bound IgG-s from 5 and 4 of 10 Graves' disease patients' sera, respectively. Neither of these two peptides showed enhanced binding to normal IgG. There were no apparent differences between the Graves' disease and normal group with respect to the other 27 peptides. We conclude that peptide 331-350 and the second extracellular loop carry important linear epitopes which may contribute to the disease process in selected Graves' patients.

Analysis of human TSH receptor gene and RNA transcripts in patients with thyroid disorders

Human TSH receptor (hTSH-R) gene and RNA transcripts were analyzed by Southern and Northern blots in patients with various thyroid disorders, and in tissue cell lines. A 1.4 Kb cDNA encoding the extracellular human TSH-R domain was used as a probe. Southern analysis revealed two constant bands of 11.0 and 5.0 Kb (hTSH-R) in the thyroid and human white cell samples studied, regardless of the disease process. Northern analysis showed a predominant band at about 4.4 Kb in the thyroid tissues but not in non-thyroid tissue or cell lines tested. There were no gene rearrangements or abnormal transcripts in Graves' disease or multinodular goiter samples. In contrast, the labelled cDNA TSH-R probe did not bind to RNA isolated from 1 of 2 papillary cancer samples. A portion of the unique area of the h-TSH receptor (approximately nucleotides 1100-1230) was directly sequenced in thyroid glands from patients with Graves' disease, multinodular goiter, and differentiated thyroid cancer. No mutations or polymorphisms were identified in these samples, as compared to normal thyroid or control placenta, although further definition of sequence variation in other areas of the TSH receptor, as well as in more samples, needs to be performed. The present study indicates the normal patterns of DNA and RNA hybridization in a variety of thyroid tissues and disease states, and demonstrates that pathologic thyroid samples, with the possible exception of thyroid cancer, were not associated with specific nucleotide abnormalities in the unique area of the TSH receptor that was studied.