Significance of antibodies reactive with a 64 kDa eye muscle membrane antigen in patients with thyroid autoimmunity

Diplopia in a patient with Hashimoto's thyroiditis: A case report and literature review

BACKGROUND

A case report of Hashimoto's thyroiditis-associated ophthalmopathy that masqueraded as double elevator palsy in 1 eye.

CASE PRESENTATION

A 54-year-old woman presented to our strabismus clinic with diplopia for 1 year. She was diagnosed with double elevator palsy in the left eye. The forced duction test yielded positive findings for the inferior rectus of the left eye; hence, computed tomography of the orbit and thyroid-associated blood tests were performed; surprisingly, the thyroid function test results were consistent with hypothyroidism and the antibody results such as antithyroglobulin and antithyroid peroxidase were markedly elevated, and the patient was diagnosed with Hashimoto's thyroiditis and treated with corticosteroids. Unfortunately, her diplopia was not relieved with medical management. Subsequently, a 9-mm left inferior rectus recession was performed.

CONCLUSION

Clinicians should be aware of the atypical signs of Hashimoto's thyroiditis for its proper diagnosis and management.

Severe thyroid-associated orbitopathy in Hashimoto's thyroiditis. Report of 2 cases

Thyroid-associated orbitopathy (TAO) is characterized by immune-mediated inflammation of the extraocular muscles surrounding orbital connective tissue and adipose tissue. Severe orbitopathy related to autoimmune thyroid disease often occurs in patients with Grave's disease, but it is rare in patients with Hashimoto's thyroiditis. The pathogenesis of TAO is unclear. Several studies have noted a strong correlation between the levels of antibodies to thyrotropin receptor antibody (TRAb) and TAO in Graves' disease. Mild upper eyelid retraction has been reported to be common in Hashimoto's thyroiditis patients, however severe orbitopathy is rare. We report two cases of severe TAO in patients with Hashimoto's thyroiditis who required systemic glucocorticoid therapy and orbital irradiation to treat the TAO. The activity of the TAO was high in both patients, because their clinical activity scores (CAS) for the orbitopathy were high, and magnetic resonance imaging (MRI) showed enlargement of the extraocular muscles and an increase in T2 signal intensity and prolonged T2 relaxation time which indicate an active stage of inflammation. We tested the presence of TRAb by three different assays and were negative in both patients. Since the eye muscle damage cannot be due to TSH receptor antibodies, other pathogenetic mechanisms may be responsible for the orbitopathy in patients with Hashimoto's thyroiditis.

Eye and eyelid abnormalities are common in patients with Hashimoto's thyroiditis

BACKGROUND

Overt ophthalmopathy is presumed to be uncommon in patients with Hashimoto's thyroiditis compared to Graves' disease, where significant eye changes are found in approximately 40% of patients. On the other hand, when observing, more subtle eye changes, particularly upper eyelid retraction (UER) and mild inflammatory signs, may be common in patients with Hashimoto's thyroiditis.

METHODS

We have determined the prevalence and characteristics of eye signs in recently diagnosed patients with Hashimoto's thyroiditis studied prospectively since 2004 till date in Sydney (Australia). We measured serum orbital antibodies in 20 of the patients in enzyme-linked immunosorbent assay.

RESULTS

The overall prevalence of eye signs in patients with Hashimoto's thyroiditis was 34%, of whom about a quarter had chronic UER, determined as a margin-reflex distance of >5 mm, as the main sign. There was no correlation between eye signs and cigarette smoking. Overall, there was only a modest correlation between eye signs and positive antibody tests, and 40% of patients with no eye signs at the time of study were antibody positive.

CONCLUSION

Eye changes, in particular UER, are common in patients with Hashimoto's thyroiditis. Since thyroid stimulating hormone-receptor antibodies are not usually associated with Hashimoto's thyroiditis, autoimmune mediated damage of the levator palpebrae superioris (eyelid) muscle cannot be due to these antibodies. Although eyelid abnormalities may be a minor problem for most patients, for some there are major cosmetic implications requiring surgical management.

Eye muscle antibodies in Graves' ophthalmopathy: pathogenic or secondary epiphenomenon?

The extra ocular (eye) muscles are one of the principal tissues involved in the autoimmune-mediated inflammation of Graves' ophthalmopathy (GO). Several eye muscle proteins are targeted by autoantibodies or sensitized T lymphocytes, or both, and include: G2s, which is now identified as the terminal 141 amino acids of the winged-helix transcription factor FOXP1, the flavoprotein (Fp) subunit of the mitochondrial enzyme succinate dehydrogenase, the so-called "64kDa protein", a non-tissue specific membrane protein called 1D and the calcium binding protein calsequestrin. Of these, antibodies against G2s and Fp are the most sensitive markers of eye muscle damage in patients with thyroid autoimmunity even though neither antigen is specific to eye muscle and neither antibody is specific to GO. However, the recent finding that the calsequestrin gene is 4.7 times more expressed in eye muscles than other skeletal muscles suggests that we should reconsider the possible role of anti-calsequestrin autoantibodies in ophthalmopathy. GO may comprise two main subtypes with different pathogenetic mechanisms, namely ocular myopathy in which eye muscle inflammation predominates and congestive ophthalmopathy where inflammatory changes occur in the periorbital connective tissues in the absence of eye muscle dysfunction. Anti-G2s and anti-Fp antibodies are closely associated with the ocular myopathy subtype of GO while antibodies targeting type XIII collagen, the only member of the collagen family to have a transmembrane domain, are closely linked to congestive ophthalmopathy. Since both G2s and Fp are intracellular antigens it is unlikely that either antibody causes eye muscle fiber damage in GO, although a role in the later stages of the disease when the fiber has released its cellular contents has not been excluded. Eye muscle antibodies that are cytotoxic to eye muscle cells in antibody-dependent cell-mediated cytotoxicity (ADCC) are more likely to play a role in eye muscle fiber damage since they target a putative eye muscle cell membrane antigen, the identity of which is currently being investigated. While anti-G2s and anti-Fp antibodies are probably secondary to an underlying reaction, such as cytotoxic T lymphocyte targeting of an eye muscle membrane antigen that has yet to be identified, they are reliable markers of immunologically mediated eye muscle fiber damage in patients with Graves' hyperthyroidism. In conclusion, while a pathogenic role for eye muscle antibodies has not been excluded, they are most likely secondary to cytotoxic T cell reactions in GO and, as such, good markers of this autoimmune disease.

Thyroid autoantibodies

Although assays to detect thyroid autoantibodies have been available for more than 40 years, their place in the clinical management of thyroid disease has remained controversial; however, novel automated detection techniques using recombinant antigens are increasing the sensitivity and specificity of the assays, particularly for antibodies to the TSH receptor. In addition, new antigenic targets have been defined including the sodium-iodide symporter and four eye muscle proteins targeted in Graves' ophthalmopathy. This article summarizes the immunobiology, assay methodology and prevalence in thyroid diseases of each of the major thyroid autoantibodies before discussing the clinical indications for their use in thyroid diseases.

Thyroid-associated ophthalmopathy: clinical features, pathogenesis, and management

Thyroid-associated ophthalmopathy (TAO) is a progressive eye disorder characterized by immune-mediated inflammation of the extraocular muscles and orbital connective tissue. TAO is linked, in a unique way, with thyroid autoimmunity, in particular Graves' hyperthyroidism. Our working hypothesis for the pathogenesis of TAO is that recognition of a thyrotropin receptor (TSHR)-like protein in the orbital preadipocytes by antibodies may be the initial event leading to homing of lymphocytes into the orbital tissues. In the course of thyroid inflammation, antibodies and T cells reactive against G2s expressed in thyroid membranes cross-react with the protein in the eye muscle fiber, leading to eye muscle damage and dysfunction. Those patients with anti-G2s antibodies develop ocular myopathy. Antibodies against flavoprotein, the 64-kDa protein, which are produced in the context of eye muscle fiber damage and mitochondrial rupture, are sensitive markers of immune-mediated fiber necrosis in patients with ophthalmopathy but do not directly damage the eye muscle. Antibodies against type XIII collagen, which is localized in the plasma membranes of orbital fibroblast, may be a new marker for the congestive ophthalmopathy subtype of TAO. The measurement of antibodies against key eye muscle and orbital connective tissue autoantigens may have a role in the management of active ophthalmopathy and its prediction in patients with Graves' hyperthyroidism.

Autoantibodies to the flavoprotein subunit of succinate dehydrogenase: analysis of specificity in autoimmune thyroid disease

OBJECTIVE

Thyroid-associated ophthalmopathy is a progressive eye disorder affecting the extraocular muscle and orbital connective tissue and is considered to have an autoimmune aetiology. A recent study reported a close relationship between serum antibodies against the flavoprotein subunit of succinate dehyhdrogenase (SDHFp) and active thyroid-associated ophthalmopathy involving eye muscle damage. The aim of the present study was to develop a sensitive and quantitative radiobinding assay for the detection of antibodies to the flavoprotein subunit of succinate dehydrogenase and to use this to determine the distribution of antibodies in different patient groups.

DESIGN AND PATIENTS

Serum samples from the following patient groups were analysed: 20 systemic lupus erythematosus; 20 Addison's disease; 26 autoimmune hypothyroidism; 28 Graves' hyperthyroidism; 12 pretibial myxoedema; 25 thyroid-associated ophthalmopathy. Sera from 20 healthy subjects were used as controls. [35S]-labelled succinate dehydrogenase flavoprotein was produced in an in vitro transcription-translation system and subsequently used in immunoprecipitation experiments with sera from patient and control groups to test for the presence of antibodies to the flavoprotein.

RESULTS

Succinate dehydrogenase flavoprotein antibodies were detected in five of the 20 (25%) patients with Addison's disease, six of the 20 (30%) with systemic lupus erythematosus, five of the 26 (19%) with autoimmune hypothyroidsm, six of the 28 (21%) with Graves' hyperthyroidism, two of the 12 (17%) with pretibial myxoedema and three of the 25 (12%) with thyroid-associated ophthalmopathy. The frequencies of flavoprotein antibodies were significantly greater than controls (P-value < 0.05) for patients with systemic lupus erythematosus (P = 0.02), but not for patients with either Addison's disease (P = 0.05), pretibial myxoedema (P = 0.13), Graves' hyperthyroidism (P = 0.07), autoimmune hypothyroidism (P = 0.06) or thyroid-associated ophthalmopathy (P = 0.24). For the patients with thyroid-associated ophthalmopathy, the frequency of SDHFp antibodies did not appear to be related to the length of time from diagnosis: the group containing samples taken less than one year from diagnosis showed no increased frequency of SDHFp antibodies when compared to controls (P = 0.10), with three of the 18 (17%) patients being positive. With respect to seven patients with thyroid-associated ophthalmopathy diagnosed for more than a year, SDHFp antibodies were not detected in any of their serum samples. In addition, the clinical severity of the disease, as recorded by the NOSPECS classification, did not correlate with the frequency of SDHFp antibodies: P = 0.13, 0.33 and 0.38, respectively, for patients with Grade II, III and IV ophthalmopathy. Similar results were also found in the case of patients with pretibial myxoedema and eye disease: P = 0.06 for patients with Grade III ophthalmopathy and, SDHFp antibodies were not detected in any of the sera taken from patients with Grade IV ophthalmopathy. In addition, no association was found between disease duration and the frequency of antibodies to the flavoprotein in this patient group.

CONCLUSIONS

Our results indicate that succinate dehydrogenase flavoprotein antibodies are not a suitable marker for thyroid-associated ophthalmopathy, at least with the assay system used, as they can be found in patients who do not have eye disease and therefore lack the disease specificity required of a diagnostic tool.

Eye muscle antibodies in patients with ocular myasthenia gravis: possible mechanism for eye muscle inflammation in acetylcholine-receptor antibody-negative patients

Myasthenia gravis is an organ-specific autoimmune disorder generally thought to be caused by an antibody-mediated attack against the skeletal muscle nicotinic acetylcholine (Ach) receptor (AchR) at the neuromuscular junction. Extraocular muscle weakness and double vision are present in about 90% of patients with myasthenia gravis and are the predominant complaints in about 20% of patients, when the condition is called ocular myasthenia gravis (OMG). While serum antibodies against the AchR are detected in most patients with generalized myasthenia gravis (GMG), they are not found in about one-third of patients with the ocular variety, and epidemiological, clinical, and serological studies suggest that OMG and GMG are two separate diseases. Both forms of myasthenia gravis are sometimes associated with thyroid autoimmunity or thyroid-associated ophthalmopathy (TAO). We have therefore tested the sera of patients with GMG and OMG by Western blotting for antibodies against porcine eye muscle membrane proteins in general, and by enzyme-linked immunosorbent assays (ELISA) specifically for reaction with two skeletal muscle antigens which are prominent marker antigens for TAO, namely, the calcium-binding protein calsequestrin and the so-called "64-kDa protein." The 64-kDa protein has recently been identified as the flavoprotein subunit of mitochondrial succinate dehydrogenase. Patients with ophthalmopathy and myasthenia were excluded. Nine of the patients had associated Graves' hyperthyroidism without evident ophthalmopathy and one had Hashimoto's thyroiditis. Antibodies against porcine eye muscle membrane antigens of M(r) 15-110 kDa were detected in patients with GMG or OMG, one or more antibodies being detected in 100% of patients with GMG and in 88% of those with OMG. The most frequently found antibodies were those targeting eye muscle membrane proteins of 15, 67, and 110 kDa. Antibodies reactive with purified calsequestrin (63 kDa) were detected in 21% of patients with OMG but in no patient with GMG. Antibodies recognizing purified succinate dehydrogenase (67 kDa) were found in 42% of patients with OMG, in 100% (5 of 5) of patients with GMG, and in 48% of all patients with myasthenia gravis not associated with Graves' hyperthyroidism. There was no close correlation between any eye muscle-reactive antibody and antibodies against the AchR in either group of myasthenic patients. The findings support the notion that immunoreactivity against skeletal muscle proteins other than the AchR may play a role in the development of the muscle weakness in AchR antibody-negative patients with OMG and GMG, although it is unlikely that any of the antibodies demonstrated in this study are directly implicated. Similarly, while the demonstration of antibodies reactive with eye muscle antigens associated with TAO in patients with OMG raises the possibility that the link between the ocular lesions of myasthenia gravis and Graves' disease may be autoimmunity against a common antigen(s), it is more likely that both disorders are mediated by cytotoxic T cells recognizing another cell membrane antigen, such as the novel thyroid and eye muscle shared protein G2s, and that serum antibodies reactive with succinate dehydrogenase Fp subunit and calsequestrin are markers of an immune-mediated eye muscle reaction.

The 64-kilodalton eye muscle protein is the flavoprotein subunit of mitochondrial succinate dehydrogenase: the corresponding serum antibodies are good markers of an immune-mediated damage to the eye muscle in patients with Graves' hyperthyroidism

Thyroid-associated ophthalmopathy (TAO) is a progressive eye disorder associated with thyroid autoimmunity, particularly Graves' hyperthyroidism, which is generally considered to have an autoimmune etiology. Eye muscle membrane proteins reportedly of 55 and 64 kDa are the best markers of the ophthalmopathy. The main focus of our recent studies has been to purify the pertinent proteins from porcine eye muscle membranes and characterize them. The 64-kDa protein is now shown from a partial sequence and by Western blotting using specific antibody probes to be the flavoprotein (Fp) subunit of succinate dehydrogenase and to have a correct molecular mass of 67 kDa. The protein was purified and cleaved with cyanogen bromide, and the N-terminal region of an immunoreactive partial peptide was determined. The 20-amino acid porcine sequence so obtained matched one within the Fp subunits of human and bovine succinate dehydrogenases in 20 and 18 of these positions, respectively. Succinate dehydrogenase is both a citric acid cycle enzyme and a component (complex II) of the mitochondrial respiratory chain. It is thus essential for aerobic energy production and is highly conserved. The mature human and bovine Fp subunits are 92% homologous and have a molecular mass of approximately 67 kDa, the same as our redetermined value for the 64-kDa marker protein. Sera from patients with TAO and from those with Graves' hyperthyroidism without evident ophthalmopathy highlighted the 64-kDa marker protein in crude porcine eye muscle membranes and the Fp subunit of highly purified bovine succinate dehydrogenase at the identical position on Western blots. Anti-beef Fp antibodies were detected in sera from 67% of patients with active TAO of more than 1-yr duration, in 30% with stable TAO of more than 3-yr duration, and in 30% of patients with Graves' hyperthyroidism without ophthalmopathy, but in only 7% of age- and sex-matched normal subjects. As succinate dehydrogenase is bound to the matrix (inside) surface of the mitochondrial inner membrane, it is unlikely to be accessible to circulating autoantibodies. We would postulate that eye muscle damage in ophthalmopathy is probably caused by cytotoxic antibodies or CD+ T lymphocytes targeting a cell membrane antigen, such as the thyroid and eye muscle shared protein G2s, and that presentation of succinate dehydrogenase is secondary. On the other hand, an autoantibody response to succinate dehydrogenase may be a good marker of immune-mediated damage to the eye muscle fiber and may support the idea that the extraocular muscles are targets of the autoimmune reactions of TAO.

Reevaluation of the prevalences of serum autoantibodies reactive with "64-kd eye muscle proteins" in patients with thyroid-associated ophthalmopathy

Serum autoantibodies reactive with eye muscle proteins of "64 kilodaltons (kd)" are frequently found in patients with Graves' hyperthyroidism and thyroid-associated ophthalmopathy (TAO). Earlier, we cloned a 64-kd protein that was identified as calsequestrin, a calcium-binding protein localized in the sarcoplasmic reticulum of striated muscle and extensively studied another cloned 64-kd protein, called 1D, which is expressed in thyroid and eye muscle, and some other tissues. Using a monoclonal antibody against calsequestrin, a polyclonal antibody against 1D and a TAO patient serum reactive with the "64-kd protein," as probes, we performed Western blots of porcine eye muscle membrane. We identified three different proteins in the 63 to 67 kd molecular weight range that were targeted by antibodies in sera from patients with TAO. It was not possible to differentiate antibodies reactive with calsequestrin and 1D because these two proteins have very similar molecular weights--63 to 64 kd--and band appearance in Western blotting. A 67-kd protein was most frequently recognized by TAO patients' sera. Serum antibodies reactive with the 67-kd protein were detected in 73% of patients with active TAO of 1 year duration or less, in 37% of patients with TAO of more than 3 years' duration, in 35% with Graves' hyperthyroidism without evident ophthalmopathy, in 30% of patients with Hashimoto's thyroiditis, and in 16% of normal subjects. Serum antibodies reactive with calsequestrin/1D were detected in 47% of patients with active TAO of less than 1 year, in 22% of patients with TAO longer than 3 years, 17% with Graves' hyperthyroidism without evident ophthalmopathy, in 10% of patients with Hashimoto's thyroiditis, and in 21% of normal subjects. The prevalence of anti-67-kd protein antibodies in TAO patients corresponded to those reactive with the so called "64-kd protein" that we have reported previously. In conclusion, we were able to improve the accuracy of the Western blots by comparing the molecular weight of positive bands using specific antibodies reactive with eye muscle antigens as probes. The previously recognized, and extensively studied, "64-kd protein" is now shown to have a molecular weight of 67 kd. The role of the various eye muscle antibodies in the diagnosis and management of the ophthalmopathy associated with Graves' hyperthyroidism needs to be addressed in prospective studies using purified or recombinant full-length proteins.

Serum antibodies reactive with eye muscle antigens and the TSH receptor in a euthyroid subject who developed ophthalmopathy and Graves' hyperthyroidism

Serum antibodies reactive with eye muscle autoantigens, in particular a 64-kDa protein that is also expressed in the thyroid, and the TSH receptor, are associated with the ophthalmopathy that occurs in about 50% of patients with Graves' hyperthyroidism. We have had the opportunity to study a euthyroid, apparently normal, 35-year-old woman with a family history of thyroid autoimmunity and "colitis" but no clinical or biochemical evidence for thyroid disease or ophthalmopathy, who developed Graves' hyperthyroidism and ophthalmopathy together 18 months later. Serum taken when the patient was first seen was positive for antibodies reactive with (i) 9 different eye muscle proteins ranging in size from 15 to 130 kDa, notably those of 64, 55, and 50 kDa, by immunoblotting with eye muscle membranes, (ii) eye muscle and Müller's muscle cell membrane antigens in antibody-dependent cell-mediated cytotoxicity (ADCC), (iii) an eye muscle cytoplasmic antigen in indirect immunofluorescence, and (iv) the TSH receptor as measured in a radioreceptor binding inhibition assay. When she developed Graves' disease, serum concentration of antibodies to the 55-kDa protein had decreased from +2 to +/-, those reactive with other eye muscle antigens had not changed significantly, and TSH receptor antibodies had increased 3-fold. This case report suggests that antibodies reactive with eye muscle antigens and the TSH receptor are markers of the ophthalmopathy and able to predict its development in predisposed subjects. The significance of these findings needs to be confirmed in a prospective study of first-degree relatives of patients with thyroid-associated ophthalmopathy and patients with Graves' hyperthyroidism without eye signs.

Failure to demonstrate cell-mediated immunity to orbital tissue antigens and epitopic fragments of a 64 kDa protein in the majority of patients with thyroid-associated ophthalmopathy

We have studied a possible role of T cell sensitization to eye muscle antigens in patients with thyroid-associated ophthalmology (TAO). Peripheral blood mononuclear cell (PBMC) proliferation in response to crude porcine orbital tissue antigens, partially purified porcine eye muscle membrane proteins and predicted epitopic fragments of the recombinant 64 kDa protein 1D, was determined in patients with TAO and thyroid autoimmunity without eye disease. When membrane and cytosol fractions were used as antigen PBMC from 43% of patients with TAO but only 12.5% of normal subjects were responsive to a crude orbital connective tissue membrane fraction, although this difference was not significant. We were unable to demonstrate specific recognition of partially purified eye muscle membrane fractions; although most of the fractions tested were occasionally recognized by T cells from patients with ophthalmopathy, this was also the case for patients with autoimmune thyroid disease without ophthalmopathy and normal subjects. We did not clearly identify epitopic sequences within the 1D protein, most of the predicted peptides tested being recognized not only by T cells from a small proportion of patients with TAO, but also by those from some patients with autoimmune thyroid disease without ophthalmopathy and normal subjects. It is noteworthy however that approximately 22% of TAO patients, but no normal subjects, were positive to one or more of three peptides, suggesting that reactivity to the 1D protein may play a role in the pathogenesis of the eye disorder in some patients with TAO. The inconsistent and generally low T cell responses to crude and purified antigens noted in a few patients with TAO could be explained by low numbers of specifically sensitized lymphocytes in peripheral blood.

New assays for the measurement of serum antibodies reactive with eye muscle membrane antigens confirm their significance in thyroid-associated ophthalmopathy

Although sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting are widely used to detect serum antibodies in patients with autoimmune disorders, this procedure unfolds and denatures proteins and may alter antibody binding sites. We have used nondenaturing methods for the purification of a 64-kDa eye muscle (EM) membrane antigen associated with thyroid-associated ophthalmopathy (TAO). Pig EM membrane proteins were prepared from crude homogenates by high-speed centrifugation and solubilized by hand homogenization. The 64-kDa protein was further purified by isoelectric focusing performed in the absence of SDS, detergents, reducing agents, and urea. Sera from patients with active TAO of recent onset and thyroid autoimmunity without ophthalmopathy were tested for reactivity against purified native 64-kDa protein in immunoblotting. Tests were positive in 64% of patients with TAO, in 37.5% of those with Graves' hyperthyroidism without eye disease, in 11% of patients with Hashimoto's thyroiditis without eye disease, and in 13% of normal subjects. Many of the same sera were also tested for cytotoxic activity against human EM cells in an antibody-dependent cell-mediated cytotoxicity (ADCC) assay. ADCC tests were positive in 69% of patients with TAO but in no normal subject. The specificity and sensitivity of these two tests in TAO surpass those for all other published results for orbital tissue reactive autoantibodies. Although there was a tendency for a relationship between reactivity to the 64-kDa protein and cytotoxic activity against EM cells in ADCC there were many exceptions and overall the relationship between the two tests was not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum antibodies reactive with eye muscle membrane antigens are detected in patients with nonspecific orbital inflammation

PURPOSE

Nonspecific orbital inflammation, also called "orbital pseudotumor," has many of the features of thyroid-associated ophthalmopathy, especially when localized to the eye muscle. The purpose of this study is to test for circulating autoantibodies against eye muscle antigens and features of possible thyroid autoimmunity in patients with nonspecific orbital inflammation.

METHODS

The authors studied eight patients with diffuse or localized nonspecific orbital inflammation. The presence of autoantibodies reactive with pig eye muscle membrane antigens and 1D, a recombinant 64 kilodaltons (kd) thyroid and eye muscle protein, were tested in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting.

RESULTS

The most frequently detected antibodies were those reactive with eye muscle membrane proteins of 55 and 64 kd, which were demonstrated in 62.5% and 62.5%, respectively, of patients with nonspecific orbital inflammation; antibodies against 95- and 45-kd proteins were each detected in 50% of patients. In health subjects, antibodies reactive with the 55- and 64-kd proteins were detected in 16% and 20% of patients, respectively; those reactive with the 95-kd protein were detected in 24% of patients and with the 45-kd protein in 20% of patients. On the other hand, antibodies to 1D were demonstrated in only one patient with nonspecific orbital inflammation and not at all in healthy subjects. The prevalence of positive tests were significantly greater in patients with nonspecific orbital inflammation than healthy patients only for antibodies reactive with a 55-kd protein. Of the four antigens, only the 55-kd protein was expressed in other (systemic) skeletal muscle. No patient had overt thyroid disease or detectable serum antibodies reactive with the thyroid-stimulating hormone receptor, and only one had antibodies reactive with the thyroid microsomal antigen.

CONCLUSION

Serum autoantibodies reactive with eye muscle membrane proteins are demonstrated in the majority of patients with nonspecific orbital inflammation. Although the pathogenesis of this condition is unknown, autoimmunity against eye muscle antigens is a likely mechanism. While antibodies reactive with the thyroid microsomal antigen were detected in only one patient and anti-thyroid-stimulating hormone receptor antibodies in none of the patients, a possible association of nonspecific orbital inflammation with thyroid autoimmunity has not been excluded.

Two dimensional gel electrophoresis identifies minor differences in immunologically cross-reactive 64 KDa autoantigens in the thyroid and eye muscle

Among the candidate eye muscle autoantigens proposed as being relevant to the pathogenesis of thyroid-associated ophthalmopathy (TAO), a 64 kDa membrane autoantigen appears to be most closely associated with the eye disorder. We have examined the tissue localization and some of the physicochemical properties of this molecule in 3 human tissues, namely thyroid (THY), eye muscle (EM) and skeletal muscle (SKE), and in pig eye muscle (PEM), by two-dimensional (2-D) [isoelectric focusing (IEF)/sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE)] gel electrophoresis followed by Western blotting. Antibody probes used were whole sera from patients with TAO and antibodies affinity purified from TAO sera by binding to, and elution from, a sepharose-4B column conjugated with D1, a 98 amino acid peptide fragment of a recombinant 64 kDa thyroid autoantigen. Soluble membrane proteins eluted from a slice of SDS-PAGE gel containing 60-70 kDa material was prepared from the four tissues and used as antigen for 2-D gel separation. The presence of a 64 kDa antigen in THY and EM recognized by sera from patients with TAO, but only rarely by those from normal individuals, was confirmed. Pretreatment of the eluted 60-70 kDa material with N-Glycosidase F to eliminate charge heterogeneity resulting from glycosylation differences, changed the pI and MW of molecules recognized by TAO sera, in THY and EM. This suggests that the 64 kDa molecule(s) in EM and THY targeted by sera from patients with TAO are glycoproteins and that they are different in the two tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies reactive with an intracellular epitope of a recombinant 64 kDa thyroid and eye muscle protein in patients with thyroid autoimmunity and ophthalmopathy

We have developed an enzyme-linked immunosorbent assay (ELISA) for the measurement of antibodies reactive with a 98 amino acid fragment, called D1, of a recombinant thyroid and eye muscle membrane protein corresponding to a MW of 64 kDa (called 1D) in the serum of patients with thyroid autoimmunity with and without ophthalmopathy. Antibodies against the D1 fragment expressed as a fusion protein with beta galactosidase, were detected in 29% of patients with thyroid-associated ophthalmopathy (TAO) of < 1 yr duration, in 33% of those with disease of > 3 yr duration, in 40% of patients with Graves' hyperthyroidism (GH) without evident eye disease, in 31% of patients with lid lag and retraction but no other signs of progressive ophthalmopathy, in 25% of patients with euthyroid Graves' disease and in 43% of patients with untreated Hashimoto's thyroiditis (HT), but in none of 14 patients with other (non-immunological) thyroid disorders. Although tests were positive in 6 out of the 15 patients with ophthalmopathy and no overt thyroid autoimmunity overall there was no close association of the antibodies with clinical features of the eye disease or its course. In those sera in which Western blotting for antibodies reactive with a 64 kDa eye muscle membrane protein and ELISA were both carried out there was no close correlation between the two tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of eye muscle antibody measurements to monitor response to plasmapheresis in patients with thyroid-associated ophthalmopathy

We have measured eye muscle antibodies, in immunoblotting, in the serum from five patients with severe ophthalmopathy associated with Graves' hyperthyroidism who underwent plasmapheresis, correlating their levels with clinical features of the eye disorder and response to treatment. Blood taken before each plasma exchange was tested in SDS-polyacrylamide gel electrophoresis and Western blotting for antibodies reactive with pig eye muscle membrane (PEMM) antigens and in a 51Cr release assay for antibodies which are cytotoxic to human eye muscle cells in antibody-dependent cell-mediated cytotoxicity (ADCC). Antibodies reactive with a 64 kDa PEMM antigen were detected in three patients who had eye disease of less than six months duration, but not in the two with more chronic disease. Antibodies against a 95 kDa PEMM antigen were detected in one patient in whom anti-64 kDa antibodies were also demonstrated. All five patients showed significant improvement in their eye disease following plasmapheresis exchange and titres of the anti-64 kDa protein antibody decreased in the three patients with detectable levels before treatment. TSH receptor stimulating antibodies were detected in all five patients before treatment, falling during plasmapheresis in four and becoming undetectable in three by the end of treatment. There was no close correlation between levels of TSH receptor antibodies and titres of anti-64 kDa protein antibodies although both tended to fall during and following plasmapheresis. ADCC tests were negative in all five patients before plasmapheresis but, surprisingly, transiently positive in three following treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Nature of 64 kDa eye muscle and thyroid membrane proteins and their significance in thyroid-associated ophthalmopathy--an hypothesis

Although a variety of eye muscle antigens are recognized by autoantibodies in the serum from patients with thyroid associated ophthalmopathy (TAO) 64 kDa membrane proteins, which are also expressed in the thyroid, are most closely linked to the development of ophthalmopathy in patients with autoimmune thyroid disease. A cloned 64 kDa protein called 1D, which shares homology with tropomodulin, appears to be closely related to a 64 kDa eye muscle protein identified in immunoblotting and both may be members of a family of cytostructural proteins. The relationship between 64 kDa proteins in eye muscle and thyroid, and its equivalent in somatic skeletal muscle, will only be understood when the various proteins are cloned from expression libraries, sequenced and their consensual and unique domains identified. Since these 64 kDa antigens are expressed in both thyroid and eye muscle, a possible mechanism for the association of ophthalmopathy with autoimmune thyroid disease is immunological cross-reactivity by autoantibodies and sensitized T lymphocytes. Autoantibodies reactive with 64 kDa eye muscle proteins are associated with ophthalmopathy in patients with autoimmune thyroid disorders and predictive of the development of ophthalmopathy in patients with Graves' hyperthyroidism.