Differentiating various abnormalities of thyroxin binding to serum proteins by radioelectrophoresis of thyroxin and immunoassay of binding proteins

Using the simple method of protein analysis described here, we could identify thyroxin (T4)-binding-protein abnormalities in euthyroid patients with hyperthyroxinemia or hypothyroxinemia. Serum incubated with [125I]thyroxin was analyzed by agarose gel electrophoresis, with bromphenol blue staining of protein. The relative distribution of radioactive T4 was determined for each binding protein--thyroxin-binding globulin (TBG), transthyretin, albumin, and T4-binding immunoglobulin (when present)--and the mass of T4 bound to each was determined. We also used sensitive immunoassays to quantify TBG, transthyretin, and albumin concentrations, then calculated the mass of T4 (as determined by electrophoresis) bound per unit mass of the respective binding protein. When the concentration of binding proteins was altered (e.g., TBG excess or TBG deficiency), the T4 binding/mass ratio for each protein remained within the expected range; but when the functional affinity of a binding protein was altered--as in dysalbuminemic hyperthyroxinemia and in low-T4 nonthyroidal illness--this ratio was abnormal. This procedure can be used to help identify TBG excess, TBG deficiency, dysalbuminemic hyperthyroxinemia, prealbumin-associated hyperthyroxinemia, variant TBG with reduced affinity for T4, euthyroid sickness, and T4-binding autoantibodies.

Concentrations of free thyroxin and free triiodothyronine in serum of patients with thyroxin- and triiodothyronine-binding autoantibodies

Between 1982 and 1989 we identified 47 subjects with spuriously increased concentrations of free thyroxin (FT4) or free triiodothyronine (FT3) related to autoantibody interference in analog FT4 and (or) FT3 methods. The incidence of autoantibody interference observed during one year (1988) was 1 in 2460. In the subjects identified, 51% and 11%, respectively, showed an increased binding of radiolabeled T4 or T3 analog alone; 38% had an increased binding of both. Of 36 patients tested, 71% had autoantibodies to thyroglobulin and microsomal fraction of the thyroid, 19% to microsomal fraction alone, and 9.5% to thyroglobulin alone. In eight subjects, spuriously increased FT4 concentrations were reported with the following FT4 methods (in decreasing order of interference): Coat-A-Count, Amerlex-M, Amerlite, Seria, Magic Lite, Amerlex-MAB. In the same eight subjects, Amerlex-M and Seria reported spuriously increased concentrations of FT3.

Autoantigenic determinants on human thyroglobulin. I. Determinant specificities of murine monoclonal antibodies

To map the antigenic determinants, a panel of 20 mouse monoclonal antibodies (mAbs) to native human thyroglobulin (Tg) was generated. Four criteria were established for distinguishing the determinants recognized by the various mAbs: (i) reactivity to Tgs from eight different species; (ii) reactivity to oxidized and reduced human Tg; (iii) the ability of thyroxine to inhibit binding of mAbs; and (iv) the pattern of antigenic determinant reactivity as determined in reciprocal competitive inhibition binding assays. Of 20 mAbs examined, 12 bound only to human Tg, 3 bound to all eight species tested, and 5 bound to human Tg and to Tg from at least one of the other seven species. Eight mAbs bound oxidized/reduced and native human Tg equally well, 2 bound to the oxidized/reduced protein better than to the native, 7 showed virtually no reactivity to oxidized/reduced human Tg, and 3 others reacted to the oxidized/reduced protein significantly less than they bound to the native. The binding of 5 mAbs to native human Tg was inhibited by thyroxine. The pattern of shared determinant specificities revealed that at least 12 determinant clusters were defined by the panel of mAbs. Among the 12 determinant clusters were 3 designated as immunodominant; 8 of 20 mAbs defined these immunodominant clusters. The four criteria taken together indicate that at least 19 different epitopes on human Tg could be distinguished by this panel of mAbs. These mAbs are useful for the study of determinant specificities of Tg autoantibodies in humans.

[Influence of the anti-T4 autoantibody cross-reacting with T3 on serum T3 level determined by RIA]

We encountered a patient who showed remarkably high binding capacities of both 125I-T4 and 125I-T3, which suggests the presence of antithyroid hormone autoantibody. However, the serum level of T3 in the patient was not abnormal. Study of the specificity of anti-thyroid autoantibody revealed that the antibody present in the patient was the anti T4 antibody, which cross-reacted with T3. In addition, the binding capacity of the T4 autoantibody with T3 was inhibited by T4. Endogenous T4 is always present when T3 is determined by radioimmunoassay. Our findings indicate that the normal T3 level in the patient was because endogenous T4 inhibited the autoantibody binding with T3.

Effect of 8-anilino-1-naphthalene sulfonic acid (ANS) on the interaction between thyroid hormone and anti-thyroid hormone antibodies

Effect of 8-anilino-1-naphthalene sulfonic acid (ANS) on the interaction between thyroid hormone and anti-thyroid hormone antibodies was examined. Addition of 5.1 x 10(6) or 6.3 x 10(6) molar excess of ANS, respectively, enhanced the binding of 125I-T3 or 125I-T4 to their respective autoantibodies. However, further increase in ANS concentration resulted in a decrease in binding. These results suggest that the optimum concentration of ANS for the detection of anti-thyroid hormone antibodies is 5 approximately 6 x 10(6) molar excess of ANS to 125I-T3 or 125I-T4. On the other hand, addition of 10(4) molar excess of ANS concentration decreased the binding of 125I-insulin to anti-insulin antibodies. It was therefore suggested that the effect of ANS could be a nonspecific one and likely due to its negative charge.

The role of thyroid hormone autoantibodies in serum transport

Eleven sera known to contain thyroid hormone autoantibodies were analysed by reverse-flow electrophoresis for the equilibrium distribution of thyroid hormones between these autoantibodies and the three normal binding proteins found in serum. The binding properties of the autoantibodies determined in vitro did not necessarily predict their contribution to transport in serum of T1 and T3. Some could both bind in vitro and transport in serum. Others were able to bind both hormones but transported only one. However, some autoantibodies could be specific, binding and transporting one hormone only. In some sera, the autoantibody was the dominant transport protein having drawn hormone from thyroxine-binding globulin which is normally the most important. The autoantibodies were not saturated even in euthyroid individuals, indicating that they bind hormone reversibly and are a part of an equilibrium system.

Age-related changes of thyroid function and immunologic abnormalities in patients with hyperthyroidism due to Graves' disease

In order to clarify the reasons why hyperthyroidism due to Graves' disease is mild in aged patients compared to young patients, we examined the degree of hyperthyroidism and immune abnormalities in 371 untreated patients. The patients were divided into nine groups based on their age; groups A to I consisted of patients aged 0-9, 10-19, 20-29, 30-39, 40-49, 50-59, 60-69, 70-79, and 80-89 years, respectively. Serum thyroxine (T4), triiodo-thyronine (T3), and thyroglobulin levels were highest in group B (patients aged 10-19 years) and decreased progressively with advancing age. T3/T4 ratio was also highest in group B and decreased progressively with age. These data reconfirmed that the degree of hyperthyroidism is milder in older patients. The prevalence of positive microsomal and thyroglobulin antibodies was highest in group B (patients aged 10-19 years) and progressively lower in older groups, suggesting that an association with Hashimoto's thyroiditis is less prevalent in aged patients. We suggest that hyperthyroidism due to Graves' disease is mild in aged patients because responsiveness of the thyrocyte to the abnormal stimulator, thyrotropin-receptor antibody, may be reduced. Such reduced responsiveness may not be due to Hashimoto's thyroiditis, since the prevalence of antithyroid antibodies is lower in aged than in younger patients with hyperthyroidism due to Graves' disease.

A new way in homogeneous immunoassay: reversed micellar systems as a medium for analysis

Possibilities of a new principle for the homogeneous enzyme immunoassay utilizing the systems of surfactant reversed micelles in organic solvents have been demonstrated taking thyroxine determination as an example. The catalytic activity of an enzyme, solubilized in such systems, is determined by the ratio of geometric dimensions of the micellar matrice and the enzyme molecule. The addition of antibodies against thyroxine to the peroxidase-thyroxine conjugate, solubilized in the system of reversed micelles of aerosol OT in octane, leads to the formation of the immune complex whose size differs substantially from that of the initial enzyme-antigen conjugate. This induces changes in the peroxidase catalytic activity. The addition of free thyroxine to the system stimulates the conjugate release from the immune complex and, consequently, the reduction of the peroxidase activity to the initial level. Sensitivity of the analysis in reversed micellar systems can be regulated by changing the surfactant hydration degree. Substances of different nature (both hydrophobic and hydrophylic) can be solubilized in reverse micellar systems under standard conditions, which allows determination of water insoluble antigens.

[Changes in anti-thyroid hormone and anti-thyroglobulin antibodies during thyroid hormone(s) or prednisolone treatments in 3 cases of Hashimoto's thyroiditis]

We have experienced 3 cases of Hashimoto's thyroiditis with anti-thyroid hormone antibodies. Changes in titers of anti-thyroglobulin(Tg) and anti-thyroid hormone antibodies during 6 year (Cases 1 and 2) and 7 year (Case 3) observation periods were examined in each case. Cases 1 (13-year-old) and 2 (10-year-old) are sisters with hypothyroidism whose chief complaint was short stature. They were diagnosed as having Hashimoto's thyroiditis by needle biopsy of the thyroid gland. Presence of anti-thyroid hormone antibodies were found in the sera of both cases (Case 1: anti-thyroxine(T4) antibodies, Case 2: anti-triiodothyronine(T3) antibodies). They were treated with synthetic T4 or combined therapy of T3 and T4, and serial sera obtained during the 6 year treatment period were tested for the titers of anti-Tg and anti-thyroid hormone antibodies. Case 3 (23-year-old female), who was diagnosed as having Hashimoto's thyroiditis associated with systemic lupus erythematosus (SLE) and Sjögren's syndrome had been treated with prednisolone(PSL) for 8 years. After one year of strating the treatment, she was found to have unusually low serum T3 measured by radioimmunoassay. Further examination revealed the presence of anti-T3 antibodies in her serum. Serial sera obtained during the 7 year observation period were tested for the titers of anti-Tg and anti-T3 antibodies. In cases 1 and 2, replacement therapy with thyroid hormone resulted in the decrease of titers of anti-thyroid hormone antibodies. In addition, increase in serum TSH concentrations was accompanied with increased titers of anti-Tg and anti-thyroid hormone antibodies in all 3 cases. The exact mechanism for it is not clear.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid hormone autoantibodies (THAA) in three sisters: a four-year follow up

We have found three sisters who had thyroid hormone autoantibodies (THAA) in serum. Two of them were hypothyroid due to Hashimoto's thyroiditis. They were treated with synthetic thyroxine (T4) (Case 1) or T4 and triiodothyronine (T3) (Case 2). The other sister (Case 3) was euthyroid throughout the investigation period. Changes in the titers of THAA, antithyroglobulin (Tg) antibodies as well as in the concentrations of thyrotropin (TSH), and total and free thyroid hormones (T3, T4, FT3, and FT4) in sera from each patient were examined for four years. A significant positive correlation was observed between titers of THAA and anti-Tg antibodies in both Case 1 (anti-T3 and anti-T4) and 2 (anti-T4). On the other hand, a significant negative correlation between titers of anti-T3 and anti-Tg antibodies was observed in Case 3. These results suggest that antigen of THAA might be Tg in Case 1 and 2 and mechanism(s) of the production of THAA of Case 1 might be different from that of Case 1 and 2 in terms of their antigen or immune recognition of Tg.

[Various aspects of the diagnosis and treatment of autoimmune thyroiditis]

The authors conducted 4-year investigation of patients with autoimmune thyroiditis. All the patients were women aged 28 to 68 with the duration of disease from 5 mos to 10 yrs. Combined diagnostic methods included radioactive iodine absorption, scanning, puncture biopsy, indirect thyroidolymphography. Antibodies to thyroglobulin, T3, T4, and TTH were determined by RIA. Chronic thyroiditis was diagnosed in all the patients. The authors proposed a method of intraparenchymatous administration of steroid agents into the thyroid. This method was shown to be simple, effective, causing no complications. Conservative therapy of Hashimoto's thyroiditis should be performed not more than 2 years and not less than one year.

Effect of dietary iodine on autoimmune thyroiditis in the BB Wistar rats

Diabetes-prone BB Wistar rats were fed a modified AIN-76 diet providing the following amounts of iodine for 10 wk: 0.2 mg/kg diet (recommended amount); 1.0 mg/kg; 2.0 mg/kg; or 3.0 mg/kg. The thyroids were examined for gross and microscopic changes and sera were assayed for antibodies to triiodothyronine (T3), thyroxine (T4), and thyroglobulin (Tg). The body weights and food consumption of the rats fed 0.2 mg of iodine/kg were significantly lower than those of the animals fed higher amounts. Urinary iodine excretion reflected dietary intakes. The thyroids from animals fed 2.0 and 3.0 mg/kg were significantly (P less than 0.01) larger than those from animals fed 0.2 mg/kg. One rat fed 0.2 mg/kg and 2 rats in each group fed 2.0 and 3.0 mg/kg had extensive lymphocytic thyroiditis. Three rats fed 1.0 mg/kg, 6 fed 2.0 mg/kg and 6 fed 3.0 mg/kg had enlarged thyroids. Two rats fed 0.2 mg/kg, 2 fed 2.0 mg/kg and 6 fed 3.0 mg/kg had detectable Tg antibodies. These data suggest that high iodine intakes increase Tg antibodies, which may be associated with an increase in autoimmune thyroiditis in these animals.

[Antibodies against thyroxine, triiodothyronine and thyroglobulin as a possible cause of error in the diagnosis of disorders of thyroid gland function]

The authors examined in a 82-year-old female patient T4, T3, free T4, TSH, thyroglobulin and made the TRH-TSH functional test because of suspected thyroid disease. For thyroid hormones they obtained controversial resulting levels: in T4 signalizing an unreasonable negative value, in T3 a very high level, in TSH and the TRH-TSH test levels suggesting normal thyroid function which was consistent with the clinical picture. A more detailed laboratory analysis revealed the presence of antibodies binding 125I-T4 and 125I-T3 (radioindicators used for assessment of T4 and T3). The authors identified antibodies against T4, T3 and thyroglobulin. Their presence influenced the radioimmunoassay of T4 and T3 and also the immunoradiometric estimation of thyroglobulin (artificially raised level). The reliable result of the eufunctional condition was not influenced in the estimation of the TSH level.

Application of solid-phase antibodies to radioimmunoassay. Improved performance of Dynospheres following affinity purification of antisera

Affinity purification of antibody before covalent binding to pre-activated micro-particles (Dynospheres) was necessary to overcome the reduced coupling capacity evident with low titre antisera, particularly antihapten sera. Optimally prepared Dynospheres anti-thyroxine provided a radioimmunoassay with good performance and economical usage of microparticles. Assay sensitivity was less than 10 nmol/l while precision across the clinically relevant dose range (50-150 nmol/l) was 3% CV using 125 micrograms particles per assay tube.

Euthyroid hyperthyroxinaemia due to endogenous antibodies to thyroxine and tri-iodothyronine. A case report

A case of euthyroid hyperthyroxinaemia caused by auto-antibodies to thyroxine and tri-iodothyronine is presented. Gel filtration chromatography of the patient's serum showed increased binding of radio-labelled thyroxine analogue to a macromolecular component, which migrated in the gammaglobulin region on electrophoresis. Precipitation by protein A confirmed that this was an immunoglobulin. The importance of recognising this condition so that inappropriate therapy can be avoided is stressed.

Simultaneous production of antibodies against T3 and T4 in a single animal; their characteristics and usefulness in radioimmunoassay

Simultaneous production of antibodies against triiodothyronine and thyroxine was attempted in a single rabbit by immunizing the animal with T3-albumin conjugate and T4-albumin conjugate at the same time. This resulted in the production of antibodies against both T3 and T4. The characteristics of each antibody were studied and the antiserum was used for determination of serum T3 and T4 concentrations by radioimmunoassay. The results were compared with those obtained with antibodies against T3 and T4 which were produced individually in different rabbits and were found to be more or less similar. From the results of the experiments, it appears that it is possible to make antibodies against T3 and T4 simultaneously in a single rabbit.

Enzyme immunoassay for antibodies to thyroxine in human serum using synthesized antibody as a calibrator

We prepared human IgG labeled with rabbit antibodies to thyroxine, and used it for the assay of antibodies to thyroxine in human serum as a calibrator. The assay system consisted of thyroxine labeled with beta-D-galactosidase and a microcolumn containing goat antibodies to human IgG immobilized on Sepharose 4B. Each serum sample or standard serum containing human IgG labeled with anti-thyroxine antibodies was incubated with the enzyme-labeled thyroxine, and the reaction mixture was passed through the microcolumn. The column was washed to remove the unbound label, and enzyme activity of the bound label was assayed. The minimum detectable amount of the anti-thyroxine antibodies was 0.3 ng/assay tube. The analytical recoveries of human IgG labeled with the antibodies added to human serum were from 103% to 108%. We measured anti-thyroxine antibodies in human sera from 187 patients with autoimmune thyroid diseases. The antibodies were detected in 32 serum samples, and the values in positive samples varied from 0.31 to 2.31 micrograms/ml. On the other hand, in 58 sera from patients with non-thyroid diseases, the antibodies were detected in only two samples.

Autoantibodies to thyroxin and triiodothyronine in the immunoglobulin G fraction of serum

Thyroid hormone antibodies (THAbs)--i.e., antibodies to thyroxin (T4) and triiodothyronine (T3)--are detected rarely in human serum, where they are searched for, possibly because of a quantitatively minimal interaction between thyroid hormones (the haptens) and serum IgGs (the antibodies). The weak binding could result from these facts: (a) there are already six physiological carrier proteins for thyroid hormones; (b) THAbs usually account for a very small fraction of the total serum IgGs; (c) THAbs may have--as reported in the literature--a relatively low affinity. To ascertain whether THAbs could pass undetected in serum, we measured antibodies to T3 and T4 in both the serum and the corresponding IgG fraction of six normal persons and 45 patients with various thyroid diseases (Graves' disease, idiopathic myxedema, Hashimoto's thyroiditis, subacute thyroiditis, tumors), using radioimmunoprecipitation. The prevalence of antibodies to T4 was 0/51 in both the sera and the IgG fractions; the prevalence of antibodies to T3 was 1/51 in both materials. Because all of the sera that tested THAb negative were confirmed to be so in the THAb assay of the IgG fraction, we conclude that the prevalence of serum THAbs is not underestimated and that autoimmunization against thyroid hormones is really a rare phenomenon.

Epitope specificity of spontaneous and induced thyroglobulin autoantibodies in the rat

We have investigated the epitope specificities of rat thyroglobulin (Tg) autoantibodies arising either spontaneously in BB hybrid and BB rats or following induction in normal rats with thyroglobulin and adjuvant. Using a panel of thyroglobulins from different animal species it was possible to identify three different patterns of reactivity. These were: 1) recognition of all species of thyroglobulin; (2) recognition restricted to rat and mouse thyroglobulins and 3) recognition biased towards dog, rat and mouse thyroglobulins. Furthermore, using human thyroglobulin manifesting different levels of iodination, it was possible to show that sera with recognition pattern 1 recognized the iodination site of thyroglobulin and that this was inhibitable by thyroxine. Taken together these data provide evidence of restricted epitope recognition by Tg autoantibodies in the rat.

Usefulness of serum thyrotropin-binding inhibitory index measurements in infantile hypothyroidism. Relationship to serum thyrotropin concentrations

Transplacental passage of thyrotropin (TSH)-binding inhibitory immunoglobulins may result in transient congenital hypothyroidism. We measured serum TSH-binding inhibitory index (TBII) in 11 infants with abnormal screening findings using a commercially available kit. Two of the infants, who were siblings, had markedly elevated TBII values (90% and 100%, respectively), as did their mother (89%, 100%), and had a clinical course consistent with transient antibody-mediated hypothyroidism. Four other infants had a borderline or mildly elevated TBII that was not present in maternal serum, suggesting that endogenous TSH was being measured in this assay. The TBII was measured in the sera of 18 additional children with primary hypothyroidism and in human TSH standards from 25 to 2000 mU/L. Increasing concentrations of TSH were associated with a linear increase in TBII. Measurement of TBII by this method may identify infants with transient antibody-mediated hypothyroidism, although simultaneous assessment of maternal serum is necessary.

Detection of protein binding abnormalities in euthyroid hyperthyroxinemia

This is a procedure for rapidly identifying the three common abnormalities in binding of thyroxin by protein. After incubation with [125I]thyroxin, serum proteins are separated by electrophoresis on agarose gel and binding of thyroxin to the various protein fractions is determined after autoradiography. Quantitatively abnormal binding to albumin or prealbumin and thyroxin autoantibodies is easily demonstrated by this technique. Normally, less than 6% is bound to albumin, and no binding by prealbumin is detected. In dysalbuminemic hyperthyroxinemia, about 30% of the serum thyroxin is bound to albumin; in prealbumin-associated hyperthyroxinemia, 7% is bound to prealbumin. With this procedure these protein-binding abnormalities can be simply identified, and it may be useful when results of a thyroxin assay are not consistent with results of a sensitive thyrotropin assay or the patient's clinical examination.

Immunoelectron microscopy of the hormonogenic sites of the thyroglobulin molecule

Hog thyroglobulin was treated with the monoclonal anti-thyroglobulin antibody, 16.3.2, which recognizes the thyroxine residues of thyroglobulin. Size-exclusion high-performance liquid chromatography of the immune complexes indicated that there were 3.5 immunoreactable thyroxine residues/mol of 19 S thyroglobulin. The immune complexes were negatively stained and observed under an electron microscope. Under antigen excess conditions, the complexes were demonstrated as branched chains in which thyroglobulin molecules were linked by antibody molecules. When the antibody was in excess, we found many single thyroglobulin molecules each connecting to 2-3 antibody molecules. Based on the morphology of the immune complexes, we conclude that thyroxine residues are formed preferentially on the molecular surface and localized near both ends of the elongated molecule of 19 S thyroglobulin and possibly at one side of the middle of the molecule.

Autoantibodies to thyroxin and triiodothyronine

Two clinically euthyroid patients with multinodular goiter were found to have high "free" thyroxin (Amerlex-M, Amersham and Coat-a-Count, DPC) and triiodothyronine (Amerlex-M) concentrations (FT4 and FT3, respectively). The presence of antibodies to T4 and T3 was confirmed by the finding that polyethylene glycol precipitated a far greater proportion of radioactivity when radiolabeled FT4 or FT3 analog (Amerlex-M) was incubated with serum from these patients than was true for normal subjects. With this method we could not demonstrate antibodies to thyroid hormones in 116 healthy volunteers. Of 101 hyperthyroid patients tested, one had antibodies to T4 but none had antibodies to T3. One patient had antibodies to T4, and one to T3, of 36 hypothyroid patients tested. All patients with thyroid hormone antibodies also demonstrated antithyroglobulin antibodies (measured immunoradiometrically). Evidently, the presence of thyroid hormone antibodies should be suspected when results of thyroid-function tests are discordant with the clinical state, and we suggest that measurement of thyrotropin by an assay with improved detection limits will aid in correctly determining thyroid status.