Chronic urticaria: association with thyroid autoimmunity

BACKGROUND

Though autoimmune phenomena have been regularly associated with chronic urticaria in adults, data in children are sparse.

AIM

To describe our experience with children and adolescents with chronic urticaria and autoimmunity.

METHODS AND RESULTS

Of 187 patients referred for evaluation of chronic urticaria during a 7.5 year period, eight (4.3%), all females aged 7-17 years, had increased levels of antithyroid antibody, either antithyroid peroxidase antibody (n = 4, >75 IU/ml), antithyroglobulin antibody (n = 2, >150 IU/ml), or both (n = 2). The duration of urticaria was four months to seven years. Five patients were euthyroid, one of whom was found to have increased antithyroid antibody levels five years after onset of the urticaria. One patient was diagnosed with Hashimoto thyroiditis three years before the urticaria, and was receiving treatment with thyroxine. Two other hypothyroid patients were diagnosed during the initial work up for urticaria (thyroxine 9.2 pmol/l, thyroid stimulating hormone (TSH) 40.2 mIU/l) and five years after onset of the urticaria (thyroxine 14 pmol/l, TSH 10.3 mIU/l). Both were treated with thyroxine but neither had remission of the urticaria. Five patients had a low positive titre of antinuclear antibodies.

CONCLUSION

Children with chronic urticaria should be screened periodically for thyroxine, TSH, and antithyroid antibodies, as thyroid autoimmunity and hypothyroidism may appear several years after onset of the urticaria.

[Clinical, hematological, biochemical and endocrinological aspects of 32 dogs with hypothyroidism]

During the years of 1996-2001, hypothyroidism was diagnosed at the clinic for small animal internal medicine, University of Zurich, in 32 dogs. Most of the dogs were large breeds. The most frequent clinical characteristics observed were exercise intolerance, obesity, dermatological, neurological and gastrointestinal signs. Predominant laboratory abnormalities were a low red blood cell count, increased concentration of cholesterol, triglycerides and fructosamin. 29 dogs had a T4 below the reference range (< 1.5 micrograms/dl), one dog had a T4 at the lower limit thereof (1.6 micrograms/dl). One dog had a T4 within the reference range (3.4 micrograms/dl), another had a very high T4 of 206.8 micrograms/dl; the results of the latter 2 dogs were interpreted as incorrectly increased T4 values due to in vitro interference with T4-autoantibodies. Diagnosis was confirmed in all of the dogs based on TSH-stimulation testing. Endogenous TSH (cTSH) measured parallelly, was elevated in only 60% of the dogs. In about 67% of the dogs, hypothyroidism was associated with thyroglobulin-autoantibodies. Canine hypothyroidism is a rather rare endocrine disorder in Switzerland. The TSH-stimulation test remains the gold standard in confirming the disease; a definitive diagnosis can be challenging for practitioners because bovine TSH, used for the TSH-stimulation test is not licensed for use in dogs. Since assessment of cTSH using current assays shows normal values in a high percentage of hypothyroid dogs, the diagnostic value is only limited. In most of the hypothyroid dogs T4 is decreased, with the presence of autoantibodies to T4, it can be normal or increased.

A major role for non-major histocompatibility complex genes but not for microorganisms in a novel murine model of Graves' hyperthyroidism

The etiology of Graves' disease is multifactorial. We investigated the role of genetic and environmental factors on the susceptibility to Graves' hyperthyroidism using a new murine model. Intramuscular injection of recombinant adenovirus expressing the thyrotropin receptor (AdCMVTSHR) induces Graves'-like hyperthyroidism (thyrotropin receptor [TSHR] antibodies, elevated thyroxine, and diffuse goiter) in more than 50% of female BALB/c mice. The relative contributions of major histocompatibility complex (MHC) and non-MHC genes on the susceptibility to hyperthyroidism were studied by immunizing BALB/c (H-2d), BALB.K (H-2k), and DBA/2J (H-2d) mice with AdCMVTSHR. Hyperthyroidism developed in approximately 50% of BALB/c and BALB.K mice but only 5% of DBA/2J mice, indicating a major role for non-MHC genes in disease development. The effect of environmental microorganisms was evaluated by comparing disease incidence in BALB/c mice maintained in pathogen-free conditions versus those in nonsterile, conventional housing, as well as by coadministering microorganism components (Escherichia coli lipopolysaccharide or yeast zymosan A) as adjuvants with AdCMVTSHR. Neither type of exposure to environmental pathogens influenced disease induction. In conclusion, non-MHC genes, but not infectious organisms, play a major role in the etiology of this novel murine model of Graves' disease.

Determination of autoantibodies to thyroglobulin, thyroxine and triiodothyronine in canine serum

Enzyme immunoassays (EIAs) for the determination of autoanti-bodies (AA) to thyroid antigens in canine serum were developed. Streptavidin (SA) was immobilized as capture molecule on microtitreplates (MTP). Thyroglobulin (Tg) purified from canine thyroids and the thyroid hormones thyroxine and triiodothyronine (T3 and T4) were conjugated to biotin labelling reagents and attached to the MTP over the SA-biotin bridge. Bound AA were detected with anti-dog-immunoglobulin G (IgG) labelled with horseradish peroxidase. Serum samples from dogs which were allotted to four groups were analysed: A (n = 31), biochemical evidence of hypothyroidism; B (n = 76), clinical signs of hypothyroidism; C (n = 47), euthyroid with non-thyroidal disease; D (n = 186), clinically healthy. The validity of the assays was tested with two different methods. After thiophilic absorption chromatography of positive sera, a positive reaction in the EIA was only detected in those fractions which coeluted with the canine IgG standard. Furthermore, the positive reaction was blocked by the addition of the corresponding antigen. In 55% of the hypothyroid dogs AA to Tg and/or T3 and T4, respectively, were found (up to a titre of 1 : 1600). In group B 34% of the dogs were diagnosed positive, but the titre was lower (up to 1 : 400). In the groups C and D the number of dogs with AA and their titre was significantly lower. Two different methods for distinguishing positive and negative test results were compared in order to increase the specificity of the tests without decreasing the sensitivity. The EIAs are precise and based on high agreement with previous reported assays able to discriminate dogs with thyroiditis from healthy ones. These assays represent a good alternative to the isotope assays generally used for the analysis of AA to T4 and T3.

Sensitive time-resolved fluoroimmunoassay for simultaneous detection of serum thyroid-stimulating hormone and total thyroxin with Eu and Sm as labels

Based on a novel cocoating strategy and dissociation enhancement lanthanide fluorescence immunoassay technique, a sensitive time-resolved fluoroimmunoassay (TRFIA) has been developed for simultaneous quantification of human serum thyroid-stimulating hormone (TSH) and thyroxin (T4) in a one-and-the-same assay procedure. The new cocoating strategy for preparing highly active surface anti-TSH and anti-T4 monoclonal antibodies (McAbs) was performed by a three-step protocol. Namely, anti-TSH McAb at high concentration (10 micro g/ml) and extensively biotinylated bovine serum albumin (BSA) at low concentration (0.5 micro g/ml) were coated on microwells by passive adsorption, then streptavidin was captured by the surface BSA-biotin, and finally biotinylated anti-T4 McAb was immobilized by the remnant binding sites of the bound streptavidin. In the present TSH/T4 TRFIA, both sandwich- and competitive-type configurations were involved, and Eu(3+) and Sm(3+) were used as labels for TSH and T4 detection, respectively. The method showed rapid kinetics; the equilibrium was reached within 30min at 37 degrees C due to the use of high concentrations of reaction reagents, rapid agitation, and small reaction volume. The lower limits of detection of the method were 0.028 mIU/L for TSH and 4.1 nmol/L for T4 with 20 micro L of sample volume. The assay ranges for TSH and T4 were 0.21-80.00 mIU/L and 20-300 nmol/L, respectively. The correlation between the TSH/T4 values obtained by the present TSH/T4 TRFIA and those obtained by commercial chemiluminescence immunoassay was satisfactory.

[Lanthanide fluorescent immune analysis for determination of hormone thyroxine in dry blood spots]

The determination of thyroxin (T4) is a basic confirmative test for congenital hypothyroidism. 70% cases of this period inborn disease are taking asymptomatic course. We developed immunofluorescent T4-assay in dried blood spots with anti-T4 monoclonal antibody and europium chelate (dianhydride of diethylentriaminipentaacetic acid (DA-DTPA)). This method requires DELFIA Plate Fluorometer 1232 (Wallac, Finland) or its sub modifications. Panel of monoclonal antibodies for T4 has been obtained. Type/subtype (IgG2b, IgG1), affinity constants (10(7)-10(8) M-1), cross reactivity to homologous structures (0-2%) were determined. Stable clones with high affinity and viability were selected for the development of the assay. Conjugates of thyroxin and europium chelate were synthesized. Inclusion of sodium salicylate (2 mg/ml) and EDTA (2 mM) into the buffer reduced the nonspecific signal. Limit for T4 detection (T4 standarts) was 10 nM with not more than 15% variation coefficient. Accuracy was estimated by Bio-Rad Lipochek Immunoassay Plus Control Kit. Obtained results were within control confidence interval.

[A case of hypothyroidism due to hashimoto disease that presented elevations of free T3 and free T4 by thyroid hormone autoantibodies]

When we commonly evaluate the thyroid function, we measure TSH, free T3 and free T4. However, there are some cases that are difficult to diagnose because of the existence of thyroid hormone autoantibodies. We experienced a case of a 14-year-old girl with diffuse struma whose TSH, free T3 and free T4 were elevated by detected with Amerlex M free T3 and free T4 kits, although she did not have any symptoms. As the free T4 level was low by the equilibrium dialysis method, we diagnosed this case as hypothyroidism due to chronic thyroiditis. Because we found thyroid hormone antibodies in her serum, we thought that this case presented pseudoelevations of free T3 and free T4 by the analogue method.

Early variations of host thyroxine and interleukin-7 favor Schistosoma mansoni development

Schistosoma mansoni induces, in the vertebrate host, cutaneous production of interleukin-7 (IL-7), which is beneficial for parasite establishment and development. Infection of mice deficient in IL-7 expression leads to parasite dwarfism. Because similar findings were previously described in hypothyroid mice, this study aimed to elucidate the potential link between IL-7 and thyroid hormones (THs), using several models including hypo- and hyperthyroid mice, modified either transiently or constitutively. Mice treated with thyroxine led to increased worm numbers and development of giant worms, whereas an iodine-deficient diet reduced parasite maturation, egg laying, and liver pathology. Conversely, mice genetically deficient for either of the nuclear TH receptors displayed normal worm development despite modifications in hormone levels, suggesting that thyroxine action is mediated through host receptors. In addition, no modification of antibody titers has been evidenced in thyroxine-treated mice, whereas antibody levels were altered in transgenic animals. These observations suggest that the immune system is not likely to be involved in the modifications of parasite development reported in this study. Interestingly, concomitant treatment with IL-7 and thyroxine had a synergistic effect, leading to recovery of very large worms, thus raising questions about the complexity of interactions between IL-7 and metabolic hormones.

Evaluation of an in-house enzyme-linked immunosorbent assay for quantitative measurement of serum total thyroxine concentration in dogs and cats

OBJECTIVE

To compare serum total thyroxine (T4) concentrations obtained with an in-house ELISA and a validated radioimmunoassay (RIA).

DESIGN

Laboratory trial.

SAMPLE POPULATION

50 canine and 50 feline serum samples submitted for measurement of total T4 concentration with the RIA; samples were selected to represent a wide range of concentrations (< 6 to 167 nmol/L).

PROCEDURE

Results of the ELISA and RIA were compared by calculating correlation coefficients, examining linearity, determining bias and precision, and evaluating clinical interpretations.

RESULTS

Correlation coefficients for results of the 2 methods were 0.84 for the canine samples and 0.59 for the feline samples. Examination of bias plots revealed large variations in ELISA results, compared with RIA results. For the feline samples, the ELISA consistently overestimated total T4 concentration obtained with the RIA. When results of the 2 methods were categorized (low, borderline low, normal, borderline high, or high), results were discordant for 24 (48%) and 29 (58%) of the canine samples and for 18 (36%) and 28 (56%) of the feline samples (depending on whether borderline high ELISA results were considered normal or high). Reliance on results of the ELISA would have led to inappropriate clinical decisions for 31 (62%) canine samples and 25 (50%) feline samples. The ELISA coefficients of variation for the pooled canine and feline samples were 18 and 28%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Substantial discrepancies between ELISA and RIA results for T4 concentrations were detected. Thus, we concluded that the in-house ELISA kit was not accurate for determining serum total T4 concentrations in dogs and cats.

Improved antibody coating protocol using a second antibody antiserum. Application to total thyroxin immunoassay

A complete antibody coating protocol for the preparation of dry antibody coated tubes is presented. This protocol is based on a recently described antibody immobilization principle. We modify this immobilization principle in order to improve and simplify the coating procedure. In addition, we propose a drying procedure that provides long-term storage stability of the antibody coated tubes. According to the modified protocol, polystyrene plastic tubes are first coated with rabbit gamma-globulins. The tubes are incubated with a sheep anti-rabbitIgG antiserum dilution. After incubation, antigen-specific antibody antiserum raised in rabbits is added directly into the tubes containing the sheep anti-rabbit IgG antiserum solution (difference from the original protocol). Finally, the tubes are washed, blocked, and dried following the drying procedure developed. The suitability of the modified protocol for the development of immunoassays requiring high loading of antibody was exemplified through the development of a RIA for total thyroxin. The estimated assay characteristics (detection limit 4 microg/L, dynamic range up to 210 microg/L, within-run CV 2.7-5.7%, between-run CV 5.1-7.3%, recovery 84.4-112%, cross-reactivity for T3 1.9%) were comparable with those provided by commercially available RIA kits for the determination of thyroxin.

Hypothalamus-hypophysis-thyroid axis, triiodothyronine and antithyroid antibodies in patients with primary and secondary Sjögren's syndrome

It has been well established that, anti-thyroglobulin antibodies (ATG) and anti-microsomal antibodies (AMC) may be present in various thyroid disorders and other systemic autoimmune diseases, including Sjögren's syndrome (SS). However, presence of circulating autoantibodies to thyroid hormones, i.e. both to triiodothyronine (T3) and tetraiodothyronine (T4), has not been studied extensively in SS. Autoantibodies to T3 and T4 are very important, because serum T3 and T4 levels may be detected spuriously higher or lower, due to the presence of these autoantibodies. Their presence should be suspected when measured serum thyroid hormone levels are not consistent with clinical status of the patient. SS is a slowly progressive, inflammatory autoimmune disease, affecting primarily the exocrine glands. Thyroid gland, being a target in some autoimmune diseases, is well known to be affected in SS as well. Keeping this possibility in mind, we investigated T3 autoantibody levels and thyroid gland involvement in patients with SS. Twenty-six SS patients (F/M:22/4) with a mean age of 46.6 years, were recruited in this study. Twelve of them were accepted as primary SS (pSS), while others had secondary SS (sSS) (7 with rheumatoid arthritis (RA), 3 with systemic lupus erythematosus (SLE), 3 with progressive systemic sclerosis (PSS) and 1 with sarcoidosis). Thyroid function tests, including T3, T4, fT3, fT4, TSH, ATG, AMC, T3 antibody measurements, thyroid scintigraphy, thyroid ultrasonography and TRH stimulation tests were performed in all patients. We compared our results with those of the twenty healthy normal controls. Serum ATG and/or AMC were detected in three patients with pSS (25%) and no patients with sSS. No significant difference could be shown in the other parameters, including T3 autoantibodies and thyroid function tests. TRH stimulation test was also normal, showing that the hypothalamus-hypophysis-thyroid axis was not affected in patients both with pSS and sSS. In conclusion, we found that T3 autoantibody levels in pSS, were not significantly higher than sSS and normal controls.

A Selenium-Containing Catalytic Antibody with Type I Deiodinase Activity

Acting as a mimic of type I deiodinase (DI), a selenium-containing catalytic antibody (Se-4C5) prepared by converting the serine residues of monoclonal antibody 4C5 raised against thyroxine (T4) into selenocysteines, can catalyze the deiodination of T(4) to 3,5,3'-triiodothyronine (T(3)) with dithiothreitol (DTT) as cosubstrate. Investigations into the deiodinative reaction by Se-4C5 revealed the relationship between the initial velocity and substrate concentration was subjected to Michaelis-Menten equation and the reaction mechanism was ping-pong one. The kinetic properties of the catalytic antibody were a little similar to those of DI, with Km values for T(4) and DTT of approximately 0.8 microM and 1.8 mM, respectively, and V(m) value of 270 pmol per mg protein per min. The activity could be sensitively inhibited by PTU with a Ki value of approximately 120 microM at 2.0 microM of T(4) concentration, revealing that PTU was a competitive inhibitor for DTT.

Morphological and functional development of the thyroid tissue in rainbow trout (Oncorhynchus mykiss) embryos

The development of the thyroid tissue in rainbow trout (Oncorhynchus mykiss) embryos between 20 and 88 days postfertilization (dpf) was studied using traditional histological methods in combination with immunostaining using antibodies raised against L-thyroxine (T4) and triiodo-L-thyronine (T3). In 20 dpf embryos, the thyroid primordium appeared as a simple tube aligned with the dorsal surface of the ventral aorta. The tubular primordium becomes progressively bifurcated at each end and follicles are formed by pinching off balls of cells from the tips of the bifurcations. The secretory activity of the thyroid tissue appears first as a synthesis phase, evident at 30 dpf, characterized by T4 and T3 immunostaining present only in the follicle lumen. A later hormone release or secretory phase was first evident for T4 immunostaining at 43 dpf and for T3 immunostaining at 46 dpf and was characterized by the presence of immunostaining both within the follicle lumen and also in the cytoplasm of some (but not all) thyrocytes. This stage was also coincident with a marked increase in the number of pituitary thyrotrophs. The proportion of embryos exhibiting immunostained thyrocytes increased progressively from 43 to 52 dpf, at which stage all embryos had T4- and T3-immunostained thyrocytes.

Site-specifically labeled photoprotein-thyroxine conjugates using aequorin mutants containing unique cysteine residues: applications for binding assays (Part II)

The jellyfish Aequorea victoria produces a protein, aequorin, which belongs to the class of Ca(2+)-dependent photoproteins known for their ability to emit visible light. This property of aequorin has allowed for its as a bioluminescent label in binding assays for a variety of analytes. Due to the excellent detection limits we demonstrated in assays for small peptides using a fusion protein between the peptide of interest and the photoprotein, our next goal was to expand the range of possible analytes for producing homogeneous populations of conjugates with the aequorin label to those that were nonpeptidic in nature. Recently, we prepared and characterized four aequorin mutants containing unique cysteine residues at various positions in the polypeptide chain. In the work reported here, the four aequorin mutants were each conjugated with a maleimide-activated methyl ester derivative of thyroxine, a hormone frequently determined to evaluate thyroid function. The thyroxine-aequorin mutant conjugates were characterized in terms of the bioluminescence activities and binding properties with an anti-thyroxine monoclonal antibody for possible future employment in either heterogeneous or homogeneous binding assays for thyroxine and/or other desired analytes.

Sequencing of anti-thyroxine monoclonal antibody fab fragment by ion trap mass spectrometry

A comprehensive mass spectrometric strategy is described for the sequencing of anti-thyroxine monoclonal antibody Fab region (48 000 Da). After reduction and S-carboxymethylation of the Fab, the modified light chain and Fd fragment were separated and subjected to multiple proteolytic digestions. The resulting digests were characterized by on-line microbore liquid chromatography/electrospray ionization ion trap mass spectrometry. Database search against published immunoglobulins (IgGs) allowed identification of all the peptides in constant domains. The homologous framework residues in the IgGs were utilized as 'sequence maps' for the sequence determination of variable domains. S-Carboxymethylation with an isotopic-enriched moiety greatly facilitated the recognition and data elucidation of cysteinyl peptides through the unique isotopic distribution patterns specific to the modified peptides. Methylation of peptide mixtures provided additional information for the interpretation of MS/MS spectra, allowing easy differentiation of Asp/Asn and Gln/Glu pairs. This study clearly demonstrates the power of mass spectrometry for the sequencing of antibodies without knowing the corresponding DNA sequences.

Time-resolved fluorescence immunoassay of thyroxine in serum: immobilized antigen approach

With T(4)-bovine IgG as a solid-phase antigen, we have developed a direct competitive-type immunoassay for serum total thyroxine (TT(4)), which depends on the competitive distribution of europium-labeled anti-T(4) monoclonal antibody between solid-phase-bound T(4) and the T(4) in the sample or standard. The captured fraction of the tracer was measured after a dissociation-enhancement step. Four different T(4) protein conjugates were synthesized, of which T(4)-bovine IgG was selected as the most favorable for the preparation of solid-phase antigen. The sensitivity was 3.5 ng/ml with a sample volume of 20 microl. T(4) values obtained by this procedure agreed well with those obtained by RIA (r = 0.967, n = 38) and EG&G Wallac TRFIA (r = 0.926, n = 64). All other quality criteria was also fulfilled with respect to precision, accuracy, and dynamic range.

Antigenic and immunogenic properties of totally synthetic peptide-based anti-fertility vaccines

In this study we describe the results of experiments in which a variety of totally synthetic luteinizing hormone releasing hormone (LHRH) vaccines were assembled and examined for their abilities to elicit antibody responses and induce sterility in mice. It is shown that totally synthetic vaccines consisting of a 15 residue-defined T cell epitope and the 10 residue LHRH epitope not only induced high titers of antibody but also induced sterility. This effect did not appear to correlate with antibody titer, antibody isotype or comparative antibody affinity, but may be related to the length of time for which antibodies are present to exert their influence.

Identification of thyroid hormone residues on serum thyroglobulin: a clue to the source of circulating thyroglobulin in thyroid diseases

Thyroglobulin (Tg) present in the serum of normal individuals and patients with thyroid disorders could be partly newly synthesized non-iodinated Tg and partly Tg containing iodine and hormone residues originating from the lumen of thyroid follicles. With the aim of examining the contribution of the latter source of Tg to the elevation of serum Tg concentration in thyroid pathophysiological situations, we devised a procedure to identify thyroxine (T4) and tri-iodothyronine (T3) residues on Tg from unfractionated serum. A two-step method, basedon (i)adsorption of Tg on an immobilized anti-human Tg (hTg) monoclonal antibody (mAb) and (ii)recognition of hormone residues on adsorbed Tg by binding of radioiodinated anti-T4 mAb and anti-T3 mAb, was used to analyze serum Tg from patients with either Graves' disease (GD), subacute thyroiditis (ST) or metastatic differentiated thyroid cancer (DTC). Purified hTg preparations with different iodine and hormone contents were used as reference. Adsorption of purified Tg and serum Tg on immobilized anti-hTg mAb ranged between 85 and 90% over a wide concentration range. Labeled anti-T4 and anti-T3 mAbs bound to adsorbed purified Tg in amounts related to its iodine content. Tg adsorbed from six out of six sera from ST exhibited anti-T4 and anti-T3 mAb binding activities. In contrast, significant mAb binding was only observed in one out of eight sera from untreated GD patients and in 1 out of 13 sera from patients with DTC. The patient with DTC, whose serum Tg contained T4 and T3, represented a case of hyperthyroidism caused by a metastatic follicular carcinoma. In conclusion, we have identified, for the first time, T4 and T3 residues on circulating Tg. The presence of Tg with hormone residues in serum is occasional in GD and DTC but is a common and probably distinctive feature of ST.

Thyroid autoimmunity in children and adolescents with Type 1 diabetes mellitus

Type 1 diabetic children and adolescents often present with autoimmune thyroid disorders. Two hundred and four diabetic patients, less than 20 years old, were studied in order to diagnose these diseases. The prevalence of thyroid autoimmune disorders was 17.6% and, of those, chronic autoimmune thyroiditis was the most frequent. Microsomal autoantibodies correlated more accurately with the presence of chronic autoimmune thyroiditis than thyroglobulin autoantibodies. The thyroid status of most of the patients with positive markers was euthyroidism (77%), but subclinical hypothyroidism (11%), overt hypothyroidism (3%), subclinical hyperthyroidism (3%) and overt hyperthyroidism (6%) were also present. Autoimmune thyroid disorders were the most prevalent immunological processes affecting diabetic patients. No significant associations of thyroid autoimmunity and other autoimmunological disorders, such as celiac disease or presence of other autoimmune antibodies, were found.

Iodination of human thyroglobulin (Tg) alters its immunoreactivity. II. Fine specificity of a monoclonal antibody that recognizes iodinated Tg

In a previous investigation, we found that murine MoAb 42C3, raised against human Tg, recognized Tg differently depending upon its level of iodination of Tg. A possible explanation for this finding is that iodine is directly involved with the specific epitope recognized by MoAb 42C3. In the present study, we report that the binding of MoAb 42C3 to iodinated Tg is inhibited by T4, T3, reverse T3 (rT3), triiodothyroacetic acid (triac), diiodothyronine (T2), diiodotyrosine (DIT), but not by thyronine (TO) or tyrosine. The order of inhibition of these iodinated compounds is T4 > T3 > rT3 > triac > T2 > DIT. The MoAb 42C3 does not have the same specificity as the T3, T4-receptor since the order of binding of these iodinated compounds on the receptor differed from the order of their inhibition of this MoAb. Monoclonal antibody 42C3 also recognized non-iodinated Tg that was subsequently iodinated in vitro. It failed to recognize another protein, bovine serum albumin, that was iodinated in vitro by the same method. These results suggest that iodinated tyrosines and thyronines determine the binding specificity of MoAb 42C3. The inhibitory effects of these compounds on MoAb 42C3 depend on their iodine content as well as location of iodine in the aromatic ring.

Thyroglobulin peptides of specific primary hormonogenic sites can generate cytotoxic T cells and serve as target autoantigens in experimental autoimmune thyroiditis

Previously we demonstrated that thyroxine (T4)-containing, 12-mer peptides from positions 5 (1-12) and 2553 (2549-2560), as well as thyronine (T0)-substituted 2553 peptide, derived from human (H) thyroglobulin (Tg) are capable of activating T cells that infiltrate the thyroid (thyroiditogenic). In contrast, peptides T4(2567) and T0(2567) (2559-2570) are not. To determine if these thyroiditogenic peptides, T4(5), T4(2553), and T0(2553), activated cytotoxic T cells (Tc) and served as target autoantigens when loaded onto indicator cells (BW5147 lymphoma, H2k), lymph node cells from CBA mice immunized with mouse (M) Tg were cultured in vitro with MTg, HTg, or Tg peptide. After MTg or HTg activation, Tc were detected for both MTg- and HTg-loaded target cells in an 18-h, 51Cr-release assay at an effector:target cell ratio of 50:1. These Tc also killed target cells labeled with T4(5), T4(2553), or T0(2553), but not the control peptide T4(2567). When MTg-primed lymphocytes were cultured with T4(5), T4(2553), or T0(2553), specific Tc were also generated against target cells labeled with the respective peptide. The data suggest that one of the thyroiditogenic properties of these peptides previously shown by adoptive transfer of thyroiditis is related to the generation of Tc. In addition, these conserved autoepitopes of Tg also serve as target antigens for Tc.