Immunoassay reagents for thyroid testing. 3. Determination of the solution binding affinities of a T4 monoclonal antibody Fab fragment for a library of thyroxine analogs using surface plasmon resonance

A library of thyroxine analogs and tracers was prepared, and their solution binding affinities for an anti-T4 Fab fragment were determined using a single high-density L-T4 biosensor surface in a BIAcore surface plasmon resonance instrument. The high-density L-T4 analog biosensor was calibrated by determination of the initial binding rate was of known concentrations of free anti-T4 Fab fragment in solution to the biosensor surface. A range of individual thyroxine analog and tracer concentrations was subsequently mixed with a fixed concentration of anti-T4 Fab fragment. The concentration of free anti-T4 Fab fragment in each solution at equilibrium was determined, and the equilibrium dissociation constant (KD) for each case was derived. The KD values determined in solution are compared to values determined by a direct kinetic analysis on the BIAcore instrument using individual biosensor surfaces.

Thyroid hormone autoantibodies elicited by diagnostic fine needle biopsy

Based on the knowledge that diagnostic fine needle biopsy of the thyroid (FNAB) results in a prompt increase in circulating thyroglobulin (Tg); we evaluated whether Tg is indeed the postulated antigen for circulating antibodies against thyroid hormones (THAb). Preliminarily, we verified that FNAB causes the release into the bloodstream of iodinated, heterologous, and thus potentially immunogenic, molecules of Tg. Of the initially enrolled 400 patients, 214 had a number of blood drawings sufficient to evaluate over time (before FNAB and 1-3 h, 3 days, 15 days, 30 days, 3 months, 6 months, and 12 months after FNAB) the following parameters: THAb of both IgM and IgG classes, Tg antibodies (TgAb; by a sensitive immunoradiometric assay), and Tg (in the 156 patients who were TgAb negative). We found the following. 1) Serum Tg most often peaks 1-3 h after FNAB (61 +/- 45% of the baseline level; mean +/- SD). 2) Only 7% of the initially TgAb-negative patients converted to positive, and only 12% of those initially positive had an increase in the levels of TgAb. 3) THAb were detected in 0 of 400 patients before FNAB, but were found in 9 of 214 (4.2%) after FNAB. This proportion is 2 orders of magnitude higher than that (149 of 369,000 or 0.04%) found in consecutive patients attending European thyroid clinics. Of the 9 cases, 6 had Hashimoto's thyroiditis (HT), 2 had euthyroid colloid goiter, and 1 had Hurthle cell carcinoma. In the 5 of 9 cases who were TgAb negative, the post-FNAB increment in Tg was 21-99%, i.e. lower than that of the majority of patients (101-12,500%). 4) THAb were of the IgM class in all 9 (6 against T3 and 3 against T4), and were accompanied and/or followed up to 3 months after FNAB by IgG-THAb of the same specificity (2 against T3 and 1 against T4) in 3 cases. In a fourth case, IgM-T3 were followed by a long-lasting synthesis of IgG-T3 (i.e. up to 1 yr post-FNAB). All 4 cases with IgG-THAb had HT and remained TgAb positive. 5) In the 2 HT and the 3 non-HT patients with undetectable TgAb, THAb were of the IgM class only. 6) In the HT group, 2 risk factors for the development of post-FNAB THAb appeared to be pre-FNAB TgAb levels below 400 U/mL that did not increase after FNAB and Tg released from a colloid nodule. We conclude that Tg release from the thyroid is sufficient to elicit THAb synthesis. In patients with autoimmune thyroid disease (HT), this synthesis occurs with a frequency 10-fold higher than that in patients with nonautoimmune thyroid diseases (21% vs. 2%). However, in only a fraction of patients with autoimmune disease, who need to be TgAb positive by a sensitive assay, the primary immune response (IgM) is followed by a secondary one (IgG). As, once present, this secondary response is long lasting in only a minority of our patients, we think that this could contribute to the rarity of naturally occurring THAb.

A thyroxine-containing thyroglobulin peptide induces both lymphocytic and granulomatous forms of experimental autoimmune thyroiditis

Mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTg can induce two histologically distinct forms of experimental autoimmune thyroiditis (EAT). MTg-sensitized cells activated with MTg alone induce a mild chronic form of EAT in which the thyroid infiltrate consists primarily of lymphocytes and other mononuclear cells (lymphocytic EAT). The same donor cells activated with MTg and anti-IL2R mAb induce a more severe and acute form of EAT with a thyroid inflammatory lesion having granulomatous histopathological features. A thyroxine-containing (T4) peptide, corresponding to positions 2549-2560 of human Tg, was shown by others to activate spleen cells of mouse thyroglobulin (MTg)-sensitized CBA/J mice to induce lymphocytic EAT. To determine if the CD4+ effector T cells that induce granulomatous EAT can respond to the same T-cell epitope, the present study was undertaken to determine if both forms of EAT could be induced by the 2549-2560 thyroxine (T4)-containing peptide. This peptide was very effective for activation of T cells from MTg-primed CBA/J donors to induce granulomatous EAT but, in contrast to MTg, did not activate T cells from AKR/J or DBA/1 mice to induce granulomatous EAT. The T4 peptide did not apparently activate peptide-specific B cells in vivo but did activate MTg-primed B cells in vitro to produce anti-MTg autoantibody in recipient mice. These results demonstrate that a single 12-amino-acid thyroxine-containing peptide can activate T cells from CBA/J mice to induce both lymphocytic and granulomatous EAT. However, this peptide does not activate T cells from some other EAT-susceptible strains of mice, suggesting that MTg contains multiple epitopes able to activate T cells to induce granulomatous EAT.

Primary hormonogenic sites as conserved autoepitopes on thyroglobulin in murine autoimmune thyroiditis: role of MHC class II

A few synthetic peptides corresponding to amino acid sequences on human thyroglobulin (Tg) have been reported to induce moderate thyroiditis or activate mouse Tg (MTg)-primed T cells to transfer thyroiditis in mice susceptible to experimental autoimmune thyroiditis. Using three pairs of 12-mer peptides (1-12, 2549-2560, 2559-2570), with thyroxine (T4) or noniodinated thyronine (T0) at the conserved, hormonogenic site 5, 2553, or 2567 respectively, we reported that iodination was not required for a Tg hormonogenic site to be a thyroiditogenic autoepitope. To determine the relative importance of MHC class II and T cell receptor (TCR) repertoire, we compared two EAT-susceptible k and s (CBA and A.SW) haplotypes and their respective MHC-identical strain (C57BR and SJL) with approximately 50% genomic deletion of TCR Vbeta genes. Whereas k and s strains develop MTg-induced EAT, vigorous immunization with peptides containing T4 or T0 at either 5 or 2553, but not at 2567, led to mild (10-20%) thyroiditis only in some mice of either k strain. TCR Vbeta gene differences played a minor role. T cell responses to all peptide pairs were quite similar in CBA and C57BR mice, and both hT0(2553) and hT4(2553) reciprocally primed and stimulated their T cells. In adoptive transfer, SJL mice were somewhat more responsive to peptide activation than A.SW but much weaker than k strains. By comparing T4- and T0-containing peptides in different haplotypes, we show further that antigenicity of conserved hormonogenic sites is intrinsic, dependent more on amino acid sequence and binding to appropriate class II molecules and less on TCR repertoire or iodination of T0.

Modulation of chronic excessive interleukin-6 production in multiple myeloma does not affect thyroid hormone concentrations

Interleukin-6 (IL6) is believed to be involved in alterations of thyroid hormone metabolism in acute nonthyroidal illness. To evaluate the effects of IL6 on thyroid hormone metabolism in a chronic IL6-mediated disease, we measured thyroid hormone concentrations in multiple myeloma patients treated with intravenous anti-IL6 chimeric monoclonal antibodies ([cMabs] Kd = 6.25 x 10(-12) mol/L). Twelve patients were studied, receiving at least one complete treatment cycle of 14 days (daily dose: 5 mg, n = 3; 10 mg, n = 3; 20 mg, n = 3; and 40 mg, n = 3). Eight of them also completed a second treatment cycle of 14 days. Thyroid hormone concentrations were measured before, during, and after treatment with the anti-IL6 cMab. Even in the group with the lowest dosage, IL6 activity measured by the B9 bioassay was blocked completely. Compared with the reference ranges, 10 of 12 patients had one or more abnormal pretreatment values for thyroid hormone concentrations. Thyroid autoantibodies were negative in all patients. There was no correlation between thyroid hormone concentrations and IL6 levels, although plasma IL6 levels were increased in all but one subject. Moreover, neutralization of free IL6 by the anti-IL6 cMab did not affect thyroid hormone concentrations, although IL6-dependent C-reactive protein (CRP) levels decreased to undetectable levels in 11 of 12 patients. Two patients developed infectious complications resulting in increased free IL6 and CRP levels and in profound alterations of thyroid hormone levels consistent with an acute euthyroid sick syndrome. We conclude that IL6 is not a major determinant of thyroid hormone abnormalities in a chronic disease like multiple myeloma, but IL6 may be involved in thyroid hormone metabolism in acute diseases (probably in combination with other factors).

Conformational isomerism of IgG antibodies

The purpose of this study was to determine why apparently homogeneous IgG antibodies were, in some cases, fractionated into at least two components by liquid-liquid partition chromatography (LLPC) in an aqueous two-phase system. Four mouse monoclonal IgG antibodies, two against albumin, one against IgG and one against thyroxine, were shown to adopt different conformational isomeric forms. The four antibodies existed in an equilibrium between two or three conformational forms, the proportion of which could also be estimated by LLPC. Since LLPC detects mainly conformational differences within the antigen-binding sites of IgG antibodies, it could be concluded that the conformational forms differed with respect to their combining sites. Moreover, the isomeric forms of an antibody directed against a protein antigen, formed antigen-antibody complexes with almost identical surface properties. In contrast, complexes with different surface properties were formed when the hapten or hapten conjugated to BSA was bound. Thus, both the conformational isomers could bind antigen, at least when the antigen was a small hapten or a hapten conjugated to a carrier protein. Our results suggest that six out of 57 monoclonal IgG antibodies exist in equilibrium between at least two conformational forms and the biological significance of this isomerism is discussed.

Immunoassay reagents for thyroid testing. 2. Binding properties and energetic parameters of a T4 monoclonal antibody and its Fab fragment with a library of thyroxine analog biosensors using surface plasmon resonance

A library of 16 thyroxine analog biosensors were prepared for use on the BIAcore surface plasmon resonance instrument. An anti-thyroxine monoclonal antibody and its Fab fragment were tested with each biosensor to generate the association and dissociation rate constants, equilibrium association constants, and Gibbs free energy values for characterizing the binding event.

Usefulness of a chromatographic method to detect circulating antithyroid hormone autoantibodies in canine serum

Antithyroid hormone autoantibodies (THBA), described in both humans and animals, result in variable interference when thyroid hormone plasma levels are measured by immunoassays. We previously described a quick chromatographic method to detect circulating THBA in humans. In the present experience, we applied the method on canine sera (10 normal dogs and 3 dogs affected by hypothyroidism) to detect the THBA presence in a dog (no. 13) with clinical evidence of hypothyroidism, in spite of apparently extremely high values of thyroid hormone. After a short incubation of samples with 125I-T3 and 125I-T4 in presence of 8-anilino-1-naphtalenesulfonic acid, samples were eluted and radioactivity values counted. Eluate radioactivity values > 10% and > 30% were considered positive for THBA presence for antiT3 and antiT4 detection, respectively. High radioactivity values were detected in dog serum no. 13 and, therefore, it was considered positive for THBA presence. The Scatchard plot analysis revealed the presence of a monoclonal autoantibody with the highest affinity for T3 and an additional tenfold lower affinity for T4. In conclusion, our chromatographic method allows the detection and the characterization of THBA in species different from humans, with species specific differences in thyroid hormone metabolism; thus, taking into account the rarely availability of canine serum TSH and anti-thyroglobulin antibody immunoassay detection methods, it was possible to correctly diagnose the hypothyroidism in a dog with apparently extremely high values of thyroid hormones due to THBA interference.

Iodine-induced autoimmune thyroiditis in NOD-H-2h4 mice

Excess iodine ingestion has been implicated in induction and exacerbation of autoimmune thyroiditis in human populations and animal models. We studied the time course and sex-related differences in iodine-induced autoimmune thyroiditis in NOD-H-2h4 mice. This strain, derived from a cross of NOD with B10.A(4R), spontaneously develops autoimmune thyroiditis but not diabetes. NOD-H-2h4 mice were given either plain water or water with 0.05% iodine for 8 weeks. Approximately 54% of female and 70% of male iodine-treated mice developed thyroid lesions, whereas only 1 of 20 control animals had thyroiditis at this time. Levels of serum thyroxin (T4) were similar in the treatment and control groups. Thyroglobulin-specific antibodies were present in the iodine-treated group after 8 weeks of treatment but antibodies to thyroid peroxidase were not apparent in the serum of any of the animals. Levels of thyroglobulin antibodies increased throughout the 8-week iodine ingestion period; however, no correlation was seen between the levels of total thyroglobulin antibodies and the degree of thyroid infiltration at the time of autopsy. The thyroglobulin antibodies consisted primarily of IgG2a, IgG2b, and IgM antibodies with no detectable IgA, IgG1, or IgG3 thyroglobulin-specific antibodies. The presence of IgG2b thyroglobulin-specific antibodies correlated well with the presence of thyroid lesions.

Plasma free thyroxine (FT4) concentrations during hemodialysis in patients with chronic renal failure: effects of plasma non-esterified fatty acids on FT4 measurement

Plasma free T4 (FT4) concentrations could be increased during hemodialysis in patients with chronic renal failure (CRF) because an increase in non-esterified fatty acids (NEFA) could interfere with the binding of T4 to thyroxine-binding globulin. To evaluate the effect of hemodialysis on the FT4 concentration in patients with CRF, we measured the FT4 in 39 patients with CRF by four assay methods including equilibrium dialysis, the 125I-T4 analog method and enzyme immunoassay. The addition of the fatty acid sodium oleate to normal pooled sera led to a marked increase in FT4 as measured by equilibrium dialysis (Model FT4). A moderate increase in the serum FT4 concentration also was observed with an IMX enzyme immunoassay kit, whereas the Coat-A-Count analog method demonstrated no interference by sodium oleate. The mean serum FT4 prior to hemodialysis measured by equilibrium dialysis did not differ significantly from that in the normal control, although those measured by analog methods (Coat-A-Count and Amerlex) and IMX were subnormal. The FT4 by IMX were albumin-dependent, and the values decreased as the samples were serially diluted, but Model FT4 was not affected by the albumin level or the serial dilution. FT4 by Model FT4 showed a marked increase beginning 10 min after the start of dialysis, and it correlated well with the plasma concentration of NEFA and the NEFA/albumin molar ratio. The other three assay methods, including one which is not affected by NEFA, did not show a change in FT4 at 10 min, but a significant increase of 11 to 17% was observed by the end of dialysis. The TSH concentration decreased significantly during hemodialysis. These data suggest that (1) the low serum FT4 in hemodialysis patients measured by some immunoassay methods may be an underestimation due to the low albumin level; (2) FT4 actually increases during hemodialysis due to the actual increase in NEFA, although the marked increase in FT4 during hemodialysis as measured by equilibrium dialysis is an overestimation due to the in vitro generation of NEFA; and (3) one should beware of aberrations in thyroid hormone parameters during hemodialysis and potential complications.

Effect of interferon-beta on thyroid function in patients of chronic hepatitis C without preexisting autoimmune thyroid disease

The effect of interferon-beta (IFN-beta) on thyroid function was studied in patients with chronic hepatitis who had no preexisting thyroid disease. Eleven patients (9 males and 2 females) aged 20 to 65 years, with a mean age of 47.7 +/- 13.5 years, were treated with 6 million units of IFN-beta intravenously every day for 8 weeks. During IFN-beta administration (4th to 8th week of treatment), both serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations decreased significantly (P < 0.0005 and P < 0.05, respectively): FT4, 1.37 +/- 0.17 to 1.09 +/- 0.12 ng/dl, and FT3, 3.71 +/- 0.45 to 3.28 +/- 0.34 pg/ml. On the other hand, serum TSH increased significantly from a baseline of 1.70 +/- 0.82 to 3.34 +/- 1.98 microU/ml during IFN-beta administration (P < 0.005). Four to eight weeks after cessation of treatment, the mean serum FT4 concentration was similar to that during IFN-beta administration (1.04 +/- 0.14 ng/dl), but mean serum FT3 and TSH concentrations returned to pre-treatment levels (FT3, 3.57 +/- 0.42 pg/ml and TSH, 1.60 +/- 0.84 microU/ml). Both reverse T3 and thyroglobulin were essentially unchanged. Tests for anti-thyroglobulin and anti-microsomal antibodies were negative in all the patients. These results indicate that IFN-beta may inhibit thyroid function in patients without preexisting thyroid disease irrespective of humoral immune responses.

Development of enzyme immunoassays for 3,5,3'-triiodo-L-thyronine and L-thyroxine: time-course studies on the effect of food deprivation on plasma thyroid hormones in two marine teleosts, sea bass (Dicentrarchus labrax L.) and sea bream (Sparus aurata L.)

The effects of short-term food deprivation and photoperiod on plasma thyroid hormone levels of sea bass and sea bream were studied. Animals were acclimated under constant photoperiod regime (15L/9D) and feeding times (2 hr after light onset and 2 hr before light offset). Time-course studies involved monitoring plasma hormone levels every 4 hr throughout 1.5 24-hr cycles. Plasma 3,5, 3'-Triiodo-L-thyronine (T3) and L-thyroxine (T4) were assayed using a newly developed competitive enzyme immunoassay, utilizing acetylcholinesterase as a label of enzymatic tracers. Enzyme immunoassays had sensitivities of 1.25-0.02 and 62.5-0.2 ng/ml for T3 and T4, respectively, and reproducibilities of 3.7 and 5.6% intraassay variation for T3 and T4, respectively; interassay variations for T3 and T4 assays respectively were 1.6%, 11% and 6.6%, 8% for sea bass and sea bream plasma similar to RIA. In sea bass, 3 days of food deprivation resulted in depressed plasma T3 and T4, overriding significant diel variations seen during the second day of starvation. Sea bream displayed a slight decrease of T4 plasma levels while T3 levels remained constant for the whole sampling period. Both thyroidal systems responded to photoperiod with a significant increase in plasma T4 level at the time of light onset. In addition, sea bass also displayed increased T3 levels and decreases in both hormone levels coinciding with "lightoff." Data show different responses of the sea bass and sea bream thyroidal systems to both nutritional state and photoperiod in that the latter state is influenced by the former. Data suggest plasma thyroid levels can be used as a rapid indicator of nutritional status.

An alternative ELISA for T4 determination based on idiotype anti-idiotype interaction and a latex method for anti-idiotype monoclonal antibody selection

This paper is the first report on the use of an idiotype-anti-idiotype monoclonal antibody reaction to develop an enzyme immunoassay for thyroxine (T4). We have developed a monoclonal antibody against T4, named 1F10 of IgG1 subclass and KA 5.21 x 10(8) M-1 which was used to obtain anti-idiotypic monoclonal antibodies. Anti-idiotypic antibodies were selected by a novel method, a passive agglutination assay with the idiotype monoclonal 1F10 absorbed on latex particles and subsequently characterized by RIA. One of these anti-idiotype antibodies, named 5B3--type beta antibody--of IgG1 subclass, was used to develop an enzyme-linked T4 idiotype-anti-idiotype immunosorbent assay. The T4 calibration curve, using the 1F10 idiotypic antibody adsorbed to solid phase and the 5B3 anti-idiotypic antibody conjugated to alkaline phosphatase (ALP), shows adequate performance in the range between 0.7-25 micrograms% of the analyte. The reliability of the proposed method is demonstrated by the correlation coefficient r = 0.74, found between T4 measured by RIA and our assay, with a panel of sera from euthyroid, hypothyroid and hyperthyroid individuals. The correlation coefficient was r = 0.93 within assays and r = 0.88 between assays. These results provide the basis for a new non isotopic assay for the study and diagnosis of T4-related human disease and provides a model to develop immunoassays for other haptens and small molecules of clinical interest.

Clinical comparison of three labeled-antibody immunoassays of free triiodothyronine

Three labeled-antibody immunoassays of free triiodothyronine (FT3) were studied in hyperthyroid patients, patients with nonthyroidal illness, and patients being treated with amiodarone; we also studied sera presenting known interferences (n for all groups = 465). The results were compared with those of a one-step labeled-analog assay. The precision of the two automated assays were similar to that of the manual assays. The three labeled-antibody FT3 assays demonstrated a satisfactory diagnostic performance for confirming hyperthyroidism and robustness to interference; nevertheless, two assays displayed unusual behavior in some patients with nonthyroidal illness, with chronic renal failure, or after amiodarone therapy.

Autoantibodies to triiodothyronine and thyroxine in a golden retriever

A golden retriever presented with signs of hypothyroidism occurring in conjunction with autoantibodies to both triiodothyronine (T3) and thyroxine (T4). The autoantibodies caused the apparent concentrations of total T3, total T4, and free T4 by analog assay to be high. However, free T4 concentration was nondetectable when measured using a dialysis assay. The dog's clinical condition markedly improved in response to L-thyroxine therapy, and the free T4 concentration by dialysis assay increased into the normal range. Thyroid hormone autoantibodies can confuse the diagnostic evaluation for suspected hypothyroidism. In dogs with autoantibodies to T4, measurement of free T4 by dialysis assay is useful for both diagnostic and therapeutic monitoring purposes.

Study of binding of thyroxin-conjugates to the thyroxin-binding proteins

In this work we studied the effects of the molecular weight (M.W.) of thyroxin (T4)-conjugates and the sample dilution factor on the binding potential (C) of serum T4-binding proteins for these T4-conjugates. We prepared six T4-conjugates with great difference in molecular weight with proteins such as IgG, apoferritin, ferritin, transferrin, and thyroglobulin using p-benzoquinone as bifunctional reagent. The conjugates prepared were characterized in terms of their M.W., the molar ratio of T4 to the carrier protein, and their affinity to bind with the anti-Tr antibody. The binding potential values of serum T4-binding proteins for the T4-conjugates were determined, following appropriate mathematical interpretation of the results, obtained through an assay system containing 125I-labeled conjugated tracers, anti-T4 antibody in great excess compared with the concentration of the tracers, and increasing concentration of T4-binding proteins. We conclude that the M.W. of the conjugates is a parameter which significantly influences the binding of a conjugate to the T4-binding proteins. Additionally, for conjugates of very high M.W. (> 650,000), zero C values were obtained using 20-fold sample dilution in the final incubation mixture.

Hormone regulation of murine T cells: potent tissue-specific immunosuppressive effects of thyroxine targeted to gut T cells

Recent studies in athymic mice indicate that the neuroendocrine hormones thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) can significantly influence the development of lymphoid cells associated with intestinal intraepithelial lymphocytes (IEL). In the present study we have examined the effects of those hormones, as well as of thyroxine (T4), a thyroid-derived hormone regulated by TSH, on IEL development in euthymic mice. As reported here, whereas IEL in euthymic mice were unaffected by TRH and TSH treatment, T4 administered to adult euthymic mice at 3 or 6 weeks of age caused a dramatic reduction in the numbers of TCR alpha beta, CD8 alpha beta IEL, i.e. the same subsets previously shown to be up-regulated ty TRH and TSH in athymic mice. When given to euthymic mice >8 weeks of age, after TCR alpha beta and CD8 alpha beta subsets had reached normal levels, T4 had minimal effect on IEL, suggesting that the mode of action of T4 is directed to developing but not mature IEL. That possibility was confirmed in experiments in which T4 treatment of bone marrow radiation chimeras during an active phase of T cell regeneration temporarily halted all IEL development at a stage characteristic of immature IEL. Most interesting, the immunosuppressive effects of T4 were selectively targeted to the intestinal immune system since T4 had no effect on developing thymocytes or on mature peripheral T cells, in either normal euthymic mice or during hematopoietic reconstitution of radiation chimeras. These findings have implications for understanding intestinal immunity and disease, including chronic intestinal inflammation, in ways not previously appreciated.

Analytical performance of free and total thyroxine assays

Excessive bias and imprecision are major analytical problems associated with some assays for free and total thyroxine (T4). Bias in free T4 methods is largely proportional to variations in serum T4 binding. In direct methods, this is attributable to requirements for substantial quantities of protein-bound T4 to replace analytical losses of free T4. In some total T4 methods, bias is inversely proportional to the amount of serum T4 binding and is attributable to the incomplete release of serum protein-bound T4. In others, bias is fixed and attributable to inaccurate calibration. Manufacturers should report the bias in their methods. Calibrations should be standardized. Imprecision varies widely among methods, but is generally less for total T4 methods than for free T4 methods. A consensus on quantitative analytical performance goals for free and total T4 methods would be helpful. Here, performance goals are proposed, based in part on the best achievements of current methods.

Performance of Opus immunoassays for thyroxine and beta-human chorionic gonadotrophin in serum

Two representative immunoassays for measuring thyroxine and beta-subunit of human chorionic gonadotrophin in serum, using the Opus immunoassay analyzer, were evaluated by comparing them to the reference RIA for T4 and beta-HCG enzyme immunoassay. Both assays were superior in accuracy and precision than the reference methods and exhibited good linearity throughout the concentration range needed for discriminating abnormally low and elevated concentrations from the established reference ranges of thyroxine and beta-human chorionic gonadotrophin in serum. Correlation between the results of the Opus immunoassays and the reference assays for T4 and beta-HCG was very good with correlation coefficients of 0.92 and 0.98, respectively.

Familial dysalbuminemic hyperthyroxinemia and thyroid hormone autoantibodies: interference in current free thyroid hormone assays

The interference of familial dysalbuminemic hyperthyroxinemia (FDH), antithyroxine (anti-T4) or antitriiodothyronine (anti-T3) antibodies in serum free T4 (FT4) or free T3 (FT3) assays depends on the assay method: two-step immunoextraction, one-step labelled ligand (analogue or derivative tracer) or labelled antibody (solid-phase antigen-linked technique: SPALT) method. For FDH subjects, only FT4 measurements by one two-step method gave reliable results in all cases. However, the overestimation was less marked with new SPALT assays than with previous analogue-based assays. In sera containing anti-T4 antibodies, two-step assays and SPALT assays with a T3-coated solid phase can be considered as reliable for FT4 determination. All other methods including SPALT assays with a T4-coated solid phase may give falsely high results. In sera containing anti-T3 antibodies, SPALT FT4 and FT3 assays with a T3-coated solid phase may give spuriously high values. Anti-T3 antibodies do not interfere in two-step FT3 assays and SPALT FT3 assays with a T2-coated solid phase, but may give high FT3 values as measured by analogue or derivative methods. Moreover, SPALT free thyroid hormone assays may also be subject to interference from antibodies directed towards the assay solid phase.

[Prospects for use of hapten-heterologous conjugates in immunoassay of thyroid hormones]

The effect of hapten heterology on the characteristics of indirect ELISA methods for determination of thyroxine and triiodothyronine using monoclonal antibodies was studied. The use of the heterologous triiodothyronine-bovine serum albumin conjugate in immunoassays for thyroxine improved the sensitivity of these assays twofold and reduced the cross-reactivity with triiodothyronine from 1 to 0.5% as compared to the homologous variant. By contrast, the heterology in the immunoassays for triiodothyronine appeared inadequate. It was shown that the specificity and sensitivity of hapten immunoassays can be modulated by altering the chemical structure of the hapten-label conjugate, which is most evident in experiments with monoclonal antibodies.

Primary hormonogenic sites as conserved autoepitopes on thyroglobulin in murine autoimmune thyroiditis. Secondary role of iodination

We hypothesized earlier that conserved T cell epitopes and those unique to mouse thyroglobulin (MTg) contributed to its total thyroiditogenicity in murine autoimmune thyroiditis. Recent studies of synthetic peptides from human Tg (HTg) revealed no immunodominant epitopes. The role of iodine residues, considered by some to render Tg immunogenic, became unclear, since only one 12-mer peptide contained thyroxine (T4) positioned at hormonogenic site 2553. It primed T cells for thyroiditis transfer, but noniodinated peptide containing thyronine (T0) was not compared. To determine 1) whether other primary hormonogenic sites were likewise immunogenic and 2) whether iodination was requisite for this and other sites to be an autoepitope, we derivatized three pairs of 12-mer peptides, 1-12, 2549-2560, 2559-2570, containing T0 or T4 at positions 5, 2553, or 2567, respectively. The six peptides were used to stimulate MTg-primed cells in vitro and to immunize mice. None directly induced thyroiditis; peptide Abs were the lowest in mice given hT0(2567) or hT4(2567). Of the three T4-containing peptides, hT4(5) and hT4(2553), but not hT4(2567), stimulated MTg-primed or HTg-primed T cells in vitro, with hT4(2553) being the stronger. Comparing hT0(2553) with hT4(2553), both activated MTg-primed, or peptide-primed, T cells to transfer thyroiditis. The marked immunogenicity of noniodinated hT0(2553) and the poor antigenicity of hT4(5) and hT4(2567) demonstrate that immunogenicity of a conserved hormonogenic site is dependent more on its amino acid sequence than on T4 substitution. Iodination may enhance antigenicity and/or binding affinity, but it is not required for a Tg hormonogenic site to be an autoepitope.

An enzymeimmunoassay for total thyroxine using avidin-biotin separation system and thyroxine-peroxidase conjugate

An avidin-biotin enzymeimmunoassay for total thyroxine in serum is described. Avidin was adsorbed to biotinylated bovine serum albumin coated tubes prepared with glutaraldehyde as coupling agent. In the enzymeimmunoassay, affinity purified biotinylated anti-thyroxine IgG, sample or standards, and thyroxine-horseradish peroxidase were simultaneously added to the avidin coated tubes. The bound enzymatic activity was then measured with o-phenylenediamine and H2O2. Results showed that the assay has good precision (within-assay CV% less than 10% and between assay 11.7% in hypo- and 6.9% in hyperthyroid range), good assay range (0-800 nmol/L), good sensitivity (4 nmol/L), and can be performed in 2.5 hours. The results obtained correlate well (r = 0.93) with those of an RIA.

A quick method to detect circulating anti-thyroid hormone autoantibodies

The aim of this study was to evaluate the feasibility of a chromatographic method to easily detect circulating anti-thyroid hormone autoantibodies (THBA), to calculate their affinity constant and the total thyroid hormone (TH) levels in presence of THBA. This method was applied to sera from 4 subject with suspected THBA and 20 controls (10 normal subjects and 10 patients with thyroid dysfunctions). After a short incubation with 125I-T3 or T4 tracer solution containing 8-anilino-1-naphthalenesulfonic acid as inhibitor of the binding of TH to plasma proteins without affecting THBA binding, the samples were chromatographied on prepacked Sephadex LH 20 columns and eluted with TRIS buffer to separate free TH from THBA-bound TH. Samples were considered THBA positive when radioactivity values in TRIS eluates were higher than in controls. THBA-bound TH were subsequently eluted with methanol and used to calculate the total TH present in patients with THBA. After a validation test using two standardized methods, we propose this method to quickly detect TH-BA in samples with suspected spuriously high values of free and total TH.