An enzyme immunoassay for the measurement of thyroglobulin in human serum

Detection of anti-SFTSV nuclear protein antibody in the acute phase sera of patients using double-antigen ELISA and immunochromatography

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening febrile illness that is caused by the SFTS virus (SFTSV). The diagnosis of SFTS is usually performed by detecting viral RNA. However, it has been reported that viral RNA is no longer detectable at 6-12 days after the onset of disease. In the current study, we have constructed a plasmid to express the recombinant nuclear protein (NP) based on the Japanese strain of SFTSV (J1). We developed a double-antigen enzyme-linked immunosorbent assay (ELISA) and immunochromatography (IC) assay using recombinant NP to detect antibody against SFTSV-NP. When we tested time-sequential samples from four patients with SFTS, antibody to SFTSV-NP were detectable not only during the recovery phase (days 10-622) but also during the acute phase (days 4-7) of the disease using both of a double-antigen ELISA and IC assay. SFTSV-RNA was detected until 8-11 days after onset, thus suggesting the coexistence of the virus and antibody during the acute phase of SFTS. These data suggest that assays for detecting antibody against SFTS-NP described in the current study may be applicable not only for the epidemiological studies but also for the diagnosis of SFTS.

Immunological and biological characteristics of recombinant human thyrotropin

Analyses of epitopes and biological activity were made on two preparations of recombinant human thyrotropin produced in Chinese hamster ovary cells. Seven monoclonal antibodies recognizing four epitopes on alpha subunit of hTSH (hTSH alpha) and three on beta subunit (hTSH beta) were used for the analysis. Binding activities of the two rhTSH with each antibody were almost identical with that of a pituitary-derived reference hTSH, except at one epitope on hTSH alpha. Their immunoreactivity measured by four commercial immunoassay kits and their bioactivity by thyrotropin dependent FRTL-5 cell system, however, agreed closely with those of the reference hTSH. From these results and its constant availability, rhTSH will be a good candidate for a future standard material in assays for hTSH.

Effective laboratory evaluation of thyroid status

This article focuses on recent developments in thyroid-related laboratory tests, including analytical methods, clinical utility, and limitations of TSH, FT4, T4, FT3/T3, thyroglobulin, and thyroid autoantibodies and the effective use of these tests in the diagnosis of various forms of hypothyroidism or hyperthyroidism, and the management of patients undergoing T4 replacement, T4 suppression, or antithyroid drug therapy.

Effect of therapy on the serum thyroglobulin concentration in patients with toxic diffuse goiter, toxic nodular goiter and toxic adenoma

Serum thyroglobulin (S-Tg) was measured in 104 patients with thyrotoxicosis, 59 of whom had toxic diffuse goiter (Graves' disease), in 30 with toxic nodular goiter and in 15 with toxic adenoma. Before treatment, most patients had increased S-Tg concentrations, regardless of what type of thyrotoxicosis they had. After therapy the course of the S-Tg varied, two major patterns being observed: the S-Tg concentration increased in some patients but decreased in others, although no relationship could be found between these patterns and the outcome of therapy, the presence or absence of thyroglobulin antibodies (Tg-ab) or changes in the Tg-ab titer. However, the median pretreatment concentrations of S-Tg were significantly higher in patients with toxic nodular goiter and toxic adenoma than in those with toxic diffuse goiter (p less than 0.001 and p less than 0.05, respectively), but did not differ significantly between patients with toxic nodular goiter and toxic adenoma. The lowest posttreatment S-Tg concentrations were found after surgery, irrespective of type of thyrotoxicosis. The median pretreatment and posttreatment S-Tg concentrations in patients with toxic diffuse goiter who relapsed, did not differ from those patients in remission. This was also true of patients with toxic nodular goiter. In both groups, however, there was a tendency towards higher pretreatment S-Tg values in patients who subsequently relapsed. Serial determinations of S-Tg, on the other hand, are of limited value in predicting the risk of recurrence, independent of which type of thyrotoxicosis is involved.

Enzyme-linked immunosorbent assay (ELISA) for IgG antibodies to thyroglobulin

We used a computer programmed standard IgG curve for computer-assisted quantification of assay results for autoantibodies to thyroglobulin (Tg) by quantitative enzyme-linked immunosorbent assay (ELISA). Specific antibody levels in unknowns were quantified by comparison of their optical density readings with a standard curve of absorbance vs concentration obtained with dilutions of the reference serum. Anti-Tg antibodies were detected in 80% of the patients with chronic thyroiditis and 90% of those with Graves' disease. Anti-Tg antibodies were also detected in 14.3% of the healthy controls. The titer of anti-Tg antibodies detected by tanned red cell hemagglutination correlated well with that detected by ELISA, although, the sensitivity of the ELISA was higher. By our computer-assisted conversion method, the anti-Tg antibody can be readily and reliably quantified and low titer antibodies to Tg can be detected with adequate precision.

TSH receptor antibody induction of thyroglobulin release from human thyroid cell monolayers

We investigated the influence of TSH receptor antibody (TRA), as detected by inhibition of 125I-bTSH binding to detergent solubilized porcine TSH receptors, on in-vitro thyroglobulin (hTg) production using normal thyroid cells in monolayer. Secretion of hTg into the culture medium was analysed by a non-competitive enzyme immunosorbent (ELISA) technique utilizing two murine monoclonal antibodies. Basal hTg release (mean +/- SD 124 +/- 27 ng/10(5) cells/6 d, n = 5) was stimulated by bTSH (10, 10(2), 10(3) microU/ml) in a dose related manner (mean +/- SD 191 +/- 24, 587 +/- 80, 695 +/- 66 ng/10(5) cells/6 d, respectively). IgG (2 mg/ml) from seven patients with hyperthyroid Graves' disease, and known titres of TRA, similarly enhanced production of hTg, in a dose and time-dependent manner, when compared to control IgG. The degree of induction varied from a 140-230% increase in total hTg release over a 6-day incubation period. There was a direct correlation between the degree of 125I-bTSH binding inhibitory activity and the hTg response (r = 0.9, P less than 0.01). These data demonstrate that TSH receptor antibodies enhance hTg release from human thyroid cell monolayers and allow an assessment to be made of antibody-activated post receptor mechanisms.

Purification and storage of thyroglobulin. Two important factors influencing the radioimmunoassay for thyroglobulin

The effect upon the assay of the quality of the thyroglobulin (Tg) used as standard and tracer was evaluated by comparison of two preparations, one purified with protease inhibitors added (Tg-PI) and the other without (Tg-O). Tg-PI proved more stable than Tg-O. After freezing in phosphate-buffered saline almost all 125I-Tg-O was found to have dissociated into 12 S Tg, while only about half the 125I-Tg-PI had done so. Storage in glycerol, 500 g/l, at -20 degrees C or freezing in goat serum improved the quality of the 125I-Tg markedly, but Tg-PI still remained more stable than Tg-O. In addition, the two antisera tested gave different results in the radioimmunoassay with Tg-PI and Tg-O. With one antiserum a gradual loss of Tg immunoreactivity occurred parallel to the dissociation of Tg, while no such effect was noted with the other antiserum. This difference is believed to depend on varying proportions of conformational antibodies in the antisera, the binding sites for the conformational antibodies being distorted by the dissociation of the Tg molecule, while the binding sites for the sequential antibodies remain intact.

Influence of thyroid substitution therapy and thyroid autoantibodies on the value of serum thyroglobulin in recurring thyroid cancer

The study was performed to evaluate the influence of thyroxine substitution therapy and the presence of thyroglobulin antibodies (TgAb) on the usefulness of serum thyroglobulin (Tg) measurements in the follow-up of patients treated for well differentiated thyroid carcinoma. Seventy-two consecutive patients with differentiated thyroid cancer and eight with medullary carcinoma as well as controls were studied on one or more occasions and blood was drawn for measurement of serum Tg, TgAb, TSH and thyroid hormones. In 23 patients the hormonal substitution was withdrawn and 3-4 weeks later new blood samples and a 131I scintigraphy was performed. Eighteen patients were shown to have recurrence or metastases. Four of these had TgAb, two had normal Tg values, and the remaining 12 had extremely elevated levels. Those with TgAb and normal Tg values all had high Tg levels off thyroxine substitution. The 54 patients without evidence of recurrence had low levels of serum Tg except for one with highly elevated values. Based on the results from this and other studies is concluded that serum Tg is an important adjunct in the follow-up of patients with well differentiated thyroid carcinoma, but certain limiting factors have to be taken into account, i.e., the radicality of surgery, the sufficiency of the substitution, the presence of TgAb and the method for measurement of Tg.

Major factors limiting sensitivity of sandwich enzyme immunoassay for ferritin, immunoglobulin E, and thyroid-stimulating hormone

By using IgG-coated polystyrene balls and beta-D-galactosidase-labelled Fab', sandwich enzyme immunoassays for human ferritin, immunoglobulin E (IgE), and thyroid-stimulating hormone (TSH) were developed, and their sensitivities were shown to be largely limited by the purity, binding efficiency, and amount of beta-D-galactosidase-labelled Fab' used. (1) Their sensitivities were enhanced 10 to 50-fold by using affinity-purified Fab' labelled with beta-D-galactosidase. (2) Their sensitivities depended upon the efficiency of specific binding of the labelled Fab' to antigens adsorbed on antibody IgG-coated polystyrene balls. (3) Their sensitivities were improved by using the minimal amount of labelled Fab' that gave a reliable calibration curve. Under optimal conditions the sensitivities obtained for ferritin, IgE, and TSH were 0.09 pg (0.2 amol), 0.48 pg (2.4 amol, 0.2 mIU), and 3.2 millimicronU (5.7 amol) per tube, respectively.

Highly sensitive sandwich enzyme immunoassay of human IgE with beta-D-galactosidase from Escherichia coli

A highly sensitive sandwich enzyme immunoassay of human IgE was developed. Polystyrene balls were coated with goat anti-human IgE immunoglobulin (IgG) by physical adsorption. Goat anti-human IgE Fab' was purified by affinity chromatography and conjugated with beta-D-galactosidase from Escherichia coli. Using thus prepared anti-IgE-coated polystyrene balls and anti-IgE-beta-D-galactosidase conjugate, 0.2 mU (2 amol)--1 U of IgE per assay could be determined. When 0.1 microliter of serum per assay was used, the range of IgE levels in serum that could be determined was 2--10000 U/ml, and even 0.01 U/ml was measurable by using 20 microliters of serum. The regression equation and coefficient for correlation to radioimmunoassay were gamma (RIA) = 0.94 chi (EIA) + 18.2 and 0.96 (n = 81), respectively. The coefficients of within- and between-assay variations ranged from 5.4 to 8.5%. The mean levels of serum IgE determined by the present assay were 103 U/ml in 70 normal children and 1064 U/ml in 38 children with bronchial asthma.

A simple micro-ELISA method for the assay of antithyroglobulin autoantibodies in human serum

An indirect, enzyme-linked immunosorbent assay is described for the assay of thyroid autoantibodies, particularly those directed against thyroglobulin. The method is specific, sensitive and precise, and may be automated. The results are shown to correlate well with those obtained by the haemagglutination method.

Determination of triiodothyronine in serum by enzyme- and radioimmunoassay: a comparative study

An evaluation of a heterogeneous enzyme immunoassay for determination of triiodothyronine in serum (Enzymun-Test T3, Boehringer Mannheim) is presented. The enzyme immunoassay was compared with the laboratory routine radioimmunoassay. The precision of both assays was satisfactory at triiodothyronine concentrations between 1.0 and 8.0 nmol/l (coefficients of variation from day to day less than or equal to 10%). Average recoveries of triiodothyronine in pool sera ranged with the Enzymun-Test T3 from 96--104% and with the radioimmunoassay from 88--111%. A comparison of the results obtained by Enzymun-Test T3 and the radioimmunoassay in a series of 103 patients showed a good correlation between both methods. L-thyroxine did not cause a relevant cross-reaction in the enzyme immunoassay. About 20 unknown samples can be analyzed in triplicate by Enzymun-Test T3 within 260 minutes.

A general and mild procedure for the purification of rabbit Fab' antibodies

A mild procedure for the purification of rabbit Fab' antibodies is described. A small column of normal goat IgG-Sepharose 4B (3 cm x 5mm) was saturated with F(ab')2 prepared from rabbit anti-goat IgG, and anti-goat IgG Fab was eluted from the column by splitting the disulfide bond in the hinge of the F(ab')2 molecule using 10 or 12 mM 2-mercaptoethylamine at pH 7. The recovery of anti-goat IgG Fab' in the eluate was about 35% of anti-goat IgG F(ab')2 bound to the column, and the purity of anti-goat IgG Fab' eluted was more than 90%. This procedure may be applicable to most kinds of rabbit IgG antibodies and useful for various immunoassays.

An enzyme immunoassay for the measurement of anti-thyroglobulin autoantibody in human serum

An enzyme-linked sandwich immunoassay using human thyroglobulin conjugated with beta-D-galactosidase and silicone rods coated with human thyroglobulin was developed for the measurement of circulating anti-thyroglobulin autoantibody. The volume of serum needed for the assay was as little as 5 microliter. The sensitivity of the assay was approximately 7 x 10(-15) mol/tube of antithyroglobulin immunoglobulin G corresponding to 220 ng/ml of serum, which was equal to or rather higher than that of radioimmunoassay. The specificity of the assay was demonstrated by (1) parallelism of the standard curve with dilution of sample sera of patients with thyroid diseases, and (2) non-detectability of anti-thyroglobulin in autoantibody in the sera of normal subjects. The precision of the assay was proven by (1) sufficient recovery of antithyroglobulin immunoglobulin G added to serum, and (2) coefficients of variance within and between assays were 6.5 to 10.3% and 4.9 to 14.1%, respectively. No effect of thyroglobulin on the present assay was observed when the ratio of the amount of thyroglobulin to that of anti-thyroglobulin immunoglobulin G was lower than 1 : 10. Furthermore, a significant correlation was observed between anti-thyroglobulin autoantibody concentrations measured by our enzyme immunoassay and those by tanned red cell hemagglutination (r = 0.78), and between those by the enzyme immunoassay and those by radioimmunoassay (r = 0.80). The application to clinical samples ensured the high sensitivity and the adequate validity of the present assay.

An improved preparation of antibody-coated polystyrene beads for sandwich enzyme immunoassay

An improved preparation of antibody-coated polystyrene beads for sandwich enzyme immunoassay of human thyroid-stimulating hormone (TSH) was described. Rabbit anti-TSH IgG was purified by eluting at pH 2.5 from a TSH-Sepharose column, diluted 3 or 9 fold with normal rabbit IgG and used for coating polystyrene beads by physical adsorption. In a sandwich enzyme immunoassay of TSH using rabbit (anti-TSH) Fab'-beta-D-galactosidase conjugate, beta-D-galactosidase activities specifically bound to thus prepared polystyrene beads in the presence of TSH was 2.8-6.3 fold higher than those bound to polystyrene beads coated with anti-TSH IgG before purification. A similar effect was observed when guinea pig anti-pork insulin IgG, rabbit (anti-human IgE) IgG and goat (anti-human IgE) IgG were treated at pH 2.5. This improvement may be based on a conformational change of Fc in IgG molecule which was caused by the treatment at pH 2.5. Other sandwich immunoassays such as fluoro- and radio-immunoassays may also be improved in the same way.