Geographical distribution of subclinical autoimmune thyroid disease in Britain: a study using highly sensitive direct assays for autoantibodies to thyroglobulin and thyroid peroxidase.

In order to determine whether the geographical distribution of autoimmune thyroid disease in Britain is influenced by the pattern of iodine intake, the prevalence of subclinical disease (detectable antithyroid antibodies in biochemically euthyroid individuals) has been measured in female blood donors from seven towns in England and Wales previously characterised in terms of past and present iodine intake. Thyroglobulin antibody and thyroid peroxidase antibody were measured by highly sensitive assays which are based on the direct interaction between antibody and radiolabelled antigen. Excluding cases of overt thyroid disease (biochemically hypo- or hyperthyroid with thyroid antibodies), the overall prevalences of the antibodies in sera from the 698 female blood donors were 17.8% for thyroglobulin antibody and 17.8% for thyroid peroxidase antibody. Both antibodies were found in 12.3% of the female blood donors. In contrast, the prevalences of thyroglobulin antibody and thyroid peroxidase antibody were 41 and 43%, respectively, in the 117 female relatives of 18 probands with autoimmune thyroid disease, but the highest prevalences were observed in groups of women patients with Graves' disease (N = 39) or Hashimoto's disease (N = 39) (51, and 97% for thyroglobulin antibody, respectively, and 72 and 97% for thyroid peroxidase antibody, respectively). Antibody prevalence increased with age in the female blood donors rising from 10.6% at age 18-24 to 30.3% at age 55-64 for thyroglobulin antibody and from 14.9% at age 18-24 to 24.2% at age 55-64 for thyroid peroxidase antibody. Geographical differences in the prevalences of both antibodies were not significant and did not correlate with either the previous goitre prevalence or with current differences in iodine intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between thyroid autoantibody spectrotype and IgG subclass.

The relationship between spectrotype and IgG subclass of autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO) has been investigated using sera from Hashimoto and Graves' patients. Isoelectric focussing (IEF) was carried out in gels over the range pI 3.5-9.5 followed by transblotting to nitrocellulose and probing the filters using 125I-labelled TPO and Tg. As has been shown previously for Tg antibodies, TPO antibody focussed over different pI values in different patients but the spectrotypes for individuals were constant over 2-5 years. Further, the pI values for TPO and Tg autoantibodies appeared to be related to IgG subclass, for example IgG1 Tg antibodies tended to focus nearer the cathode (pI 8.0-9.5) than IgG4 antibodies (pI 6.5-8.5) while antibodies of subclasses IgG1 + 2 + 4 produced spectrotypes covering a broad pI range (5.7-9.5). Consequently, it seems likely that the characteristic spectrotypes described by others for Tg autoantibodies, and those we now report for TPO antibodies, reflect the IgG subclass "fingerprints" which we suggest may be a measure of the ability of an individual to respond to different epitopes on these two thyroid antigens.

Highly sensitive assays of autoantibodies to thyroglobulin and to thyroid peroxidase.

These highly sensitive assays are based on the interaction between thyroid autoantibodies and 125I-labeled autoantigens. Serum samples are incubated with labeled thyroid peroxidase (TPO) or thyroglobulin (Tg) to allow the formation of antibody-labeled antigen complexes. The complexes are then precipitated by addition of solid-phase Protein A. In the presence of high concentrations of TPO antibody or Tg antibody, more than 50% of the respective labeled antigen was precipitated, whereas only 1-2% was precipitated in the absence of autoantibody. Interassay CVs were 3.2% and 5.7%, respectively, for the anti-TPO and anti-Tg assays. There was no cross-reactivity between Tg antibody and TPO antibody. Results correlated highly significantly with results from other assay systems based on antigen-coated cells or plastic supports, but the assays described here were considerably more sensitive. Scatchard analysis of the assay data provided information on the affinity and serum concentration of TPO autoantibodies (ka approximately 10(9) L/mol and concentrations up to 1 g/L) and Tg autoantibodies (ka approximately 4 x 10(10) L/mol and concentrations up to 1 g/L). Overall, these assays provide a sensitive, precise, and convenient system for measuring and investigating the properties of thyroid autoantibodies.

A human-mouse hybridoma which secretes monoclonal thyroglobulin autoantibody with properties similar to those of the donor patient's serum autoantibody.

Human monoclonal antibodies produced by Epstein Barr (EB) virus transformation and/or cell fusion are frequently IgM antibodies which tend to cross react with a range of antigens and often bear little relationship to the highly specific IgG antibodies associated with human autoimmune disease. By fusing EB virus transformed B lymphocytes from a Hashimoto patient with a mouse myeloma line and selecting for synthesis of IgG class thyroglobulin (Tg) antibody, we have developed a hybridoma (VB/5) secreting Tg antibody of IgG2 subclass and lambda light chain type which has the characteristics of a monoclonal antibody on isoelectric focussing. The antibody has a high affinity for human Tg and recognises Tg from other primates but not non-primate Tg. However, it does not react with human thyroid peroxidase or a panel of other autoantigens. In terms of affinity constant, functional affinity and affinity heterogeneity, the antibody closely resembles the IgG2 lambda Tg antibody present in the serum of the Hashimoto patient whose B lymphocytes were used to develop the hybridoma. In addition to providing a useful reference standard for Tg antibody IgG subclass assays, VB/5 antibody and the hybridoma line provide a valuable starting point for detailed studies of Tg autoantibodies and the genes coding for the variable regions of their heavy and light chains.

Photoaffinity labelling of the TSH receptor on FRTL5 cells.

An investigation of the properties of TSH receptors on FRTL5 cells using affinity labelling with a 125I-labelled photoactive derivative of TSH is described. Our studies suggest that FRTL5 cells contain 2 principal types of cell surface TSH receptors. One form, probably a precursor, consists of a single polypeptide chain (Mr 120,000) with an intrachain loop of amino acids formed by a disulphide bridge. The other type of receptor consists of a water-soluble A chain (Mr 55,000) linked to an amphiphilic B chain (Mr 35,000) by a disulphide bridge. The 2 chain structure is probably derived from the single chain 120,000 protein by enzymatic cleavage of peptide sequences within the loop of amino acids formed by the intrachain disulphide bridge.