We have characterized four murine monoclonal antibodies (mAbs) to the extracellular domain of the human TSH receptor (TSH-R.E), the target autoantigen of Graves' disease. Recombinant TSH-R.E used as immunogen, was produced in E. coli as a fusion protein with glutathione-S-transferase or in a baculovirus-insect cell system, as a non-fusion glycoprotein. To increase the epitope specificity of the mAbs, two different strains of mice (H-2(b) and H-2(d)) were immunized. The epitopes recognized by the mAbs were characterized by immunoblotting with various recombinant constructs of TSH-R.E and by binding to overlapping synthetic peptides of the receptor. The four IgG mAbs characterized recognized epitopes localized to different regions on the TSH-R.E; amino acids 22-35 (A1O and A11, both IgG2b from H-2(b) animals), amino acids 402-415 (A7, IgG2b from H-2(b) animals) and amino acids 147-228 (A9, IgG1 from H-2(d) animals). Immunolocalization studies showed that mAb A9 recognized TSH-R.E on unfixed cryostat sections, where binding was localized to the basolateral plasma membrane of thyroid follicular cells, suggesting that this antibody reacts with the native receptor on thyroid cells. The binding of the mAbs A7, A10 and A11 was also restricted to the basal surface of thyroid cells, but only after acetone fixation of the sections, implying that the epitopes recognized on the amino and carboxyl terminus of the extracellular region of the receptor are not accessible on the native molecule. None of the mAbs stimulated cyclic AMP responses in COS-7 cells transiently transfected with full-length functioning TSH-R.E, whilst weak inhibition of binding of radiolabelled TSH to porcine membranes in a radioreceptor assay was apparent with mAb A10 and A11, but only at high concentrations of IgG. The ability of mAb A9 to bind to the native receptor without stimulating activity or inhibition of TSH binding suggests that antibody can bind to the central region of the TSH-R.E without perturbing receptor function. The availability of mAbs that recognize epitopes on different regions of the extracellular domain of TSH-R will lead to a better understanding of the autoantigenic regions on TSH-R implicated in disease activity.

An increased prevalence of Type 1 (insulin-dependent) diabetes has been reported in patients with congenital rubella. Rubella virus multiplies in the pancreas, and we have hypothesized that studies of children with congenital rubella would be of great importance in following the development of Type 1 diabetes in a defined, susceptible population. Two hundred and forty-one children with congenital rubella (mean age 17.4 +/- 0.3 years; 65% black and hispanic) have been evaluated, 30 of whom already have diabetes and 17 of whom have borderline glucose tolerance. In these latter two groups, HLA-DR3 is significantly increased and HLA-DR2 significantly decreased. Pancreatic islet cell cytotoxic surface antibodies are found in 20% of the total congenital rubella population, including in more than 50% in the time period before they develop diabetes and are not related to any specific HLA type. In addition, anti-microsomal and anti-thyroglobulin antibodies are found in 34% of this population. The data demonstrate that Type 1 diabetes developing in congenital rubella patients has the genetic and immunological features of classical Type 1 diabetes, namely the presence of HLA-DR3, the absence of HLA-DR2, islet cell surface antibodies before decompensation and an increased prevalence of anti-thyroid antibodies. Patients with non-diabetic congenital rubella represent an easily identifiable group in whom other immunological factors associated with Type 1 diabetes can be elucidated and possibly modified.

To evaluate the B cell response to the extracellular domain of the human TSH receptor (hTSHR-ecd), we used recombinant hTSHR-ecd to immunize BALB/c mice (group A) and CBA/J mice (groups B and C). Mice from groups A and B were boosted once, and mice from group C received three antigen boosts. All individual mice developed highly specific hTSHR-ecd antibodies (hTSHR-ecd-Ab), confirmed by Western blot analyses. The B cell epitopes recognized by these murine hTSHR-ecd-Ab were mapped by enzyme-linked immunoassays using 26 synthetic overlapping peptides spanning the entire mature hTSHR-ecd [amino acids (aa) 22-415], i.e. without the signal sequence. Although all BALB/c and CBA/J mice antisera recognized peptide 1 (aa 22-41), the hyperimmunized CBA/J mice (group C) demonstrated recognition of additional peptides (numbers 21-26) clustered toward the carboxyl-terminus of the hTSHR-ecd (aa 322-415). Furthermore, group C serum blocked the binding of [125I]bTSH to native porcine TSHR, whereas sera from groups A and B were inactive. We were also able to map the B cell epitopes of antisera from rabbits immunized repeatedly with hTSHR-ecd and found the same recognition pattern of peptide 1 and additional peptides clustered near the carboxyl-terminus of the hTSHR-ecd (aa 322-341 and 367-415). These rabbit antisera also inhibited the binding of [125I]bTSH to native porcine TSHR. These data provide a comprehensive B cell epitope-mapping study of induced hTSHR-ecd-Ab and demonstrate intramolecular spreading of the epitopes recognized. Although the N-terminal region was highly antigenic, repeated immunization induced hTSHR-ecd-Ab targeted to a region critical for TSH binding.

We have developed a series of human intrathyroidal T-T cell hybridomas and evaluated their phenotypic characteristics and lymphokine secretions in order to further understand the role of the T cell in Graves' disease. Mitogen-stimulated T cell blasts were generated from intrathyroidal lymphocyte preparations and fused with a hypoxanthine-, aminopterin-, and thymidine-sensitive variant of the Molt 4 human leukemia T cell line. The resulting intrathyroidal T-T cell hybridomas and T-T cell hybridomas obtained from normal peripheral blood mitogen-stimulated T cell blasts were expanded and tested for their biological function. None of the generated T cell hybridomas exhibited antigen-specific IL-2 secretion when stimulated with autologous thyrocytes, although 60% of the hybridomas expressed CD3 antigen and the T cell receptor alpha/beta heterodimer. However, 9 intrathyroidal and 11 peripheral blood T cell hybridomas secreted a factor(s) that significantly enhanced immunoglobulin G secretion in vitro (P less than 0.005, by Student-Newman-Keuls test; mean +/- SEM, 338 +/- 60% increase). In summary, we have successfully used a technique that allows the construction of T-T cell hybridomas derived from intrathyroidal T cell cultures. The data demonstrated that a predominance of helper factor-secreting T cells were available for fusion within the Graves' thyroid gland. Such observations are further evidence for intact T cell help within the thyroid gland of patients with Graves' disease.

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