B-cell autoepitopes on the acetylcholinesterase-homologous region of human thyroglobulin: association with Graves' disease and thyroid eye disease

Abstract

Objective: Thyroglobulin (Tg) is a large autoantigen involved in autoimmune thyroid diseases. Tg epitopes have, so far, been identi®ed within large peptides. In the present study, we used small synthetic peptides to ®nely map serological epitopes on the highly immunogenic C-terminal region of Tg. Homology of this region to acetylcholinesterase (AChE) has been implicated in the pathogenesis of thyroid eye disease (TED) through cross-reactive antibodies. Methods: We tested total IgG puri®ed from four pilot Graves' disease (GD) sera reactive with both Tg and AChE and from three healthy controls, for reactivity against overlapping 20mer peptides (pin synthesis) covering the sequence 2171±2748 of human Tg. Antibody-reactive peptides were subsequently synthesized by a solid-phase technique for con®rmation with a large number of sera: 99 GD, 32 Hashimoto's thyroiditis (HT) and 45 healthy controls. Results: Peptides TgP15, TgP26 and TgP41 (amino acids 2339±2358, 2471±2490 and 2651±2670 respectively) were found to be targets of autoantibodies on intact Tg, recognized by a statistically signi®cant proportion of GD sera (22.2%, 35.4% and 30.3% respectively), compared with HT (0%, 15.6% and 6.3% respectively) and healthy controls (0%, 4.4% and 4.4% respectively). The majority of GD sera (56.6%) were positive for at least one of the three peptides. In GD, TgP26 reactivity was found to be associated with TED (48.6% with TED versus 25.5% without TED, P , 0X05X Conclusion: Some epitopes on the C-terminal region of Tg are associated with GD. A subset of Tgreactive autoantibodies, directed to this region, is associated with TED and may be involved in the development of the disease.

Recognition of Thyroglobulin by T Cells: The Role of Iodine

“…The majority of the determinants encompassed within these sites are recognized by CD4 þ and mouse MHC class II-restricted T cells; one was recognized by an MHC class I-restricted, cytotoxic T-cell (CTL) hybridoma (18); recently, four hTg peptides were described eliciting EAT in HLA-DR3-transgenic mice (21,26). Within the last group, of note are hTg peptides p2079, which elicits considerable EAT both directly and by adoptive transfer assays (21), and p2340 (23,26), which was originally shown to be a target of Tg-reactive Abs in patients with Graves' disease (27). To a large extent, these findings reflected the bias of the screening approach; for example, since susceptibility to EAT is A k controlled, computerized algorithms were used to search for A k -binding, pathogenic Tg peptides.…”

Human thyroglobulin peptide p2340 induces autoimmune thyroiditis in HLA-DR3 transgenic mice

“…The hTg peptide PYEFSRKVPT FATPWPDFVP (aa 2652e2671, p2652) was synthesized by Genosys Biotechnologies (Cambridge, UK) and used as control. Its properties are previously described [9]. Both peptides were used in all experiments at O80% purity as determined by analytical HPLC and mass spectral analyses.…”

“…Eight of them have been identified in mouse Tg (mTg), three in human Tg (hTg) and two, sharing identical amino acid sequence between mTg and hTg (contain the hormonogenic sites of Tg). In this study, we focused on hTg 20-mer peptide p2340 (aa 2340e2359) which was initially shown to be a target of Tg-reactive autoantibodies occurring in Tg/acetylcholinesterase reactive sera from patients with Graves' disease [9]. Furthermore, p2340 was found to be able to elicit E k -restricted thyroiditis in AKR/J (H-2 k ) mice.…”

The Cryptic Self in Thyroid Autoimmunity: The Paradigm of Thyroglobulin

“…[6] This site is known to also contain an epitope recognized by autoantibodies in patients with Graves' disease. [13] Lastly, the 14 mer (2730 -2743) has been reported to induce EAT in CBA mice only after adoptive transfer of LNC that were primed in vivo with mTg and boosted in vitro with the peptide. [14] Direct challenge of mice with this peptide or adoptive transfer of peptide-specific spleen cells did not induce thyroid pathology.…”