Proliferative Responses of Peripheral Blood Mononuclear Cells from Patients with Autoimmune Thyroid Disease to Synthetic Peptide Epitopes of Human Thyroid Peroxidase

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Abstract
In order to analyze T cell epitopes of human thyroid peroxidase (TPO), 60 peptides based on the sequence of TPO were synthesized and used as antigens in a peripheral blood mononuclear cell (PBMC)-proliferation assay. PBMCs were obtained from 19 patients with Graves' disease, 19 patients with Hashimoto's thyroiditis, and 24 normal subjects. Significant proliferation of PBMC to these peptides occurred only among the autoimmune thyroid disease (AITD) patients, whereas normal subjects did not respond to any of the peptides with a stimulation index over 2. Many peptides induced isolated positive responses and eight produced stimulation of PBMCs from multiple patients on comparison to control PBMC responses. To confirm the significance of reactivity to the peptides PBMCs from four patients were studied on two occasions, and the proliferative responses found to be reproducible. Four peptides, designated according to the amino acid sequence as pi 10-129, p211-230, p842-861, and p882-901, stimulated patients' PBMCs in a dose-dependent manner. The optimal concentration was 10μg/ml. An anti-HLA-DR monoclonal antibody directed against a mono-morphic determinant of the DR molecule was able to block the responses. A significant correlation was found between the PBMC responses to these peptides and responses to microsomal antigen (McAg)ZTPO. These data suggest that four peptides corresponding to the amino acid sequences 110-129, 211-230, 842-861 and 882-901 are T cell epitopes of TPO.

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