Identification of thyroiditogenic epitope on porcine thyroid peroxidase for C57BL/6 mice.

C57BL/6 mice show thyroid lesions when immunized with porcine thyroid peroxidase (pTPO) emulsified in CFA. We attempted to clarify a thyroiditogenic epitope on pTPO. Thyroid peroxidase treated with cyanogen bromide was fractionated by reverse phase chromatography, and six fractions (A to F) were obtained. Two of these fractions (D and E) stimulated lymph node cells (LNC) primed with pTPO in vitro and induced thyroiditis in vivo. Tricine-SDS-PAGE and rechromatography showed that fraction D consisted solely of a fragment of Mr 9500 Da and that fraction E contained mainly fragments of Mr of 5400 and 9500 Da. The fragment of fraction D was rechromatographed and 20 NH2-terminal amino acids were analyzed. This segment was found to correspond to residue 726-745 of pTPO deduced from cDNA at a probability of 80%. Four peptides ranging from residue 746-827 were first synthesized and tested for their thyroiditogenicity. Only Pep-2 (29 amino acids) could stimulate LNC primed with pTPO and induce thyroiditis. Pep-2 was divided into two smaller peptides (Pep-2-1 and -2-2) and their thyroiditogenicity was tested again. Pep-2-1 corresponding to residue 774-788, GPA-QITCTPRGWDSP, had thyroiditogenicity as well as the ability to stimulate LNC. It was thought that this segment was at least one of the thyroiditogenic epitopes on porcine thyroid peroxidase for C57BL/6 mice.