CD26 (DIPEPTIDYL AMINOPEPTIDASE IV) EXPRESSION IN NORMAL AND DISEASEDHUMAN THYROID-GLANDS

The objective of the present study was to investigate CD26 (dipeptidyl aminopeptidase IV) expression in normal and diseased thyroids and its relation to differentiation and cell proliferation. CD 26 was also ev aluated as a possible marker of malignancy in thyroid neoplasias. A to tal of 38 normal thyroids and 117 diseased thyroids (neoplastic and no n-neoplastic) were evaluated. CD26 and thyroglobulin (Tg) expression w as determined by analyzing at least 200 cells/specimen. A minimum of 5 00 cells/specimen were counted to calculate the MIB-1-positive cell ra te expressed as a percentage of total nucleated epithelial cells. CD26 expression was absent in all thyroids from fetuses and children. Amon g the adults, 7.1% had CD26 expression only in oncocytic metaplastic a reas. In 3 of the 7 elderly subjects, CD26 expression was present in 0 .2-90% of epithelial cells. CD26 expression was observed in all diseas ed thyroids. Since this enzyme is also expressed in benign conditions, it is not useful as a marker of malignancy. There was no relationship between CD26 and Tg expression. The MIB-1-positive cell rate was foun d to be low for all kinds of thyroid tissues, and when the cell prolif eration rate was analyzed according to CD26 expression, a greater cell proliferation rate was found in CD26-positive differentiated (follicu lar and papillary) carcinomas than in CD26-negative carcinomas. These results demonstrate that expression of this enzyme is related to the p roliferative activity of follicular cells.