COEXPRESSION OF VIMENTIN AND 19S-THYROGLOBULIN IN FOLLICULAR CELLS LOCATED IN THE C-CELL COMPLEX OF DOG THYROID-GLAND

The localization of vimentin, an intermediate filament protein, in the dog thyroid cells was examined by immunohistochemistry with a monoclo nal antibody against vimentin and polyclonal anti-19S-thyroglobulin an d anti-calcitonin antibodies. In the dog thyroid gland, C-cells are us ually distributed as large cell groups in an interfollicular location. In addition, C-cell complexes that are special C-cell clusters associ ated with other epithelial elements and cysts are frequently located a round the parathyroid gland IV. The C-cell complexes are remnants of e mbryonic ultimobranchial bodies and retain fetal characteristics for l ong periods. Follicular cells in various stages of differentiation are observed in the C-cell complexes and large C-cell groups of postnatal dogs: (a) cell masses not yet organized into follicles, (b) primitive and small follicles storing colloid, and (c) small follicles without colloid storage. The immature follicular cells in the C-cell complexes and large C-cell groups express immunoreactivity for vimentin in addi tion to 19S-thyroglobulin. When the follicular cells stored considerab le amounts of colloid in the follicular lumina, vimentin immunoreactiv ity disappeared from them. Typical thyroid follicles showed no immunor eactivity for vimentin. In dog fetuses in which follicular cells were arranged in cell clusters or were vigorously forming follicles, no imm unoreactivity for vimentin was observed in the thyroid parenchyma. The se results indicate that vimentin is specifically expressed in the imm ature follicular cells derived from the ultimobranchial anlage. The vi mentin filaments may participate in increased cellular activities in t he cells, i.e., thyroglobulin synthesis and folliculogenesis.