Immunohistochemical reactions of C-cell complexes in dogs after induced hypercalcemia, antithyroid drug treatment and hypophysectomy.

The C-cell complexes are remnants of ultimobranchial bodies retaining fetal characteristics. They contain C cells in various stages of differentiation, primordial follicles with small lacunae, follicular cell masses not yet forming follicles, and undifferentiated epithelial cells. By immunoperoxidase method using specific anti-calcitonin, anti-C-thyroglobulin and anti-19S thyroglobulin sera, the responses of C-cell complexes to hypercalcemia, thiourea, hypophysectomy and hypercalcemia after hypophysectomy were investigated systematically. These experimental conditions induced rapid differentiation and increased numbers of cells in the complexes. After chronic hypercalcemia, most of the complexes were occupied by mature C cells. The C cells in complexes similar to the cells in thyroid parenchyma presented increased mitotic activity, enlarged cell bodies and a marked decrease in materials immunoreactive for calcitonin and C-thyroglobulin. After prolonged administration of thiourea, follicular cell masses and small follicles, which underwent conspicuous hyperplasia and hypertrophy, markedly increased in the complexes and exceeded C cells in number. Typical undifferentiated cells were not recognized after hypercalcemia and treatment with thiourea, though they were unaffected by hypophysectomy. It is considered that undifferentiated cells develop into C cells after hypercalcemia and into follicular cells after treatment with thiourea; that is, undifferentiated cells seem to be the common precursor cell for both C cells and follicular cells.