C cells in Hashimoto's thyroiditis. Ultrastructural and immunohistochemical observations

C cells in the thyroid tissue of a 46-year-old female patient who showed typical Hashimoto's thyroiditis clinically and histopathologically were examined immunohistochemically and electron microscopically. By immunohistochemical investigation using anti-calcitonin (CT) serum, CT-positive cells were found frequently in the interstitium either singly or attached to several degenerative follicular cells mingled with infiltrated inflammatory cells. Occasionally, cellular clusters of up to 10 cells were seen. Electron microscopically, we detected three cells considered to be C cells which were characterized by the presence of numerous membrane-bound secretory granules, well developed Golgi complex, and rough endoplasmic reticulum arranged in lamellae. These cells were attached to degenerative follicular cells, and their apparent ultrastructural changes were not distinct in comparison with the marked changes seen in the follicular cells (i.e., increased numbers of mitochondria, dilation of the endoplasmic reticulum, etc.). From these morphological findings, it was suggested that the C cells were maintained in a relatively intact state even after the destruction of the thyroid follicles in Hashimoto's thyroiditis.