It has been well demonstrated that C-cells are the source of the hypocalcemic polypeptide hormone calcitonin (CT), and that they are the origin of medullary thyroid carcinoma. However, our knowledge of the morphology of normal human C-cells is still primitive. The purpose of this study is to present a detailed report concerning the morphology, distribution and population of C-cells in fresh normal thyroid glands using the high specificity immunoperoxidase staining method.
In addition, the carcinoembryonic antigen (CEA) activity in the C-cells and the solid cell nest are studied.
Fifteen fresh thyroid glands with no abnormal histological or laboratory findings were examined for C-cells by Sternberger's PAP method, and five thyroid glands obtained at autopsy 6-8 hours after death with no evidence of thyroid or parathyroid disease were examined as the control group. The CEA activity in the C-cells was examined by the anti-CEA and anti-CT double staining method.
The C-cells were detected in all 15 fresh glands examined. They were oval, spindle or polygonal in shape, and at the interfollicular or parafollicular position. Except for one gland which contained very rare C-cells, no C-cells were detected in the control autopsy glands. C-cells were most numerous at the junction of the upper and middle third of the lateral lobe, and in these areas the C-cell population ranged from 47 to 111 per section. Morphologically, the C-cells appeared not only singly but in groups in a parafollicular position as clusters or enclosing the follicular epithelium in the form of lamina.
Solid cell nests were easily distinguished from follicular epithelium by a routine H-E staining examination. None of these areas revealed a positive reaction with anti-CT, although scattered C-cells were seen occasionally in the neighboring area.
CEA activity in the C-cells was evident from the brown color by a DAB reaction product, while the CT was indicated by the violet color using a 4-chloro-1-naphthol reaction product. These two colors were identified in the same cells simultaneously.
From these results, it is concluded :
1) The autopsy thyroids obtained a few hours after death were not suitable for C-cell examination by the immunoperoxidase staining method.
2) The most numerous C-cells were distributed at the junction of the upper and middle third rather than the middle third of the lateral lobe, and the population in these areas averaged from 47 to 111 per section, or about 3 times as many as reported before.
3) C-cell clusters and lamina were clearly observable in the fresh thyroid glands, so the conventional C-cell hyperplasia approach must be reconsidered.
4) The solid cell nest was different from the cluster of C-cells, probably deriving from the metaplasia of follicular epithelium.
5) CEA activity in normal C-cells was confirmed.