Quantitative study of endocrine cells immunoreactive for calcitonin in the normal adult human lung.

There was no significant variation in the numbers of bronchopulmonary endocrine cells immunoreactive for calcitonin in five pairs of adult human lungs either from case to case or between groups of anatomically equivalent lobes. This was the case whether their numbers were expressed in relation to epithelial length or to the total number of epithelial cells. The mean (SD) values for the frequency of occurrence of these cells in all 25 lobes studied were 4.3 (1.9) per 10 cm of epithelial length or 1.70 (0.78) per 10 000 epithelial cells. Most immunoreactive cells were single and situated in the airways; only three neuroepithelial bodies were observed, and no cells were present in the parenchyma examined. This study provides further evidence that the functional character of these cells may not be confined to early life.