MORPHOMETRIC ANALYSIS OF THE IMMUNOHISTOCHEMICAL EXPRESSION OF CLARA CELL 10-KDA PROTEIN AND SURFACTANT APOPROTEIN-A AND APOPROTEIN-B IN THE DEVELOPING BRONCHI AND BRONCHIOLES OF HUMAN FETUSES AND NEONATES

Morphometric analyses of the immunohistochemical expression of the Cla ra cell secretory 10-kDa protein (CC10) and surfactant apoproteins A a nd B (SP-A and -B) were carried out on the developing bronchi and bron chioles of human fetuses and neonates. We analysed the ratio of the nu mber of CC10-positive cells per subepithelial length of the bronchial or bronchiolar basement membrane and found that both the bronchial and the bronchiolar population of CC10-positive cells was significantly h igher than that of either SP-A or SP-B. In addition, CC10 was found to be distributed mainly in the bronchiole. CC10-positive cells began to be recognized in the late pseudoglandular phase (15 weeks of gestatio n) and thereafter gradually increased in the canalicular and terminal sac phases, which correspond to the active development period of the a cini or peripheral airways. The earliest expression of SP-A was also n oted at 15 weeks of gestation, but its positive epithelial cells were present mainly in the larger bronchi. Double immunohistochemical stain ing for CC10 and SP-A revealed that the CC10-positive cells lining bot h the bronchi and bronchioles were different from the SP-A-positive ce lls. This finding suggests that CC10-positive cells are functionally a nd developmentally heterogeneous in both fetal and neonatal lungs in h umans.