Protein gene product 9.5-like and calbindin-like immunoreactivity in the nasal respiratory mucosa of perinatal humans.

Protein gene product 9.5 (PGP) and calbindin-D28k (calbindin) are neuroendocrine markers that have been localized to neuroendocrine cells in the developing tracheobronchial epithelium. Neuroendocrine cells may play some role in the development of the tracheobronchial epithelium. Little is known about the development of the nasal respiratory epithelium (RE). Nasal respiratory mucosa from fetal and newborn humans was examined to determine immunoreactivity for PGP and calbindin. At all stages studied, cells of different morphologies displayed PGP-like immunoreactivity (-LI) and calbindin-LI. Columnar immunoreactive cells for both markers predominated, but labeled cells of different shapes were also observed. Most labeled columnar cells were in the RE at its border with olfactory epithelium (OE); a few similarly labeled columnar cells also appeared in this OE. In the lamina propria, PGP-LI was also seen in numerous thin branching fibers. Some of these branches penetrated into the epithelium, where fiber varicosities appeared to contact cells, some of which also exhibited PGP-LI. This study demonstrates that during development the human nasal RE contains different cell types, as illustrated by the assortment of epithelial cells displaying PGP-LI and calbindin-LI among unlabeled cells. Because PGP and calbindin immunoreactivities were found within neuroendocrine cells in previous studies, the present results indicate that the developing human nasal RE also may support a number of neuroendocrine cells. Furthermore, at least some of these cells may form synaptic contacts with nerve fibers from outside the epithelium.