Supporting cells as phagocytes in the olfactory epithelium after bulbectomy

Macrophages are known to be phagocytes in the olfactory epithelium of adult rats. The participation of other cell types in phagocytosis in association with the cell death process was examined in the olfactory epithelium after unilateral bulbectomy of neonatal mice. The terminal deoxynucleotidyl transferase (TdT)-mediated biotinylated dUTP nick end-labeling (TUNEL) method revealed that the process of olfactory cell death consists of acute and chronic periods. The number of apoptotic cell profiles on the operated side peaked at 1 day, and the percentage of labeled cell profiles was 13.6%. The number of dying cells rapidly decreased at 3 days and decreased further at 5 days. Only 3% of the cells were labeled at 5 days. The percentage of dying cells increased again at the end of first postoperative week and remained two- to four-fold higher than control values for 2 months (4.7-5.3%). Electron micrographs of sections from early postbulbectomy stages (1-7 days) showed that as many as 30% of supporting cell profiles contained apoptotic bodies, cellular debris and phagosomes in the cytoplasm. The number of supporting cell profiles containing phagosomes declined to a plateau 2 weeks following bulbectomy and remained at 8-12% of the supporting cell population for 2 months. The results indicate that supporting cells in the olfactory epithelium play a significant role in phagocytosis in both acute and chronic of cell death after bulbectomy in newborn mice. However, supporting cells are not the exclusive phagocytic cell type in the bulbectomized epithelium; a small number of macrophages was also observed. Moreover, the phagocytosis by supporting cells was observed in unperturbed epithelium in the early stages during postnatal development.