Response of the tracheobronchial epithelium to hemoprotein tracers

Abstract

The response of the tracheobronchial epithelium to intratracheal administration of microperoxidase, cytochrome c, myoglobin, and horseradish peroxidase (HRP) was investigated in hamsters and gerbils. Using diaminobenzidine cytochemistry and transmission electron microscopy, we found that cytochrome c was the only tracer to reach lateral intercellular spaces, most probably due to its toxic effect on the airway epithelium. Myoglobin did not bind to the plasma membrane and hence was not internalized by the epithelial cells. Both HRP and microperoxidase were seen in contact with the plasma membrane and within pinocytotic vesicles, the fate of which was not apparent. As early as 5 min after administration, HRP was distributed in a diffuse and intense manner in a small percentage of ciliated and nonciliated cells but by 30 min this effect had decreased significantly. HRP was seen in the basement membrane and lamina propria beneath some intensely reactive cells at 5 and 30 min. Whether these cells reflect a degenerate condition and hence are incapable of excluding HRP or whether HRP is itself toxic is unknown. The rapid rate at which these cells appear raises the possibility that they may represent a conduit that allows small but significant amounts of foreign molecules to reach subepithelial mast cells thus triggering or augmenting the Type I hypersensitivity response.