In vivo effects of endotoxin on nasal epithelial mucosubstances: quantitative histochemistry

Airway inflammation induced by gram-negative bacteria is often characterized by an influx of neutrophils and hypersecretion of mucus. The purpose of this study was to determine how endotoxin, a component of gram-negative bacteria and a chemotaxinogen for neutrophils, affects the amount of stored intraepithelial mucosubstances in the rat nasal airway. Rats were intranasally instilled, once a day for 3 days, with endotoxin or saline (controls). Before the first and third instillation, half of the animals were depleted of circulating blood neutrophils by administering a rabbit anti-rat neutrophil antiserum. Rats were sacrificed 6 or 24 h after the last instillation. Nasal tissues were processed for light microscopy and histochemical detection of stored intraepithelial mucosubstances. The numbers of nasal epithelial cells and intraepithelial neutrophils per millimeter of basal lamina in the anterior nasal septum and the amounts of intraepithelial mucosubstances in the same nasal tissue were determined by image analysis. We did not observe a neutrophil influx in the nasal tissues of neutrophil-depleted rats at 6 or 24 h after the last endotoxin instillation; however, we did observe a significant increase in intraepithelial mucosubstances, compared to saline-instilled controls. In contrast, nonneutrophil-depleted animals had a marked neutrophilic influx and a concomitant decrease in stored mucosubstances, compared to saline-instilled controls. There was no significant difference in the number of nasal epithelial cells per millimeter of basal lamina among any of the experimental groups. These results indicate (1) that endotoxin induces an increase in the amount of intraepithelial mucosubstances only when intraepithelial neutrophils are absent, and (2) that the endotoxin-induced, neutrophil influx probably triggers mucous hypersecretion.