[Effects of dexamethasone on apoptosis of eosinophils infiltrated into bronchoalveolar lavage fluid after Sephadex bead treatment in rat].

ABSTRACT

Eosinophilic inflammation of the airways is a key characteristic of asthma. Glucocorticoids can suppress the inflammatory response in part by promotion of eosinophilic apoptosis. We investigated the effects of glucocorticoids on leukocyte infiltration and apoptotic resolution of eosinophils and neutrophils in Sephadex-treated rat lung. Sephadex beads were injected intravenously, followed 24 h later by i.p. administration of dexamethasone (DEX, 0.1 mg/kg) or its vehicle. At 24 h post-DEX treatment, the bronchoalveolar lavage fluid (BALF) was collected. Differential leukocyte counts and the numbers of apoptotic eosinophils and neutrophils, and macrophages with engulfed eosinophils or neutrophils in BALF were determined microscopically from Diff-Quik stained cytospin preparations. Sephadex beads markedly increased cell counts of eosinophils and neutrophils in BALF. Compared with a vehicle-treated group, the DEX treatment significantly decreased the number of eosinophils, but not neutrophils, in BALF. Dexamethasone in BALF also significantly increased eosinophilic apoptosis and engulfment of apoptotic eosinophils by macrophages, but had no effect on neutrophilic apoptosis and engulfment of apoptotic neutrophils by macrophages. These results suggest that the increased clearance of eosinophils from airways by glucocorticoids may be partly due to the promotion of eosinophilic apoptosis.