NEUTROPHILS ENHANCE REMOVAL OF OZONE-INJURED ALVEOLAR EPITHELIAL-CELLS IN-VITRO

After acute exposure to oxidant gases in vivo, migration and accumulat ion of inflammatory cells in pulmonary epithelium coincides with epith elial cell necrosis. The present study was designed to test quantitati vely the hypothesis that quiescent neutrophils enhance the removal of oxidant-injured pulmonary epithelial cells after exposure to ozone in vitro. Primary isolated rat alveolar type II cells were cultured as mo nolayers, using serum-free medium. After exposure to 0.1-0.5 ppm ozone for 0.5 h, apical sides of monolayers were administered either fresh nutrient medium only or medium containing quiescent human neutrophils. Monolayer bioelectric properties and cellular uptake of vital dye wer e recorded from 5 to 48 h after ozone exposure. Ozone dose-dependent i ncreases in monolayer permeability were associated with proportionally higher numbers of injured epithelial cells. However, the direction an d magnitude of neutrophil effects on monolayer permeability after ozon e exposure were dependent on ozone concentration. Furthermore, neutrop hil-treated monolayers exposed to 0.1 ppm ozone had significantly fewe r attached cells positive for uptake of vital dye relative to monolaye rs exposed to the low level of ozone only; this effect was ablated wit h increasing ozone concentration. These data suggest that at high leve ls of ozone neutrophils may exacerbate injury to oxidant-impaired epit helial cells, whereas the presence of neutrophils after exposure to am bient concentrations of ozone may expedite the restoration of epitheli al barrier function. We conclude that, by enhancing the removal of inj ured cells, neutrophils may facilitate the repair of centriacinar epit helium after ozone exposure in vivo.