Mass cells contribute to O3-induced epithelial damage and proliferation in nasal and bronchial airways of mice

Ozone (O3) exposure produces inflammation in the airways of humans and animal models. However, the mechanism by which O3 affects these changes is uncertain. Mast cells are strategically located below the epithelium of the airways and are capable of releasing a number of proinflammatory mediators. We tested the hypothesis that mast cells contribute to inflammation, epithelial sloughing, and epithelial proliferation in the nasal and terminal bronchiolar murine airways after O3 exposure. Mast cell-sufficient (+/+), mast cell-deficient (W/Wv), and mast cell-repleted [bone marrow-transplanted (BMT) W/Wv] mice were exposed to 2 ppm O3 or filtered air for 3 h. Nasal and bronchoalveolar lavage fluids were collected 6 and 24 h after exposure. Differential cell counts and protein content of the lavage fluids were used as indicators of inflammation and permeability changes in the airways. O3-induced epithelial injury was assessed by light microscopy, and O3-induced DNA synthesis in airway epithelium was estimated by using a 5-bromo-2′-deoxyuridine-labeling index in the nasal and terminal bronchiolar epithelia. Relative to air control mice, O3 caused significant increases in inflammation, epithelial injury, and epithelial DNA synthesis in +/+ mice. There was no significant effect of O3 exposure on any measured parameter in the W/Wv mice. To further assess the role of mast cells in O3-induced epithelial damage, mast cells were restored in W/Wv mice by BMT from +/+ congeners. Relative to sham-transplanted W/Wv mice, O3 caused significant increases in epithelial damage and DNA synthesis as well as inflammatory indicators in BMT W/Wv mice. These observations are consistent with the hypothesis that mast cells significantly modulate the inflammatory and proliferative responses of the murine airways to O3.