The air pollutant sodium sulfite enhances mite crude extract-stimulated detachment of A549 airway epithelium cells.

BACKGROUND AND PURPOSE It has been previously reported that the pollutant sodium sulfite (Na2SO3) can activate airway epithelial cells; however, there is as yet no evidence of any direct relationship between house dust mite allergen exposure and Na2SO3 with regards to the pathogenesis of airway allergy. This study investigated the effect of sulfite on mite-stimulated human airway epithelial cells. METHODS The A549 human lung epithelial cell line was used as an in vitro model. Cells were treated with 10 microg/mL mite crude extract for 8 h and/or Na2SO3 (0, 10, 100, 500, 1000 and 5000 microM) for 16 h, and cell adhesion and dissociation on a cell culture plastic surface were quantitated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. Changes in cell adhesion were also analyzed by monitoring the expression of the cell surface of adhesion molecules integrin alpha2 (CD49b) and integrin alpha6 (CD49f) using flow cytometry. RESULTS A549 cells treated with either mite crude extract only or Na2SO3 only did not show a significant increase in dissociation from the cell culture plastic surface. However, when cells were pretreated with mite extract for 8 h, followed by 16-h incubation with various concentrations of Na2SO3, cell dissociation was enhanced in a dose-dependent manner. A dose-dependent decrease of CD49b and CD49f expression was also seen in cells treated with Na2SO3 only and in mite-pretreated cells. Mite treatment decreased CD49b expression, and a cumulative effect was seen in cells further treated with Na2SO3. CONCLUSION Significant dissociation of airway epithelial cells with Na2SO3 stimulation only occurred in cells pretreated with mite extract. Mite pretreatment enhanced Na2SO3-induced CD49f down-regulation; Na2SO3 and/or mite extract down-regulated CD49b expression of A549 cells. These findings indicate that a synergistic effect of mite extract and sulfite can severely disrupt the airway bronchial epithelial barrier.