Biological responses of human tracheobronchial mucociliary pseudo-epithelium repeatedly exposed at the air-liquid interface to PM10 indoor particles

The PM₁₀ fraction of representative indoor pollution (SRM® 2585) was repeatedly nebulized (1 and 6 μg/cm²/day) on functional mucociliary pseudo-epithelia (NHBE cells differentiated at the Air Liquide Interface, ALI). Four consecutive daily exposures have been performed and the biomarkers were analyzed on day 4, 8 and 11. Exposures at the lower dose induced at day 4 a significant increase in cellular ROS and modulations of the expression of few genes associated with genotoxicity and oxidative stress. IL-6 expression was strongly upregulated accompanied by a delayed increased secretion in the basal medium, whereas IL-8 expression was downregulated. At the highest dose, a weak and transient decrease in epithelial cohesion was observed, as well as a potential alteration of the cilia. The mucus secretion tended to increase whereas expression of MUC5AC and MUC5B was downregulated. Co-exposure to macrophage mediators (produced by pre-exposure of human macrophages to the PM_2.5 fraction of SRM® 2585) induced significant overexpression of MUC5AC, IL-6 and IL-8 in the pseudo-epithelium. Three genes involved in oxidative processes, distinct from those highlighted with PM₁₀ alone, were modulated. Despite repeated exposures, the magnitude of the mucociliary pseudo-epithelial responses remained low overall. Trapping of PM₁₀ in the mucus associated with efficient ciliary beating contributed to limit cellular responses. Thus, this physiological process must be considered for realistic in vitro toxicity assessments. Co-exposure protocol allowed to integrate the role of the innate immune system into the overall response of the lung tissue.