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 PM2.5 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.