Responses of well-differentiated nasal epithelial cells exposed to particles: Role of the epithelium in airway inflammation

Numerous epidemiological studies support the contention that ambient air pollution particles can adversely affect human health. To explain the acute inflammatory process in airways exposed to particles, a number of in vitro studies have been performed on cells grown submerged on plastic and poorly differentiated, and on cell lines, the physiology of which is somewhat different from that of well-differentiated cells. In order to obtain results using a model system in which epithelial cells are similar to those of the human airway in vivo, apical membranes of well-differentiated human nasal epithelial (HNE) cells cultured in an air-liquid interface (ALI) were exposed for 24 h to diesel exhaust particles (DEP) and Paris urban air particles (PM2.5). DEP and PM2.5 (10-80 μg/cm2) stimulated both IL-8 and amphiregulin (ligand of EGFR) secretion exclusively towards the basal compartment. In contrast, there was no IL-1β secretion and only weak non-reproducible secretion of TNF-α. IL-6 and GM-CSF were consistently stimulated towards the apical compartment and only when cells were exposed to PM2.5. ICAM-1 protein expression on cell surfaces remained low after particle exposure, although it increased after TNF-α treatment. Internalization of particles, which is believed to initiate oxidative stress and proinflammatory cytokine expression, was restricted to small nanoparticles (≤ 40 nm). Production of reactive oxygen species (ROS) was detected, and DEP were more efficient than PM2.5. Collectively, our results suggest that airway epithelial cells exposed to particles augment the local inflammatory response in the lung but cannot alone initiate a systemic inflammatory response