D2.509 - Do macrophages modulate the response of injured bronchial epithelium after PM2.5 and microplastic exposure?

The toxic effects of air pollutants on the airway epithelium are associated with oxidative stress, pro-inflammatory responses, and tissue damage. In chronic exposure to noxious factors, repair processes are either insufficient or impaired. Crosstalk between the external environment and the internal tissue matrix in the respiratory tract occurs through transepithelial interactions with macrophages.The main aim of this study was to evaluate whether macrophages modify bronchial epithelial damage induced by particulate matter and microplastics in an in vitro model of lung injury.

Primary normal bronchial epithelial cells were cultivated at the air–liquid interface (ALI) under normal, acute (lipopolysaccharide (LPS)-treated), chronic (cigarette smoke extract (CSE)-treated for 14 days), and allergic (house dust mite (HDM) + IL-13-treated for 3 days) conditions. Cells were divided into two groups: uninjured or physically injured by a scratch. Subsequently, epithelial cells were co-cultivated with monocyte-derived macrophages and stimulated with microplastic fibres (200 µg/cm²) and PM_2.5 (50 µg per insert) applied to the apical surface of the epithelial layer for 48 hours.

We detected a significant increase in LDH release, indicative of enhanced cytotoxicity, in injured macrophage–epithelial co-cultures exposed to PM2.5, LPS in combination with PM2.5, as well as HDM/IL-13. Macrophage co-culture significantly attenuated IL-6 secretion by injured epithelial cells following exposure to microplastics under control conditions, LPS stimulation, combined LPS and microplastic exposure, and cigarette smoke extract (CSE) stimulation. In macrophages cultured in monoculture, exposure to PM_2.5 and microplastics significantly upregulated the expression of C15orf48 and IFN-γ mRNA.

Co-cultivation with macrophages does not enhance epithelial cell viability following exposure to air pollutants; however, it attenuates the inflammatory response in injured respiratory epithelium after microplastic exposure. This suggests a potential protective role of macrophages in epithelial repair processes following microplastic-induced, but not PM_2.5-induced, injury.