Alveolar macrophages promote lung organoid outgrowth but do not protect against negative effects of PA6,6 microplastics on developing airway organoids

Airborne microplastics can be inhaled and have been found deep in the lungs, but potential harmful effects on lung health remain elusive. Our recent studies showed that polyamide 6,6 (PA6,6) microplastics are detrimental to developing airway organoids and that leaching chemicals are responsible for this effect. Yet, the first line of defense against particulates in the lung, the alveolar macrophages, is not represented in this lung organoid model. The objective of the present study was therefore to incorporate alveolar macrophages in a murine lung organoid model in the presence or absence of PA6,6 particles to investigate both the separate and combined effects of alveolar macrophages and PA6,6 exposure on airway and alveolar organoid development. Monocultures of developing lung organoids and co-cultures with alveolar macrophages were exposed to 1-5 µm PA6,6 particles for 14 days. The presence of alveolar macrophages resulted in significantly more alveolar organoids and a similar trend was observed for airway organoids. Exposure to PA6,6 particles led to a significant drop in number of airway organoids in both monocultures and co-cultures. Organoid size was unaffected by the presence of macrophages or exposure to PA6,6 particles. These findings together indicate that alveolar macrophages can facilitate lung organoid outgrowth but fail to protect against the negative impact of PA6,6 particles and/or leaching compounds on airway organoid development. This co-culture model is a valuable tool for further exploration of interactions between macrophages and epithelial cells in the context of microplastic exposure and beyond.