Late Breaking Abstract - Alveolar macrophages preferentially take up microvesicles in the alveolar space

Abstract

Background: Microvesicles (MV) are important mediators of inter-cellular communication within the alveolar space, causing significant alveolar epithelial cell (AEC) injury (Soni et al. Thorax 2016;71:1020-29). Here we investigate, for the first time, MV uptake profile by individual intra-alveolar cells during resting/inflamed lung conditions. Methods: Macrophage- or murine lung epithelial cell (MLE)-derived MVs were labelled with membrane intercalating dye DiD, and incubated for 1-4h with coculture of primary alveolar macrophages (AM) and MLE cells, with/without LPS priming. AM-derived or in vivo-generated MVs (a mixed population consisting mainly of AM/AEC-derived MVs harvested from intratracheal (i.t.) LPS treated mice) were DiD-labelled and i.t. instilled into mice for 1h, with/without LPS pre-treatment. Cellular MV uptake was evaluated by flow cytometry, using cell surface markers and DiD mean fluorescence intensity (MFI). Results: In vitro, the majority of MVs were taken up by AMs compared to MLE cells, irrespective of MV cell sources or LPS priming. In vivo, preferential uptake by AMs vs AEC was also observed: for AM-derived MVs, AM MFI 1175±544 vs AEC MFI 8±2, p Conclusion: Surprisingly, and in contrast to a previous report of significant MV uptake by AEC (Bourdonnay et al. J Exp Med 2015;212:729-42), we found that MV uptake/internalisation was performed almost exclusively by AMs, irrespective of MV phenotype under both resting and inflamed conditions. The results strongly suggest that AMs play a crucial modulating role in MV-mediated intra-alveolar inflammation.