107 Luring out alveolar macrophage to enhance pulmonary particle clearance: a functional study using SiglecF-cell tracking

Abstract For clearance of inhaled particles alveolar macrophages (AMs) play the central role. Traditionally considered sessile, more recent evidence shows their alert migratory behaviour and programming particle-laden AMs to jump on the mucociliary escalator would enhance particle clearance kinetics tremendously. This study investigates whether resident AMs can be attracted to leave the alveolar space and enter the mucociliary escalator to enhance pulmonary clearance. Using SiglecF-cre × Ai14 mice, we trace AM positioning via tdTomato expression validated by flow cytometry, immunohistochemistry, intravital microscopy. A panel of macrophage chemoattractants (eg CCL2, CCL4, CCL7) will be screened in vitro using Boyden chamber assays (MHS cells and primary AMs as models) to identify selective candidates. The most specific chemokine will be delivered as aerosol to induce AM emigration in vivo. Particle clearance will be assessed via fluorescent nanoparticle tracking and AM tracing, and unintended inflammation evaluated through cytokine profiling and BAL analysis. Initial scRNAseq and gene array data comparisons to identify potential candidates, show differential CCR expression between MHS and primary AMs. Comparative transcriptomic data show that Ccr2 and Ccr5 typical candidates for macrophage chemoattraction are barely detectable in primary AMs and expressed at much higher levels in MHS cells, exemplifying the difficulties working will cell lines as models. Ccr3 and Fpr1 look more promising with higher levels in resident AM as compared to monocyte derived macrophages. Redirecting AM positioning through chemokine-mediated migration shall offer a novel therapeutic strategy for enhancing lung particle clearance. This approach may serve as a novel therapeutic approach to mitigate lung injury related to environmental and occupational exposures or even COPD.