Deciphering the Heterogeneity of Pulmonary Macrophages in Response to Fine Particles

The heterogeneity of pulmonary cells affects their response to inhaled fine particles. However, the most critical responder cells in particle exposure still remain controversial, and their functional heterogeneity warrants detailed exploration. Herein, a gold nanoparticle model dual-labeled with sulfo-cyanine3 and Tag RNAs is developed, aiming to capture prominent fine particle-responsive cell subpopulations using fluorescence-activated cell sorting and single-cell RNA sequencing. Alveolar macrophages (AMs), recruited macrophages (recMacs), and interstitial macrophages (IMs) exhibited the strongest responsiveness to particles, among which 14 subsets are identified with partially overlapping yet distinct functions. Notably, AMs_3, AMs_7, and recMacs_4 subsets are highlighted in the particle-responsive single-cell atlas, as evinced from their functional scoring and Tag RNA levels. AMs_3 and AMs_7 showed function enrichment for acute-phase responses to inhaled particles, while recMacs_4 exhibited enrichment for cell chemotaxis and phagocytosis. Fine particle engulfment led to enhanced outgoing interactions between these three macrophage subsets and other cell populations within particle-responsive cellular communication networks. This study reveals that specific macrophage subpopulations act as the primary responsive cell subpopulations in engulfing inhaled particles and link their transcriptional heterogeneity to functional diversity, thereby opening a new avenue to explore the heterogeneity of immune cells in pulmonary disorders.