Dynamics of Stage-specific Immune Remodeling by Neutrophils and Macrophages in Acute Lung Injury
Acute lung injury (ALI) is driven by dysregulated alveolar immune responses. While granulocytes and macrophages are critical effectors, their coordinated molecular reprogramming remains poorly defined. However, the evolving crosstalk and stage-specific functional transitions of these populations have been overlooked. Here, we performed single-cell RNA sequencing (scRNA-seq) of bronchoalveolar lavage fluid from intermediate and late-stage ALI patients to map immune microenvironment remodeling. We observed pronounced granulocyte expansion coupled with macrophage depletion. Granulocytes exhibit distinct trajectories from acute migratory states toward pro-inflammatory, metabolically reprogrammed subsets, dominated by TNF and MAPK signaling. Simultaneously, macrophages transition toward inflammatory M1-like phenotypes, characterized by distinct metabolic reprogramming and reduced oxidative phosphorylation. Furthermore, we identify a granulocyte-centric inflammatory network mediated through TNF, IFN, and RESISTIN pathways, establishing pathogenic feedback loops. Collectively, this study elucidates the transcriptional and metabolic reprogramming driving ALI progression, providing a framework for stage-adapted therapeutic interventions to restore pulmonary homeostasis. Overall design: We conducted  single-cell RNA sequencing (scRNA-seq) of bronchoalveolar lavage fluid from intermediate and late-stage ALI patients