Dynamics of severity-associated immune remodeling by granulocytes 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 and severity-associated crosstalk shape immune remodeling during disease progression. Here, we performed single-cell RNA sequencing (scRNA-seq) of bronchoalveolar lavage fluid from patients with intermediate- and late-severity ALI to map immune microenvironment remodeling. We observed pronounced granulocyte expansion coupled with macrophage depletion. Granulocytes exhibit distinct transcriptional states along a continuum from acute migratory states toward pro-inflammatory, metabolically reprogrammed subsets, dominated by TNF and MAPK signaling. Simultaneously, macrophages shift toward inflammatory M1-like phenotypes, characterized by distinct metabolic reprogramming and reduced oxidative phosphorylation. Furthermore, we infer a granulocyte-centric inflammatory network mediated through TNF, IFN, and RESISTIN pathways, suggesting a feedforward inflammatory loop. Collectively, this study elucidates the transcriptional and metabolic reprogramming associated with escalating ALI severity, providing a framework for severity-adapted therapeutic interventions to restore pulmonary homeostasis.