Single-Cell Atlas Reveals Neutrophil Heterogeneity in Hypervirulent Klebsiella Pneumoniae Infection-Induced Sepsis.

Hypervirulent Klebsiella pneumoniae (hvKp) infection often induces sepsis characterised by remarkable phenotypic and functional diversity among neutrophils. However, the roles of distinct lung neutrophil compartments involved in hvKp infection remain poorly understood. Here, utilising single-cell RNA sequencing, we identified four neutrophil subsets in the lungs of hvKp-infected mice: N1, N2, N3a, and N3b, which were organised along a maturation trajectory. Functionally, early-stage subsets exhibited proinflammatory and phagocytic activities with high levels of activation, whereas terminal subsets displayed enhanced pathogen sensing and immunoregulatory properties. Notably, the N3b population showed pronounced immunosuppressive features and was predicted to inhibit lymphocyte responses through Lgals9 and Ceacam1 ligands, potentially associated with hvKp-induced lymphopenia. Projection onto NeuMap further validated the functional states of identified subsets, linking N1 to proliferative programmes, N2 to granules and hypoxia-associated metabolic activity, N3a to antigen-presentation signatures and N3b to immunosuppressive hubs. Morphologically, N3a/b were predicted to be enriched for segmented neutrophils, consistent with a more mature phenotype compared with N1 and N2. Notably, segmented neutrophils were markedly expanded in infected lungs, suggesting their association with hvKp pathogenesis. Together, our findings delineate the lung neutrophil landscape in hvKp-induced sepsis, providing insights for understanding hvKp pathogenesis and developing targeted therapeutic interventions at a neutrophil subset level.