ABSTRACT Hypervirulent Klebsiella pneumoniae (hvKP) has spread globally, causing severe liver abscesses. Neutrophil extracellular trap formation (NETosis) is an essential defense mechanism of neutrophils. However, the role of pathogenicity and molecular mechanism of liver abscesses induced by hvKP on neutrophil extracellular trap formation remain unclear. Here, we revealed abscesses and severe neutrophil infiltrates in the livers of hvKP-infected mice, which can be compared to the mice infected with classical Klebsiella pneumoniae (cKP). hvKP infection significantly increased reactive oxygen species production, NETosis, and apoptosis-associated speck-like protein containing a CARD foci formation in neutrophils compared to cKP. In addition, hvKP infection upregulated the mRNA levels and protein expression levels of key NETosis-associated molecules (Caspase-1, MPO, PAD4, and CitH3) relative to cKP, whereas NLRP3 expression remained unchanged in neutrophils. Furthermore, hvKP infection also maintained a higher survival rate within neutrophils compared with cKP and promoted neutrophil extracellular trap formation in an NLRP3 inflammasome activation and PAD4-dependent manner in vitro and in vivo . Moreover, hvKP infection promoted the production of IL-1β, IL-18, and TNF-α from patients’ serum compared to cKP. Our findings demonstrate that hvKP induces NETosis formation, which might contribute to tissue injury rather than bacterial clearance in mice. This suggests a pathogenic role of NETosis in hvKP-mediated infection and identifies a potential target for therapeutic intervention. IMPORTANCE Hypervirulent Klebsiella pneumoniae (hvKP) has emerged as a globally prevalent pathogen that triggers severe liver abscesses, posing a substantial threat to public health. Neutrophil extracellular trap formation (NETosis) serves as a core innate immune defense against invading microbes. However, how hvKP manipulates NETosis to drive liver abscess progression remains undefined. This study demonstrates that hvKP induces more severe hepatic lesions and neutrophil infiltration than classical Klebsiella pneumoniae , while enhancing reactive oxygen species production, NETosis, and the expression of key NET-related proteins in neutrophils. Additionally, hvKP infection elevates pro-inflammatory cytokine levels in patient serum. These findings provide a novel insight into hvKP-mediated innate immune evasion and the pathogenesis of liver abscesses induced by hvKP.
Ou et al. (Mon,) studied this question.