Targeted nuclear degranulation of neutrophils in the shock stage of severe burns drives rapid neutrophil extracellular trap release during infection to mediate acute lung injury

Immune dysfunction during the shock stage of severe burns is a critical factor that mediates immunosuppression in the subsequent Infection stage; however, the specific mechanism remains unclear. As key components of the immune system, neutrophils have a lifespan of 4-7 days, which enables them to exert biological effects across both burn stages. In this study, enzyme-linked immunosorbent assay (ELISA) and immunofluorescence revealed that neutrophils during the shock stage were extensively activated, exhibited delayed Apoptosis, and showed increased "targeted nuclear degranulation". Furthermore, these neutrophils rapidly released neutrophil extracellular traps (NETs) upon further activation in vitro, a state called the "NETs pre-release state". Neutrophils in this state were associated with massive NET release and subsequent lung injury when patients progressed to Infection stage. Using immunofluorescence, ELISA, and Other techniques, we further verified that "targeted nuclear degranulation"-which transports myeloperoxidase (MPO) into the nucleus-is critical for the "NETs pre-release state". Specifically, MPO promotes chromatin decondensation via two mechanisms: catalyzing the conversion of Reactive Oxygen Species (ROS) into hypochlorous acid (HClO) and relieving the inhibition of peptidylarginine deiminase 4 (PAD4) activity by reducing nuclear ROS levels. This process ultimately facilitated the excessive and rapid release of NETs upon secondary activation. In a severe burn model using MPO-deficient (MPO^-/^-) mice, we further confirmed the importance of MPO in NETs formation via light sheet microscopy, following LPS-induced pulmonary stimulation after the shock stage. By investigating the mechanism by which "targeted nuclear degranulation" of neutrophils during the shock stage leads to excessive NETs release during Infection, this study aims to clarify how immune dysfunction in the shock stage of severe burns mediates infection-stage immunosuppression. This study has provided new insights into the maintenance of early immune homeostasis in severe burns and identifies a novel target for inhibiting excessive NETs release.

acute lung injury; neutrophil extracellular traps; severe burns; targeted nuclear degranulation.