Sepsis is a prevalent disease that has alarmingly high mortality rates and, for several survivors, long-term morbidity. The modern definition of sepsis is an aberrant host response to infection followed by a life-threatening organ dysfunction. Sepsis has a complicated pathophysiology and involves multiple immune and non-immune mediators. It is now believed that in the initial stages of sepsis, excessive immune system activation and cascading inflammation are usually accompanied by immunosuppression. During the pathophysiology of severe sepsis, neutrophils are crucial. Recent researches have demonstrated a clear link between the process of neutrophil cell death and the emergence of organ dysfunction in sepsis. During sepsis, spontaneous apoptosis of neutrophils is inhibited and neutrophils may undergo some other types of cell death. In this review, we describe various types of neutrophil cell death, including necrosis, apoptosis, necroptosis, pyroptosis, NETosis, and autophagy, to reveal their known effects in the development and progression of sepsis. However, the exact role and mechanisms of neutrophil cell death in sepsis have not been fully elucidated, and this remains a major challenge for future neutrophil research. We hope that this review will provide hints for researches regarding neutrophil cell death in sepsis and provide insights for clinical practitioners.

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Sepsis-associated encephalopathy (SAE), as shown as acute and long-term cognitive impairment, is associated with increased mortality of sepsis. The causative factors of SAE are diverse and the underlying pathological mechanisms of SAE remain to be fully elucidated. Multiple studies have demonstrated a crucial role of microglia in the development of SAE, but the role of neutrophils and neutrophil extracellular traps (NETs) in SAE is still unclear. Here, we firstly show that in murine sepsis model, neutrophils and NETs promote blood-brain barrier (BBB) disruption, neuronal apoptosis and microglia activation in hippocampus and induce hippocampus-dependent memory impairment. Anti-Gr-1 antibody or DNase I treatment attenuates these sepsis-induced changes. Then, we find that genetic deletion of neutrophil GSDMD or PD-L1 reduces NET release and improves SAE in murine sepsis model. Finally, in human septic neutrophils, p-Y705-Stat3 binds to PD-L1, promotes PD-L1 nuclear translocation and enhances transcription of the gasdermin D (GSDMD) gene. In summary, our findings firstly identify a novel function of PD-L1 in maintaining transcriptional activity of p-Y705-Stat3 to promote GSDMD-dependent NET release in septic neutrophils, which plays a critical role in the development of SAE.

Sepsis is defined as a life-threatening dysfunction due to a dysregulated host response to infection. It is a common and complex syndrome and is the leading cause of death in intensive care units. The lungs are most vulnerable to the challenge of sepsis, and the incidence of respiratory dysfunction has been reported to be up to 70%, in which neutrophils play a major role. Neutrophils are the first line of defense against infection, and they are regarded as the most responsive cells in sepsis. Normally, neutrophils recognize chemokines including the bacterial product N-formyl-methionyl-leucyl-phenylalanine (fMLP), complement 5a (C5a), and lipid molecules Leukotriene B4 (LTB4) and C-X-C motif chemokine ligand 8 (CXCL8), and enter the site of infection through mobilization, rolling, adhesion, migration, and chemotaxis. However, numerous studies have confirmed that despite the high levels of chemokines in septic patients and mice at the site of infection, the neutrophils cannot migrate to the proper target location, but instead they accumulate in the lungs, releasing histones, DNA, and proteases that mediate tissue damage and induce acute respiratory distress syndrome (ARDS). This is closely related to impaired neutrophil migration in sepsis, but the mechanism involved is still unclear. Many studies have shown that chemokine receptor dysregulation is an important cause of impaired neutrophil migration, and the vast majority of these chemokine receptors belong to the G protein-coupled receptors (GPCRs). In this review, we summarize the signaling pathways by which neutrophil GPCR regulates chemotaxis and the mechanisms by which abnormal GPCR function in sepsis leads to impaired neutrophil chemotaxis, which can further cause ARDS. Several potential targets for intervention are proposed to improve neutrophil chemotaxis, and we hope that this review may provide insights for clinical practitioners.