Acute pancreatitis (AP) is a life-threatening disease that requires early identification of patients at risk of developing infectious complications. Immunosuppression is an initial event that is key to AP pathogenesis. The programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) system is reported to mediate evasion of host immune surveillance in many diseases; however, the relationship between PD-1/PD-L1 expression and these parameters or infectious complications in AP has not been elucidated. This study was conducted to determine whether PD-1 and PD-L1 are upregulated and to reveal the relationship between PD-1/PD-L1 expression and the development of infectious complications in AP. Sixty-three patients with AP and 32 sex- and age-matched healthy control subjects were prospectively enrolled. On days 1 and 3 after the onset of AP, we measured PD-1 expression in peripheral CD4+ T cells and PD-L1 and human leukocyte antigen-DR (HLA-DR) expression in CD14+ monocytes using flow cytometry. Plasma interleukin (IL)-10 levels were measured by enzyme-linked immunosorbent assay. Compared with healthy volunteers, the percentages of PD-1-expressing CD4+ lymphocytes and PD-L1-expressing CD14+ monocytes were increased in patients with AP on days 1 and 3 after onset, especially those with infectious complications. Moreover, increased PD-1/PD-L1 expression was associated with increased occurrence of infectious complications, decreased circulating lymphocytes, and increased plasma IL-10 concentration. Multivariate regression analysis indicated that the increased percentage of PD-L1-expressing CD14+ monocytes was an independent risk factor for infectious complications in AP. Area under the ROC curve analysis showed the combination of Acute Physiology and Chronic Health Evaluation II score and PD-L1 and HLA-DR expression in CD14+ monocytes had high accuracy in predicting infectious complications in patients with AP. The PD-1/PD-L1 system plays an essential role in the early immunosuppression of AP. PD-L1 expression in CD14+ monocytes may be a new marker for predicting risk of infectious complications in patients with AP.

Neutrophils are essential components of the innate immune system that defend against the invading pathogens, such as bacteria, viruses, and fungi, as well as having regulatory roles in various conditions, including tissue repair, cancer immunity, and inflammation modulation. The function of neutrophils is strongly related to their mode of cell death, as different types of cell death involve various cellular and molecular alterations. Apoptosis, a non-inflammatory and programmed type of cell death, is the most common in neutrophils, while other modes of cell death, including NETOsis, necrosis, necroptosis, autophagy, pyroptosis, and ferroptosis, have specific roles in neutrophil function regulation. Immunometabolism refers to energy and substance metabolism in immune cells, and profoundly influences immune cell fate and immune system function. Intercellular and intracellular signal transduction modulate neutrophil metabolism, which can, in turn, alter their activities by influencing various cell signaling pathways. In this review, we compile an extensive body of evidence demonstrating the role of neutrophil metabolism in their various forms of cell death. The review highlights the intricate metabolic characteristics of neutrophils and their interplay with various types of cell death.

Background: Delayed neutrophil apoptosis during sepsis may impact neutrophil organ accumulation and tissue immune homeostasis. Elucidating the mechanisms underlying neutrophil apoptosis may help identify potential therapeutic targets. Glycolysis is critical to neutrophil activities during sepsis. However, the precise mechanisms through which glycolysis regulates neutrophil physiology remain under-explored, especially those involving the non-metabolic functions of glycolytic enzymes. In the present study, the impact of programmed death ligand-1 (PD-L1) on neutrophil apoptosis was explored. The regulatory effect of the glycolytic enzyme, pyruvate kinase M2 (PKM2), whose role in septic neutrophils remains unaddressed, on neutrophil PD-L1 expression was also explored. Methods: Peripheral blood neutrophils were isolated from patients with sepsis and healthy controls. PD-L1 and PKM2 levels were determined by flow cytometry and Western blotting, respectively. Dimethyl sulfoxide (DMSO)-differentiated HL-60 cells were stimulated with lipopolysaccharide (LPS) as an in vitro simulation of septic neutrophils. Cell apoptosis was assessed by annexin V/propidium iodide (annexin V/PI) staining, as well as determination of protein levels of cleaved caspase-3 and myeloid cell leukemia-1 (Mcl-1) by Western blotting. An in vivo model of sepsis was constructed by intraperitoneal injection of LPS (5 mg/kg) for 16 h. Pulmonary and hepatic neutrophil infiltration was assessed by flow cytometry or immunohistochemistry. Results: PD-L1 level was elevated on neutrophils under septic conditions. Administration of neutralizing antibodies against PD-L1 partially reversed the inhibitory effect of LPS on neutrophil apoptosis. Neutrophil infiltration into the lung and liver was also reduced in PD-L1^−/− mice 16 h after sepsis induction. PKM2 was upregulated in septic neutrophils and promoted neutrophil PD-L1 expression both in vitro and in vivo. In addition, PKM2 nuclear translocation was increased after LPS stimulation, which promoted PD-L1 expression by directly interacting with and activating signal transducer and activator of transcription 1 (STAT1). Inhibition of PKM2 activity or STAT1 activation also led to increased neutrophil apoptosis. Conclusion: In this study, a PKM2/STAT1-mediated upregulation of PD-L1 on neutrophils and the anti-apoptotic effect of upregulated PD-L1 on neutrophils during sepsis were identified, which may result in increased pulmonary and hepatic neutrophil accumulation. These findings suggest that PKM2 and PD-L1 could serve as potential therapeutic targets.

Microcirculatory dysfunction is one of the main characteristics of sepsis. Shenfu Injection (SFI) as a traditional Chinese medicine is widely applied in clinical severe conditions. Recent studies have shown that SFI has the ability to ameliorate sepsis-induced inflammation and to improve microcirculation perfusion. This study aims to investigate the underlying mechanism of SFI for ameliorating sepsis-associated endothelial dysfunction and organ injury. Side-stream dark-field (SDF) imaging was used to monitor the sublingual microcirculation of septic patients treated with or without SFI. Septic mouse model was used to evaluate the effects of SFI in vivo. Metabolomics and transcriptomics were performed on endothelial cells to identify the underlying mechanism for SFI-related protective effect on endothelial cells. SFI effectively abolished the disturbance and loss of sublingual microcirculation in septic patients. Twenty septic shock patients with or without SFI administration were enrolled and the data showed that SFI significantly improved the levels of total vessel density (TVD), perfused vessel density (PVD), microvascular flow index (MFI), and the proportion of perfused vessels (PPV). The administration of SFI significantly decreased the elevated plasma levels of Angiopoietin-2 (Ang2) and Syndecan-1, which are biomarkers indicative of endothelial damage in sepsis patients. In the mouse septic model in vivo, SFI inhibited the upregulation of endothelial adhesion molecules and Ly6G + neutrophil infiltration while restored the expression of VE-Cadherin in the vasculature of the lung, kidney, and liver tissue. Additionally, SFI reduced the plasma levels of Ang2, Monocyte Chemoattractant Protein-1(MCP1), and Interleukin-6 (IL6), and alleviated liver and kidney injury in septic mice. Moreover, SFI significantly inhibited the inflammatory activation and increased permeability of endothelial cells induced by endotoxins in vitro. By performing metabolomics and transcriptomics, we identified the activation of PI3K/Akt-mediated glycolysis as the underlying mechanism for SFI-related protective effect on endothelial cells. Our findings revealed that SFI may improve microcirculation perfusion and endothelial function in sepsis via inhibiting PI3K/Akt-mediated glycolysis, providing theoretical evidence for the clinical application of SFI.

Background: The effect of gut microbiota on enteral nutrition tolerance in critically ill patients is unclear. Methods: Non-abdominal sepsis patients in an ICU, sorted by whether they reached 20 Kcal/kg/day on the 3rd day of EN, were divided into tolerance and intolerance groups. Their feces on day 1 and day 3 of EN initiation were collected for 16s rDNA and short-chain fatty acid (SCFA) testing. Results: There were 14 patients included in the tolerance group and 10 in the intolerance group. On EN day 1, the OTUs and microbiota diversity were higher in the tolerance group than in the intolerance group. The ratio of Firmicutes to Bacteroidetes was higher in the intolerance group on EN day 1. The genus Parabacteroides were the most significantly elevated in the tolerance group. On EN day 3, the genus Escherichia-Shigella was the most significantly elevated in the tolerance group. On EN day 3, the levels of SCFA decreased more significantly in the intolerance group. Conclusion: Enteral nutrition tolerance is associated with microbiota features and short-chain fatty acid levels. A higher ratio of Firmicutes to Bacteroidetes and microbiota diversity on EN day 1 may help in the early prediction of EN tolerance.