PD-L1 is a ligand for PD-1, and its expression has been shown to be upregulated in neutrophils harvested from septic patients. However, the effect of PD-L1 on neutrophil survival and sepsis-induced lung injury remains largely unknown. In this study, PD-L1 expression correlated negatively with rates of apoptosis in human neutrophils harvested from patients with sepsis. Coimmunoprecipitation assays on control neutrophils challenged with interferon-γ and LPS showed that PD-L1 complexes with the p85 subunit of phosphatidyl 3-kinase (PI3K) to activate AKT-dependent survival signaling. Conditional CRE/LoxP deletion of neutrophil PD-L1 in vivo further protected against lung injury and reduced neutrophil lung infiltration in a cecal ligation and puncture (CLP) experimental sepsis animal model. Compared with wild-type animals, PD-L1–deficient animals presented lower levels of plasma tumor necrosis factor-α and interleukin-6 (IL-6) and higher levels of IL-10 after CLP, and reduced 7-day mortality in CLP PD-L1–knockout animals. Taken together, our data suggest that increased PD-L1 expression on human neutrophils delays cellular apoptosis by triggering PI3K–dependent AKT phosphorylation to drive lung injury and increase mortality during clinical and experimental sepsis.

Sepsis-associated encephalopathy (SAE) is one of the common serious complications in sepsis, and the pathogenesis of SAE remains unclear. Sirtuin 1 (SIRT1) has been reported to be downregulated in the hippocampus and SIRT1 agonists can attenuated the cognitive dysfunction in septic mice. Nicotinamide adenine dinucleotide (NAD+) is a key substrate to maintain the deacetylation activity of SIRT1. As an intermediate of NAD+, β-Nicotinamide Mononucleotide (NMN) has been reported to be promising in treating neurodegenerative diseases and cerebral ischemic injury. Thus we sought to investigate the potential role of NMN in SAE treatment. The SAE model was established by cecal ligation and puncture (CLP) in vivo, and neuroinflammation model was established with LPS-treated BV-2 cells in vitro. Memory impairment was assessed by Morris water maze and fear conditioning tests. As a result, the levels of NAD+, SIRT1 and PGC-1α were significantly reduced in the hippocampus of septic mice, while the acetylation of total lysine, phosphorylation of P38 and P65 were enhanced. All these changes induced by sepsis were inverted by NMN. Treating with NMN resulted in improved behavior performance in the fear conditioning tests and Morris water maze. Apoptosis, inflammatory and oxidative responses in the hippocampus of septic mice were attenuated significantly after NMN administration. These protective effect of NMN against memory dysfunction, inflammatory and oxidative injuries were reversed by the SIRT1 inhibitor, EX-527. Similarly, LPS-induced activation of BV-2 cells were attenuated by NMN, EX-527 or SIRT1 knockdown could reverse such effect of NMN in vitro. In conclusion, NMN is protective against sepsis-induced memory dysfunction, and the inflammatory and oxidative injuries in the hippocampus region of septic mice. The NAD+/SIRT1 pathway might be involved in one of the mechanisms of the protective effect.

Programmed cell death 1 ligand 1 is up-regulated on neutrophils during sepsis, which may be associated with sepsisinduced immunosuppression. Supplemental Digital Content is available in the text. Background: Recent studies have shown that neutrophils may display an antigen-presenting function and inhibit lymphocyte proliferation by expressing programmed cell death 1 ligand 1 (PD-L1). The current study was performed to investigate the effect of neutrophils and their pathophysiological significance during sepsis. Methods: Neutrophil PD-L1 expression was determined in both septic mice (n = 6) and patients (n = 41). Neutrophils from septic mice were subtyped into PD-L1⁻ and PD-L1⁺ populations to determine their phenotypes and functions. Septic neutrophils were cocultured with lymphocytes to observe the effect of septic neutrophils on lymphocyte apoptosis. Results: The PD-L1 level on neutrophils from septic mice was significantly up-regulated (21.41 ± 4.76%). This level increased with the progression of sepsis and the migration of neutrophils from the bone marrow to the blood and peritoneal cavity. The percentages of CD11a, CD62L, and C-C chemokine receptor type 2 were lower, whereas the percentages of CD16 and CD64 were higher on PD-L1⁺ neutrophils than on PD-L1⁻ neutrophils. The migratory capacity of PD-L1⁺ neutrophils was compromised. Septic neutrophils induced lymphocyte apoptosis via a contact mechanism, and this process could be reversed by anti-PD-L1 antibody. PD-L1 was also up-regulated on neutrophils from patients with severe sepsis (14.6% [3.75%, 42.1%]). The levels were negatively correlated with the monocyte human leukocyte antigen-DR level and positively correlated with the severity of septic patients. Neutrophil PD-L1 was a predictor for the prognosis of severe sepsis, with an area of 0.74 under the receiver operating curve. Conclusions: PD-L1 is up-regulated on neutrophils during sepsis, which may be related to sepsis-induced immunosuppression.

Sepsis-associated encephalopathy (SAE) is characterized as brain dysfunction associated with sepsis. In this study we sought to investigate the effects of resveratrol in mice with SAE, as well as its effects in NLRP3 inflammasome and IL-1β, which were critical in the pathogenesis of SAE. SAE was induced in mice via cecal ligation and puncture (CLP), and resveratrol was administered at two doses after surgery. Spatial learning memory functions were evaluated by Morris water maze testing. Apoptosis in the hippocampus was quantified using TUNEL assay. Inflammation in the hippocampus was quantified by measuring the levels of microglial activation, NLRP3, and IL-1β. CLP mice treated with resveratrol demonstrated a better spatial memory during water maze training. The TUNEL assay demonstrated significantly attenuated rates of apoptosis, in resveratrol treated mice, while decreasing the number of iba-1 positive microglia in the hippocampus region. NLRP3 expression and IL-1βcleavage were well inhibited by resveratrol dose-dependently. Thein vitroresults showed that in the BV2 cell lines resveratrol prevents ATP induced NLRP3 activation and IL-1βcleavage, which were reversed by the sirtuin 1 inhibitor, nicotinamide. In conclusion, resveratrol improves the spatial memory in mice with SAE and inhibits the NLRP3/IL-1βaxis in the microglia.