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Our prior study found that transforming growth factor beta-induced (TGFBI) is an important negative regulator in TLR-induced inflammation. However, whether TGFBI may affect inflammation during lipopolysaccharide (LPS)-induced endotoxin tolerance (ET) is still unclear. This study aimed to investigate whether TGFBI was involved in the mechanisms of ET in human through dampening nuclear factor-kappa B (NF-κB) mediated pathway. ET models of isolated healthy volunteers peripheral blood mononuclear cells (PBMCs) were established by pretreating with a low dose of LPS to observe the changes of TGFBI expression during ET induction, compared with ten healthy controls. Moreover, a vector-based short hairpin RNA expression system was used to specifically inhibit TGFBI expression to further explore its role in ET induction. The expression was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. The responses to LPS were determined by the activation of NF-κB, the production of tumor necrosis factor-α (TNF-α) and Nitric Oxide (NO), which were analysed by enzyme-linked immuno sorbent assay (ELISA). The results showed that TGFBI expression in the ET group obviously increased; ET also led to a hyporesponse of PBMCs to LPS with less activation of NF-κB, less production of TNF-α and NO, as well as more expression of TGFBI than those of non-ET group. Moreover, the inhibitory effect was partly refracted in plasmid TGFBI short hairpin RNA (pTGFBI-shRNA) transfected PBMCs. Meanwhile, the absence of TGFBI caused abnormal enhancement of inflammatory cytokine production and it was involved in ET induction through dampening NF-κB mediated pathway. Therefore, TGFBI may be a new target for the clinical treatment of inflammatory disorders.

Interleukin 6 (IL-6) is a major pro-inflammatory cytokine and dysregulation of IL-6 is relevant to many inflammatory diseases. Endotoxin induced tolerance of IL-6 is an important mechanism to avoid the excessive immune reaction. But to date, the molecular mechanisms of endotoxin tolerance of IL-6 remain unclear. Here we reported that IL-6 secretion and microRNA-181b (miR-181b) expression were inversely correlated following LPS stimulation. We also demonstrated that miR-181b targeting the 3'-UTR of IL-6 transcripts and up-regulation of miR-181b was associated with NF-kB. We further demonstrated that up-regulation of miR-181b in response to LPS was required for inducing IL-6 tolerance in macrophage. Our results suggested that the post-transcriptional control mediated by miR-181b could be involved in fine tuning the critical level of IL-6 expression in endotoxin tolerance.

Background: Sepsis involves aberrant immune responses to infection, but the exact nature of this immune dysfunction remains poorly defined. Bacterial endotoxins like lipopolysaccharide (LPS) are potent inducers of inflammation, which has been associated with the pathophysiology of sepsis, but repeated exposure can also induce a suppressive effect known as endotoxin tolerance or cellular reprogramming. It has been proposed that endotoxin tolerance might be associated with the immunosuppressive state that was primarily observed during late-stage sepsis. However, this relationship remains poorly characterised. Here we clarify the underlying mechanisms and timing of immune dysfunction in sepsis., Methods: We defined a gene expression signature characteristic of endotoxin tolerance. Gene-set test approaches were used to correlate this signature with early sepsis, both newly and retrospectively analysing microarrays from 593 patients in 11 cohorts. Then we recruited a unique cohort of possible sepsis patients at first clinical presentation in an independent blinded controlled observational study to determine whether this signature was associated with the development of confirmed sepsis and organ dysfunction., Findings: All sepsis patients presented an expression profile strongly associated with the endotoxin tolerance signature (p < 0.01; AUC 96.1%). Importantly, this signature further differentiated between suspected sepsis patients who did, or did not, go on to develop confirmed sepsis, and predicted the development of organ dysfunction., Interpretation: Our data support an updated model of sepsis pathogenesis in which endotoxin tolerance-mediated immune dysfunction (cellular reprogramming) is present throughout the clinical course of disease and related to disease severity. Thus endotoxin tolerance might offer new insights guiding the development of new therapies and diagnostics for early sepsis.

Mechanism-based sepsis treatments are unavailable, and their incidence is rising worldwide. Deaths occur during the early acute phase of hyperinflammation or subsequent postacute hypoinflammatory phase with sustained organ failure. The acute sepsis phase shifts rapidly, and multiple attempts to treat early excessive inflammation have uniformly failed. We reported in a sepsis cell model and human sepsis blood leukocytes that nuclear NAD+ sensor SIRT1 deacetylase remodels chromatin at specific gene sets to switch the acute-phase proinflammatory response to hypoinflammatory. Importantly, SIRT1 chromatin reprogramming is reversible, suggesting that inhibition of SIRT1 might reverse postacute-phase hypoinflammation. We tested this concept in septic mice, using the highly specific SIRT1 inhibitor EX-527, a small molecule that closes the NAD+ binding site of SIRT1. Strikingly, when administered 24 h after sepsis, all treated animals survived, whereas only 40% of untreated mice survived. EX-527 treatment reversed the inability of leukocytes to adhere at the small intestine MVI, reversed in vivo endotoxin tolerance, increased leukocyte accumulation in peritoneum, and improved peritoneal bacterial clearance. Mechanistically, the SIRT1 inhibitor restored repressed endothelial E-selectin and ICAM-1 expression and PSGL-1 expression on the neutrophils. Systemic benefits of EX-527 treatment included stabilized blood pressure, improved microvascular blood flow, and a shift toward proimmune macrophages in spleen and bone marrow. Our findings reveal that modifying the SIRT1 NAD+ axis may provide a novel way to treat sepsis in its hypoinflammatory phase., (© 2014 Society for Leukocyte Biology.)

Abstract: In order to evaluate the degree of endotoxin tolerance, expressed by the reduced cytokine/releasing capacity of the whole blood, data from a group of patients with trauma, severe acute pancreatitis (SAP), and diffuse peritonitis were analyzed. In SAP endotoxin levels and the tumor necrosing factor (TNF-α)–releasing capacity of the whole blood under lipopolysaccharide (LPS) stimulation were of an intermediate degree between systemic inflammatory response syndrome and severe sepsis. A mathematical model of ordinary differential equations of LPS signaling based on endotoxin kinetics and endotoxin tolerance was constructed. The mathematical model was used to reproduce the TNF-α production in trauma, SAP and peritonitis patients. The results of these numerical simulations are very similar to the determinations in real patients and argue that endotoxin tolerance may be a component of the immune dysregulation that complicates the clinical evolution of the patient with SAP. [Copyright &y& Elsevier]

Endotoxin tolerance (ET) is an important phenomenon, which affects inflammation and phagocytosis. Pretreatment with low dose of lipopolysaccharide (LPS) can protect liver injury from various hepatotoxicants such as acetaminophen and pseudomonas aeruginosa exotoxin A. The current study aimed to investigate the protecting mechanisms of endotoxin tolerance in acute liver failure induced by D-galactosamine (D-GalN)/LPS and possible role of toll-like receptors 4 (TLR4) signaling pathway in this phenomenon. Acute liver failure was induced by Injection of D-GalN/LPS. To mimic endotoxin tolerance, male Sprague-Dawley rats were treated with low dose of LPS (0.1 mg/kg once a day intraperitoneally for consecutive five days) before subsequent injection of D-GalN/LPS. Rat survival was determined by survival rate. Liver injury was confirmed by serum biochemical and liver histopathological examination. Inflammatory cytokines were determined by ELISA and nuclear factor-kappa B (NF-κB) (P65), toll-like receptors 4 (TLR4) and Interleukin-1 receptor-associated kinase-1 (IRAK-1) were measured by reverse transcriptase polymerase chain reaction and western blot respectively. Pretreatment of LPS significantly improved rat survival. Moreover, rats pretreated with LPS exhibited lower serum enzyme (ALT, AST and TBiL) level, lower production of inflammatory cytokines and more minor liver histopathological damage than rats without pretreatment of LPS. LPS pretreatment suppressed production of TLR4 and IRAK-1. LPS pretreatment also inhibited activation of hepatic NF-κB. These results indicated that endotoxin tolerance contributed to liver protection against D-GalN/LPS induced acute liver failure through down-regulation of TLR4 and NF-κB pathway.

RelB is one of the more unusual members of the NF-κB family. This family, arguably the best known group of transcription regulators, regulates an astonishing array of cell types and biological processes. This includes regulation of cell growth, differentiation and death by apoptosis, and the development and function of the innate and adaptive-immune system. RelB is best known for its roles in lymphoid development, DC biology, and noncanonical signaling. Within the last few years, however, surprising functions of RelB have emerged. The N-terminal leucine zipper motif of RelB, a motif unique among the NF-κB family, may associate with more diverse DNA sequences than other NF-κB members. RelB is capable of direct binding to the AhR that supports the xenobiotic-detoxifying pathway. RelB can regulate the circadian rhythm by directly binding to the BMAL partner of CLOCK. Finally, RelB also couples with bioenergy NAD(+) sensor SIRT1 to integrate acute inflammation with changes in metabolism and mitochondrial bioenergetics. In this review, we will explore these unique aspects of RelB, specifically with regard to its role in immunity.

Increasing evidence indicates that "functional plasticity" is not solely a neuronal attribute but a hallmark of microglial cells, the main brain resident macrophage population. Far from being a univocal phenomenon, microglial activation can originate a plethora of functional phenotypes, encompassing the classic M1 proinflammatory and the alternative M2 anti-inflammatory phenotypes. This concept overturns the popular view of microglial activation as a synonym of neurotoxicity and neurogenesis failure in brain disorders. The characterization of the alternative programs is a matter of intense investigation, but still scarce information is available on the course of microglial activation, on the reversibility of the different commitments and on the capability of preserving molecular memory of previous priming stimuli. By using organotypic hippocampal slice cultures as a model, we developed paradigms of stimulation aimed at shedding light on some of these aspects. We show that persistent stimulation of TLR4 signaling promotes an anti-inflammatory response and microglial polarization toward M2-like phenotype. Moreover, acute and chronic preconditioning regimens permanently affect the capability to respond to a later challenge, suggesting the onset of mechanisms of molecular memory. Similar phenomena could occur in the intact brain and differently affect the vulnerability of mature and newborn neurons to noxious signals., (Copyright © 2013 Wiley Periodicals, Inc.)

Inflammation in response to infection or trauma can lead to CARS, which is characterized by leukocyte dysfunction. In this study, we used a human model system for CARS to study the effect of GM-CSF and IFN-γ treatment on this immunoparalyzed state. Healthy human volunteers were treated with GM-CSF (4 μg/kg), IFN-γ (100 μg), or placebo in between two challenges with Escherichia coli LPS/endotoxin (2 ng/kg). Serial leukocyte blood counts were measured. Neutrophil subsets were discriminated using CD16 and CD62L expression. LPS rechallenge resulted in increased mobilization of mature neutrophils, whereas banded neutrophils decreased. GM-CSF and IFN-γ treatment did not restore these changes. GM-CSF treatment did, however, increase the number of CD16(bright)/CD62L(dim) neutrophils that were previously shown be able to suppress T cell proliferation. IFN-γ treatment decreased neutrophilia seen after LPS rechallenge. Our study shows that LPS rechallenge was associated with changes in the distribution of neutrophil subsets, whereas no additional changes in kinetics of other granulocyte populations were observed. GM-CSF and IFN-γ treatment induced a shift in granulocyte composition toward an anti-inflammatory direction by increasing CD16(bright)/CD62L(dim) cells or decreasing neutrophil counts, respectively.

Sepsis-associated immunosuppression (SAIS) is regarded as one of main causes for the death of septic patients at the late stage because of the decreased innate immunity with a more opportunistic infection. LPS-tolerized macrophages, which are re-challenged by LPS after prior exposure to LPS, are regarded as the common model of hypo-responsiveness for SAIS. However, the molecular mechanisms of endotoxin tolerance and SAIS remain to be fully elucidated. In addition, negative regulation of the Toll-like receptor (TLR)-triggered innate inflammatory response needs further investigation. Here we show that expression of immune responsive gene 1 (IRG1) was highly up-regulated in the peripheral blood mononuclear cells of septic patients and in LPS-tolerized mouse macrophages. IRG1 significantly suppressed TLR-triggered production of proinflammatory cytokines TNF-α, IL-6, and IFN-β in LPS-tolerized macrophages, with the elevated expression of reactive oxygen species (ROS) and A20. Moreover, ROS enhanced A20 expression by increasing the H3K4me3 modification of histone on the A20 promoter domain, and supplement of the ROS abrogated the IRG1 knockdown function in breaking endotoxin tolerance by increasing A20 expression. Our results demonstrate that inducible IRG1 promotes endotoxin tolerance by increasing A20 expression through ROS, indicating a new molecular mechanism regulating hypoinflammation of sepsis and endotoxin tolerance.