Endotoxin tolerance: A review. Crit Care Med. 2002;30:S64-S73. [PMID: 11891406 DOI: 10.1097/00003246-200201001-00009]

Grass carp TGF-β1 impairs IL-1β signaling in the inflammatory responses: Evidence for the potential of TGF-β1 to antagonize inflammation in fish

In the present study, effects of TGF-β1 on IL-1β signaling during inflammatory response were examined in grass carp. In grass carp head kidney leukocytes (HKLs), LPS significantly induced the mRNA expression of grass carp TGF-β1 (gcTGF-β1) and IL-1β, indicating the involvement of TGF-β1 and IL-1β in inflammatory process. Using anti-IL-1β antibody to neutralize the endogenous IL-1β, we found that stimulation of IL-1β mRNA expression by LPS was independent on IL-1β itself. Interestingly, recombinant gcTGF-β1 (rgcTGF-β1) suppressed basal and LPS-stimulated IL-1β mRNA expression in spite of immunoneutralizing endogenous IL-1β or not. Given that IL-1β receptor signaling molecule and natural IL-1β inhibitors are the important regulators in IL-1β signaling and activity, the effect of LPS on these molecules' expression was determined in HKLs. Results showed that LPS significantly enhanced the mRNA levels of IL-1 receptor type I (IL-1RI) and II (IL-1RII), IL-1R accessory protein (IL-1Racp) and novel IL-1 family member (nIL-1F). Moreover, the induction of IL-1RII, IL-1Racp and nIL-1F by LPS was IL-1β-dependent since IL-1β immunoneutralization abolished these inductions, implying the involvement of IL-1β auto-induction in these effects. Consistently, TGF-β1 could block basal IL-1RI and nIL-1F mRNA expression, and LPS-induced IL-1RI, IL-1Racp and nIL-1F mRNA expression, suggesting these molecules as the regulatory sites for TGF-β1 to modulate IL-1β signaling. Subsequent in vivo studies showed that bacterial challenge significantly up-regulated IL-1β mRNA expression with a rapid and transient pattern and TGF-β1 mRNA expression with a relatively time-delayed kinetics in head kidney. These expression patterns coincide with their pro-inflammatory and anti-inflammatory roles, respectively. As expected, rgcTGF-β1 could suppress bacterial-induced IL-1β mRNA expression, strengthening the anti-inflammatory role of TGF-β1 in vivo. Taken together, these results to our knowledge provide the first evidence for inducible TGF-β1 expression in inflammatory process, as well as the induction of inflammatory stimuli on IL-1β expression and signaling. In turn, TGF-β1 suppressed the proinflammatory process in vitro and in vivo presumably via interfering IL-1β expression and signaling in inflammatory response, highlighting the potential of TGF-β1 in the control of inflammation in fish.

Neonatal lipopolysaccharide exposure does not diminish the innate immune response to a subsequent lipopolysaccharide challenge in Holstein bull calves

The innate immune response following experimental mastitis is quite variable between individual dairy cattle. An inflammatory response that minimizes collateral damage to the mammary gland while still effectively resolving the infection following pathogen exposure is beneficial to dairy producers. The ability of a lipopolysaccharide (LPS) exposure in early life to generate a low-responding phenotype and thus reduce the inflammatory response to a later-life LPS challenge was investigated in neonatal bull calves. Ten Holstein bull calves were randomly assigned to either an early life LPS (ELL) group (n=5) or an early life saline (ELS) group (n=5). At 7d of age, calves received either LPS or saline, and at 32d of age, all calves were challenged with an intravenous dose of LPS to determine the effect of the early life treatment (LPS or saline) on the immune response generated toward a subsequent LPS challenge. Dermal fibroblast and monocyte-derived macrophage cultures from each calf were established at age 20 and 27d, respectively, to model sustained effects from the early life LPS exposure on gene expression and protein production of components within the LPS response pathway. The ELL calves had greater levels of plasma IL-6 and tumor necrosis factor-α than the ELS calves following the early life LPS or saline treatments. However, levels of these 2 immune markers were similar between ELL and ELS calves when both groups were subsequently challenged with LPS. A comparison of the in vitro LPS responses of the ELL and ELS calves revealed similar patterns of protein production and gene expression following an LPS challenge of both dermal fibroblast and monocyte-derived macrophage cultures established from the treatment groups. Whereas an early life exposure to LPS did not result in a dampened inflammatory response toward a later LPS challenge in these neonatal bull calves, the potential that exposure to inflammation or stress in early life or in utero can create an offspring with a low-responding phenotype as an adult is intriguing and has been documented in rodents. Further work is needed to determine if an inflammatory exposure in utero in a dairy animal would result in a low-responding innate immune phenotype.

Epigenetic Regulation of Tolerance to Toll-Like Receptor Ligands in Alveolar Epithelial Cells

To protect the host against exuberant inflammation and injury responses, cells have the ability to become hyporesponsive or "tolerized" to repeated stimulation by microbial and nonmicrobial insults. The lung airspace is constantly exposed to a variety of exogenous and endogenous Toll-like receptor (TLR) ligands, yet the ability of alveolar epithelial cells (AECs) to be tolerized has yet to be examined. We hypothesize that type II AECs will develop a tolerance phenotype upon repeated TLR agonist exposure. To test this hypothesis, primary AECs isolated from the lungs of mice and a murine AEC cell line (MLE-12) were stimulated with either a vehicle control or a TLR ligand for 18 hours, washed, then restimulated with either vehicle or TLR ligand for an additional 6 hours. Tolerance was assessed by measurement of TLR ligand-stimulated chemokine production (monocyte chemoattractant protein [MCP]-1/CCL2, keratinocyte chemoattractant [KC]/CXCL1, and macrophage inflammatory protein [MIP]-2/CXCL2). Sequential treatment of primary AECs or MLE-12 cells with TLR agonists resulted in induction of either tolerance or cross-tolerance. The induction of tolerance was not due to expression of specific negative regulators of TLR signaling (interleukin-1 receptor associated kinase [IRAK]-M, Toll-interacting protein [Tollip], single Ig IL-1-related receptor [SIGIRR], or suppressor of cytokine signaling [SOCS]), inhibitory microRNAs (miRs; specifically, miR-155 and miR146a), or secretion of inhibitory or regulatory soluble mediators (prostaglandin E2, IL-10, transforming growth factor-β, or IFN-α/β). Moreover, inhibition of histone demethylation or DNA methylation did not prevent the development of tolerance. However, treatment of AECs with the histone deacetylase inhibitors trichostatin A or suberoylanilide hyrozamine resulted in reversal of the tolerance phenotype. These findings indicate a novel mechanism by which epigenetic modification regulates the induction of tolerance in AECs.

Hydrogen sulfide modulates chromatin remodeling and inflammatory mediator production in response to endotoxin, but does not play a role in the development of endotoxin tolerance

Background

Pretreatment with low doses of LPS (lipopolysaccharide, bacterial endotoxin) reduces the pro-inflammatory response to a subsequent higher LPS dose, a phenomenon known as endotoxin tolerance. Moreover, hydrogen sulfide (H₂S), an endogenous gaseous mediator (gasotransmitter) can exert anti-inflammatory effects. Here we investigated the potential role of H₂S in the development of LPS tolerance. THP1 differentiated macrophages were pretreated with the H₂S donor NaHS (1 mM) or the H₂S biosynthesis inhibitor aminooxyacetic acid (AOAA, 1 mM).

Methods

To induce tolerance, cells were treated with a low concentration of LPS (0.5 μg/ml) for 4 or 24 h, and then treated with a high concentration of LPS (1 μg/ml) for 4 h or 24 h. In in vivo studies, male wild-type and CSE^-/- mice were randomized to the following groups: Control (vehicle); Endotoxemic saline for 3 days before the induction of endotoxemia with 10 mg/kg LPS) mg/kg; Tolerant (LPS at 1 mg/kg for 3 days, followed LPS at 10 mg/kg). Animals were sacrificed after 4 or 12 h; plasma IL-6 and TNF-α levels were measured. Changes in histone H3 and H4 acetylation were analyzed by Western blotting.

Results

LPS tolerance decreased pro-inflammatory cytokine production. AOAA did not affect the effect of tolerance on reducing cytokine production. Treatment of the cells with the H₂S donor reduced cytokine production. Induction of the tolerance increased the acetylation of H3; AOAA reduced histone acetylation. H₂S donation increased histone acetylation. Tolerance did not affect the responses to H₂S with respect to histone acetylation.

Conclusions

In conclusion, both LPS tolerance and H₂S donation decrease LPS-induced cytokine production in vitro and modulate histone acetylation. However, endogenous, CSE-derived H₂S does not appear to play a significant role in the development of LPS tolerance.

Induction of Inducible Nitric Oxide Synthase by Lipopolysaccharide and the Influences of Cell Volume Changes, Stress Hormones and Oxidative Stress on Nitric Oxide Efflux from the Perfused Liver of Air-Breathing Catfish, Heteropneustes fossilis

The air-breathing singhi catfish (Heteropneustes fossilis) is frequently being challenged by bacterial contaminants, and different environmental insults like osmotic, hyper-ammonia, dehydration and oxidative stresses in its natural habitats throughout the year. The main objectives of the present investigation were to determine (a) the possible induction of inducible nitric oxide synthase (iNOS) gene with enhanced production of nitric oxide (NO) by intra-peritoneal injection of lipopolysaccharide (LPS) (a bacterial endotoxin), and (b) to determine the effects of hepatic cell volume changes due to anisotonicity or by infusion of certain metabolites, stress hormones and by induction of oxidative stress on production of NO from the iNOS-induced perfused liver of singhi catfish. Intra-peritoneal injection of LPS led to induction of iNOS gene and localized tissue specific expression of iNOS enzyme with more production and accumulation of NO in different tissues of singhi catfish. Further, changes of hydration status/cell volume, caused either by anisotonicity or by infusion of certain metabolites such as glutamine plus glycine and adenosine, affected the NO production from the perfused liver of iNOS-induced singhi catfish. In general, increase of hydration status/cell swelling due to hypotonicity caused decrease, and decrease of hydration status/cell shrinkage due to hypertonicity caused increase of NO efflux from the perfused liver, thus suggesting that changes in hydration status/cell volume of hepatic cells serve as a potent modulator for regulating the NO production. Significant increase of NO efflux from the perfused liver was also observed while infusing the liver with stress hormones like epinephrine and norepinephrine, accompanied with decrease of hydration status/cell volume of hepatic cells. Further, oxidative stress, caused due to infusion of t-butyl hydroperoxide and hydrogen peroxide separately, in the perfused liver of singhi catfish, resulted in significant increase of NO efflux accompanied with decrease of hydration status/cell volume of hepatic cells. However, the reasons for these cell volume-sensitive changes of NO efflux from the liver of singhi catfish are not fully understood with the available data. Nonetheless, enhanced or decreased production of NO from the perfused liver under osmotic stress, in presence of stress hormones and oxidative stress reflected its potential role in cellular homeostasis and also for better adaptations under environmental challenges. This is the first report of osmosensitive and oxidative stress-induced changes of NO production and efflux from the liver of any teleosts. Further, the level of expression of iNOS in this singhi catfish could also serve as an important indicator to determine the pathological status of the external environment.

The role of nitric oxide in the epigenetic regulation of THP-1 induced by lipopolysaccharide

AIMS

Changes in the gene expression are one of the molecular events involved in the Systemic of Inflammatory Response Syndrome during sepsis. The preconditioning with low doses of lipopolysaccharide (LPS) reduces the expression of pro-inflammatory genes leading to less tissue damage and better outcome. This hyporesponsive state called tolerance is associated to alterations in chromatin structure and nitric oxide (NO) production. In the current study, we demonstrated that tolerance induced by LPS was found to be NO-dependent and related to epigenetic changes.

MAIN METHODS

THP-1 cells were cultivated in RPMI medium (Control), submitted to tolerance (500ng/mL of LPS 24h before challenge with 1000ng/mL of LPS during 24h Tolerant group) and challenge (1000ng/mL of LPS during 24h Directly challenged group). The analyses performed were: cytokines production, histone acetyl transferases/histone deacetylases (HAT/HDAC) activity, nitrosylation of HDAC-2 and -3, expression of acetylated histones H3 and H4. HDAC and Nitric Oxide Synthases (NOS) activities were inhibited with 30mM trichostatin (TSA) and 100μM LNAME, respectively.

KEY FINDINGS

Administration of low doses of LPS repressed the production of IL-6 and IL-10, however this effect was abolished with the inhibition of NOS activity and by TSA in the case of IL-10. Tolerance modulates the activity of HAT and, consequently, the acetylation of histones H3 and H4. Inhibition of NO decreases acetylation of Histones. The HDACs 2 and 3 were nitrosylated after the tolerance induction.

SIGNIFICANCE

The tolerance to LPS regulates the cytokine production by modulating chromatin structure and this event is NO dependent.

Low-grade inflammatory polarization of monocytes impairs wound healing

Impaired wound healing often accompanies low-grade inflammatory conditions, during which circulating levels of subclinical super-low-dose endotoxin may persist. Low-grade inflammatory monocyte polarization may occur during chronic inflammation and deter effective wound repair. However, little is understood about the potential mechanisms of monocyte polarization by sustained insult of subclinical super-low-dose endotoxin. We observed that super-low-dose endotoxin preferentially programmes a low-grade inflammatory monocyte state in vitro and in vivo, as represented by the elevated population of CD11b(+) Ly6C(high) monocytes and sustained expression of CCR5. Mechanistically, super-low-dose endotoxin caused cellular stress, altered lysosome function and increased the transcription factor IRF5. TUDCA, a potent inhibitor of cellular stress, effectively blocked monocyte polarization and improved wound healing in mice injected with super-low-dose endotoxin. Our data revealed the polarization of low-grade inflammatory monocytes by sustained endotoxin challenge, its underlying mechanisms and a potential intervention strategy. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

SIGIRR participates in negative regulation of LPS response and tolerance in human bladder epithelial cells

Background

The innate immune response of urinary tract is critically important in the defense to microbial attack. Toll-like receptor 4 (TLR4) controls initial mucosal response to uropathogenic Escherichia coli (UPEC). However, excessive and dysfunctional TLR signaling may result in severe inflammation and inappropriate tissue damage. Previous studies have demonstrated that single immunoglobulin IL-1R-related receptor/Toll IL-1 receptor 8 (SIGIRR/TIR8) is a member of the toll-interleukin-1 receptor (TIR) family that can negatively modulate TLR4 mediated signaling, but its role in the innate immunity of urinary tract infection remains incompletely defined. In this study, we investigated its cellular distribution and mechanisms involved within the human bladder epithelial cells after LPS stimulation.

Results

Immunostaining, reverse transcription PCR and Western blot results showed that SIGIRR was constitutively expressed in the human bladder epithelial cell lines and was downregulated after LPS stimulation. To further define the role of SIGIRR, cells were transiently transfected with SIGIRR siRNA and stimulated with LPS. SIGIRR gene silencing augmented chemokine expression in response to LPS, as indicated by increased levels of IL-6 and IL-8 secretions in the supernatants compared with negative control siRNA. Furthermore, LPS tolerance, a protective mechanism against second LPS stimulation, was significantly reduced in SIGIRR siRNA transfected cells. Moreover, transient gene silencing augmented LPS-induced NF-κB and MAPK activation.

Conclusions

In conclusion, our results suggest that SIGIRR plays an important role in the negative regulation of LPS response and tolerance in human bladder epithelial cells, possibly through its impact on TLR-mediated signaling.

Immature myeloid Gr-1+ CD11b+ cells from lipopolysaccharide-immunosuppressed mice acquire inhibitory activity in the bone marrow and migrate to lymph nodes to exert their suppressive function

Secondary infections due to post-sepsis immunosuppression are a major cause of death in patients with sepsis. Repetitive inoculation of increasing doses of lipopolysaccharide (LPS) into mice mimics the immunosuppression associated with sepsis. Myeloid-derived suppressor cells (MDSCs, Gr-1(+) CD11b(+)) are considered a major component of the immunosuppressive network, interfering with T-cell responses in many pathological conditions. We used LPS-immunosuppressed (IS) mice to address whether MDSCs acquired their suppressive ability in the bone marrow (BM) and whether they could migrate to lymph nodes (LNs) to exert their suppressive function. Our results showed that Gr-1(+) CD11b(+) cells of IS mice already had the potential to inhibit T-cell proliferation in the BM. Moreover, soluble factors present in the BM from IS mice were responsible for inducing this inhibitory ability in control BM cells. In addition, migration of Gr-1(+) CD11b(+) to LNs in vivo was maximal when cells obtained from the BM of IS mice were inoculated into an IS context. In this regard, we found chemoattractant activity in cell-free LN extracts (LNEs) from IS mice and an increased expression of the LN-homing chemokine receptor C-C chemokine receptor type 7 (CCR7) in IS BM Gr-1(+) CD11b(+) cells. These results indicate that Gr-1(+) CD11b(+) cells found in BM from IS mice acquire their suppressive activity in the same niche where they are generated, and migrate to LNs to exert their inhibitory role. A better understanding of MDSC generation and/or regulation of factors able to induce their inhibitory function may provide new and more effective tools for the treatment of sepsis-associated immunosuppression.

The effect of lipopolysaccharide-induced obesity and its chronic inflammation on influenza virus-related pathology

Obese individuals show increased susceptibility to infection, low vaccine efficacy, and worse pathophysiology. However, it is unclear how obesity affects these events. The aim of this study was to investigate the effect of obesity-triggered chronic inflammation on immune cells after influenza virus infection. Control and lipopolysaccharide mice, in which an osmotic pump continually released Tween saline or lipopolysaccharide, were prepared and 3 weeks later were infected with pandemic H1N1 2009 influenza A virus. In lipopolysaccharide mice, we found a reduction in macrophage activation markers in the steady state, and reduced production of pro-inflammatory cytokines including tumor necrosis factor-α, interleukin-1β, and interleukin-6, in restimulated peritoneal macrophages. Interestingly, lipopolysaccharide-triggered chronic inflammation exacerbated the severity of pathological symptoms in the lungs after challenge with influenza virus. Taken together, the increased severity of virus-induced symptoms in obese individuals with chronic inflammation may be, at least partially, caused by macrophage dysfunction.

Fish Oil-Derived Long-Chain n-3 Polyunsaturated Fatty Acids Reduce Expression of M1-Associated Macrophage Markers in an ex vivo Adipose Tissue Culture Model, in Part through Adiponectin

Adipose tissue (AT) macrophages (ATM) play a key role in obesity-associated pathologies, and their phenotype can be influenced by the local tissue microenvironment. Interestingly, long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) and the LC n-3 PUFA-upregulated adipokine, adiponectin (Ad), may mitigate excessive ATM inflammatory M1-polarization responses. However, to what extent LC n-3 PUFA and Ad work in concert to affect macrophage phenotype has not been examined. Thus, we used an established ex vivo AT organ culture model using visceral AT from mice fed a control (CON; 10% w/w safflower oil) n-6 PUFA-rich diet or an isocaloric fish oil (FO; 3% w/w menhaden oil + 7% w/w safflower oil)-derived LC n-3 PUFA-rich diet to generate AT conditioned media (ACM). We then evaluated if CON or FO ACM affected macrophage polarization markers in a model designed to mimic acute [18 h ACM plus lipopolysaccharide (LPS) for the last 6 h] or chronic (macrophages treated with LPS-challenged CON or FO ACM for 24 h) inflammation ± Ad-neutralizing antibody and the LPS-neutralizing agent, polymyxin B. In the acute inflammation model, macrophages treated with FO ACM had decreased lipid uptake and mRNA expression of M1 markers (Nos2, Nfκb, Il6, Il18, Ccl2, and Ccl5) compared with CON ACM (p ≤ 0.05); however, these effects were largely attenuated when Ad was neutralized (p > 0.05). Furthermore, in the chronic inflammation model, macrophages treated with FO ACM had decreased mRNA expression of M1 markers (Nos2, Tnfα, Ccl2, and Il1β) and IL-6 and CCL2 secretion (p ≤ 0.05); however, some of these effects were lost when Ad was neutralized, and were further exacerbated when both Ad and LPS were neutralized. Taken together, this work shows that LC n-3 PUFA and Ad work in concert to suppress certain M1 macrophage responses. Thus, future strategies to modulate the ATM phenotype should consider the role of both LC n-3 PUFA and Ad in mitigating obese AT inflammation.

Vibrio cholerae porin OmpU induces LPS tolerance by attenuating TLR-mediated signaling

Porins can act as pathogen-associated molecular patterns, can be recognized by the host immune system and modulate immune responses. Vibrio choleraeporin OmpU aids in bacterial survival in the human gut by increasing resistance against bile acids and anti-microbial peptides. V. choleraeOmpU is pro-inflammatory in nature. However, interestingly, it can also down-regulate LPS-mediated pro-inflammatory responses. In this study, we have explored how OmpU-pretreatment affects LPS-mediated responses. Our study indicates that OmpU-pretreatment followed by LPS-activation does not induce M2-polarization of macrophages/monocytes. Further, OmpU attenuates LPS-mediated TLR2/TLR6 signaling by decreasing the association of TLRs along with recruitment of MyD88 and IRAKs to the receptor complex. This results in decreased translocation of NFκB in the nucleus. Additionally, OmpU-pretreatment up-regulates expression of IRAK-M, a negative regulator of TLR signaling, in RAW 264.7 mouse macrophage cells upon LPS-stimulation. Suppressor cytokine IL-10 is partially involved in OmpU-induced down-regulation of LPS-mediated TNFα production in human PBMCs. Furthermore, OmpU-pretreatment also affects macrophage function, by enhancing phagocytosis in LPS-treated RAW 264.7 cells, and down-regulates LPS-induced cell surface expression of co-stimulatory molecules. Altogether, OmpU causes suppression of LPS-mediated responses by attenuating the LPS-mediated TLR signaling pathway.

Bone Components Downregulate Expression of Toll-Like Receptor 4 on the Surface of Human Monocytic U937 Cells: A Cell Model for Postfracture Immune Dysfunction

To mimic the immune status of monocyte in the localized fracture region, toll-like receptor 4 (TLR4) surface expression in human monocytic U937 cells was used as the main target to assess immune dysfunction following bone component exposure. We first identified the effects of bone components (including the marrow content) on TLR4 surface expression and then examined the mechanisms underlying the changes. The level of microRNA-146a expression, an indicator of endotoxin tolerance, was also assayed. Bone component exposure downregulated TLR4 surface expression at 24 h by flow cytometry analysis, compatible with the result obtained from the membranous portion of TLR4 by western blot analysis. The cytoplasmic portion of TLR4 paradoxically increased after bone component exposure. Impaired TLR4 trafficking from the cytoplasm to the membrane was related to gp96 downregulation, as observed by western blot analysis, and this was further evidenced by gp96-TLR4 colocalization under confocal microscopy. TaqMan analysis revealed that the expression of microRNA-146a was also upregulated. This cell model demonstrated that bone component exposure downregulated TLR4 surface expression in a gp96-related manner in human monocytic U937 cells, an indicator of immunosuppression at 24 h. Immune dysfunction was further evidenced by upregulation of microRNA-146a expression at the same time point.

Receptor-Interacting Protein 140 Orchestrates the Dynamics of Macrophage M1/M2 Polarization

Macrophage classical (M1) versus alternative (M2) polarization is critical for the homeostatic control of innate immunity. Uncontrolled macrophage polarization is frequently implicated in diseases. This study reports a new functional role for receptor-interacting protein 140 (RIP140) in regulating this phenotypic switch. RIP140 is required for M1 activation, and its degradation is critical to LPS-induced endotoxin tolerance (ET). Here, we found that failure to establish RIP140 degradation-mediated ET prevents M2 polarization, and reducing RIP140 level facilitates an M1/M2 switch, resulting in more efficient wound healing in animal models generated with either transgenic or bone marrow transplant procedures. The M2-suppressive effect is elicited by a new function of RIP140 that, in macrophages exposed to M2 cues, is exported to cytosol, forming complexes with CAPNS1 (calpain regulatory subunit) to activate calpain 1/2, that activates PTP1B phosphatase. The activated PTP1B then reduces STAT6 phosphorylation, thereby suppressing the efficiency of M2 polarization. It is concluded that RIP140 plays dual roles in regulating the M1-M2 phenotype switch: the first, in the nucleus, is an M1 enhancer and the second, in the cytosol, is an M2 suppressor. Modulating the level and/or subcellular distribution of RIP140 can be a new therapeutic strategy for diseases where inflammatory/anti-inflammatory responses are critical.

Is the developmentally immature immune response in paediatric sepsis a recapitulation of immune tolerance?

Immunologically immature neonates suffer the highest incidence of paediatric sepsis. Postnatal immunological maturation is characterized by a relatively hypo-inflammatory immune response. The mechanisms that differentiate the mature and immature immune responses resemble those that differentiate the hyper- and hypo-inflammatory responses in severe sepsis. Immunological maturational differences likely affect the neonate's ability to mount an appropriate hyper-inflammatory response, a counteractive hypo-inflammatory response, and subsequent return to immune system homeostasis. To better understand the role of the hypo-inflammatory response in paediatric sepsis, we will explore the maturation of the immune system and the effect it may have on the sepsis-induced hypo-inflammatory response.

Super-low dose endotoxin pre-conditioning exacerbates sepsis mortality

Sepsis mortality varies dramatically in individuals of variable immune conditions, with poorly defined mechanisms. This phenomenon complements the hypothesis that innate immunity may adopt rudimentary memory, as demonstrated in vitro with endotoxin priming and tolerance in cultured monocytes. However, previous in vivo studies only examined the protective effect of endotoxin tolerance in the context of sepsis. In sharp contrast, we report herein that pre-conditioning with super-low or low dose endotoxin lipopolysaccharide (LPS) cause strikingly opposite survival outcomes. Mice pre-conditioned with super-low dose LPS experienced severe tissue damage, inflammation, increased bacterial load in circulation, and elevated mortality when they were subjected to cecal-ligation and puncture (CLP). This is in contrast to the well-reported protective phenomenon with CLP mice pre-conditioned with low dose LPS. Mechanistically, we demonstrated that super-low and low dose LPS differentially modulate the formation of neutrophil extracellular trap (NET) in neutrophils. Instead of increased ERK activation and NET formation in neutrophils pre-conditioned with low dose LPS, we observed significantly reduced ERK activation and compromised NET generation in neutrophils pre-conditioned with super-low dose LPS. Collectively, our findings reveal a mechanism potentially responsible for the dynamic programming of innate immunity in vivo as it relates to sepsis risks.

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Super-low dose endotoxin pre-conditioning exacerbates, while higher dose endotoxin alleviates sepsis mortality.

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Super-low dose endotoxin reduces, while higher dose endotoxin facilitates neutrophil extracellular trap (NET) formation.

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Super-low dose endotoxin suppresses, while higher dose endotoxin induces ERK activation required for NET formation.

Dietary calcium concentration and cereals differentially affect mineral balance and tight junction proteins expression in jejunum of weaned pigs

Ca plays an essential role in bone development; however, little is known about its effect on intestinal gene expression in juvenile animals. In the present study, thirty-two weaned pigs (9·5 (SEM 0·11) kg) were assigned to four diets that differed in Ca concentration (adequate v. high) and cereal composition (wheat-barley v. maize) to assess the jejunal and colonic gene expression of nutrient transporters, tight junction proteins, cytokines and pathogen-associated molecular patterns, nutrient digestibility, Ca balance and serum acute-phase response. To estimate the impact of mucosal bacteria on colonic gene expression, Spearman's correlations between colonic gene expression and bacterial abundance were computed. Faecal Ca excretion indicated that more Ca was available along the intestinal tract of the pigs fed high Ca diets as compared to the pigs fed adequate Ca diets (P> 0.05). High Ca diets decreased jejunal zonula occludens 1 (ZO1) and occludin (OCLN) expression, up-regulated jejunal expression of toll-like receptor 2 (TLR2) and down-regulated colonic GLUT2 expression as compared to the adequate Ca diets (P< 0.05). Dietary cereal composition up-regulated jejunal TLR2 expression and interacted (P= 0.021) with dietary Ca on colonic IL1B expression; high Ca concentration up-regulated IL1B expression with wheat-barley diets and down-regulated it with maize diets. Spearman's correlations (r> 0·35; P< 0·05) indicated an association between operational taxonomic units assigned to the phyla Bacteroidetes, Firmicutes and Proteobacteria and bacterial metabolites and mucosal gene expression in the colon. The present results indicate that high Ca diets have the potential to modify the jejunal and colonic mucosal gene expression response which, in turn, interacts with the composition of the basal diet and mucosa-associated bacteria in weaned pigs.

Innate immune programing by endotoxin and its pathological consequences

Monocytes and macrophages play pivotal roles in inflammation and homeostasis. Recent studies suggest that dynamic programing of macrophages and monocytes may give rise to distinct "memory" states. Lipopolysaccharide (LPS), a classical pattern recognition molecule, dynamically programs innate immune responses. Emerging studies have revealed complex dynamics of cellular responses to LPS, with high doses causing acute, resolving inflammation, while lower doses are associated with low-grade and chronic non-resolving inflammation. These phenomena hint at dynamic complexities of intra-cellular signaling circuits downstream of the Toll-like receptor 4 (TLR4). In this review, we examine pathological effects of varying LPS doses with respect to the dynamics of innate immune responses and key molecular regulatory circuits responsible for these effects.

Current knowledge and future directions of TLR and NOD signaling in sepsis

The incidence of sepsis is increasing over time, along with an increased risk of dying from the condition. Sepsis care costs billions annually in the United States. Death from sepsis is understood to be a complex process, driven by a lack of normal immune homeostatic functions and excessive production of proinflammatory cytokines, which leads to multi-organ failure. The Toll-like receptor (TLR) family, one of whose members was initially discovered in Drosophila, performs an important role in the recognition of microbial pathogens. These pattern recognition receptors (PRRs), upon sensing invading microorganisms, activate intracellular signal transduction pathways. NOD signaling is also involved in the recognition of bacteria and acts synergistically with the TLR family in initiating an efficient immune response for the eradication of invading microbial pathogens. TLRs and NOD1/NOD2 respond to different pathogen-associated molecular patterns (PAMPs). Modulation of both TLR and NOD signaling is an area of research that has prompted much excitement and debate as a therapeutic strategy in the management of sepsis. Molecules targeting TLR and NOD signaling pathways exist but regrettably thus far none have proven efficacy from clinical trials.

A unique role for p53 in the regulation of M2 macrophage polarization

P53 is critically important in preventing oncogenesis but its role in inflammation in general and in the function of inflammatory macrophages in particular is not clear. Here, we show that bone marrow-derived macrophages exhibit endogenous p53 activity, which is increased when macrophages are polarized to the M2 (alternatively activated macrophage) subtype. This leads to reduced expression of M2 genes. Nutlin-3a, which destabilizes the p53/MDM2 (mouse double minute 2 homolog) complex, promotes p53 activation and further downregulates M2 gene expression. In contrast, increased expression of M2 genes was apparent in M2-polarized macrophages from p53-deficient and p53 mutant mice. Furthermore, we show, in mice, that p53 also regulates M2 polarization in peritoneal macrophages from interleukin-4-challenged animals and that nutlin-3a retards the development of tolerance to Escherichia coli lipopolysaccharide. P53 acts via transcriptional repression of expression of c-Myc (v-myc avian myelocytomatosis viral oncogene homolog) gene by directly associating with its promoter. These data establish a role for the p53/MDM2/c-MYC axis as a physiological 'brake' to the M2 polarization process. This work reveals a hitherto unknown role for p53 in macrophages, provides further insight into the complexities of macrophage plasticity and raises the possibility that p53-activating drugs, many of which are currently being trialled clinically, may have unforeseen effects on macrophage function.

Effect of electroacupuncture on the inflammatory response in patients with acute pancreatitis: an exploratory study

OBJECTIVES

To examine the effects of electroacupuncture (EA) on inflammatory responses in patients with acute pancreatitis (AP).

METHODS

Eighty patients with mild or severe AP were randomly allocated to a control group or an EA group. All patients were managed conservatively. In addition, the EA group received acupuncture for 30 min per day for 7 days at bilateral points ST36, LI4, TE6, ST37 and LR3. Interleukin (IL)-6, IL-10 and C-reactive protein (CRP) levels were measured on admission and on day 7. The time to re-feeding and length of stay in hospital were also recorded.

RESULTS

A total of 58 patients provided complete data. The characteristics of the patients in the EA and control groups were similar. After 7 days the serum concentrations of IL-10 were higher in the EA group than in the control group (mild AP: 6.2±1.2 vs 5.2±0.9 pg/mL, p<0.05; severe AP: 14.9±7.8 vs 7.9±6.3 pg/mL, p<0.05). For patients with severe AP, the CRP level in the EA group was lower than in the control group (p<0.05).

CONCLUSIONS

EA may reduce the severity of AP by inducing anti-inflammatory effects and reducing the time to re-feeding; however, it did not reduce the length of hospital stay.

TRIAL REGISTRATION NUMBER

ChiCTR-TRC-13003572.

The fifth dimension of innate immunity

Innate immunity has evolved as a first line defense against invading pathogens. Cellular and humoral elements of the innate immune system detect infectious parasites, initiate inflammatory resistance reactions and finally contribute to the elimination of the invaders. Repeated attacks by pathogenic agents induce adaptive responses of the innate immune system. Typically, reapplication of pathogens provokes tolerance of the affected organism. However, also stimulatory effects of primary infections on subsequent innate immune responses have been observed. The present overview touches an undervalued aspect in the innate immune response: Its pronounced dependency on pathogen load. In addition to localization and timing of innate immune responses the pathogen dose dependency might be considered as a "fifth dimension of innate immunity". Experimental results and literature data are presented proposing a hormetic reaction pattern of innate immune cells depending on the dose of pathogens.

Chemokines responses to Plasmodium falciparum malaria and co-infections among rural Cameroonians

Malaria remains the major cause of disease morbidity and mortality in sub-Saharan Africa with complex immune responses associated with disease outcomes. Symptoms associated with severe malaria have generally shown chemokine upregulation but little is known of responses to uncomplicated malaria. Eight villages in central Cameroon of 1045 volunteers were screened. Among these, malaria-positive individuals with some healthy controls were selected for chemokine analysis using Enzyme-Linked Immunosorbent Assay (ELISA) kits. Depressed serum levels of CXCL5 and raised CCL28 were observed in malarial positives when compared with healthy controls. The mean concentration of CXCL11 was higher in symptomatic than asymptomatic group, while CCL28 was lower in symptomatic individuals. Lower chemokine levels were associated with symptoms of uncomplicated malaria except for CXCL11 which was upregulated among fever-positive group. The mean CXCL5 level was higher in malaria sole infection than co-infections with HIV and Loa loa. Also, there was a raised mean level of malaria+HIV co-infection for CXCL9. This study hypothesises a situation where depressed chemokines in the face of clinical presentations could indicate an attempt by the immune system in preventing a progression process from uncomplicated to complicated outcomes with CXCL11 being identified as possible biomarker for malarial fever.

Computational modelling of the inflammatory response in trauma, sepsis and wound healing: implications for modelling resilience

Resilience refers to the ability to recover from illness or adversity. At the cell, tissue, organ and whole-organism levels, the response to perturbations such as infections and injury involves the acute inflammatory response, which in turn is connected to and controlled by changes in physiology across all organ systems. When coordinated properly, inflammation can lead to the clearance of infection and healing of damaged tissues. However, when either overly or insufficiently robust, inflammation can drive further cell stress, tissue damage, organ dysfunction and death through a feed-forward process of inflammation → damage → inflammation. To address this complexity, we have obtained extensive datasets regarding the dynamics of inflammation in cells, animals and patients, and created data-driven and mechanistic computational simulations of inflammation and its recursive effects on tissue, organ and whole-organism (patho)physiology. Through this approach, we have discerned key regulatory mechanisms, recapitulated in silico key features of clinical trials for acute inflammation and captured diverse, patient-specific outcomes. These insights may allow for the determination of individual-specific tolerances to illness and adversity, thereby defining the role of inflammation in resilience.

LPS-conditioned dendritic cells confer endotoxin tolerance contingent on tryptophan catabolism

Dendritic cells (DCs) are specialized antigen-presenting cells with a bipolar nature. Depending on environmental factors, DCs will promote either inflammatory or anti-inflammatory effects. Lipopolysaccharide (LPS), a ligand of Toll-like receptor (TLR)4 and a most potent proinflammatory stimulus, is responsible for complex signaling events in different cell types, including DCs. LPS effects range from protective inflammation-capable of counteracting growth and dissemination of gram-negative bacteria - to hyperacute detrimental responses, as it occurs in endotoxic shock. Consistent with the plasticity of TLR4 signaling, a low dosage of LPS will induce a regulatory response capable of protecting mice against a subsequent, otherwise lethal challenge ('endotoxin tolerance'). By examining CD11c(+) DCs ('conventional' DCs, or cDCs), we investigated whether DC flexibility in promoting either inflammation or tolerance can be differentially affected by single vs. repeated exposure to LPS in vitro. cDCs stimulated twice with LPS expressed high levels of indoleamine 2,3-dioxygenase 1 (IDO1) - one of the most effective mediator of anti-inflammatory activity by DCs - and of TGF-β, an immunoregulatory cytokine capable of upregulating IDO1 expression and function. In contrast, a single exposure to LPS failed to upregulate IDO1, and it was instead associated with high-level production of IL-6, a cytokine that promotes inflammation and proteolysis of IDO1. When adoptively transferred in vivo, only cDCs on double endotoxin exposure greatly improved the outcome of an otherwise lethal LPS challenge. The protective effect required that the transferred cDCs be fully competent for IDO1 and the host for TGF-β production. Thus cDCs, conditioned by LPS in vitro to mimic an endotoxin-tolerant state, can protect recipients from endotoxic shock, pointing to adoptive transfer of tolerance as a new option for controlling potentially harmful responses to TLR4 signaling.

Characterisation of temporal microglia and astrocyte immune responses in bile duct-ligated rat models of cirrhosis

BACKGROUND & AIMS

Microglia and astrocyte related pro-inflammatory responses are thought to underpin cerebral sequelae of acute liver failure. Conversely, despite background pro-inflammatory responses in cirrhosis, overt brain swelling and coma associated with acute-on-chronic liver failure, is infrequent unless precipitated (e.g. sepsis). Moreover in other chronic neurodegenerative disorders and sepsis, the brain is protected from recurrent microbial insults by compensatory microglial-associated immune responses. To characterise longitudinal cerebral immune responses in a bile duct-ligated (BDL) rat model of cirrhosis.

METHOD

Rats underwent BDL or sham operation before sacrifice at either 1-day, 1, 2 and 4 weeks post-surgery. We analysed consciousness, brain water, biochemistry and immunohistochemistry to assess activation of microglia (ED-1, OX6 and Iba-1), astrocytes (Glial fibrillary acidic protein - GFAP), cellular stress (Heat shock protein - Hsp 25) and pro-inflammatory mediator expression (inducible nitric oxide synthase (iNOS), interleukin-1beta (IL-1β) and tumour growth factor-beta (TGF-β)).

RESULTS

BDL significantly increased ammonia and bilirubin (P < 0.01 respectively). The classical microglial markers OX6, ED1 and Iba-1 and pro-inflammatory IL-1β and iNOS were not significantly increased. However, the alternative microglial marker and regulatory cytokine TGF-β was elevated from day 1 to 4 weeks post-BDL. GFAP expression was significantly increased in corpus callosum in all groups. In BDL rats, Hsp 25 was also increased in the corpus callosum, peaking at 2 weeks.

CONCLUSION

BDL triggers early alternative, but not classical, microglial activation. There was a correlation between astrocyte activation and cellular stress. These findings indicate early cerebral immune responses, which may be associated with immune tolerance to further challenge.

Identification of a novel molluscan short-type peptidoglycan recognition protein in disk abalone (Haliotis discus discus) involved in host antibacterial defense

Peptidoglycan recognition proteins (PGRPs) are a widely studied group of pattern recognition receptors found in invertebrate as well as vertebrate lineages, and are involved in bacterial pathogen sensing. However, in addition to this principal role, they can also function in multiple host defense processes, including cell phagocytosis and hydrolysis of peptidoglycans (PGNs). In this study, a novel invertebrate short-type PGRP was identified in disk abalone (Haliotis discus discus) designated as AbPGRP. The complete coding sequence of AbPGRP was 534 bp, encoding a 178-amino acid protein with a predicted molecular mass of 20 kDa. The AbPGRP gene had a bipartite arrangement consisting of two exons separated by a single intron. Homology analysis revealed that AbPGRP shares conserved features, including amino acid residues critical for substrate and ion binding as well as for its amidase activity, with homologs of other species. Phylogenetic analysis of AbPGRP revealed that it likely evolved from a common ancestor of invertebrates, having significant homology with other molluscan PGRPs. Recombinant AbPGRP exhibited detectable, dose-dependent PGN-hydrolyzing activity with the presence of Zn(2+), and strong antibacterial activity against Vibrio tapetis, consistent with the functional properties previously reported for PGRPs in other mollusks. Moreover, AbPGRP transcription was induced upon treatment of healthy abalones with bacterial peptidoglycan and lipopolysaccharide, although the expression profiles differed with treatment, suggesting a capacity for discriminating between bacterial pathogens through molecular pattern recognition. Collectively, the findings of this study indicate that AbPGRP is a true homolog of invertebrate PGRPs and likely plays an indispensable role in host immunity.

Exposure-dependent control of malaria-induced inflammation in children

In malaria-naïve individuals, Plasmodium falciparum infection results in high levels of parasite-infected red blood cells (iRBCs) that trigger systemic inflammation and fever. Conversely, individuals in endemic areas who are repeatedly infected are often asymptomatic and have low levels of iRBCs, even young children. We hypothesized that febrile malaria alters the immune system such that P. falciparum re-exposure results in reduced production of pro-inflammatory cytokines/chemokines and enhanced anti-parasite effector responses compared to responses induced before malaria. To test this hypothesis we used a systems biology approach to analyze PBMCs sampled from healthy children before the six-month malaria season and the same children seven days after treatment of their first febrile malaria episode of the ensuing season. PBMCs were stimulated with iRBC in vitro and various immune parameters were measured. Before the malaria season, children's immune cells responded to iRBCs by producing pro-inflammatory mediators such as IL-1β, IL-6 and IL-8. Following malaria there was a marked shift in the response to iRBCs with the same children's immune cells producing lower levels of pro-inflammatory cytokines and higher levels of anti-inflammatory cytokines (IL-10, TGF-β). In addition, molecules involved in phagocytosis and activation of adaptive immunity were upregulated after malaria as compared to before. This shift was accompanied by an increase in P. falciparum-specific CD4⁺Foxp3⁻ T cells that co-produce IL-10, IFN-γ and TNF; however, after the subsequent six-month dry season, a period of markedly reduced malaria transmission, P. falciparum–inducible IL-10 production remained partially upregulated only in children with persistent asymptomatic infections. These findings suggest that in the face of P. falciparum re-exposure, children acquire exposure-dependent P. falciparum–specific immunoregulatory responses that dampen pathogenic inflammation while enhancing anti-parasite effector mechanisms. These data provide mechanistic insight into the observation that P. falciparum–infected children in endemic areas are often afebrile and tend to control parasite replication.

Malaria remains a major cause of disease and death worldwide. When mosquitoes infect people with malaria parasites for the first time, the parasite rapidly multiplies in the blood and the body responds by producing molecules that cause inflammation and fever, and sometimes the infection progresses to life-threatening disease. However, in regions where people are repeatedly infected with malaria parasites, most infections do not cause fever and parasites often do not multiply uncontrollably. For example, in Mali where this study was conducted, children are infected with malaria parasites ≥100 times/year but only get malaria fever ∼2 times/year and often manage to control parasite numbers in the blood. To understand these observations we collected immune cells from the blood of healthy children before the malaria season and 7 days after malaria fever. We simulated malaria infection at these time points by exposing the immune cells to malaria parasites in a test-tube. We found that re-exposing immune cells to parasites after malaria fever results in reduced expression of molecules that cause fever and enhanced expression of molecules involved in parasite killing. These findings help explain how the immune system prevents fever and controls malaria parasite growth in children who are repeatedly infected with malaria parasites.

Virulent Type A Francisella tularensis actively suppresses cytokine responses in human monocytes

BACKGROUND

Human monocyte inflammatory responses differ between virulent and attenuated Francisella infection.

RESULTS

A mixed infection model showed that the virulent F. tularensis Schu S4 can attenuate inflammatory cytokine responses to the less virulent F. novicida in human monocytes.

CONCLUSION

F. tularensis dampens inflammatory response by an active process.

SIGNIFICANCE

This suppression may contribute to enhanced pathogenicity of F. tularensis. Francisella tularensis is a Gram-negative facultative bacterium that can cause the disease tularemia, even upon exposure to low numbers of bacteria. One critical characteristic of Francisella is its ability to dampen or subvert the host immune response. Previous work has shown that monocytes infected with highly virulent F. tularensis subsp. tularensis strain Schu S4 responded with a general pattern of quantitatively reduced pro-inflammatory signaling pathway genes and cytokine production in comparison to those infected with the less virulent related F. novicida. However, it has been unclear whether the virulent Schu S4 was merely evading or actively suppressing monocyte responses. By using mixed infection assays with F. tularensis and F. novicida, we show that F. tularensis actively suppresses monocyte pro-inflammatory responses. Additional experiments show that this suppression occurs in a dose-dependent manner and is dependent upon the viability of F. tularensis. Importantly, F. tularensis was able to suppress pro-inflammatory responses to earlier infections with F. novicida. These results lend support that F. tularensis actively dampens human monocyte responses and this likely contributes to its enhanced pathogenicity.

Immunization alters body odor

Infections have been shown to alter body odor. Because immune activation accompanies both infection and immunization, we tested the hypothesis that classical immunization might similarly result in the alteration of body odors detectable by trained biosensor mice. Using a Y-maze, we trained biosensor mice to distinguish between urine odors from rabies-vaccinated (RV) and unvaccinated control mice. RV-trained mice generalized this training to mice immunized with the equine West Nile virus (WNV) vaccine compared with urine of corresponding controls. These results suggest that there are similarities between body odors of mice immunized with these two vaccines. This conclusion was reinforced when mice could not be trained to directly discriminate between urine odors of RV- versus WNV-treated mice. Next, we trained biosensor mice to discriminate the urine odors of mice treated with lipopolysaccharide (LPS; a general elicitor of innate immunological responses) from the urine of control mice. These LPS-trained biosensors could distinguish between the odors of LPS-treated mouse urine and RV-treated mouse urine. Finally, biosensor mice trained to distinguish between the odors of RV-treated mouse urine and control mouse urine did not generalize this training to discriminate between the odors of LPS-treated mouse urine and control mouse urine. From these experiments, we conclude that: (1) immunization alters urine odor in similar ways for RV and WNV immunizations; and (2) immune activation with LPS also alters urine odor but in ways different from those of RV and WNV.

Glucose and lipopolysaccharide regulate proatherogenic cytokine release from mononuclear cells in polycystic ovary syndrome

Women with polycystic ovary syndrome (PCOS) have chronic low-grade inflammation, which can increase the risk of atherogenesis. We examined the effect of glucose ingestion and lipopolysaccharide (LPS) on markers of proatherogenic inflammation in the mononuclear cells (MNC) and plasma of women with PCOS. Sixteen women with PCOS (8 lean, 8 obese) and 15 weight-matched controls (8 lean, 7 obese) underwent a 3-h oral glucose tolerance test (OGTT). Interleukin-6 (IL-6) and interleukin-1β (IL-1β) release from MNC cultured in the presence of LPS and plasma IL-6, C-reactive protein (CRP), and soluble vascular adhesion molecule-1 (sVCAM-1) were measured from blood samples drawn while fasting and 2h after glucose ingestion. Truncal fat was measured by dual-energy absorptiometry (DEXA). Lean women with PCOS and obese controls failed to suppress LPS-stimulated IL-6 and IL-1β release from MNC after glucose ingestion. In contrast, obese women with PCOS suppressed these MNC-derived cytokines under the same conditions. In response to glucose ingestion, plasma IL-6 and sVCAM-1 increased and CRP suppression was attenuated in both PCOS groups and obese controls compared with lean controls. Fasting plasma IL-6 and CRP correlated positively with percentage of truncal fat. The absolute change in plasma IL-6 correlated positively with testosterone. We conclude that glucose ingestion promotes proatherogenic inflammation in PCOS with a systemic response that is independent of obesity. Based on the suppressed MNC-derived cytokine responses suggestive of LPS tolerance, chronic low-grade inflammation may be more profound in obese women with PCOS. Excess abdominal adiposity and hyperandrogenism may contribute to atherogenesis in PCOS.

all-trans-retinoic acid improves immunocompetence in a murine model of lipopolysaccharide-induced immunosuppression

Secondary infections due to post-sepsis immunosuppression are a major cause of death in patients with sepsis. Strategies aimed at restoring immune functions offer a new perspective in the treatment of sepsis. In the present study, we used LPS (lipopolysaccharide)-immunosuppressed mice to analyse the effects of ATRA (all-trans retinoic acid) on different immune parameters. The IS (immunocompromised) group had decreased lymphocyte and increased MDSC (myeloid-derived suppressor cell) counts in lymph nodes. They also had an impaired in vitro T-cell proliferation, mediated by MDSCs. ATRA administration restored T-cell proliferation, which was associated with a decreased number of live MDSCs. The IS group treated with ATRA had an increased number of CD4+ and CD8+ T-cells. ATRA partially improved the primary humoral immune response, even when immunosuppression was established first and ATRA was administered subsequently. Our results demonstrate that ATRA restores immunocompetence by modulating the number of leucocytes and the survival of MDSCs, and thus represents an additional potential strategy in the treatment of the immunosuppressive state of sepsis.

Towards clinical applications of anti-endotoxin antibodies; a re-appraisal of the disconnect

Endotoxin is a potent mediator of a broad range of patho-physiological effects in humans. It is present in all Gram negative (GN) bacteria. It would be expected that anti-endotoxin therapies, whether antibody based or not, would have an important adjuvant therapeutic role along with antibiotics and other supportive therapies for GN infections. Indeed there is an extensive literature relating to both pre-clinical and clinical studies of anti-endotoxin antibodies. However, the extent of disconnect between the generally successful pre-clinical studies versus the failures of the numerous large clinical trials of antibody based and other anti-endotoxin therapies is under-appreciated and unexplained. Seeking a reconciliation of this disconnect is not an abstract academic question as clinical trials of interventions to reduce levels of endotoxemia levels are ongoing. The aim of this review is to examine new insights into the complex relationship between endotoxemia and sepsis in an attempt to bridge this disconnect. Several new factors to consider in this reappraisal include the frequency and types of GN bacteremia and the underlying mortality risk in the various study populations. For a range of reasons, endotoxemia can no longer be considered as a single entity. There are old clinical trials which warrant a re-appraisal in light of these recent advances in the understanding of the structure-function relationship of endotoxin. Fundamentally however, the disconnect not only remains, it has enlarged.

Does prior sepsis alter subsequent circadian and sickness behaviour response to lipopolysaccharide treatment in mice?

Previous data has shown that prior history of immune challenge may affect central and behavioural responses to subsequent immune challenge, either leading to exaggerated responses via priming mechanisms or lessened responses via endotoxin tolerance. In this set of experiments we have examined how previously lipopolysaccharide (LPS)-induced sepsis shapes the response to subsequent treatment with lower dose LPS. After treatment with LPS (5 mg/kg) or saline mice were allowed to recover for 3-4 months before being challenged with a lower dose of LPS (100 μg/kg) for assessment of sickness behaviours. Performance on the open field test and the tail suspension test was assessed, and no evidence was found that prior sepsis altered sickness or depressive-like behaviour following LPS treatment. We then examined the responsiveness of the circadian system of mice to LPS. We found that in control animals, LPS induced a significant phase delay of the behavioural rhythm and that this was not the case in post-septic animals (4-6 weeks after sepsis), indicating that prior sepsis alters the responsivity of the circadian system to subsequent immune challenge. We further assessed the induction of the immediate early genes c-Fos and EGR1 in the hippocampus and the suprachiasmatic nucleus (SCN; the master circadian pacemaker) by LPS in control or post-septic animals, and found that post-septic animals show elevated expression in the hippocampus but not the SCN. These data suggest that previous sepsis has some effect on behavioural and molecular responses to subsequent immune challenge in mice.

Lung protective ventilation induces immunotolerance and nitric oxide metabolites in porcine experimental postoperative sepsis

Low tidal volume ventilation is beneficial in patients with severe pulmonary dysfunction and would, in theory, reduce postoperative complications if implemented during routine surgery. The study aimed to investigate whether low tidal volume ventilation and high positive end-expiratory pressure (PEEP) in a large animal model of postoperative sepsis would attenuate the systemic inflammatory response and organ dysfunction. Thirty healthy pigs were randomized to three groups: Group Prot-7h, i.e. protective ventilation for 7 h, was ventilated with a tidal volume of 6 mL x kg^-1 for 7 h; group Prot-5h, i.e. protective ventilation for 5 h, was ventilated with a tidal volume of 10 mL x kg^-1 for 2 h, after which the group was ventilated with a tidal volume of 6 mL x kg^-1; and a control group that was ventilated with a tidal volume of 10 mL x kg^-1 for 7 h. In groups Prot-7h and Prot-5h PEEP was 5 cmH₂O for 2 h and 10 cmH₂O for 5 h. In the control group PEEP was 5 cmH₂O for the entire experiment. After surgery for 2 h, postoperative sepsis was simulated with an endotoxin infusion for 5 h. Low tidal volume ventilation combined with higher PEEP led to lower levels of interleukin 6 and 10 in plasma, higher PaO₂/FiO2, better preserved functional residual capacity and lower plasma troponin I as compared with animals ventilated with a medium high tidal volume and lower PEEP. The beneficial effects of protective ventilation were seen despite greater reductions in cardiac index and oxygen delivery index. In the immediate postoperative phase low V_T ventilation with higher PEEP was associated with reduced ex vivo plasma capacity to produce TNF-α upon endotoxin stimulation and higher nitrite levels in urine. These findings might represent mechanistic explanations for the attenuation of systemic inflammation and inflammatory-induced organ dysfunction.

The cytokine mRNA increase induced by withdrawal from chronic ethanol in the sterile environment of brain is mediated by CRF and HMGB1 release

BACKGROUND

Many neurobiological factors may initiate and sustain alcoholism. Recently, dysregulation of the neuroimmune system by chronic ethanol (CE) has implicated Toll-like receptor 4 (TLR4) activation. Even though TLR4s are linked to CE initiation of brain cytokine mRNAs, the means by which CE influences neuroimmune signaling in brain in the absence of infection remains uncertain. Therefore, the hypothesis is tested that release of an endogenous TLR4 agonist, high-mobility group box 1 (HMGB1) and/or corticotropin-releasing factor (CRF) during CE withdrawal are responsible for CE protocols increasing cytokine mRNAs.

METHODS

Acute ethanol (EtOH; 2.75 g/kg) and acute lipopolysaccharide (LPS; 250 μg/kg) dosing on cytokine mRNAs are first compared. Then, the effects of chronic LPS exposure (250 μg/kg for 10 days) on cytokine mRNAs are compared with changes induced by CE protocols (15 days of continuous 7% EtOH diet [CE protocol] or 3 intermittent 5-day cycles of 7% EtOH diet [CIE protocol]). Additionally, TLR4, HMGB1, and downstream effector mRNAs are assessed after CE, CIE, and chronic LPS. To test whether HMGB1 and/or CRF support the CE withdrawal increase in cytokine mRNAs, the HMGB1 antagonists, glycyrrhizin and ethyl pyruvate, and a CRF1 receptor antagonist (CRF1RA) are administered during 24 hours of CE withdrawal.

RESULTS

While cytokine mRNAs were not increased following acute EtOH, acute LPS increased all cytokine mRNAs 4 hours after injection. CE produced no change in cytokine mRNAs prior to CE removal; however, the CE and CIE protocols increased cytokine mRNAs by 24 hours after withdrawal. In contrast, chronic LPS produced no cytokine mRNA changes 24 hours after LPS dosing. TLR4 mRNA was elevated 24 hours following both CE protocols and chronic LPS exposure. While chronic LPS had no effect on HMGB1 mRNA, withdrawal from CE protocols significantly elevated HMGB1 mRNA. Systemic administration of HMGB1 antagonists or a CRF1RA significantly reduced the cytokine mRNA increase following CE withdrawal. The CRF1RA and the HMGB1 antagonist, ethyl pyruvate, also reduced the HMGB1 mRNA increase that followed CE withdrawal.

CONCLUSIONS

By blocking HMGB1 or CRF action during CE withdrawal, evidence is provided that HMGB1 and CRF release are critical for the CE withdrawal induction of selected brain cytokine mRNAs. Consequently, these results clarify a means by which withdrawal from CE exposure activates neuroimmune function in the sterile milieu of brain.

Dehydroepiandrosterone and metyrapone partially restore the adaptive humoral and cellular immune response in endotoxin immunosuppressed mice

Prior exposure to endotoxins renders the host temporarily refractory to subsequent endotoxin challenge (endotoxin tolerance). Clinically, this state has also been pointed out as the initial cause of the non-specific humoral and cellular immunosuppression described in these patients. We recently demonstrated the restoration of immune response with mifepristone (RU486), a receptor antagonist of glucocorticoids. Here we report the treatment with other modulators of glucocorticoids, i.e. dehydroepiandrosterone (DHEA), a hormone with anti-glucocorticoid properties, or metyrapone (MET) an inhibitor of corticosterone synthesis. These drugs were able to partially, but significantly, restore the humoral immune response in immunosuppressed mice. A significant recovery of proliferative responsiveness was also observed when splenocytes were obtained from DHEA- or MET-treated immunosuppressed mice. In addition, these treatments restored the hypersensitivity response in immunosuppressed mice. Finally, although neither DHEA nor MET improved the reduced CD4 lymphocyte count in spleen from immunosuppressed mice, both treatments promoted spleen architecture reorganization, partially restoring the distinct cellular components and their localization in the spleen. The results from this study indicate that DHEA and MET could play an important role in the restoration of both adaptive humoral and cellular immune response in LPS-immunosuppressed mice, reinforcing the concept of a central involvement of endogenous glucocorticoids on this phenomenon.

Effects of Pseudomonas aeruginosa mannose-sensitive hemagglutinin (PA-MSHA) pretreatment on septic rats

To evaluate the effects of Pseudomonas aeruginosa mannose-sensitive hemagglutinin (PA-MSHA) injection on the survival rate of rats post cecal ligation and puncture (CLP), Sprague-Dawley (SD) rats were subcutaneously injected with 0.125 ml, 0.25 ml or 0.5 ml PA-MSHA for 8 days or 16 days before CLP. The survival rate and physiological appearance of rats in each group were monitored daily post CLP. The expression of Toll-like receptor 4 (TLR4) and cytokines related to inflammation was evaluated. We found that the 0.5 ml-8d (0.5 ml PA-MSHA injected for 8 days) group had the highest 7-day survival rate (91.7%), which was significantly improved compared with the CLP-only group (33.3%). Furthermore, our results showed that PA-MSHA effectively increased serum pro-inflammatory mediators (TNF-α, IL-1β and IL-6) at the early stage (8 days) but increased anti-inflammatory mediators (IL-4 and IL-10) at the late stage (16 days). PA-MSHA significantly up-regulated the mRNA expression of TLR4 at 8 and 16 days. After PA-MSHA pretreatment, CLP had no marked effect on the levels of most inflammatory factors. To explore potential protective mechanisms of PA-MSHA against CLP, we examined the effect of PA-MSHA on murine macrophage-like RAW264.7 cells and found that PA-MSHA induced endotoxin tolerance. In conclusion, this study suggested that precisely controlling the dosage and time of PA-MSHA administration can effectively increase the rat survival rate post CLP, which may be mediated through regulating inflammatory mediators and inducing endotoxin tolerance.

Genome wide transcriptome analysis of dendritic cells identifies genes with altered expression in psoriasis

Activation of dendritic cells by different pathogens induces the secretion of proinflammatory mediators resulting in local inflammation. Importantly, innate immunity must be properly controlled, as its continuous activation leads to the development of chronic inflammatory diseases such as psoriasis. Lipopolysaccharide (LPS) or peptidoglycan (PGN) induced tolerance, a phenomenon of transient unresponsiveness of cells to repeated or prolonged stimulation, proved valuable model for the study of chronic inflammation. Thus, the aim of this study was the identification of the transcriptional diversity of primary human immature dendritic cells (iDCs) upon PGN induced tolerance. Using SAGE-Seq approach, a tag-based transcriptome sequencing method, we investigated gene expression changes of primary human iDCs upon stimulation or restimulation with Staphylococcus aureus derived PGN, a widely used TLR2 ligand. Based on the expression pattern of the altered genes, we identified non-tolerizeable and tolerizeable genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (Kegg) analysis showed marked enrichment of immune-, cell cycle- and apoptosis related genes. In parallel to the marked induction of proinflammatory mediators, negative feedback regulators of innate immunity, such as TNFAIP3, TNFAIP8, Tyro3 and Mer are markedly downregulated in tolerant cells. We also demonstrate, that the expression pattern of TNFAIP3 and TNFAIP8 is altered in both lesional, and non-lesional skin of psoriatic patients. Finally, we show that pretreatment of immature dendritic cells with anti-TNF-α inhibits the expression of IL-6 and CCL1 in tolerant iDCs and partially releases the suppression of TNFAIP8. Our findings suggest that after PGN stimulation/restimulation the host cell utilizes different mechanisms in order to maintain critical balance between inflammation and tolerance. Importantly, the transcriptome sequencing of stimulated/restimulated iDCs identified numerous genes with altered expression to date not associated with role in chronic inflammation, underlying the relevance of our in vitro model for further characterization of IFN-primed iDCs.

Genome-wide transcriptional analysis of differentially expressed genes in flagellin-pretreated mouse corneal epithelial cells in response to Pseudomonas aeruginosa: involvement of S100A8/A9

We previously showed that pre-exposure of the cornea to Toll-like receptor 5 ligand flagellin induces profound mucosal innate protection against infections by modifying gene expression. Taking advantage of easily procurable epithelial cell population, this study is the first report to use genome-wide cDNA microarray approach to document genes associated with flagellin-induced protection against Pseudomonas aeruginosa in corneal epithelial cells (CECs). Infection altered the expression of 675 genes (497 up and 178 down), while flagellin pretreatment followed by infection resulted in a great increase in 890 gene upregulated and 37 genes downregulated. Comparing these two groups showed 209 differentially expressed genes (157 up, 52 down). Notably, among 114 genes categorized as defense related, S100A8/A9 are the two most highly induced genes by flagellin, and their expression in the corneal was confirmed by realtime PCR and immunohistochemistry. Neutralization of S100A8 and, to a less extent, A9, resulted in significantly increased bacterial burden and severe keratitis. Collectively, our study identifies many differentially expressed genes by flagellin in CECs in response to Pseudomonas. These novel gene expression signatures provide new insights and clues into the nature of protective mechanisms established by flagellin and new therapeutic targets for reducing inflammation and for controlling microbial infection.

Lactobacillus plantarum MYL26 induces endotoxin tolerance phenotype in Caco-2 cells

BACKGROUND

Crohn's disease and ulcerative colitis are the major types of chronic inflammatory bowel disease occurring in the colon and small intestine. A growing body of research has proposed that probiotics are able to attenuate the inflammatory symptoms of these diseases in vitro and in vivo. However, the mechanism of probiotic actions remains unclear.

RESULTS

Our results suggested Lactobacillus plantarum MYL26 inhibited inflammation in Caco-2 cells through regulation of gene expressions of TOLLIP, SOCS1, SOCS3, and IκBα, rather than SHIP-1 and IRAK-3.

CONCLUSIONS

We proposed that live/ heat-killed Lactobacillus plantarum MYL26 and bacterial cell wall extract treatments impaired TLR4-NFκb signal transduction through Tollip, SOCS-1 and SOCS-3 activation, thus inducing LPS tolerance. Our findings suggest that either heat-killed probiotics or probiotic cell wall extracts are able to attenuate inflammation through pathways similar to that of live bacteria.

Various roles of astrocytes during recovery from repeated exposure to different doses of lipopolysaccharide

Previous studies have demonstrated that the outcomes associated with neuroinflammation induced by intraperitoneal injection of lipopolysaccharide (LPS) at different dosages vary and either resolve or result in sepsis. The mechanisms underlying differential recoveries from varying doses of LPS are unclear. Additionally, changes in recovery involving chronic or continuous systemic inflammatory responses remain unclear. The present experiments were designed to evaluate the effects of systemic inflammation induced by repeated intraperitoneal injection of LPS at different doses on cognitive impairment. These experiments were also designed to investigate the roles of microglia and astrocytes in systemic inflammation and confirm the mechanisms that influence these processes. Kunming mice were given intraperitoneal injections of LPS at either 5mg/kg or 10mg/kg or saline for 7 consecutive days. Following the 7-day course of injections, a number of mice were kept undisturbed in their home cage for 30 days (30-day recovery), and other mice were similarly kept for 90 days (90-day recovery). The results revealed that the cognitive and physiological changes induced by 5mg/kg LPS included weight loss, impairments in spatial learning and memory, phenotypic changes in glia cells, and altered levels of pro-inflammatory cytokines; all of which were reversible. A potential recovery mechanism involves a neuroprotective function of activated astrocytes that secreted glial-derived neurotrophic factor (GDNF) following 30-day recovery. The changes induced by 10mg/kg LPS included weight loss, phenotypic changes in glia cells, and altered levels of pro-inflammatory cytokines were also reversible; however, a longer recovery was required (90 days). Although 10mg/kg LPS-induced neuroinflammation was reversible, the associated impairments in spatial learning and memory were permanent. A potential mechanism underlying permanent damage associated with 10mg/kg LPS involves the role of the activated astrocytes changing from neuroprotection to destruction, which is mediated by increased pro-inflammatory cytokines in more serious neuroinflammation.

Mitogen-activated protein kinase phosphatase 1 disrupts proinflammatory protein synthesis in endotoxin-adapted monocytes

Autotoxic production of proinflammatory mediators during early sepsis induces excessive inflammation, and their later suppression may limit the immune response. We previously reported that sepsis differentially represses transcription and translation of tumor necrosis factor alpha (TNF-α) and interleukin 1β (IL-1β) to reprogram sepsis inflammation. This switch is gene specific and plays a crucial role in the clinically relevant syndrome of endotoxin adaptation/tolerance, multiorgan failure, and poor sepsis outcome. To further define the mechanisms responsible for translation disruption that follows inflammation induction, we used THP-1 human promonocytes as a model of Toll-like receptor 4 (TLR4) responses found in sepsis. We showed that phosphorylation-dependent activation of p38 mitogen-activated protein kinase (MAPK) and translation disruption of TNF-α and IL-6 follow increased MAPK phosphatase 1 (MKP-1) expression and that MKP-1 knockdown rephosphorylates p38 and restores the capacity to translate TNF-α and IL-6 mRNAs. We also observed that the RNA-binding protein motif 4 (RBM4), a p38 MAPK target, accumulates in an unphosphorylated form in the cytosol in endotoxin-adapted cells, suggesting that dephosphorylated RBM4 may function as a translational repressor. Moreover, MKP-1 knockdown promotes RBM4 phosphorylation, blocks its transfer from the nucleus to the cytosol, and reverses translation repression. We also found that microRNA 146a (miR-146a) knockdown prevents and miR-146a transfection induces MKP-1 expression, which lead to increases or decreases in TNF-α and IL-6 translation, respectively. We conclude that a TLR4-, miR-146a-, p38 MAPK-, and MKP-1-dependent autoregulatory pathway regulates the translation of proinflammatory genes during the acute inflammatory response by spatially and temporally modifying the phosphorylation state of RBM4 translational repressor protein.

Combined in silico, in vivo, and in vitro studies shed insights into the acute inflammatory response in middle-aged mice

We combined in silico, in vivo, and in vitro studies to gain insights into age-dependent changes in acute inflammation in response to bacterial endotoxin (LPS). Time-course cytokine, chemokine, and NO₂^−/NO₃⁻ data from “middle-aged” (6–8 months old) C57BL/6 mice were used to re-parameterize a mechanistic mathematical model of acute inflammation originally calibrated for “young” (2–3 months old) mice. These studies suggested that macrophages from middle-aged mice are more susceptible to cell death, as well as producing higher levels of pro-inflammatory cytokines, vs. macrophages from young mice. In support of the in silico-derived hypotheses, resident peritoneal cells from endotoxemic middle-aged mice exhibited reduced viability and produced elevated levels of TNF-α, IL-6, IL-10, and KC/CXCL1 as compared to cells from young mice. Our studies demonstrate the utility of a combined in silico, in vivo, and in vitro approach to the study of acute inflammation in shock states, and suggest hypotheses with regard to the changes in the cytokine milieu that accompany aging.

Endogenous HMGB1 is required in endotoxin tolerance

BACKGROUND

High-mobility group box 1 protein (HMGB1), a downstream inflammatory response modifier in sepsis and endotoxemia, alters endotoxin tolerance by affecting cellular hyporesponsiveness and tumor necrosis factor α and interleukin 1 production.

OBJECTIVE

Endogenous HMGB1 signaling mechanisms during low-dose lipopolysaccharide (LPS)-induced endotoxin tolerance were investigated.

METHODS

BALB/c mice were preconditioned with either 0.1 mL low-dose LPS (0.2 mg/kg) or phosphate-buffered saline (PBS) (control) followed by treatment with three consecutive injections of anti-HMGB1, IgY (an nonspecific antibody), or PBS, at 2, 12, and 22 h, respectively, Mice were then subjected to 0.1 mL high-dose LPS (10 mg/kg) or PBS at 24 h. Serum and hepatic tissue samples were obtained 1 or 3 h after final treatments. Signaling mechanisms were further investigated in the serum and hepatic tissues of mice preconditioned with 0.1 mL HMGB1 (1 mg/kg), low-dose LPS (0.2 mg/kg), or PBS for 1 h, and then high-dose LPS treatment for 3 h.

RESULTS

The signaling mechanisms involved in low-dose LPS preconditioning required enhanced endogenous HMGB1 expression and secretion. Neutralizing endogenous HMGB1 with anti-HMGB1 antibodies following low-dose LPS preconditioning altered endotoxin tolerance by increasing serum tumor necrosis factor α, reducing hepatic interleukin-1R-associated kinase M expression, and partially restoring nuclear factor κB in vivo. The translocation from nucleus to cytoplasm of endogenous HMGB1 in RAW264.7 cells was also observed during low-dose LPS-induced endotoxin tolerance.

CONCLUSIONS

Increased interleukin-1R-associated kinase M and decreased nuclear factor κB activity in endotoxin tolerance is associated with endogenous HMGB1 expression after low-dose LPS preconditioning. These findings provide a basis for a better mechanistic understanding and the development of safer clinical therapeutics utilizing induced endotoxin tolerance.