Differential ex vivo and in vivo endotoxin tolerance kinetics following human endotoxemia*:

Induction of endotoxin tolerance in murine monocyte and macrophage cell populations - optimal LPS dose and compartment-specific reversal by β-glucan

Beta-glucans, naturally present in foods like wheat, mushrooms, and yeast, have shown potential in reversing immunosuppression. However, the existing evidence solely relies on ex vivo studies assessing direct effects of β-glucans on macrophages. To investigate whether such effects also occur after their oral administration, this study first systematically examined the immunosuppressive effects of LPS in mice. Subsequently, we assessed the ability of yeast-derived whole β-glucan particles (yWGP), administered through the diet, to counteract LPS-induced immunological tolerance. Immunosuppression following intraperitoneal administration of 20, 200, or 2000 μg kg-1 LPS was demonstrated by reduced TNF-α and IL-6 release upon ex vivo LPS stimulation of immune cells harvested from the peritoneal fluid, spleen, and bone marrow. Immunosuppression in blood was detected only after 200 and 2000 μg kg-1 LPS. LPS tolerance extended to heterologous stimuli (PAM3Cys, heat-killed Pseudomonas aeruginosa), indicating cross-tolerance. Due to animal discomfort at 2000 μg kg-1 LPS, as evidenced by a significantly enhanced clinical severity score, a dose of 200 μg kg-1 LPS was selected for the follow-up trial. In this experiment, mice fed a yWGP-supplemented diet for two weeks prior to LPS administration showed effective reversal of LPS tolerance, reflected by restored TNF-α levels in peritoneal cells but not in other monocyte- and macrophage-containing cell populations. Together, these studies demonstrate that peritoneal administration of 200 μg kg-1 LPS induced ex vivo LPS tolerance in all immunological organs studied, without significantly compromising animal welfare. The selective efficacy of dietary β-glucans to counteract immunosuppression, which is often observed in vulnerable and immunocompromised patient populations, warrants further clinical evaluation.

SARS-CoV-2 envelope protein regulates innate immune tolerance

Severe COVID-19 often leads to secondary infections and sepsis that contribute to long hospital stays and mortality. However, our understanding of the precise immune mechanisms driving severe complications after SARS-CoV-2 infection remains incompletely understood. Here, we provide evidence that the SARS-CoV-2 envelope (E) protein initiates innate immune inflammation, via toll-like receptor 2 signaling, and establishes a sustained state of innate immune tolerance following initial activation. Monocytes in this tolerant state exhibit reduced responsiveness to secondary stimuli, releasing lower levels of cytokines and chemokines. Mice exposed to E protein before secondary lipopolysaccharide challenge show diminished pro-inflammatory cytokine expression in the lung, indicating that E protein drives this tolerant state in vivo. These findings highlight the potential of the SARS-CoV-2 E protein to induce innate immune tolerance, contributing to long-term immune dysfunction that could lead to susceptibility to subsequent infections, and uncovers therapeutic targets aimed at restoring immune function following SARS-CoV-2 infection.

Endotoxin tolerance and trained immunity: breaking down immunological memory barriers

For decades, innate immune cells were considered unsophisticated first responders, lacking the adaptive memory of their T and B cell counterparts. However, mounting evidence demonstrates the surprising complexity of innate immunity. Beyond quickly deploying specialized cells and initiating inflammation, two fascinating phenomena - endotoxin tolerance (ET) and trained immunity (TI) - have emerged. ET, characterized by reduced inflammatory response upon repeated exposure, protects against excessive inflammation. Conversely, TI leads to an enhanced response after initial priming, allowing the innate system to mount stronger defences against subsequent challenges. Although seemingly distinct, these phenomena may share underlying mechanisms and functional implications, blurring the lines between them. This review will delve into ET and TI, dissecting their similarities, differences, and the remaining questions that warrant further investigation.

Myeloid-Derived Suppressor-like Cells as a Prognostic Marker in Critically Ill Patients: Insights from Experimental Endotoxemia and Intensive Care Patients

Patients admitted to the intensive care unit (ICU) often experience endotoxemia, nosocomial infections and sepsis. Polymorphonuclear and monocytic myeloid-derived suppressor cells (PMN-MDSCs and M-MDSCs) can have an important impact on the development of infectious diseases, but little is known about their potential predictive value in critically ill patients. Here, we used unsupervised flow cytometry analyses to quantify MDSC-like cells in healthy subjects challenged with endotoxin and in critically ill patients admitted to intensive care units and at risk of developing infections. Cells phenotypically similar to PMN-MDSCs and M-MDSCs increased after endotoxin challenge. Similar cells were elevated in patients at ICU admission and normalized at ICU discharge. A subpopulation of M-MDSC-like cells expressing intermediate levels of CD15 (CD15int M-MDSCs) was associated with overall mortality (p = 0.02). Interestingly, the high abundance of PMN-MDSCs and CD15int M-MDSCs was a good predictor of mortality (p = 0.0046 and 0.014), with area under the ROC curve for mortality of 0.70 (95% CI = 0.4-1.0) and 0.86 (0.62-1.0), respectively. Overall, our observations support the idea that MDSCs represent biomarkers for sepsis and that flow cytometry monitoring of MDSCs may be used to risk-stratify ICU patients for targeted therapy.

CytoSorb hemoperfusion markedly attenuates circulating cytokine concentrations during systemic inflammation in humans in vivo

BACKGROUND

The CytoSorb hemoadsorption device has been demonstrated to be capable of clearing inflammatory cytokines, but has not yet been shown to attenuate plasma cytokine concentrations. We investigated the effects of CytoSorb hemoperfusion on plasma levels of various cytokines using the repeated human experimental endotoxemia model, a highly standardized and reproducible human in vivo model of systemic inflammation and immunological tolerance induced by administration of bacterial lipopolysaccharide (LPS).

METHODS

Twenty-four healthy male volunteers (age 18-35) were intravenously challenged with LPS (a bolus of 1 ng/kg followed by continuous infusion of 0.5 ng/kg/hr for three hours) twice: on day 0 to quantify the initial cytokine response and on day 7 to quantify the degree of endotoxin tolerance. Subjects either received CytoSorb hemoperfusion during the first LPS challenge (CytoSorb group), or no intervention (control group). Plasma cytokine concentrations and clearance rates were determined serially. This study was registered at ClinicalTrials.gov (NCT04643639, date of registration November 24th 2020).

RESULTS

LPS administration led to a profound increase in plasma cytokine concentrations during both LPS challenge days. Compared to the control group, significantly lower plasma levels of tumor necrosis factor (TNF, - 58%, p < 0.0001), interleukin (IL)-6 ( - 71%, p = 0.003), IL-8 ( - 48%, p = 0.02) and IL-10 ( - 26%, p = 0.03) were observed in the CytoSorb group during the first LPS challenge. No differences in cytokine responses were observed during the second LPS challenge.

CONCLUSIONS

CytoSorb hemoperfusion effectively attenuates circulating cytokine concentrations during systemic inflammation in humans in vivo, whereas it does not affect long-term immune function. Therefore, CytoSorb therapy may be of benefit in conditions characterized by excessive cytokine release.

Ex vivo and in vitro Monocyte Responses Do Not Reflect in vivo Immune Responses and Tolerance

Cytokine production by ex vivo (EV)-stimulated leukocytes is commonly used to gauge immune function and frequently proposed to guide immunomodulatory therapy. However, whether EV cytokine production capacity accurately reflects the in vivo (IV) immune status is largely unknown. We investigated relationships between EV monocyte cytokine responses and IV cytokine responses in a large cohort of healthy volunteers using a highly standardized IV model of short-lived LPS-induced systemic inflammation, which captures hallmarks of both hyperinflammation and immunological tolerance. Therefore, 110 healthy volunteers were intravenously challenged with 1 ng/kg LPS twice: on day 0 to determine the extent of the IV (hyper)inflammatory response and on day 7 to determine the degree of IV endotoxin tolerance. Baseline EV monocyte cytokine production capacity was assessed prior to LPS administration. Short-term and long-term EV tolerance was assessed in monocytes isolated 4 h and 7 days after LPS administration, respectively. No robust correlations were observed between baseline EV cytokine production capacity and IV cytokine responses following LPS administration. However, highly robust inverse correlations were observed between IV cytokine responses and EV cytokine responses of monocytes isolated 4 h after IV LPS administration. No correlations between IV and EV tolerance were found. In conclusion, attenuated EV cytokine production capacity reflects ongoing IV inflammation rather than immune suppression. Results of EV assays should be interpreted with caution at the risk of improper use of immuno-stimulatory drugs.

Early IFNβ secretion determines variable downstream IL-12p70 responses upon TLR4 activation

The interleukin-12 (IL-12) family comprises the only heterodimeric cytokines mediating diverse functional effects. We previously reported a striking bimodal IL-12p70 response to lipopolysaccharide (LPS) stimulation in healthy donors. Herein, we demonstrate that interferon β (IFNβ) is a major upstream determinant of IL-12p70 production, which is also associated with numbers and activation of circulating monocytes. Integrative modeling of proteomic, genetic, epigenomic, and cellular data confirms IFNβ as key for LPS-induced IL-12p70 and allowed us to compare the relative effects of each of these parameters on variable cytokine responses. Clinical relevance of our findings is supported by reduced IFNβ-IL-12p70 responses in patients hospitalized with acute severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or chronically infected with hepatitis C (HCV). Importantly, these responses are resolved after viral clearance. Our systems immunology approach defines a better understanding of IL-12p70 and IFNβ in healthy and infected persons, providing insights into how common genetic and epigenetic variation may impact immune responses to bacterial infection.

Functional Transcriptomic Studies of Immune Responses and Endotoxin Tolerance in Early Human Sepsis

BACKGROUND

Limited studies have functionally evaluated the heterogeneity in early ex vivo immune responses during sepsis. Our aim was to characterize early sepsis ex vivo functional immune response heterogeneity by studying whole blood endotoxin responses and derive a transcriptional metric of ex vivo endotoxin response.

METHODS

Blood collected within 24 h of hospital presentation from 40 septic patients was divided into two fractions and incubated with media (unstimulated) or endotoxin. Supernatants and cells were isolated, and responses measured using: supernatant cytokines, lung endothelial permeability after supernatant exposure, and RNA expression. A transcriptomic signature was derived in unstimulated cells to predict the ex vivo endotoxin response. The signature was tested in a separate cohort of 191 septic patients to evaluate for association with clinical outcome. Plasma biomarkers were quantified to measure in vivo host inflammation.

RESULTS

Ex vivo response to endotoxin varied and was unrelated to immunosuppression, white blood cell count, or the causative pathogen. Thirty-five percent of patients demonstrated a minimal response to endotoxin, suggesting early immunosuppression. High ex vivo cytokine production by stimulated blood cells correlated with increased in vitro pulmonary endothelial cell permeability and was associated with attenuated in vivo host inflammation. A four-gene signature of endotoxin response detectable without the need for a functional assay was identified. When tested in a separate cohort of septic patients, its expression was inversely associated with hospital mortality.

CONCLUSIONS

An attenuated ex vivo endotoxin response in early sepsis is associated with greater host in vivo inflammation and a worse clinical outcome.

Protective effects of endotoxin tolerance on peripheral lipopolysaccharide-induced neuroinflammation and dopaminergic neuronal injury

CONTEXT

Parkinson's disease is a common chronic neurodegenerative disease characterized by massive loss of dopaminergic neurons in the substantia nigra. Neuroinflammation has been shown to play an important role in the pathogenesis of neurodegenerative diseases such as Parkinson's disease. The role of immune tolerance in neuroinflammation and neurodegenerative diseases induced by peripheral factors is unclear.

OBJECTIVE

This study established a model of endotoxin tolerance to explore the protective effect of endotoxin tolerance on Parkinson-like changes induced by repeated peripheral injections of high-dose LPS, and to explore its inflammatory mechanism.

MATERIALS AND METHODS

In this study, mice were injected intraperitoneally with low dose (0.5 mg/kg) LPS for 4 days to induce endotoxin tolerance (ET). Then, high-dose (1 mg/kg) LPS was injected continuously intraperitoneally for 4 days to induce Parkinson-like changes. Cytokines were detected by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Activation of microglial cells was detected by protein expression of CD68 and ionized calcium binding adapter molecule 1(Iba-1) by Western blotting and immunofluorescence. Hematoxylin and eosin staining and expression of tyrosine hydroxylase (TH) and dopamine (DA) were used to assess dopaminergic neuronal injury. The open field test and muscle tension test were used to assess behavioral disorders.

RESULTS

As expected, compared with non-ET animals, ET preconditioning significantly reduced the production of inflammatory cytokines in the substantia nigra, inhibited microglial activation, and alleviated the pathological changes of dopaminergic neurons.

CONCLUSIONS

ET may be a promising intervention method for neurodegenerative diseases.HighlightsET was successfully induced by continuous low-dose intraperitoneal LPS injection in mice.ET pretreatment inhibited neuroinflammation in the SN induced by continuous peripheral high doses of LPS.ET pretreatment inhibited continuous peripheral high-dose LPS injection-induced microglial activation in the SN.ET pretreatment decreased LPS-induced functional impairment of dopaminergic neurons.ET reversed the morphological changes of dopaminergic neurons induced by peripheral high-dose LPS.ET pretreatment improved continuous peripheral high-dose LPS injection-induced behavioral impairment.

Differential Effects of Toll-Like Receptor Signaling on the Activation of Immune Responses in the Upper Respiratory Tract

Vaccination through the upper respiratory tract (URT) is highly effective for the prevention of respiratory infectious diseases. Toll-like receptor (TLR)-based adjuvants are immunostimulatory and considered potential adjuvant candidates. However, the patterns of immune response to different TLRs at the URT have not been revealed. In this study, SPF mice were preexposed to TLR agonists intranasally to simulate the status of humans. Inflammatory response to TLR agonists and TLR signal-mediated adaptive immune responses were analyzed. The results revealed that similar to human tonsils, inflammatory response to stimulation with TLR4 or TLR2 agonist was attenuated in agonist-exposed mice but not in mice without this exposure. In contrast, TLR9 or TLR3 agonist preexposure did not affect the inflammatory response to restimulation by matching agonists. For the adaptive immune response, after agonist preexposure the antibody response to antigens adjuvanted with TLR4 or TLR2 agonist was substantially restricted, whereas, both antibody and T cell responses to antigens adjuvanted with TLR9 or TLR3 agonist were activated as robustly as in mice without agonist exposure. Moreover, we demonstrate that the mechanisms underlying the differential activation of TLRs are regulated at the level of TLR expression in innate and adaptive immune cells. These results indicate that TLRs on the cell surface (TLR4 and 2) and in the endolysosomal compartments (TLR9 and 3) display distinct immune response patterns. The findings provide important information for the use of TLR agonists as mucosal adjuvants and enhance our understanding of immune responses to bacterial and viral infections in the respiratory mucosa. IMPORTANCE Agonists of TLRs are potential adjuvant candidates for mucosal vaccination. We demonstrated that the TLR-mediated inflammatory and antibody responses in the URT of SPF mice exposed to extracellular TLR agonists were substantially restricted. In contrast, inflammatory and adaptive immune responses, including B and T cell activation, were not desensitized in mice exposed to intracellular TLR agonists. The distinct responsive patterns of extra and intracellular TLRs regulated at TLR expression in immune cells. The results indicated that TLRs differentially impact the innate and adaptive immune response in the URT, which contributes to the selection of TLR-based mucosal adjuvants and helps understand the difference between the immune response in bacterial and viral infections.

A systematic review and meta-analyses of interleukin-1 receptor associated kinase 3 (IRAK3) action on inflammation in in vivo models for the study of sepsis

Background

Interleukin-1 receptor associated kinase 3 (IRAK3) is a critical modulator of inflammation and is associated with endotoxin tolerance and sepsis. Although IRAK3 is known as a negative regulator of inflammation, several studies have reported opposing functions, and the temporal actions of IRAK3 on inflammation remain unclear. A systematic review and meta-analyses were performed to investigate IRAK3 expression and its effects on inflammatory markers (TNF-α and IL-6) after one- or two-challenge interventions, which mimic the hyperinflammatory and immunosuppression phases of sepsis, respectively, using human or animal in vivo models.

Methods

This systematic review and meta-analyses has been registered in the Open Science Framework (OSF) (Registration DOI: 10.17605/OSF.IO/V39UR). A systematic search was performed to identify in vivo studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data was available.

Results

The search identified 7778 studies for screening. After screening titles, abstracts and full texts, a total of 49 studies were included in the systematic review. The review identified significant increase of IRAK3 mRNA and protein expression at different times in humans compared to rodents following one-challenge, whereas the increases of IL-6 and TNF-α protein expression in humans were similar to rodent in vivo models. Meta-analyses confirmed the inhibitory effect of IRAK3 on TNF-α mRNA and protein expression after two challenges.

Conclusions

A negative correlation between IRAK3 and TNF-α expression in rodents following two challenges demonstrates the association of IRAK3 in the immunosuppression phase of sepsis. Species differences in underlying biology affect the translatability of immune responses of animal models to human, as shown by the dissimilarity in patterns of IRAK3 mRNA and protein expression between humans and rodents following one challenge that are further influenced by variations in experimental procedures.

Ex vivo tolerization and M2 polarization of macrophages dampens both pro- and anti-inflammatory cytokine production in response to diabetic wound fluid stimulation

Monocytes/macrophages play a prominent role in cutaneous wound healing. Persistent inflammation in diabetic wounds is associated with the inability of monocytic cells to switch from a phagocytic M1 (classically activated) to an anti-inflammatory, pro-regenerative M2 (alternatively activated) phenotype and as consequence, the proliferative phase of healing does not commence. A targeted cell therapy approach could potentially restore the pathological wound microenvironment through paracrine signalling to enable healing. This study investigated whether in vitro pre-treatment of monocytic (J774.1 A) cells - using a combination of endotoxin-induced immune tolerance (Pam3CSK4) and M2 polarization (IL-4) - could make these cells impervious to the pathological wound microenvironment and enhance the release of anti-inflammatory cytokines/growth factors. The effect of Pam3CSK4-induced tolerance and IL-4-associated polarization was assessed independently and in combination, on the expression of intracellular (flow cytometry) and secreted (ELISA) cytokines (TNF-ɑ, IL-6, IL-10, TGF-β) with and without re-stimulation to define the optimal pre-treatment conditions. Successive pre-treatment approach consisting of endotoxin tolerance followed by IL-4 priming, dampened TNF-ɑ release and induced intracellular TGF-β production upon re-stimulation. To mimic a chronic wound microenvironment, the J774A.1 monocytes were differentiated into macrophages using GM-CSF prior to pre-treatment (optimal condition) and subsequently exposed to diabetic wound fluid. The data demonstrated that in the presence of wound fluid, the successive pre-treatment, promoted M2 polarization (CD206) of monocytic cells and significantly dampened the intracellular production of both pro-inflammatory (TNF-ɑ, IL-6) and anti-inflammatory (IL-10, TGF-β) cytokines.

Systemic inflammation down-regulates glyoxalase-1 expression: an experimental study in healthy males

Background: Hypoxia and inflammation are hallmarks of critical illness, related to multiple organ failure. A possible mechanism leading to multiple organ failure is hypoxia- or inflammation-induced down-regulation of the detoxifying glyoxalase system that clears dicarbonyl stress. The dicarbonyl methylglyoxal (MGO) is a highly reactive agent produced by metabolic pathways such as anaerobic glycolysis and gluconeogenesis. MGO leads to protein damage and ultimately multi-organ failure. Whether detoxification of MGO into D-lactate by glyoxalase functions appropriately under conditions of hypoxia and inflammation is largely unknown. We investigated the effect of inflammation and hypoxia on the MGO pathway in humans in vivo.

Methods: After prehydration with glucose 2.5% solution, ten healthy males were exposed to hypoxia (arterial saturation 80–85%) for 3.5 h using an air-tight respiratory helmet, ten males to experimental endotoxemia (LPS 2 ng/kg i.v.), ten males to LPS+hypoxia and ten males to none of these interventions (control group). Serial blood samples were drawn, and glyoxalase-1 mRNA expression, MGO, methylglyoxal-derived hydroimidazolone-1 (MG-H1), D-lactate and L-lactate levels, were measured serially.

Results: Glyoxalase-1 mRNA expression decreased in the LPS (β (95%CI); -0.87 (-1.24; -0.50) and the LPS+hypoxia groups; -0.78 (-1.07; -0.48) (P<0.001). MGO was equal between groups, whereas MG-H1 increased over time in the control group only (P=0.003). D-Lactate was increased in all four groups. L-Lactate was increased in all groups, except in the control group.

Conclusion: Systemic inflammation downregulates glyoxalase-1 mRNA expression in humans. This is a possible mechanism leading to cell damage and multi-organ failure in critical illness with potential for intervention.

Wearable Patch Heart Rate Variability is An Early Marker of Systemic Inflammation During Experimental Human Endotoxemia

INTRODUCTION

Early diagnosis and treatment can reduce the risk of organ failure and mortality in systemic inflammatory conditions. Heart rate variability (HRV) has potential for early identification of the onset of systemic inflammation, as it may detect changes in sympathetic nervous system activity resulting from the developing inflammatory response before clinical signs appear. With the use of new methodologies, we investigated the onset and kinetics of HRV changes as well as several inflammatory parameters and symptoms during experimental human endotoxemia, a model of systemic inflammation in humans in vivo.

MATERIAL AND METHODS

Healthy volunteers were intravenously administered lipopolysaccharide (LPS, n = 15) or placebo (n = 15). HRV was determined using a wireless wearable device, and parameters low to high frequency (LF:HF) ratio, root mean square of the successive differences (RMSSD), and standard deviation of normal-to-normal R-R intervals (SDNN)were calculated through 1-min-rolling 6-minute windows. Plasma cytokine levels and flu-like symptoms and vital signs were serially assessed.

RESULTS

The increase in LF:HF ratio, reflecting sympathetic predominance, was more pronounced in the LPS group compared to the placebo group, with the difference becoming statistically significant 65 minutes following LPS administration (1.63 [1.42-1.83] vs. 1.28 [1.11-1.44], p = 0.005). Significant between-group differences in RMSSD and SDNN were observed from 127 and 140 minutes post-LPS administration onwards, respectively. Plasma cytokine levels showed significant between-group differences staring 60 minutes post-LPS. For symptom score, heart rate, temperature and diastolic blood pressure, significant differences compared with the placebo group were observed at 90, 118, 120, and 124 minutes post-LPS, respectively.

CONCLUSION

In a controlled human model of systemic inflammation, elevations in the LF:HF ratio followed very shortly after elevations in plasma cytokine levels and preceded onset of flu-like symptoms and alterations in vital signs. HRV may represent a promising non-invasive tool for early detection of a developing systemic inflammatory response.

PARP Traps Rescue the Pro-Inflammatory Response of Human Macrophages in the In Vitro Model of LPS-Induced Tolerance

Secondary infections cause sepsis that lead to patient disability or death. Contact of macrophages with bacterial components (such as lipopolysaccharide—LPS) activates the intracellular signaling pathway downstream of Toll-like receptors (TLR), which initiate an immune proinflammatory response. However, the expression of nuclear factor-kappa B (NF-κB)-dependent proinflammatory cytokines significantly decreases after single high or multiple LPS stimulations. Knowing that poly(ADP-ribose) polymerase-1 (PARP1) serves as a cofactor of NF-κB, we aimed to verify a hypothesis of the possible contribution of PARP1 to the development of LPS-induced tolerance in human macrophages. Using TNF-α mRNA expression as a readout, we demonstrate that PARP1 interaction with the TNF-α promoter, controls macrophage immunoparalysis. We confirm that PARP1 is extruded from the gene promoter, whereas cell pretreatment with Olaparib maintains macrophage responsiveness to another LPS treatment. Furthermore, cell pretreatment with proteasome inhibitor MG132 completely abrogates the effect of Olaparib, suggesting that PARP1 acts with NF-κB in the same regulatory pathway, which controls pro-inflammatory cytokine transcription. Mechanistically, PARP1 trapping allows for the re-rebinding of p65 to the TNF-α promoter in LPS-stimulated cells. In conclusion, PARP traps prevent PARP1 extrusion from the TNF-α promoter upon macrophage stimulation, thereby maintaining chromatin responsiveness of TLR activation, allowing for the re-binding of p65 and TNF-α transcription.

Participation of Monocyte Subpopulations in Progression of Experimental Endotoxemia (EE) and Systemic Inflammation

Systemic inflammation plays a crucial role in formation of various pathological conditions, including sepsis, burns, and traumas. The main effector cells participating in progression of systemic inflammation response and sepsis are monocytes, which regulate both innate and acquired immunity via phagocytosis, synthesis of cytokines and chemokines, antigen presentation, and lymphocyte activation. Thus, the monocytes are considered as a link between innate and acquired immunity. The monocyte subpopulations taken into consideration in the study essentially determine the progression of systemic inflammation and could serve as targets for therapeutic intervention. The complexity of the analysis of pathophysiology of systemic inflammation lies in its high variability conditioned by individual peculiarities of the patients and inflammation progression specifications. To overcome these limitation, model of experimental endotoxemia (EE) is used. The results of EE, in turn, cannot be directly extrapolated on patients with the systemic inflammatory response. This review is dedicated to discussing the role of monocyte subpopulations in progression of systemic inflammation/sepsis and EE.

Rethinking animal models of sepsis - working towards improved clinical translation whilst integrating the 3Rs

Sepsis is a major worldwide healthcare issue with unmet clinical need. Despite extensive animal research in this area, successful clinical translation has been largely unsuccessful.

We propose one reason for this is that, sometimes, the experimental question is misdirected or unrealistic expectations are being made of the animal model.

As sepsis models can lead to a rapid and substantial suffering – it is essential that we continually review experimental approaches and undertake a full harm:benefit impact assessment for each study. In some instances, this may require refinement of existing sepsis models. In other cases, it may be replacement to a different experimental system altogether, answering a mechanistic question whilst aligning with the principles of reduction, refinement and replacement (3Rs).

We discuss making better use of patient data to identify potentially useful therapeutic targets which can subsequently be validated in preclinical systems. This may be achieved through greater use of construct validity models, from which mechanistic conclusions are drawn. We argue that such models could provide equally useful scientific data as face validity models, but with an improved 3Rs impact. Indeed, construct validity models may not require sepsis to be modelled, per se. We propose that approaches that could support and refine clinical translation of research findings, whilst reducing the overall welfare burden on research animals.

Human lipopolysaccharide models provide mechanistic and therapeutic insights into systemic and pulmonary inflammation

Inflammation is a key feature in the pathogenesis of sepsis and acute respiratory distress syndrome (ARDS). Sepsis and ARDS continue to be associated with high mortality. A key contributory factor is the rudimentary understanding of the early events in pulmonary and systemic inflammation in humans, which are difficult to study in clinical practice, as they precede the patient's presentation to medical services. Lipopolysaccharide (LPS), a constituent of the outer membrane of Gram-negative bacteria, is a trigger of inflammation and the dysregulated host response in sepsis. Human LPS models deliver a small quantity of LPS to healthy volunteers, triggering an inflammatory response and providing a window to study early inflammation in humans. This allows biological/mechanistic insights to be made and new therapeutic strategies to be tested in a controlled, reproducible environment from a defined point in time. We review the use of human LPS models, focussing on the underlying mechanistic insights that have been gained by studying the response to intravenous and pulmonary LPS challenge. We discuss variables that may influence the response to LPS before considering factors that should be considered when designing future human LPS studies.

Glucocorticoid receptor sensitivity in early pregnancy in an African American cohort

PROBLEM

Disruption in homeostatic feedback loops between inflammatory mediators and the hypothalamic-pituitary-adrenal (HPA) axis is a key mechanism linking chronic stress to inflammation and adverse health outcomes, including those occurring during pregnancy. In particular, alterations in glucocorticoid sensitivity may occur as a result of chronic stress, including that due to racial discrimination, and may be implicated in the persistent adverse maternal and infant health outcomes experienced by African Americans. While there are a few large-scale studies in human pregnancy that measure both cytokines and HPA axis hormones, to our knowledge, none directly measure glucocorticoid sensitivity at the cellular level, especially in an African American population.

METHOD OF STUDY

We measured the full range of the dexamethasone (DEX) dose-response suppression of TNF-α in first-trimester blood samples from 408 African American women and estimated leukocyte cell type contribution to the production of TNF-α.

RESULTS

The mean (SD) DEX level needed to inhibit TNF-α production by 50% (ie, DEX IC50 ) was 9.8 (5.8) nmol/L. Monocytes appeared to be the main driver of Uninhibited TNF-α production, but monocyte counts explained only 14% of the variation. Monocyte counts were only weakly correlated with the DEX IC50 (r = -.11, P < .05). Moreover, there was no statistically significant correlation between the DEX IC50 and circulating pro-inflammatory (CRP, IL-6, IFN-γ) or anti-inflammatory (IL-10) mediators (P > .05).

CONCLUSION

These findings challenge some prior assumptions and position this comprehensive study of glucocorticoid sensitivity as an important anchor point in the growing recognition of interindividual variation in maternal HPA axis regulation and inflammatory responses.

Protective effect of metformin on a rat model of lipopolysaccharide-induced preeclampsia

Recent in vitro and clinical studies have found that metformin (MET) may play a preventive or therapeutic role in preeclampsia (PE) and may be a candidate drug for the prevention and/or treatment of PE. In this study, we used lipopolysaccharide (LPS) to induce a PE-like rat model and investigated the intervention effect of MET from the perspectives of clinical manifestations, placental morphology, serum marker for placental injury, systemic inflammatory response and oxidative/nitrative stress, and placental nuclear factor-κB (NF-κB) signaling. The results showed that MET improved LPS-induced hypertension, proteinuria, fetal growth restriction (FGR) and stillbirth, alleviated placental injury and decreased maternal serum marker alpha-fetoprotein (MS-AFP) level; MET suppressed LPS-induced TNF-α and IL-6 productions, reduced oxidative/nitrative stress as evidenced by increased superoxide dismutase (SOD) activity, decreased inducible nitric oxide synthase (iNOS) activity, and decreased levels of malondialdehyde (MDA) and nitric oxide (NO); MET inhibited LPS-induced NF-κB activation in placentas. Based on these findings, it can be concluded that MET is beneficial to the PE-like rat model by protecting placentas from injury, suppressing systemic inflammatory response and oxidative/nitrative stress, and inhibiting placental NF-κB signaling pathway. MET is a promising drug for prevention and/or treatment of PE.

A rat model of placental inflammation explains the unexplained elevated maternal serum alpha-fetoprotein associated with adverse pregnancy outcomes

AIM

It has been reported in numerous studies that elevated maternal serum alpha-fetoprotein (MS-AFP) is associated with adverse pregnancy outcomes (APO), such as pre-eclampsia, stillbirth, preterm birth and fetal growth restriction. However, the mechanism linking elevated MS-AFP and APO is obscure. In this study, we tried to explore the mechanism by using pregnant rats.

METHODS

Lipopolysaccharide (LPS) was used to induce placental inflammation in pregnant rats. Maternal serum and placental inflammatory cytokines and placental morphology were used to assess the level of placental inflammation. The incidences of APO and the levels of MS-AFP were evaluated. The expressions of alpha-fetoprotein (AFP) in the related organs and fetal serum AFP levels were detected.

RESULTS

Compared to saline-treated pregnant rats, LPS led to elevated maternal serum and placental inflammatory cytokines and a higher rate of placental inflammation. Lipopolysaccharide resulted in the features of APO and at the same time elevated MS-AFP. Maternal serum alpha-fetoprotein levels were significantly correlated to the evaluation parameters of APO. Lipopolysaccharide did not increase the expressions of AFP in fetal liver, maternal liver and placenta, but reduced the fetal serum AFP levels.

CONCLUSION

The phenomenon that elevated MS-AFP is associated with APO, which has been reported in human pregnancies, is observed in our rat model. Placental inflammation can be the potential cause linking the two manifestations together. Although the source of elevated MS-AFP is not identified, fetal blood circulation is suspected. Our study may provide an animal model for the future studies on this subject.

Children With Noncritical Infections Have Increased Intestinal Permeability, Endotoxemia and Altered Innate Immune Responses

BACKGROUND

Children with critical illness have increased intestinal permeability and a period of immunoparalysis, mediated by elevated circulating endotoxin. Whether children with less severe infections have similar changes is uncertain.

METHODS

We conducted a proof-of-concept pilot study, enrolling children 6-59 months of age hospitalized for noncritical infections (cases, n = 11) and noninfected controls (n = 19). Intestinal permeability was measured by lactulose-mannitol recovery. Plasma endotoxin, blood monocyte and neutrophil immunophenotypes and cytokine elaboration following 24-hour whole-blood culture with antigens targeting distinct innate pathogen recognition receptor signaling pathways were evaluated.

RESULTS

Cases had higher intestinal permeability and plasma endotoxin levels than controls. Among cases versus controls, fewer monocytes expressed human leukocyte antigen DR isotype (HLA-DR) (87.1% vs. 96.4%, P = 0.001), and more expressed CD64 (99.6% vs. 97.6%, P = 0.041). Following zymosan stimulation of whole blood, cases versus controls produced less interleukin 1 beta (IL-1β) (median 1101 vs. 2604 pg/mL, P = 0.048) and tumor necrosis factor alpha (TNF-α) (2342 vs. 5130 pg/mL, P = 0.031). Children with higher (≥0.1 endotoxin unit (EU)/mL) versus lower (<0.1 EU/mL) circulating endotoxin had fewer monocytes expressing CD86 (69.8% vs. 92.4%, P = 0.003) and less expression of CD64 following 24-hour zymosan stimulation (median fluorescence intensity (MFI) 1514 vs. 2196, P = 0.022).

CONCLUSIONS

Children hospitalized with noncritical infections had increased intestinal permeability, endotoxemia and altered monocyte phenotype and function. Collectively, these changes are typical of immunoparalysis seen in children with critical illness and may increase the risk of subsequent infections.

Frontline Science: Endotoxin-induced immunotolerance is associated with loss of monocyte metabolic plasticity and reduction of oxidative burst

Secondary infections are a major complication of sepsis and associated with a compromised immune state, called sepsis-induced immunoparalysis. Molecular mechanisms causing immunoparalysis remain unclear; however, changes in cellular metabolism of leukocytes have been linked to immunoparalysis. We investigated the relation of metabolic changes to antimicrobial monocyte functions in endotoxin-induced immunotolerance, as a model for sepsis-induced immunoparalysis. In this study, immunotolerance was induced in healthy males by intravenous endotoxin (2 ng/kg, derived from Escherichia coli O:113) administration. Before and after induction of immunotolerance, circulating CD14⁺ monocytes were isolated and assessed for antimicrobial functions, including cytokine production, oxidative burst, and microbial (Candida albicans) killing capacity, as well metabolic responses to ex vivo stimulation. Next, the effects of altered cellular metabolism on monocyte functions were validated in vitro. Ex vivo lipopolysaccharide stimulation induced an extensive rewiring of metabolism in naive monocytes. In contrast, endotoxin-induced immunotolerant monocytes showed no metabolic plasticity, as they were unable to adapt their metabolism or mount cytokine and oxidative responses. Validation experiments showed that modulation of metabolic pathways, affected by immunotolerance, influenced monocyte cytokine production, oxidative burst, and microbial (C. albicans) killing in naive monocytes. Collectively, these data demonstrate that immunotolerant monocytes are characterized by a loss of metabolic plasticity and these metabolic defects impact antimicrobial monocyte immune functions. Further, these findings support that the changed cellular metabolism of immunotolerant monocytes might reveal novel therapeutic targets to reverse sepsis-induced immunoparalysis.

Extract from Coriolus versicolor fungus partially prevents endotoxin tolerance development by maintaining febrile response and increasing IL-6 generation

Endotoxin tolerance is defined as a reduced endotoxin-induced fever following repeated injections of lipopolysaccharide (LPS). Clinical examples of endotoxin tolerance include sepsis or cystic fibrosis. This state is characterized by inhibition of pro-inflammatory cytokines production and decrease in nuclear factor-kappa B (NF-κB) activation. Extract from Coriolus versicolor (CV) fungus is classified as a biological response modifier, which exhibits various biological activities, including immunopotentiating properties. The aim of study was to examine the effect of CV extract injection on body core temperature of Wistar rats during LPS-induced endotoxin tolerance. Body temperature was measured using biotelemetry. CV extract was injected intraperitoneally (100 mg kg^-1) 2 h prior to the first LPS peritoneal administration (50 μg/kg). Endotoxin tolerance was induced by three consecutive daily injections of LPS at the same dose. We also investigated the influence of CV extract pre-injection on the properties of peripheral blood mononuclear cells (PBMCs) isolated from LPS-treated rats in response to LPS stimulation ex vivo. PBMCs were isolated 2 h after the first LPS injection. After 24 h pre-incubation, the cells were stimulated with LPS (1 μg ml^-1) for 4 h. Our results revealed that CV extract partially prevents endotoxin tolerance through maintaining febrile response in rats following consecutive exposure to LPS. This state was accompanied by the ability of PBMCs isolated from rats injected with CV extract and LPS to release larger amounts of interleukin 6 and greater NF-κB activation in response to LPS stimulation ex vivo compared with the cells derived from rats injected only with LPS. Data also showed that CV extract augmented mitogenic effect of LPS on PBMCs and caused increase in reactive oxygen species generation. We concluded that CV extract, by a modifying effect on body temperature during endotoxin tolerance, can be consider as the immunostimulating agent, which prevents the non-specific refractoriness described in patients with sepsis or ischemia.

Low interleukin-10 release after ex vivo stimulation of whole blood is associated with persistent organ dysfunction in sepsis: A prospective observational study

BACKGROUND

Sepsis profoundly alters immune homeostasis. Cytokine release after whole blood lipopolysaccharide (LPS)-stimulation reflects cell function across multiple immune cell classes and represents the immune response to LPS. The main goal of this study was to evaluate the prognostic value of ex vivo stimulation of whole blood with LPS in sepsis.

METHODS

Blood was drawn on day 1 and day 7 after admission, and stimulated ex vivo with LPS. Tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-10 were measured with and without stimulation. Our primary outcome measure was the persistence of at least one organ dysfunction at day 7. Organ dysfunction was defined according to the SOFA components by a score ≥ 2.

RESULTS

Forty-nine patients with sepsis from a 21-bed intensive care unit, and 23 healthy volunteers were enrolled. The blood of septic patients was less responsive to ex vivo stimulation with LPS than that of healthy controls at day 1 and 7, as demonstrated by lower TNF-α, IL-1β, IL-6 and IL-10 release. Persistent organ dysfunction was more frequent in patients with lower IL-10 release at day 1 but such an association was not found for pro-inflammatory cytokines. A persistent low IL-10 release at day 7 was also associated with persistent organ dysfunction.

CONCLUSION

These data suggest that the capacity to produce IL-10 in response to whole blood ex vivo stimulation early in sepsis, as well as persistent low IL-10 response over time, may help in prognostication and patient stratification. These results will need to be confirmed in future studies.

The Itaconate Pathway Is a Central Regulatory Node Linking Innate Immune Tolerance and Trained Immunity

Sepsis involves simultaneous hyperactivation of the immune system and immune paralysis, leading to both organ dysfunction and increased susceptibility to secondary infections. Acute activation of myeloid cells induced itaconate synthesis, which subsequently mediated innate immune tolerance in human monocytes. In contrast, induction of trained immunity by β-glucan counteracted tolerance induced in a model of human endotoxemia by inhibiting the expression of immune-responsive gene 1 (IRG1), the enzyme that controls itaconate synthesis. β-Glucan also increased the expression of succinate dehydrogenase (SDH), contributing to the integrity of the TCA cycle and leading to an enhanced innate immune response after secondary stimulation. The role of itaconate was further validated by IRG1 and SDH polymorphisms that modulate induction of tolerance and trained immunity in human monocytes. These data demonstrate the importance of the IRG1-itaconate-SDH axis in the development of immune tolerance and training and highlight the potential of β-glucan-induced trained immunity to revert immunoparalysis.

New frontiers in precision medicine for sepsis-induced immunoparalysis

INTRODUCTION

In the last decade, the sepsis research field has shifted focus from targeting hyperinflammation to reversing sepsis-induced immunoparalysis. Sepsis-induced immunoparalysis is very heterogeneous: the magnitude and the nature of the underlying immune defects differ considerably between patients, but also within individuals over time. Therefore, a 'one-treatment-fits-all' strategy for sepsis-induced immunoparalysis is bound to fail, and an individualized 'precision medicine' approach is required. Such a strategy is nevertheless hampered by the unsuitability of the currently available markers to identify the many immune defects that can manifest in individual patients. Areas covered: We describe the currently available markers for sepsis-induced immunoparalysis and limitations pertaining to their use. Furthermore, future prospects and caveats are discussed, focusing on 'omics' approaches: genomics, transcriptomics, epigenomics, and metabolomics. Finally, we present a contemporary overview of adjuvant immunostimulatory therapies. Expert opinion: The integration of multiple omics techniques offers a systems biology approach which can yield biomarker profiles that accurately and comprehensively gauge the extent and nature of sepsis-induced immunoparalysis. We expect this development to be instrumental in facilitating precision medicine for sepsis-induced immunoparalysis, consisting of the application of targeted immunostimulatory therapies and follow-up measurements to monitor the response to treatment and to titrate or adjust medication.

Exposure of Monocytic Cells to Lipopolysaccharide Induces Coordinated Endotoxin Tolerance, Mitochondrial Biogenesis, Mitophagy, and Antioxidant Defenses

In order to limit the adverse effects of excessive inflammation, anti-inflammatory responses are stimulated at an early stage of an infection, but during sepsis these can lead to deactivation of immune cells including monocytes. In addition, there is emerging evidence that the up-regulation of mitochondrial quality control mechanisms, including mitochondrial biogenesis and mitophagy, is important during the recovery from sepsis and inflammation. We aimed to describe the relationship between the compensatory immune and mitochondrial responses that are triggered following exposure to an inflammatory stimulus in human monocytic cells. Incubation with lipopolysaccharide resulted in a change in the immune phenotype of THP-1 cells consistent with the induction of endotoxin tolerance, similar to that seen in deactivated septic monocytes. After exposure to LPS there was also early evidence of oxidative stress, which resolved in association with the induction of antioxidant defenses and the stimulation of mitochondrial degradation through mitophagy. This was compensated by a parallel up-regulation of mitochondrial biogenesis that resulted in an overall increase in mitochondrial respiratory activity. These observations improve our understanding of the normal homeostatic responses that limit the adverse cellular effects of unregulated inflammation, and which may become ineffective when an infection causes sepsis.

The effects of CD14 and IL-27 on induction of endotoxin tolerance in human monocytes and macrophages

Upon repeated exposure to endotoxin or lipopolysaccharide (LPS), myeloid cells enter a refractory state called endotoxin tolerance as a homeostatic mechanism. In innate immune cells, LPS is recognized by co-receptors Toll-like receptor 4 (TLR4) and CD-14 to initiate an inflammatory response for subsequent cytokine production. One such cytokine, interleukin (IL)-27, is produced by myeloid cells in response to bacterial infection. In monocytes, IL-27 has proinflammatory functions such as up-regulating TLR4 expression for enhanced LPS-mediated cytokine production; alternatively, IL-27 induces inhibitory functions in activated macrophages. This study investigated the effects of IL-27 on the induction of endotoxin tolerance in models of human monocytes compared with macrophages. Our data demonstrate that IL-27 inhibits endotoxin tolerance by up-regulating cell surface TLR4 expression and soluble CD14 production to mediate stability of the surface LPS-TLR4-CD14 complex in THP-1 cells. In contrast, elevated basal expression of membrane-bound CD14 in phorbol 12-myristate 13-acetate (PMA)-THP-1 cells, primary monocytes, and primary macrophages may promote CD14-mediated endocytosis and be responsible for the preservation of an endotoxin-tolerized state in the presence of IL-27. Overall, the efficacy of IL-27 in inhibiting endotoxin tolerance in human THP-1 monocytes and PMA-THP-1 macrophages is affected by membrane-bound and soluble CD14 expression.

Precision Immunotherapy for Sepsis

Decades of sepsis research into a specific immune system-targeting adjunctive therapy have not resulted in the discovery of an effective compound. Apart from antibiotics, source control, resuscitation and organ support, not a single adjunctive treatment is used in current clinical practice. The inability to determine the prevailing immunological phenotype of patients and the related large heterogeneity of study populations are regarded by many as the most important factors behind the disappointing results of past clinical trials. While the therapeutic focus has long been on immunosuppressive strategies, increased appreciation of the importance of sepsis-induced immunoparalysis in causing morbidity and mortality in sepsis patients has resulted in a paradigm shift in the sepsis research field towards strategies aimed at enhancing the immune response. However, similar to immunosuppressive therapies, precision medicine is imperative for future trials with immunostimulatory compounds to succeed. As such, identifying those patients with a severely suppressed or hyperactive immune system who will most likely benefit from either immunostimulatory or immunosuppressive therapy, and accurate monitoring of both the immune and treatment response is crucial. This review provides an overview of the challenges lying ahead on the path towards precision immunotherapy for patients suffering from sepsis.

Sex differences in how inflammation affects behavior: What we can learn from experimental inflammatory models in humans

Human models demonstrate that experimental activation of the innate immune system has profound effects on brain activation and behavior, inducing fatigue, worsened mood and pain sensitivity. It has been proposed that inflammation is a mechanism involved in the etiology and maintenance of depression, chronic pain and long-term fatigue. These diseases show a strong female overrepresentation, suggesting that a better understanding of sex differences in how inflammation drives behavior could help the development of individualized treatment interventions. For this purpose, we here review sex differences in studies using experimental inflammatory models to investigate changes in brain activity and behavior. We suggest a model in which inflammation accentuates sex differences in brain networks and pre-existing vulnerability factors. This effect could render women more vulnerable to the detrimental effects of immune-to-brain communication over time. We call for systematic and large scale investigations of vulnerability factors for women in the behavioral response to inflammation.

Experimental human endotoxemia as a model of systemic inflammation

Systemic inflammation plays a pivotal role in a multitude of conditions, including sepsis, trauma, major surgery and burns. However, comprehensive analysis of the pathophysiology underlying this systemic inflammatory response is greatly complicated by variations in the immune response observed in critically ill patients, which is a result of inter-individual differences in comorbidity, comedication, source of infection, causative pathogen, and onset of the inflammatory response. During experimental human endotoxemia, human subjects are challenged with purified endotoxin (lipopolysaccharide) intravenously which induces a short-lived, well-tolerated and controlled systemic inflammatory response, similar to that observed during sepsis. The human endotoxemia model can be conducted in a highly standardized and reproducible manner, using a carefully selected homogenous study population. As such, the experimental human endotoxemia model does not share the aforementioned clinical limitations and enables us to investigate both the mechanisms of systemic inflammation, as well as to evaluate novel (pharmacological) interventions in humans in vivo. The present review provides a detailed overview of the various designs, organ-specific changes, and strengths and limitations of the experimental human endotoxemia model, with the main focus on its use as a translational model for sepsis research.

Pro-Inflammatory Th1 and Th17 Cells Are Suppressed During Human Experimental Endotoxemia Whereas Anti-Inflammatory IL-10 Producing T-Cells Are Unaffected

Objective

Sepsis is one of the leading causes of the deaths in hospitals. During sepsis, patients are exposed to endotoxemia, which may contribute to the dysregulation of the immune system frequently observed in sepsis. This dysregulation leads to impaired pro-inflammatory responses and may increase the risk for secondary infections in sepsis. The experimental human endotoxemia model is widely used as a model system to study the acute effects of endotoxemia. Under physiological circumstances, the immune system is tightly regulated. Effector T-cells exert pro-inflammatory function and are restrained by regulatory T-cells (Tregs), which modulate pro-inflammatory effector responses. Endotoxemia may induce inadequate Treg activity or render effector T-cells dysfunctional. It was the aim of the study to investigate effector T-cell and Treg responses in an experimental human endotoxemia model.

Methods

In a cross-over designed placebo-controlled study, 20 healthy male volunteers received an intravenous injection of either lipopolysaccharide (LPS) (0.8 ng/kg body weight) or a placebo (saline 0.9%). CD3⁺ T-cells, CD4⁺ T-cells, CD8⁺ T-cells, and intracellular cytokine profiles were measured with flow cytometry at baseline and at repeated points after LPS/placebo injection. Complete blood cell counts were obtained with an automated hematology analyzer and cytokines were quantified by ELISA.

Results

Circulating neutrophils were significantly increased 2 h after LPS injection (p < 0.001) while absolute number of CD3⁺ T-cells, CD4⁺ T-cells, and CD8⁺ T-cells decreased (p < 0.001). Effector T-helper-cells (THs) showed a significant—but transient—decrease of pro-inflammatory IFNγ, interleukin (IL)-2, TNFα, and IL-17A production after LPS injection (p < 0.001). In contrast, the frequency of Treg and the capacity to produce IL-10 were unchanged (p = 0.21).

Conclusion

Effector THs fail to produce pro-inflammatory Th1-/Th17-associated cytokines after LPS challenge. In contrast, IL-10 production by Treg is not affected. Thus, endotoxemia-induced suppression of pro-inflammatory THs might be considered as a contributing factor to immunoparalysis in sepsis.

Reduced ex vivo release of pro-inflammatory cytokines and elevated plasma interleukin-6 are inflammatory signatures of post-stroke delirium

Background

Experimental studies suggest that systemic inflammation contributes to the pathophysiology of delirium. The aim of our study was to determine blood-derived inflammatory signatures of post-stroke delirium.

Methods

We included 144 ischemic stroke patients. We assessed delirium on a daily basis during the first 7 days of hospitalization. Venous blood was collected at day 3 after the onset of stroke and stimulated ex vivo with lipopolysaccharide (LPS). We measured LPS-induced cytokine concentration (TNFα, IP-10, IL-1β, IL-6, IL-8, IL-10, and IL-12p70) as well as plasma levels of IL-6 and TNFα.

Results

Delirium was diagnosed in 21.5% of patients. After correction for monocyte count, patients with delirium had reduced LPS-induced TNFα, IP-10, IL-1β, IL-6, and IL-12 release. The plasma IL-6 level was higher in delirious patients compared to patients without delirium. After adjusting for stroke severity and infections, higher ex vivo TNFα (OR 0.29, 95%CI 0.11–0.72, P = 0.01), IP-10 (OR 0.25, 95%CI 0.08–0.73, P = 0.01), IL-1β (OR 0.42, 95%CI 0.20–0.89, P = 0.02), and IL-12 (OR 0.07, 95%CI 0.01–0.70, P = 0.02) release was associated with the reduced risk of delirium. In multivariate analysis, the higher plasma IL-6 was associated with the increased risk of delirium (OR 1.61, 95%CI 1.00–2.58, P = 0.04).

Conclusions

Reduced ex vivo release of pro-inflammatory cytokines after LPS stimulation and the elevated plasma IL-6 are signatures of post-stroke delirium.

Short-term repeated HRV-16 exposure results in an attenuated immune response in vivo in humans

INTRODUCTION

Naturally, development of adaptive immunity following HRV infection affects the immune response. However, it is currently unclear whether or not HRV re-exposure within a short time frame leads to an altered innate immune response. The "experimental cold model" is used to investigate the pathogenesis of HRV infection and allows us to investigate the effects of repeated exposure on both local and systemic innate immunity.

METHODS

40 healthy male and female (1:1) subjects were nasally inoculated with HRV-16 or placebo. One week later, all subjects received HRV-16. Baseline seronegative subjects (n = 18) were included for further analysis.

RESULTS

Infection rate was 82%. Primary HRV infection induced a marked increase in viral load and IP-10 levels in nasal wash, while a similar trend was observed for IL-6 and IL-10. Apart from an increase in IP-10 plasma levels, HRV infection did not induce systemic immune effects nor lower respiratory tract inflammation. With similar viral load present during the second HRV challenge, IP-10 and IL-6 in nasal wash showed no increase, but gradually declined, with a similar trend for IL-10.

CONCLUSION

Upon a second HRV challenge one week after the first, a less pronounced response for several innate immune parameters is observed. This could be the result of immunological tolerance and possibly increases vulnerability towards secondary infections.

Development of Endotoxin Tolerance Does Not Influence the Response to a Challenge with the Mucosal Live-Attenuated Influenza Vaccine in Humans In Vivo

Introduction

The effects of bacterial infections on the response to subsequent viral infections are largely unknown. This is important to elucidate to increase insight into the pathophysiology of bacterial and viral co-infections, and to assess whether bacterial infections may influence the course of viral infections.

Methods

Healthy male subjects received either bacterial endotoxin [Escherichia coli-derived lipopolysaccharide (LPS), 2 ng/kg, n = 15] or placebo (n = 15) intravenously, followed by intranasal Fluenz (live-attenuated influenza vaccine) 1 week later.

Results

LPS administration resulted in increased plasma cytokine levels and development of endotoxin tolerance in vivo and ex vivo, illustrated by attenuated cytokine production upon rechallenge with LPS. Following Fluenz administration, infectivity for the Fluenz A/B strains was similar between the LPS-Fluenz and placebo-Fluenz groups (13/15 subjects in both groups). Also, the Fluenz-induced increase in temperature and IL-6, G-CSF and IP-10 concentrations in nasal wash were similar between both groups.

Conclusion

While endotoxemia profoundly attenuates the immune response upon a second LPS challenge, it does not influence the Fluenz-induced immune response. These results suggest immune suppression after bacterial infection does not alter the response to a subsequent viral infection.

Peripheral immune tolerance alleviates the intracranial lipopolysaccharide injection-induced neuroinflammation and protects the dopaminergic neurons from neuroinflammation-related neurotoxicity

BACKGROUND

Neuroinflammation plays a critical role in the onset and development of neurodegeneration disorders such as Parkinson's disease. The immune activities of the central nervous system are profoundly affected by peripheral immune activities. Immune tolerance refers to the unresponsiveness of the immune system to continuous or repeated stimulation to avoid excessive inflammation and unnecessary by-stander injury in the face of continuous antigen threat. It has been proved that the immune tolerance could suppress the development of various peripheral inflammation-related diseases. However, the role of immune tolerance in neuroinflammation and neurodegenerative diseases was not clear.

METHODS

Rats were injected with repeated low-dose lipopolysaccharide (LPS, 0.3 mg/kg) intraperitoneally for 4 days to induce peripheral immune tolerance. Neuroinflammation was produced using intracranial LPS (15 μg) injection. Inflammation cytokines were measured using enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Microglial activation were measured using immunostaining of Iba-1 and ED-1. Dopaminergic neuronal damage was evaluated using immunochemistry staining and stereological counting of TH-positive neurons. Behavioral impairment was evaluated using amphetamine-induced rotational behavioral assessment.

RESULTS

Compared with the non-immune tolerated animals, pre-treatment of peripheral immune tolerance significantly decreased the production of inflammatory cytokines, suppressed the microglial activation, and increased the number of dopaminergic neuronal survival in the substantia nigra.

CONCLUSIONS

Our results indicated that peripheral immune tolerance attenuated neuroinflammation and inhibited neuroinflammation-induced dopaminergic neuronal death.

Characterization of immune cell, endothelial, and renal responses upon experimental human endotoxemia

INTRODUCTION

Although the effects of relatively high concentrations of endotoxin on endothelial activation/dysfunction and kidney markers has been described in literature, detailed insight in the LPS concentration-effect relationship, the magnitude, variability and timing of the response, and potential effects of endotoxemia on the kidneys is lacking. A study was performed to assess the effects of low- to moderate dose (0.5, 1 or 2ng/kg) endotoxemia on the endothelium and kidneys as measured by a panel of novel highly sensitive kidney injury markers.

METHODS

This was a randomized, double-blind, placebo-controlled study with single ascending doses of LPS (0.5, 1 or 2ng/kg) administered to healthy male volunteers (3 cohorts of 8 subjects, LPS:placebo 6:2). Endothelial measures included selectins, cell adhesion molecules, and thrombomodulin. Renal measures included novel, sensitive and specific biomarkers of acute kidney injury.

RESULTS

Endotoxin exposure resulted in consistent LPS dose-dependent responses in inflammatory markers, E- and P- Selectin, VCAM1, ICAM1, and thrombomodulin. The observed biological responses were transient, reaching a level of significance of at least <0.01 in the highest dose group and with an effect size which was dependent on the administered LPS dose. LPS-induced inflammatory and endothelial effects did not translate into a change in renal damage biomarkers, although at 2ng/kg LPS, subtle and transient biomarker changes were observed that may relate to (subclinical) tubular damage.

DISCUSSION

We demonstrated that administration of a single LPS dose of 2ng/kg to healthy volunteers results in significant inflammatory and endothelial responses, without inducing clinically relevant signs of kidney injury. These findings support the application of the human endotoxemia model in future clinical pharmacology studies.

Stimulated Whole Blood Cytokine Release as a Biomarker of Immunosuppression in the Critically Ill: The Need for a Standardized Methodology

OBJECTIVE

Reduced ex vivo lipopolysaccharide (LPS) stimulated whole blood pro-inflammatory cytokine release is a hallmark of immunosuppression in the critically ill and predicts adverse clinical outcomes. No standard technique for performing the assay currently exists. The impact of methodological heterogeneity was determined.

DESIGN, SETTING, SUBJECTS, AND INTERVENTIONS

Clinical experimental study set in a research laboratory. Venous blood from 5 to 10 healthy volunteers/experiment (total participant group: 18 subjects, 72% men, mean age 32) was stimulated ex vivo to evaluate the effect of variables identified via literature review on tumor necrosis factor-α (TNFα) release. These included sample handling, stimulation technique, and incubation conditions. Reporting convention was additionally assessed.

MAIN RESULTS

Measured TNFα release was significantly altered by source of LPS, concentration of LPS employed, duration and temperature of incubation prior to supernatant aspiration, and predilution of blood (repeated measures ANOVA, all P < 0.01). Sample handling prior to stimulation (anticoagulant employed, time to LPS addition, and storage temperature) also caused significant alterations in TNFα release. Considerable interindividual variation was observed (range 1,024-4,649 pg/mL, mean 2,339 pg/mL). Normalization by monocyte count and pretreatment with a cyclooxygenase inhibitor (indomethacin 10  μM) reduced the coefficient of variation from 47.17% to 32.09%.

CONCLUSIONS

Inconsistency in interlaboratory methodology and reporting impairs interpretation, comparability, and reproducibility of the ex vivo LPS-stimulated whole blood cytokine release assay. A standardized validated technique is required. The advent of trials of immunoadjuvant agents renders this a clinical imperative.

Kinetics of plasma procalcitonin, soluble CD14, CCL2 and IL-10 after a sublethal infusion of lipopolysaccharide in horses

Endotoxemia represents a significant clinical and economic problem for the equine industry. This study assesses the kinetics of soluble CD14 (sCD14), chemokine (CC motif) ligand 2 (CCL2), interleukin 10 (IL-10) and plasma procalcitonin (PCT) in healthy horses after the intravenous infusion of lipopolysaccharide (LPS). The aim was to contribute to the basic understanding of the equine species-specific kinetics of these molecules in response to LPS exposure, which could support further findings in clinical studies and identify valuable inflammatory biomarkers for equine practice. Eleven healthy horses were involved in this experimental in vivo study. Horses were classified as healthy before the LPS infusion. After the pre-infusion blood collection (T0), all horses received an infusion of E. coli endotoxin (30ng/kg over 30min). Data and samples were collected 1h (T1), 2 (T2), 3 (T3) and 24h (T24) after infusion. Plasma sCD14, CCL2 and IL-10 were evaluated with a fluorescent bead-based assay, while PCT was evaluated with an equine PCT ELISA assay. A one-way ANOVA test was performed between each blood-sampling time for PCT, sCD14 and IL-10, and a Friedman test was performed for CCL2. Plasma PCT, IL-10 and CCL2 concentrations increased statistically significantly at T1, T2 and T3 compared to T0. No statistically significant differences were found between plasma IL-10 and CCL2 concentrations between T0 vs T24, although plasma PCT values remained high 24h after LPS infusion. Plasma sCD14 concentration showed no statistically significant differences for any of sampling times. Our results demonstrate that LPS injection into healthy horses results in PCT, CCL2 and IL-10 increases in plasma without an increase in sCD14. The increases in PCT, CCL2 and IL-10 are related to the inflammatory response induced by circulating lipopolysaccharide.

Pain perception in healthy volunteers: effect of repeated exposure to experimental systemic inflammation

We aimed to study the relationship between pain perception and cytokine release during systemic inflammation. We present a randomized crossover trial in healthy volunteers (n = 17) in 37 individual trials. Systemic inflammation was induced by an i.v. bolus of Escherichia coli LPS (2 ng/kg) on two separate trial days, with or without a nicotine patch applied 10 h previously. Pain perception at baseline, and 2 and 6 h after LPS was assessed by pressure algometry and tonic heat stimulation at an increasing temperature (45-48℃) during both trials. Compared with baseline, pain pressure threshold was reduced 2 and 6 h after LPS, while heat pain perception was accentuated at all testing temperatures after 2 but not 6 h. The magnitude of changes in pain perception did not correlate to cytokine release. No effect of transdermal nicotine or training status was observed. In conclusion, LPS administration in healthy human volunteers leads to reduction in pain pressure threshold and an increase in pain perception to heat stimuli, supporting a relationship between acute systemic inflammation and pain perception.

Intravenous Endotoxin Challenge in Healthy Humans: An Experimental Platform to Investigate and Modulate Systemic Inflammation

Activation of inflammatory pathways represents a central mechanism in multiple disease states both acute and chronic. Triggered via either pathogen or tissue damage-associated molecular motifs, common biochemical pathways lead to conserved yet variable physiological and immunological alterations. Dissection and delineation of the determinants and mechanisms underlying phenotypic variance in response is expected to yield novel therapeutic advances.

Intravenous (IV) administration of endotoxin (gram-negative bacterial lipopolysaccharide), a specific Toll-like receptor 4 agonist, represents an in vivo model of systemic inflammation in man. National Institutes for Health Clinical Center Reference Endotoxin (CCRE, Escherichia coli O:113:H10:K negative) is employed to reliably and reproducibly generate vascular, hematological, endocrine, immunological and organ-specific functional effects that parallel, to varying degrees, those seen in the early stages of pathological states. Alteration of dose (0.06 - 4 ng/kg) and time-scale of exposure (bolus vs. infusion) allows replication of either acute or chronic inflammation and a range of severity to be elicited, with higher doses (2 - 4 ng/kg) frequently being used to create a 'sepsis-like' state. Established and novel medicinal compounds may additionally be administered prior to or post endotoxin exposure to appreciate their effect on the inflammatory cascade. Despite limitations in scope and generalizability, human IV endotoxin challenge offers a unique platform to gain mechanistic insights into inducible physiological responses and inflammatory pathways. Rationally employed it may aid translation of this knowledge into therapeutic innovations.

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.