The late phase of sepsis is characterized by an increased microbiological burden and death rate

Pathogenic, immunologic, and clinical aspects of sepsis - update 2016

INTRODUCTION

Sepsis is a major cause of death worldwide but its orchestrating components remain incompletely understood. On the one hand, development of sepsis results from an infectious focus that cannot be controlled by the immune system, but on the other, responding immune cells that can eliminate the infection inflict damage to the host by contributing to complications such as endothelial leakage, septic shock, and multiorgan failure.

AREAS COVERED

In this review we give a comprehensive overview of how sepsis occurs, which exogenous and endogenous factors might affect the immune-pathophysiological course of sepsis and finally how this knowledge translates into up-to-date definitions and therapeutic approaches. Expert commentary: Although new immunological mechanisms altering the course of sepsis have been identified recently, future research needs to address the limitations of experimental approaches, redirect the research focus into translational approaches, and finally evaluate personalized treatment strategies.

Sirtuin-2 Regulates Sepsis Inflammation in ob/ob Mice

OBJECTIVE

Obesity increases morbidity and resource utilization in sepsis patients. Sepsis transitions from early/hyper-inflammatory to late/hypo-inflammatory phase. Majority of sepsis-mortality occurs during the late sepsis; no therapies exist to treat late sepsis. In lean mice, we have shown that sirtuins (SIRTs) modulate this transition. Here, we investigated the role of sirtuins, especially the adipose-tissue abundant SIRT-2 on transition from early to late sepsis in obese with sepsis.

METHODS

Sepsis was induced using cecal ligation and puncture (CLP) in ob/ob mice. We measured microvascular inflammation in response to lipopolysaccharide/normal saline re-stimulation as a "second-hit" (marker of immune function) at different time points to track phases of sepsis in ob/ob mice. We determined SIRT-2 expression during different phases of sepsis. We studied the effect of SIRT-2 inhibition during the hypo-inflammatory phase on immune function and 7-day survival. We used a RAW264.7 (RAW) cell model of sepsis for mechanistic studies. We confirmed key findings in diet induced obese (DIO) mice with sepsis.

RESULTS

We observed that the ob/ob-septic mice showed an enhanced early inflammation and a persistent and prolonged hypo-inflammatory phase when compared to WT mice. Unlike WT mice that showed increased SIRT1 expression, we found that SIRT2 levels were increased in ob/ob mice during hypo-inflammation. SIRT-2 inhibition in ob/ob mice during the hypo-inflammatory phase of sepsis reversed the repressed microvascular inflammation in vivo via activation of endothelial cells and circulating leukocytes and significantly improved survival. We confirmed the key finding of the role of SIRT2 during hypo-inflammatory phase of sepsis in this project in DIO-sepsis mice. Mechanistically, in the sepsis cell model, SIRT-2 expression modulated inflammatory response by deacetylation of NFκBp65.

CONCLUSION

SIRT-2 regulates microvascular inflammation in obese mice with sepsis and may provide a novel treatment target for obesity with sepsis.

Immunotherapy: A promising approach to reverse sepsis-induced immunosuppression

Sepsis is defined as life-threatening organ dysfunction caused by dysregulated host responses to infection (Third International Consensus definition for Sepsis and septic shock). Despite decades of research, sepsis remains the leading cause of death in intensive care units. More than 40 clinical trials, most of which have targeted the sepsis-associated pro-inflammatory response, have failed. Thus, antibiotics and fluid resuscitation remain the mainstays of supportive care and there is intense need to discover and develop novel, targeted therapies to treat sepsis. Both pre-clinical and clinical studies over the past decade demonstrate unequivocally that sepsis not only causes hyper-inflammation, but also leads to simultaneous adaptive immune system dysfunction and impaired antimicrobial immunity. Evidences for immunosuppression include immune cell depletion (T cells most affected), compromised T cell effector functions, T cell exhaustion, impaired antigen presentation, increased susceptibility to opportunistic nosocomial infections, dysregulated cytokine secretion, and reactivation of latent viruses. Therefore, targeting immunosuppression provides a logical approach to treat protracted sepsis. Numerous pre-clinical studies using immunomodulatory agents such as interleukin-7, anti-programmed cell death 1 antibody (anti-PD-1), anti-programmed cell death 1 ligand antibody (anti-PD-L1), and others have demonstrated reversal of T cell dysfunction and improved survival. Therefore, identifying immunosuppressed patients with the help of specific biomarkers and administering specific immunomodulators holds significant potential for sepsis therapy in the future. This review focusses on T cell dysfunction during sepsis and discusses the potential immunotherapeutic agents to boost T cell function during sepsis and improve host resistance to infection.

Immunoproteomic Analysis of Antibody Responses to Extracellular Proteins of Candida albicans Revealing the Importance of Glycosylation for Antigen Recognition

During infection, the human pathogenic fungus Candida albicans undergoes a yeast-to-hypha transition, secretes numerous proteins for invasion of host tissues, and modulates the host's immune response. Little is known about the interplay of C. albicans secreted proteins and the host adaptive immune system. Here, we applied a combined 2D gel- and LC-MS/MS-based approach for the characterization of C. albicans extracellular proteins during the yeast-to-hypha transition, which led to a comprehensive C. albicans secretome map. The serological responses to C. albicans extracellular proteins were investigated by a 2D-immunoblotting approach combined with MS for protein identification. On the basis of the screening of sera from candidemia and three groups of noncandidemia patients, a core set of 19 immunodominant antibodies against secreted proteins of C. albicans was identified, seven of which represent potential diagnostic markers for candidemia (Xog1, Lip4, Asc1, Met6, Tsa1, Tpi1, and Prx1). Intriguingly, some secreted, strongly glycosylated protein antigens showed high cross-reactivity with sera from noncandidemia control groups. Enzymatic deglycosylation of proteins secreted from hyphae significantly impaired sera antibody recognition. Furthermore, deglycosylation of the recombinantly produced, secreted aspartyl protease Sap6 confirmed a significant contribution of glycan epitopes to the recognition of Sap6 by antibodies in patient's sera.

Sepsis and septic shock

For more than two decades, sepsis was defined as a microbial infection that produces fever (or hypothermia), tachycardia, tachypnoea and blood leukocyte changes. Sepsis is now increasingly being considered a dysregulated systemic inflammatory and immune response to microbial invasion that produces organ injury for which mortality rates are declining to 15-25%. Septic shock remains defined as sepsis with hyperlactataemia and concurrent hypotension requiring vasopressor therapy, with in-hospital mortality rates approaching 30-50%. With earlier recognition and more compliance to best practices, sepsis has become less of an immediate life-threatening disorder and more of a long-term chronic critical illness, often associated with prolonged inflammation, immune suppression, organ injury and lean tissue wasting. Furthermore, patients who survive sepsis have continuing risk of mortality after discharge, as well as long-term cognitive and functional deficits. Earlier recognition and improved implementation of best practices have reduced in-hospital mortality, but results from the use of immunomodulatory agents to date have been disappointing. Similarly, no biomarker can definitely diagnose sepsis or predict its clinical outcome. Because of its complexity, improvements in sepsis outcomes are likely to continue to be slow and incremental.

Why a second look might be worth it: immuno-modulatory therapies in the critically ill patient

Sepsis and septic shock are associated with high mortality rates and remain a serious menace for the critically ill patient. Concurrent activation of pro- and anti-inflammatory pathways and an excessive cytokine release represent initial key features in the deregulation of the humoral and cellular antimicrobial defense. Research of the last decades addressed both the ebullient inflammation as well as the resulting long-term failure of the host immunity. While the reestablishment of an adequate immune-competence is still under investigation, many promising experimental trials to limit the inflammatory response during sepsis were challenged by missing beneficial effects in clinical studies. Nevertheless, due to advanced knowledge about the complex regulation of inflammatory mediators and their overlapping involvement in other potentially life-threatening diseases, further evaluation of these approaches in relevant subgroups could help to identify critically ill patients with potential benefit from anti-inflammatory therapies.

Adaptive immune function in critical illness

PURPOSE OF REVIEW

This review is being published to update the literature on the function of the adaptive immune system in critical illness, specifically sepsis and acute lung injury. We have focused on the role of T cells in these syndromes.

RECENT FINDINGS

The adaptive immune response becomes dysfunctional during sepsis and acute lung injury in very similar ways. Many of the abnormalities contribute to morbidity and mortality. Immunoparalysis captures the breadth of the dysfunction in that T-cell functions are broadly suppressed after the early proinflammatory stages of illness. Lymphocyte apoptosis, decreased antigen responsiveness, decreased and altered cytokine expression, upregulation of inhibitory molecules, and expansion of the suppressive regulatory T-cell population are mechanisms involved. Each of these abnormalities can be reversed with improvement in experimental outcomes.

SUMMARY

Immunoparalysis of the adaptive immune system occurs in sepsis and acute lung injury, and is critical to the outcome. Blocking the inhibited pathways and immunostimulant cytokines improved lymphocyte function and outcome. Many such blocking agents are already effective for other diseases and could be used for immunoparalysis. Unfortunately, there is no diagnostic marker yet. In order to provide the right therapy at the right time, advancements in immunomonitoring are necessary.

Diagnostic value of elevated serum miRNA-143 levels in sepsis

Objective

To evaluate serum micro RNA-143 (miR-143) levels in patients with sepsis or non-infectious systemic inflammatory response syndrome (SIRS), and investigate its possible diagnostic or prognostic value.

Methods

Serum was obtained from patients with sepsis or SIRS and healthy control subjects. Relative miR-143 expression was determined using quantitative real time polymerase chain reaction. The diagnostic and prognostic value of serum miR-143 was evaluated.

Results

Serum miR-143 levels were significantly higher in patients with sepsis (n = 103) than patients with SIRS (n = 95) and healthy controls (n = 40). There were significant positive correlations between serum miR-143 level and SOFA and APACHE II scores in patients with sepsis (r = 0.794 and r = 0.825, respectively). Serum miR-143 had a sensitivity of 78.6% and specificity of 91.6% for distinguishing between sepsis and SIRS. There was no association between serum miR-143 and 28-day survival in patients with sepsis.

Conclusion

Serum miR-143 is elevated in patients with sepsis, and may be a useful biomarker for distinguishing between sepsis and SIRS.

Targeting cytokines as a treatment for patients with sepsis: A lost cause or a strategy still worthy of pursuit?

Despite often knowing the aetiology of sepsis and its clinical course there has not been the anticipated advances in treatment strategies. Cytokines are influential mediators of immune/inflammatory reactions and in patients with sepsis high circulating levels are implicated in the onset and perpetuation of organ failure. Antagonising the activities of pro-inflammatory cytokines enhances survival in animal models of sepsis but, so far, such a therapeutic strategy has not improved patient outcome. This article addresses the questions of why encouraging laboratory findings have failed to be translated into successful treatments of critically ill patients and whether modifying cytokine activity still remains a promising avenue for therapeutic advance in severe sepsis. In pursuing this task we have selected reports that we believe provide an incisive, critical and balanced view of the topic.

Balanced control of both hyper and hypo-inflammatory phases as a new treatment paradigm in sepsis

The immune response of the host against invading pathogens is clinically manifested as sepsis. Sepsis is a complicated process characterized by distinct phases that usually occur in a sequential manner. The initial hyper-inflammation helps in elimination of the pathogen, but potentially may lead to excessive tissue injury. Hypo-inflammation helps in restoring immune homeostasis, but may lead to significant immune suppression and death from secondary infections if not appropriately controlled. Immune-modulating intervention in sepsis should be based on a balanced control of both the hyper and the hypo-inflammatory phase.

Induction of Siglec-1 by Endotoxin Tolerance Suppresses the Innate Immune Response by Promoting TGF-β1 Production

Sepsis is one of the leading causes of death worldwide. Although the prevailing theory for the sepsis syndrome is a condition of uncontrolled inflammation in response to infection, sepsis is increasingly being recognized as an immunosuppressive state known as endotoxin tolerance. We found sialylation of cell surface was significantly increased on LPS-induced tolerant cells; knockdown of Neu1 in macrophage cell line RAW 264.7 cells resulted in enhanced LPS-induced tolerance, whereas overexpression of Neu1 or treatment with sialidase abrogated LPS-induced tolerance, as defined by measuring TNF-α levels in the culture supernatants. We also found that the expression of Siglec-1 (a member of sialic acid-binding Ig (I)-like lectin family members, the predominant sialic acid-binding proteins on cell surface) was specifically up-regulated in endotoxin tolerant cells and the induction of Siglec-1 suppresses the innate immune response by promoting TGF-β1 production. The enhanced TGF-β1 production by Siglec-1 was significantly attenuated by spleen tyrosine kinase (Syk) inhibitor. Knockdown of siglec-1 in RAW 264.7 cells resulted in inhibiting the production of TGF-β1 by ubiquitin-dependent degradation of Syk. Mechanistically, Siglec-1 associates with adaptor protein DNAX-activation protein of 12 kDa (DAP12) and transduces a signal to Syk to control the production of TGF-β1 in endotoxin tolerance. Thus, Siglec-1 plays an important role in the development of endotoxin tolerance and targeted manipulation of this process could lead to a new therapeutic opportunity for patients with sepsis.

Sepsis-induced long-term immune paralysis--results of a descriptive, explorative study

Background

Long-lasting impairment of the immune system is believed to be the underlying reason for delayed deaths after surviving sepsis. We tested the hypothesis of persisting changes to the immune system in survivors of sepsis for the first time.

Methods

In our prospective, cross-sectional pilot study, eight former patients who survived catecholamine-dependent sepsis and eight control individuals matched for age, sex, diabetes and renal insufficiency were enrolled. Each participant completed a questionnaire concerning morbidities, medications and infection history. Peripheral blood was collected for determination of i) immune cell subsets (CD4⁺, CD8⁺ T cells; CD25⁺ CD127^- regulatory T cells; CD14⁺ monocytes), ii) cell surface receptor expression (PD-1, BTLA, TLR2, TLR4, TLR5, Dectin-1, PD-1 L), iii) HLA-DR expression, and iv) cytokine secretion (IL-6, IL10, TNF-α, IFN-γ) of whole blood stimulated with either α-CD3/28, LPS or zymosan.

Results

After surviving sepsis, former patients presented with increased numbers of clinical apparent infections, including those typically associated with an impaired immune system. Standard inflammatory markers indicated a low-level inflammatory situation in former sepsis patients. CD8⁺ cell surface receptor as well as monocytic HLA-DR density measurements showed no major differences between the groups, while CD4⁺ T cells tended towards two opposed mechanisms of negative immune cell regulation via PD-1 and BTLA. Moreover, the post-sepsis group showed alterations in monocyte surface expression of distinct pattern recognition receptors; most pronouncedly seen in a decrease of TLR5 expression. Cytokine secretion in response to important activators of both the innate (LPS, zymosan) and the adaptive immune system (α-CD3/28) seemed to be weakened in former septic patients.

Conclusions

Cytokine secretion as a reaction to different activators of the immune system seemed to be comprehensively impaired in survivors of sepsis. Among others, this could be based on trends in the downregulation of distinct cell surface receptors. Based on our results, the conduct of larger validation studies seems feasible, aiming to characterize alterations and to find potential therapeutic targets to engage.

Prognostic utility of plasma lactate measured between 24 and 48 h after initiation of early goal-directed therapy in the management of sepsis, severe sepsis, and septic shock

Background

Based on the proven efficacy of lactate in predicting mortality and morbidity in sepsis when measured early in the resuscitative protocol, our group hypothesized that this utility extends later in the course of care. This study sought to investigate the prognostic potential of plasma lactate clearance measured 24–48 h after the initiation of treatment for nonsurgical patients with sepsis, severe sepsis, and septic shock.

Methods

Plasma lactate values, measured 24–48 h after the initiation of treatment, were collected in nonsurgical septic, severe septic, and septic shock patients. The primary outcome was 30-day mortality, while secondary outcomes included requirements for vasopressors and boluses of intravenous fluids. Analysis of these three outcomes was performed while controlling for clinical severity as measured by Sequential Organ Failure Assessment (SOFA), renal dysfunction, and hepatic dysfunction. Lactate clearance was defined as the percent change in plasma lactate levels measured after 24–48 h of treatment from the plasma lactate level at initial presentation.

Results

Two hundred twenty-nine nonsurgical patients were divided into two groups, clearers (above median lactate clearance [31.6 %]) and nonclearers (below median lactate clearance [31.6 %]). The adjusted odds ratio of mortality in clearers compared to nonclearers was 0.39 (CI 0.20–0.76) (p = 0.006). For vasopressor requirement, the adjusted odds ratio was 0.41 (CI 0.21–0.79) in clearers compared to nonclearers (p = 0.008). For intravenous fluid bolus requirement, the adjusted odds ratio was 0.81 (CI 0.48–1.39) in clearers compared to nonclearers (p = 0.45).

Conclusions

Lower plasma lactate clearance 24–48 h after the initiation of treatment is associated with higher 30-day mortality and requirements for vasopressors in nonsurgical septic patients and may be a useful noninvasive measurement for guiding late-sepsis treatment. Further investigation looking at mechanisms and therapeutic targets to improve lactate clearance in late sepsis may improve patient mortality and outcomes.

Post-Sepsis State Induces Tumor-Associated Macrophage Accumulation through CXCR4/CXCL12 and Favors Tumor Progression in Mice

Survivors from sepsis are in an immunosuppressed state that is associated with higher long-term mortality and risk of opportunistic infections. Whether these factors contribute to neoplastic proliferation, however, remains unclear. Tumor-associated macrophages (TAM) can support malignant cell proliferation, survival, and angiogenesis. We addressed the relationship between the post-sepsis state, tumor progression and TAM accumulation, and phenotypic and genetic profile, using a mouse model of sepsis resolution and then B16 melanoma in mice. In addition, we measured the serum concentrations of TNFα, TGFβ, CCL2, and CXCL12 and determined the effect of in vivo CXCR4/CXCL12 inhibition in this context. Mice that survived sepsis showed increased tumor progression both in the short and long term, and survival times were shorter. TAM accumulation, TAM local proliferation, and serum concentrations of TGFβ, CXCL12, and TNFα were increased. Naïve mice inoculated with B16 together with macrophages from post-sepsis mice also had faster tumor progression and shorter survival. Post-sepsis TAMs had less expression of MHC-II and leukocyte activation-related genes. Inhibition of CXCR4/CXCL12 prevented the post-sepsis-induced tumor progression, TAM accumulation, and TAM in situ proliferation. Collectively, our data show that the post-sepsis state was associated with TAM accumulation through CXCR4/CXCL12, which contributed to B16 melanoma progression.

Critical Illness-Induced Immune Suppression: Current State of the Science

Critical illness comprises a heterogeneous group of serious medical conditions that typically involve an initial proinflammatory process. A compensatory anti-inflammatory response may occur that, if severe and persistent, places the patient at high risk for adverse outcomes including secondary infection and death. Monitoring strategies can identify these patients through measurement of innate and adaptive immune function. Reductions in monocyte HLA-DR expression, reduced cytokine production capacity, increased inhibitory cell surface molecule expression, and lymphopenia have all been associated with this immune-suppressed state. Intriguing data suggest that critical illness-induced immune suppression may be reversible with agents such as interferon-γ, granulocyte macrophage colony-stimulating factor, interleukin 7, or anti-programmed death-1 therapy. Future approaches for characterization of patient-specific immune derangements and individualized treatment could revolutionize how we recognize and prevent complications in critically ill patients.

Reversal of neutrophil-to-lymphocyte count ratio in early versus late death from septic shock

Introduction

Septic shock is one of the most frequent causes of admission to the intensive care unit (ICU) and is associated with a poor prognosis. Early and late death in septic shock should be distinguished because they may involve different underlying mechanisms. In various conditions, the neutrophil-to-lymphocyte count ratio (NLCR) has been described as an easily measurable parameter to express injury severity. In the present study, we investigated whether the timing of death was related to a particular NLCR.

Methods

We conducted a prospective, single-center, observational study that included consecutive septic shock patients. Severity scores, early (before day 5) or late (on or after day 5 of septic shock onset) ICU mortality, and daily leukocyte counts were collected during the ICU stay. We assessed the association between leukocyte counts at admission and their evolution during the first 5 days with early or late death. The association between patient characteristics (including cell counts) and prognosis was estimated using Cox proportional cause-specific hazards models.

Results

The study included 130 patients who were diagnosed with abdominal (n = 99) or extra-abdominal (n = 31) septic shock. The median (interquartile range) NLCR was 12.5 (6.5–21.2) in survivors and 6.2 (3.7–12.6) in nonsurvivors (p = 0.001). The NLCR at admission was significantly lower in patients who died before day 5 than in survivors (5 [3.5–11.6] versus 12.5 [6.5–21.2], respectively; p = 0.01). From day 1 to day 5, an increased NLCR related to an increase in neutrophil count and a decrease in lymphocyte count was associated with late death (+34.8 % [−8.2 to 305.4] versus −20 % [−57.4 to 45.9]; p = 0.003). Those results were present in patients with abdominal origin sepsis as well as in those with extra-abdominal sepsis, who were analyzed separately.

Conclusions

In the present study, a reversed NLCR evolution was observed according to the timing of death. Septic shock patients at risk of early death had a low NLCR at admission, although late death was associated with an increased NLCR during the first 5 days.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1144-x) contains supplementary material, which is available to authorized users.

A Review of GM-CSF Therapy in Sepsis

Determine what clinical role, if any, GM-CSF may have in the clinical treatment of sepsis in the adult patient. Advancements in the management of sepsis have led to significant decreases in early mortality; however, sepsis remains a significant source of long-term mortality and disability which places strain on healthcare resources with a substantial growing economic impact. Historically, early multiple organ failure (MOF) and death in patients with severe sepsis was thought to result from an exaggerated proinflammatory response called the systemic inflammatory response syndrome (SIRS). Numerous prospective randomized controlled trials (PRCTs) tested therapies aimed at decreasing the organ injury associated with an exaggerated inflammatory response. With few exceptions, the results from these PRCTs have been disappointing, and currently no specific therapeutic agent is approved to counteract the early SIRS response in patients with severe sepsis. It has long been recognized that there is a delayed immunosuppressive state that contributes to long-term morbidity. However, recent findings now support a concurrent proinflammatory and anti-inflammatory response present throughout sepsis. Multiple immunomodulating agents have been studied to combat the immunosuppressive phase of sepsis with the goal of decreasing secondary infection, reducing organ dysfunction, decreasing ICU stays, and improving survival. Granulocyte-macrophage colony stimulating factor (GM-CSF), a myelopoietic growth factor currently used in patients with neutropenia secondary to chemotherapy-induced myelosuppression, has been studied as a potential immune-activating agent. The applicability of GM-CSF as a standard therapy for generalized sepsis is still largely understudied; however, small-scale studies available have demonstrated some improved recovery from infection, decreased hospital length of stay, decreased days requiring mechanical ventilation, and decreased medical costs.

Modulatory Effects of Astragalus Polysaccharides on T-Cell Polarization in Mice with Polymicrobial Sepsis

BACKGROUND

This study evaluated the impact of different doses of Astragalus polysaccharides (APS) on the functional status and phenotype of T cells during polymicrobial sepsis.

METHODS

On day 1 after cecal ligation and puncture, mice were treated with either saline, 100 (A100), 200 (A200), or 400 mg APS/kg body weight (BW) (A400) by an intraperitoneal injection daily for 4 days. All mice were sacrificed 5 days after the operation.

RESULTS

APS treatment reversed the sepsis-induced decrement in the T helper (Th) cell population, and the percentage of activated Th cells also increased in the spleen and Peyer's patches. APS administration downregulated the percentages of circulating Th2 cells and regulatory T cells (Treg), and the percentage of Th17 cells in blood was upregulated in the A400 group. Weight loss and kidney injury were attenuated in the A100 and A200 groups but not in the A400 group at the end of the study.

CONCLUSIONS

Treatments with 100 and 200 mg APS/kg BW reduced Treg populations and elicited a more-balanced Th1/Th2 response that consequently attenuated immunosuppression in polymicrobial sepsis. High-dose APS administration led to excessive responses of Th17 cells which may have adverse effects in sepsis-induced organ injury.

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.

Lactate kinetics in sepsis and septic shock: a review of the literature and rationale for further research

Over the last two decades, there have been vast improvements in sepsis-related outcomes, largely resulting from the widespread adoption of aggressive fluid resuscitation and infection control. With increased understanding of the pathophysiology of sepsis, novel diagnostics and resuscitative interventions are being discovered. In recent years, few diagnostic tests like lactate have engendered more attention and research in the sepsis arena. Studies highlighting lactate’s prognostic potential for mortality and other outcomes are ubiquitous and largely focus on the early stage of sepsis management, defined as the initial 6 h and widely referred to as the “golden hours.” Additional investigations, although more representative of surgical and trauma patients, suggest that lactate measurements beyond 24 h from the initiation of resuscitation continue to have predictive and prognostic utility. This review summarizes the current research and evidence regarding lactate’s utility as a prognosticator of clinical outcomes in both early and late sepsis management, defines the mechanism of lactate production and clearance, and identifies areas warranting further research.

Biomarkers for Sepsis: What Is and What Might Be?

Every year numerous individuals develop the morbid condition of sepsis. Therefore, novel biomarkers that might better inform clinicians treating such patients are sorely needed. Difficulty in identifying such markers is in part due to the complex heterogeneity of sepsis, resulting from the broad and vague definition of this state/condition based on numerous possible clinical signs and symptoms as well as an incomplete understanding of the underlying pathobiology of this complex condition. This review considers some of the attempts that have been made so far, looking at both the pro- and anti-inflammatory response to sepsis, as well as genomic analysis, as sources of potential biomarkers. Irrespective, for functional biomarker(s) of sepsis to successfully translate from the laboratory to a clinical setting, the biomarker must be target specific and sensitive as well as easy to implement/interpret, and be cost effective, such that they can be utilized routinely in patient diagnosis and treatment.

CD1d- and MR1-Restricted T Cells in Sepsis

Dysregulated immune responses to infection, such as those encountered in sepsis, can be catastrophic. Sepsis is typically triggered by an overwhelming systemic response to an infectious agent(s) and is associated with high morbidity and mortality even under optimal critical care. Recent studies have implicated unconventional, innate-like T lymphocytes, including CD1d- and MR1-restricted T cells as effectors and/or regulators of inflammatory responses during sepsis. These cell types are typified by invariant natural killer T (iNKT) cells, variant NKT (vNKT) cells, and mucosa-associated invariant T (MAIT) cells. iNKT and vNKT cells are CD1d-restricted, lipid-reactive cells with remarkable immunoregulatory properties. MAIT cells participate in antimicrobial defense, and are restricted by major histocompatibility complex-related protein 1 (MR1), which displays microbe-derived vitamin B metabolites. Importantly, NKT and MAIT cells are rapid and potent producers of immunomodulatory cytokines. Therefore, they may be considered attractive targets during the early hyperinflammatory phase of sepsis when immediate interventions are urgently needed, and also in later phases when adjuvant immunotherapies could potentially reverse the dangerous state of immunosuppression. We will highlight recent findings that point to the significance or the therapeutic potentials of NKT and MAIT cells in sepsis and will also discuss what lies ahead in research in this area.

NFI-A disrupts myeloid cell differentiation and maturation in septic mice

Mounting evidence supports that sepsis-associated immunosuppression increases mortality. As potential contributors to poor sepsis outcomes, myeloid-derived suppressor cells, which are Gr1(+) CD11b(+) innate-immune cell progenitors unable to differentiate and possess suppressive activities, expand dramatically in septic mice by a process requiring increased microRNA-21 and microRNA-181b expression. The inhibition of these microRNAs in vivo in septic mice restores Gr1(+) CD11b(+) cell differentiation and maturation and improves survival. Here, we show that during sepsis-induced generation of myeloid-derived suppressor cells, transcription factor nuclear factor 1 A type represses cyclin-dependent kinase inhibitor p21 to arrest differentiation of Gr1(+) CD11b(+) cells. Our findings include the following: 1) Gr1(+) CD11b(+) myeloid cells from late septic mice genetically lacking nuclear factor 1 A type cannot suppress CD4(+) T cell proliferation and activation; 2) the reconstitution of nuclear factor 1 A type in microRNA-21 and microRNA-181b-depleted Gr1(+) CD11b(+) myeloid-derived suppressor cells inhibits cyclin-dependent kinase inhibitor p21 and restores the immune-suppressor phenotype; 3) ex vivo nuclear factor 1 A type knockdown in Gr1(+) CD11b(+) myeloid-derived suppressor cells from late septic mice restores cyclin-dependent kinase inhibitor p21 expression and promotes monocyte and dendritic cell differentiation; and 4) ectopic nuclear factor 1 A type expression in normal Gr1(+) CD11b(+) cells generates an immunosuppressive phenotype. We suggest that therapeutically targeting nuclear factor 1 A type during late sepsis might improve survival.

HS-23, a Lonicera japonica extract, reverses sepsis-induced immunosuppression by inhibiting lymphocyte apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Lonicera japonica Thunberg, a widely used traditional Chinese medicine, possesses antibacterial, antiviral, and antiendotoxin activities. This study investigated the molecular mechanisms of HS-23, the ethanol extract of the dried flower buds of L. japonica, on sepsis-induced immunosuppression.

MATERIALS AND METHODS

Male ICR mice were intravenously administered HS-23 (10, 20, and 40mg/kg) immediately (0h) and 22h after cecal ligation and puncture (CLP). The spleen was isolated for biochemical assays 24h after CLP.

RESULTS

HS-23 improved sepsis-induced mortality. CLP induced a marked decrease in the number of splenocytes, B cells, and natural killer cells, which was attenuated by HS-23. HS-23 also attenuated CLP-induced apoptosis in CD4(+) and CD8(+) T cells and inhibited both the intrinsic and extrinsic apoptotic pathway in the spleen. HS-23 attenuated the CLP-induced decrease in interleukin (IL)-17 production. CLP significantly decreased splenic production of tumor necrosis factor-α and IL-2, and these effects were attenuated by HS-23.

CONCLUSION

Our findings suggest that HS-23 reverses immunosuppression during the late phase of sepsis by inhibiting lymphocyte apoptosis and enhancing Th1 cytokine production. HS-23 warrants further evaluation as a potential therapeutic agent for the treatment of sepsis.

Sepsis-induced immune alterations monitoring by flow cytometry as a promising tool for individualized therapy

Septic syndromes remain a major although largely under-recognized health care problem and represent the first cause of mortality in intensive care units. While sepsis has, for long, been solely described as inducing a tremendous systemic inflammatory response, novel findings indicate that sepsis indeed initiates a more complex immunologic response that varies over time, with the concomitant occurrence of both pro- and anti-inflammatory mechanisms. As a resultant, after a short proinflammatory phase, septic patients enter a stage of protracted immunosuppression. This is illustrated in those patients by reactivation of dormant viruses (CMV or HSV) or infections due to pathogens, including fungi, which are normally pathogenic solely in immunocompromised hosts. Although mechanisms are not totally understood, these alterations might be directly responsible for worsening outcome in patients who survived initial resuscitation as nearly all immune functions are deeply compromised. Indeed, the magnitude and persistence over time of these dysfunctions have been associated with increased mortality and health-care associated infection rate. Consequently, new promising therapeutic avenues are currently emerging from those recent findings such as adjunctive immunostimulation (IFN-γ, GM-CSF, IL-7, anti-PD1/L1 antibodies) for the most immunosuppressed patients. Nevertheless, as there is no clinical sign of immune dysfunctions, the prerequisite for such therapeutic intervention relies on our capacity in identifying the patients who could benefit from immunostimulation. To date, the most robust biomarkers of sepsis-induced immunosuppression are measured by flow cytometry. Of them, the decreased expression of monocyte HLA-DR appears as a "gold standard." This review reports on the mechanisms sustaining sepsis-induced immunosuppression and its related biomarkers measurable by flow cytometry. The objective is to integrate the most recent facts in an up-to-date account of clinical results, flow cytometry aspects as well as issues in results standardization for multicenter studies. © 2015 International Clinical Cytometry Society.

Glucocorticoid-Induced Leucine Zipper: A Critical Factor in Macrophage Endotoxin Tolerance

Induction of glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids plays a key role in their anti-inflammatory action. In activated macrophages, GILZ levels are downregulated via tristetraprolin-mediated GILZ mRNA destabilization. To assess the functional significance of GILZ downregulation, we generated myeloid-specific GILZ knockout (KO) mice. GILZ-deficient macrophages displayed a higher responsiveness toward LPS, as indicated by increased TNF-α and IL-1β expression. This effect was due to an activation of ERK, which was significantly amplified in GILZ KO cells. The LPS-induced activation of macrophages is attenuated upon pretreatment of macrophages with low-dose LPS, an effect termed endotoxin tolerance. In LPS-tolerant macrophages, GILZ mRNA was stabilized, whereas ERK activation was strongly decreased. In contrast, GILZ KO macrophages exhibited a strongly reduced desensitization. To explore the contribution of GILZ expression in macrophages to endotoxin tolerance in vivo, we treated GILZ KO mice with repeated i.p. injections of low-dose LPS followed by treatment with high-dose LPS. LPS pretreatment resulted in reduced proinflammatory mediator expression upon high-dose LPS treatment in serum and tissues. In contrast, cytokine induction was preserved in tolerized GILZ KO animals. In summary, our data suggest that GILZ is a key regulator of macrophage functions.

Neutrophil extracellular traps in sepsis

Sepsis is the leading cause of death in critically ill patients in intensive care units. Early recognition of sepsis and proper therapy are essential to reduce patient mortality. Moreover, treatment options for this deleterious inflammatory response to infection are limited. Neutrophils play an essential role in the innate immune response, providing the first line of host defense. It has recently been shown that these cells can trap and kill microorganisms by releasing neutrophil extracellular traps (NETs) composed of chromatin and antimicrobial proteins. Although the beneficial role of NETs during infections has been demonstrated, there is increasing evidence that NETs and their components contribute to the pathogenesis of several diseases, including sepsis. The aim of this review was to summarize the current evidence implicating NETs, as well as their components, in the development of sepsis and to discuss their potential use as novel therapeutic targets and as prognostic markers in septic patients.

The macrophage mediates the renoprotective effects of endotoxin preconditioning

Preconditioning is a preventative approach, whereby minimized insults generate protection against subsequent larger exposures to the same or even different insults. In immune cells, endotoxin preconditioning downregulates the inflammatory response and yet, preserves the ability to contain infections. However, the protective mechanisms of preconditioning at the tissue level in organs such as the kidney remain poorly understood. Here, we show that endotoxin preconditioning confers renal epithelial protection in various models of sepsis in vivo. We also tested the hypothesis that this protection results from direct interactions between the preconditioning dose of endotoxin and the renal tubules. This hypothesis is on the basis of our previous findings that endotoxin toxicity to nonpreconditioned renal tubules was direct and independent of immune cells. Notably, we found that tubular protection after preconditioning has an absolute requirement for CD14-expressing myeloid cells and particularly, macrophages. Additionally, an intact macrophage CD14-TRIF signaling pathway was essential for tubular protection. The preconditioned state was characterized by increased macrophage number and trafficking within the kidney as well as clustering of macrophages around S1 proximal tubules. These macrophages exhibited increased M2 polarization and upregulation of redox and iron-handling molecules. In renal tubules, preconditioning prevented peroxisomal damage and abolished oxidative stress and injury to S2 and S3 tubules. In summary, these data suggest that macrophages are essential mediators of endotoxin preconditioning and required for renal tissue protection. Preconditioning is, therefore, an attractive model to investigate novel protective pathways for the prevention and treatment of sepsis.

Analysis of circulating plasmacytoid dendritic cells during the course of sepsis

BACKGROUND

Sepsis is characterized as a biphasic immune reaction in response to invading micro-organisms causing a life-threatening condition. This reaction is triggered by the activation of many different immune cells causing a dramatic inflammatory response often followed by immunosuppression. The balance of the immune response in this complex interplay of pro- and anti-inflammatory processes is crucial for the course of sepsis and host survival. For a better understanding of the involved mechanisms, a precise knowledge of participating immune cells in a timely manner is necessary.

METHODS

We analyzed circulating plasmacytoid dendritic cells (pDCs) by using multicolor, flow cytometric analysis in septic patients over 28 days. In addition, we assessed disease severity, organ failure, and outcome in these septic patients.

RESULTS

The numbers of circulating pDCs started to increase at day 1 after the onset of sepsis and were greatly increased from day 4 after sepsis onset. At days 7 and 14, the numbers of circulating pDCs peaked and returned to normal values at day 28 after the onset of sepsis. These changes were accompanied by increased expression of CD11b, which is known as crucial factor for transendothelial migration. In addition, the circulating pDCs in nonsurvivors showed greatly decreased values compared with survivors over the course of sepsis.

CONCLUSION

The results presented here support the concept that circulating pDCs might have an important role in the immune response during sepsis and might function as an early predictive biomarker for the outcome of sepsis.

Gamma-irradiated bacille Calmette-Guérin vaccination does not modulate the innate immune response during experimental human endotoxemia in adult males

Bacille Calmette-Guérin (BCG) vaccine exerts nonspecific immunostimulatory effects and may therefore represent a novel therapeutic option to treat sepsis-induced immunoparalysis. We investigated whether BCG vaccination modulates the systemic innate immune response in humans in vivo during experimental endotoxemia. We used inactivated gamma-irradiated BCG vaccine because of the potential risk of disseminated disease with the live vaccine in immunoparalyzed patients. In a randomized double-blind placebo-controlled study, healthy male volunteers were vaccinated with gamma-irradiated BCG (n = 10) or placebo (n = 10) and received 1 ng/kg lipopolysaccharide (LPS) intravenously on day 5 after vaccination to assess the in vivo immune response. Peripheral blood mononuclear cells were stimulated with various related and unrelated pathogens 5, 8 to 10, and 25 to 35 days after vaccination to assess ex vivo immune responses. BCG vaccination resulted in a scar in 90% of vaccinated subjects. LPS administration elicited a profound systemic immune response, characterized by increased levels of pro- and anti-inflammatory cytokines, hemodynamic changes, and flu-like symptoms. However, BCG modulated neither this in vivo immune response, nor ex vivo leukocyte responses at any time point. In conclusion, gamma-irradiated BCG is unlikely to represent an effective treatment option to restore immunocompetence in patients with sepsis-induced immunoparalysis. This trial is registered with NCT02085590.

Toll-like receptor 4 is essential to preserving cardiac function and survival in low-grade polymicrobial sepsis

BACKGROUND

Toll-like receptor 4 (TLR4), the receptor for endotoxin, mediates hyperinflammatory response and contributes to high mortality during both endotoxin shock and severe sepsis. However, little is known about the role of TLR4 in the pathogenesis of low-grade polymicrobial sepsis, which is often associated with immunosuppression.

METHODS

Low-grade polymicrobial sepsis was generated by cecum ligation and puncture. Mortality was monitored in wild- type (C57BL/10ScSn) and TLR4def (C57BL/10ScCr) mice. Ex vivo heart and individual cardiomyocyte function were assessed in Langendorff (Hugo Sachs Elektronik; Harvard Apparatus, Holliston, MA) and IonOptix systems (IonOptix, Milton, MA), respectively. Serum chemistry was tested for liver and kidney injury. Cytokines were examined using a multiplex immunoassay. Neutrophil migratory and phagocytic functions were assessed using flow cytometry. Reactive oxygen species were measured using redox-sensitive dichlorodihydrofluorescein dye.

RESULTS

Following cecum ligation and puncture, wild-type mice developed bacterial peritonitis with mild cardiac dysfunction (n=3 in sham and n=8 in cecum ligation and puncture) and a mortality of 23% within 14 days (n=22). In comparison, septic TLR4def mice had deleterious cardiac dysfunction (n=6 in sham and n=10 in cecum ligation and puncture), kidney and liver injury (n=7), and much higher mortality at 81% (n=21). The deleterious effects observed in septic TLR4def mice were associated with increased local and systemic cytokine response, reduced neutrophil migratory and phagocytic function, increased reactive oxygen species generation in leukocytes, and impaired bacterial clearance.

CONCLUSION

TLR4 plays an essential role in host defense against low-grade polymicrobial sepsis by mediating neutrophil migratory/phagocytic functions, attenuating inflammation, reducing reactive oxygen species generation, and enhanced bacterial clearance.

Immunosuppression after sepsis: systemic inflammation and sepsis induce a loss of naïve T-cells but no enduring cell-autonomous defects in T-cell function

Sepsis describes the life-threatening systemic inflammatory response (SIRS) of an organism to an infection and is the leading cause of mortality on intensive care units (ICU) worldwide. An acute episode of sepsis is characterized by the extensive release of cytokines and other mediators resulting in a dysregulated immune response leading to organ damage and/or death. This initial pro-inflammatory burst often transits into a state of immune suppression characterised by loss of immune cells and T-cell dysfunction at later disease stages in sepsis survivors. However, despite these appreciations, the precise nature of the evoked defect in T-cell immunity in post-acute phases of SIRS remains unknown. Here we present an in-depth functional analysis of T-cell function in post-acute SIRS/sepsis. We document that T-cell function is not compromised on a per cell basis in experimental rodent models of infection-free SIRS (LPS or CpG) or septic peritonitis. Transgenic antigen-specific T-cells feature an unaltered cytokine response if challenged in vivo and ex vivo with cognate antigens. Isolated CD4(+)/CD8(+) T-cells from post-acute septic animals do not exhibit defects in T-cell receptor-mediated activation at the the level of receptor-proximal signalling, activation marker upregulation or expansion. However, SIRS/sepsis induced transient lymphopenia and gave rise to an environment of immune attenuation at post acute disease stages. Thus, systemic inflammation has an acute impact on T-cell numbers and adaptive immunity, but does not cause major cell-autonomous enduring functional defects in T-cells.

[Epigenetic regulation in sepsis : current state of knowledge]

Sepsis is known to be a severe systemic immune reaction based on an infection of various origins. The initial immune response is accompanied by excess activation of immune cells and release of proinflammatory cytokines. Simultaneously initiated compensatory mechanisms lead to high levels of anti-inflammatory mediators to counterbalance the generalized inflammatory reaction; however, the compensatory immunoreaction itself equally overreacts and results in a prolonged sepsis-induced immunosuppression. The underlying mechanisms for these exaggerated immune responses and the resulting global immunosuppression that increase the risk for secondary infection are still unknown. Recent findings indicate that epigenetic mechanisms change basic properties of important immune cells by mechanisms leading to changes in gene expression. Dynamic exchanges of histone modifications result in a variation of transcription and seem to play a key role in cell function of macrophages and other immune cells. This article provides a current overview of epigenetic sepsis research and the sepsis-induced effects on the immune system.

Serum procalcitonin level and SOFA score at discharge from the intensive care unit predict post-intensive care unit mortality: a prospective study

Purpose

The final decision for discharge from the intensive care unit (ICU) is uncertain because it is made according to various patient parameters; however, it should be made on an objective evaluation. Previous reports have been inconsistent and unreliable in predicting post-ICU mortality. To identify predictive factors associated with post-ICU mortality, we analyzed physiological and laboratory data at ICU discharge.

Methods

Patients admitted to our ICU between September 2012 and August 2013 and staying for critical care>2 days were included. Sequential Organ Failure Assessment (SOFA) score; systemic inflammatory response syndrome score; white blood cell count; and serum C reactive protein, procalcitonin (PCT), interleukin-6 (IL-6), lactate, albumin, and hemoglobin levels were recorded. The primary end point was 90-day mortality after ICU discharge. Two hundred eighteen patients were enrolled (195 survivors, 23 non-survivors).

Results

Non-survivors presented a higher SOFA score and serum PCT, and IL-6 levels, as well as lower serum albumin and hemoglobin levels. Serum PCT, albumin, and SOFA score were associated with 90-day mortality in multiple logistic regression analysis. Hosmer-Lemeshow test showed chi-square value of 6.96, and P value of 0.54. The area under the curve (95% confidence interval) was 0.830 (0.771–0.890) for PCT, 0.688 (0.566–0.810) for albumin, 0.861 (0.796–0.927) for SOFA score, and increased to 0.913 (0.858–0.969) when these were combined. Serum PCT level at 0.57 ng/mL, serum albumin at 2.5 g/dL and SOFA score at 5.5 predict 90-day mortality, and high PCT, low albumin and high SOFA groups had significantly higher mortality. Serum PCT and SOFA score were significantly associated with survival days after ICU discharge in Cox regression analysis.

Conclusions

Serum PCT level and SOFA score at ICU discharge predict post-ICU mortality and survival days after ICU discharge. The combination of these two and albumin level might enable accurate prediction.

An integrated transcriptome and expressed variant analysis of sepsis survival and death

Background

Sepsis, a leading cause of morbidity and mortality, is not a homogeneous disease but rather a syndrome encompassing many heterogeneous pathophysiologies. Patient factors including genetics predispose to poor outcomes, though current clinical characterizations fail to identify those at greatest risk of progression and mortality.

Methods

The Community Acquired Pneumonia and Sepsis Outcome Diagnostic study enrolled 1,152 subjects with suspected sepsis. We sequenced peripheral blood RNA of 129 representative subjects with systemic inflammatory response syndrome (SIRS) or sepsis (SIRS due to infection), including 78 sepsis survivors and 28 sepsis non-survivors who had previously undergone plasma proteomic and metabolomic profiling. Gene expression differences were identified between sepsis survivors, sepsis non-survivors, and SIRS followed by gene enrichment pathway analysis. Expressed sequence variants were identified followed by testing for association with sepsis outcomes.

Results

The expression of 338 genes differed between subjects with SIRS and those with sepsis, primarily reflecting immune activation in sepsis. Expression of 1,238 genes differed with sepsis outcome: non-survivors had lower expression of many immune function-related genes. Functional genetic variants associated with sepsis mortality were sought based on a common disease-rare variant hypothesis. VPS9D1, whose expression was increased in sepsis survivors, had a higher burden of missense variants in sepsis survivors. The presence of variants was associated with altered expression of 3,799 genes, primarily reflecting Golgi and endosome biology.

Conclusions

The activation of immune response-related genes seen in sepsis survivors was muted in sepsis non-survivors. The association of sepsis survival with a robust immune response and the presence of missense variants in VPS9D1 warrants replication and further functional studies.

Trial registration

ClinicalTrials.gov NCT00258869. Registered on 23 November 2005.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-014-0111-5) contains supplementary material, which is available to authorized users.

T helper type 2-polarized invariant natural killer T cells reduce disease severity in acute intra-abdominal sepsis

Sepsis is characterized by a severe systemic inflammatory response to infection that is associated with high morbidity and mortality despite optimal care. Invariant natural killer T (iNK T) cells are potent regulatory lymphocytes that can produce pro- and/or anti-inflammatory cytokines, thus shaping the course and nature of immune responses; however, little is known about their role in sepsis. We demonstrate here that patients with sepsis/severe sepsis have significantly elevated proportions of iNK T cells in their peripheral blood (as a percentage of their circulating T cells) compared to non-septic patients. We therefore investigated the role of iNK T cells in a mouse model of intra-abdominal sepsis (IAS). Our data show that iNK T cells are pathogenic in IAS, and that T helper type 2 (Th2) polarization of iNK T cells using the synthetic glycolipid OCH significantly reduces mortality from IAS. This reduction in mortality is associated with the systemic elevation of the anti-inflammatory cytokine interleukin (IL)-13 and reduction of several proinflammatory cytokines within the spleen, notably interleukin (IL)-17. Finally, we show that treatment of sepsis with OCH in mice is accompanied by significantly reduced apoptosis of splenic T and B lymphocytes and macrophages, but not natural killer cells. We propose that modulation of iNK T cell responses towards a Th2 phenotype may be an effective therapeutic strategy in early sepsis.

Assessing the immune status of critically ill trauma patients by flow cytometry

BACKGROUND

Unintentional injury or trauma remains the leading cause of death among young adults. About one fifth of these trauma patients require care in an intensive care unit (ICU) because of severity of injuries and comorbidities. Patients hospitalized in an ICU are at increased risk for nosocomial infections, such as urinary tract infections, pneumonia, bacteremia, and wound infections. Many of these patients will develop sepsis or septic shock, and some will progress to multiple organ failure and death. The balance between the proinflammatory and counterinflammatory immune response appears to be a driving factor in this progression. At present, there is no proposed method for the timely detection of the immune status in trauma patients, making rational decisions to use immune-altering therapies difficult.

OBJECTIVE

We demonstrate that flow cytometry, with its capabilities to characterize and/or enumerate (a) leukocyte subtypes, (b) leukocyte activation markers, (c) leukocyte-derived cytokines and microvesicles, and (d) leukocyte function is well suited to monitor the immune status of critically ill trauma patients.

METHODS

Information for the review was obtained from the extant literature.

DISCUSSION

We suggest that flow cytometry is a research method that might aid nurse scientists in investigating the immune status of critically ill patients, the recovery status of conditions such as hemorrhagic shock and tissue injury and the relationship between cancer disease progression and symptoms. Therefore, flow cytometry has the potential to broaden nursing research priority areas so that a comprehensive approach to understanding the cellular response is attained.

An Endotoxin Tolerance Signature Predicts Sepsis and Organ Dysfunction at Initial Clinical Presentation

Background

Sepsis involves aberrant immune responses to infection, but the exact nature of this immune dysfunction remains poorly defined. Bacterial endotoxins like lipopolysaccharide (LPS) are potent inducers of inflammation, which has been associated with the pathophysiology of sepsis, but repeated exposure can also induce a suppressive effect known as endotoxin tolerance or cellular reprogramming. It has been proposed that endotoxin tolerance might be associated with the immunosuppressive state that was primarily observed during late-stage sepsis. However, this relationship remains poorly characterised. Here we clarify the underlying mechanisms and timing of immune dysfunction in sepsis.

Methods

We defined a gene expression signature characteristic of endotoxin tolerance. Gene-set test approaches were used to correlate this signature with early sepsis, both newly and retrospectively analysing microarrays from 593 patients in 11 cohorts. Then we recruited a unique cohort of possible sepsis patients at first clinical presentation in an independent blinded controlled observational study to determine whether this signature was associated with the development of confirmed sepsis and organ dysfunction.

Findings

All sepsis patients presented an expression profile strongly associated with the endotoxin tolerance signature (p < 0.01; AUC 96.1%). Importantly, this signature further differentiated between suspected sepsis patients who did, or did not, go on to develop confirmed sepsis, and predicted the development of organ dysfunction.

Interpretation

Our data support an updated model of sepsis pathogenesis in which endotoxin tolerance-mediated immune dysfunction (cellular reprogramming) is present throughout the clinical course of disease and related to disease severity. Thus endotoxin tolerance might offer new insights guiding the development of new therapies and diagnostics for early sepsis.

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Addresses sepsis that affects up to 18 million persons annually with up to 5 million deaths worldwide.

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Describes an endotoxin tolerance gene expression signature associated with consecutive treatments with endotoxin and reflecting cellular reprogramming.

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Using a meta-analysis of the literature demonstrates the statistically significant association (p < 0.01; AUC 96.1%) of this endotoxin tolerance signature with early (day 1–3 after ICU admission) sepsis in 593 patients in 11 adult or child cohorts.

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Demonstrates, at first clinical presentation, the ability of this signature to predict the eventual diagnosis of sepsis and organ failure in an independent blinded controlled observational study of a unique cohort of possible sepsis patients.

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This study provides new insights that have the potential to guide the development of new therapies and diagnostics for early sepsis.

Post-infectious immune suppression: a new paradigm of severe infections

Infectious diseases remain a major public health issue in both developing and developed countries. For instance, there is still a high rate of morbidity and mortality due to seasonal influenza outbreaks and severe bacterial sepsis, despite major advances in their prevention and treatment. It is now clear that severe influenza and bacterial infections promote susceptibility for superinfections worsening the prognosis. Various immune defects acquired during severe infection may result in complex immunosuppression and may affect both innate and adaptive components. Some animal models of these common clinical situations have demonstrated the increased susceptibility of infected hosts to secondary infectious insult and allowed assessing the regulatory mechanisms. Such pathophysiological advances may help create new immunomodulatory therapeutics for infected patients exposed to severe secondary sepsis.

Modulatory role of vitamin A on the Candida albicans-induced immune response in human monocytes

Beyond its well-documented role in reproduction, embryogenesis and maintenance of body tissues, vitamin A has attracted considerable attention due to its immunomodulatory effects on both the innate and the adaptive immune responses. In infectious diseases, vitamin A has been shown to have a host-protective effect in infections of bacterial, viral or protozoan origin. Nevertheless, its impact in fungal infections remains unknown. Meanwhile, the frequency of invasive mycoses keeps on growing, with Candida albicans being the major opportunistic fungal pathogen and associated with high mortality. In the present work, we explored the impact of all-trans retinoic acid (atRA), the most active metabolite of vitamin A, on the innate immune response against C.albicans in human monocytes. Our results show a strong immunomodulatory role for atRA, leading to a significant down-regulation of the fungi-induced expression and secretion of the pro-inflammatory cytokines TNFα, IL6 and IL12. Moreover, atRA significantly suppressed the expression of Dectin-1, a major fungal pattern recognition receptor, as well as the Dectin-1-dependent cytokine production. Both RAR-dependent and RAR-independent mechanisms seem to play a role in the atRA-mediated immunomodulation. Our findings open a new direction to elucidate the role of vitamin A on the immune function during fungal infections.

Activation of central muscarinic receptor type 1 prevents development of endotoxin tolerance in rat liver

Endotoxin tolerance is a mechanism in which cells receiving low doses of endotoxin, enter a transient phase with less inflammatory response to the next endotoxin challenges. Central nervous system is known to modulate systemic inflammation through activation of the cholinergic system; however, the role of central anti-inflammatory pathway in pathophysiology of hepatic endotoxin tolerance is unknown. Our study was designed to assess the effect central muscarinic type 1 receptor (M1) activation on development of endotoxin tolerance in rat liver. Endotoxin tolerance was induced by daily intraperitoneal injection of endotoxin (1 mg/kg) for 5 days. Animals were randomly divided into two groups which received intracerebroventricular injection of either MCNA-343 (an M1 agonist, 5 ng/kg) or saline 1h after intraperitoneal injection of saline or endotoxin. The responsiveness to endotoxin was assessed by measuring hepatic MCP-1 (monocyte chemotactic protein-1), iNOS (inducible nitric oxide synthase) and TNF-α (tumor necrosis-α) mRNA expression 3h after intraperitoneal administration of endotoxin using quantitative RT-PCR. A significant reduction in hepatic expression of MCP-1, iNOS and TNF-α was observed in rats with 5 days endotoxin challenge in comparison with rats given a single dose of endotoxin. There was no significant difference in hepatic expression of MCP-1, iNOS or TNF-α between acute and chronic LPS-treated groups in rats given MCNA-343. Central MCNA-343 stimulation could prevent the induction of hepatic endotoxin tolerance in animals receiving repeated doses of endotoxin. This indicates that M1 cholinergic receptor activation in the central nervous system can modulate endotoxin tolerance in rat liver.

Sepsis induced immunosuppression: Implications for secondary infections and complications

Sepsis is the commonest cause of admission to medical ICUs across the world. Mortality from sepsis continues to be high. Besides shock and multi-organ dysfunction occurring following the intense inflammatory reaction to sepsis, complications arising from sepsis-related immunoparalysis contribute to the morbidity and mortality from sepsis. This review explores the basis for sepsis related immune dysfunction and discusses its clinical implications for the treating intensivist. Recent trends indicate that a significant proportion of septic patients succumb to the complications of secondary infections and chronic critical care illness from the initial bout of sepsis. Therefore care-givers in the ICU need to be aware of the impediments posed by sepsis-related immune dysfunction that can impair recovery in patients with sepsis and contribute to sepsis-related mortality.