The role of T regulatory cells in human sepsis

Analysis of signature genes and association with immune cells infiltration in pediatric septic shock

Background

Early diagnosis of septic shock in children is critical for prognosis. This study committed to investigate the signature genes and their connection with immune cells in pediatric septic shock.

Methods

We screened a dataset of children with septic shock from the GEO database and analyzed differentially expressed genes (DEGs). Functional enrichment analysis was performed for these DEGs. Weighted gene co-expression network analysis (WCGNA) was used to screen the key modules. Least absolute shrinkage and selection operator (LASSO) and random forest analysis were finally applied to identify the signature genes. Then gene set enrichment analysis (GSEA) was exerted to explore the signaling pathways related to the hub genes. And the immune cells infiltration was subsequently classified via using CIBERSORT.

Results

A total of 534 DEGs were screened from GSE26440. The data then was clustered into 17 modules via WGCNA, which MEgrey module was significantly related to pediatric septic shock (cor=-0.62, p<0.0001). LASSO and random forest algorithms were applied to select the signature genes, containing UPP1, S100A9, KIF1B, S100A12, SLC26A8. The receiver operating characteristic curve (ROC) of these signature genes was 0.965, 0.977, 0.984, 0.991 and 0.989, respectively, which were verified in the external dataset from GSE13904. GSEA analysis showed these signature genes involve in positively correlated fructose and mannose metabolism and starch and sucrose metabolism signaling pathway. CIBERSORT suggested these signature genes may participate in immune cells infiltration.

Conclusion

UPP1, S100A9, KIF1B, S100A12, SLC26A8 emerge remarkable diagnostic performance in pediatric septic shock and involved in immune cells infiltration.

Interleukin 35 contributes to immunosuppression by regulating inflammatory cytokines and T cell populations in the acute phase of sepsis

Cytokines interact closely with each other and play a crucial role in the progression of sepsis. We focused on the associations of a cytokine network with IL-35 in sepsis. First, the retrospective study included 42 patients with sepsis and 23 healthy controls. Blood samples were collected from patients on days 1, 2, 4. Levels of IL-35, IL-1β, IL-4, IL-6, IL-10, IL-17A, TNF-α and IFN-γ were measured. They all increased to various extend on days 1, 2, 4, and strongly associated with markers of disease severity. Network analysis revealed a network formed by IL-35, with IL-6, IL-10, IL-17A, TNF-α and IFN-γ throughout the acute phase of sepsis(days 1, 2 and4). Then, the CLP-induced septic rats were used. The recombinant human IL-35(rIL-35) upregulated the levels of IL-10, but downregulated IL-4, IL-6, IL-17A, TNF-α and IFN-γ, while it had no significant effect on IL-1β, and upregulated the percentages of CD4⁺CD25⁺Tregs, and iTR35, but downregulated Teff cells in the peripheral blood. The rIL-35 reduced inflammation damage and improved prognosis of the septic rats. IL-35 forms a network with other cytokines and plays a major role in the immunopathogenesis of sepsis.

Natural killer cell deficiency experiences higher risk of sepsis after critical intracerebral hemorrhage

Background: Lymphopenia is common in intracerebral hemorrhage (ICH) and may predispose to severe infections such as sepsis. However, what specific kind of lymphocytes subsets decreases is still unclear. We investigated the impact of lymphocytes subsets on post-critical ICH infections and mortality.

Methods: Consecutive ICH patients (admitted to a single center between January 2017 and January 2018) were prospectively assessed to evaluate the following main parameters: peripheral blood lymphocytes, infections, and clinical scores. Predicting factors of sepsis were measured using multivariate Logistic regressions analysis. A Kaplan–Meier survival curve was performed to compare the mortality between septic and nonseptic patients. Survival status was evaluated by multivariate Cox regression analysis.

Results: In total, 112 critical ICH cases were enrolled including 29 septic patients. Total counts of lymphocytes decreased accordingly with reduced lymphocyte subsets, especially natural killer (NK) cells and CD8⁺T lymphocytes after ICH. Septic patients had a higher incidence of pneumonia, a longer length of stay, higher 90-day mortality, and worse long-term outcomes. Multivariate Logistic regression analysis showed venous catheterization, high APACHE-II score (>15), low GCS score (3–5), and NK cells percentages on admission were independently associated with ensuing sepsis. After sepsis, the percentages of CD4+T and NK cells percentages decreased, CD8+T cells increased followed by a significantly decreased CD4/CD8 ratio. Bloodstream infection alone directly affected the survival status of patients with sepsis.

Conclusions: Critical ICH patients underwent immune dysfunction and NK cells deficiency could favor nosocomial threatening sepsis after ICH.

The clinical outcomes and biomarker features of severe sepsis/septic shock with severe neutropenia: a retrospective cohort study

BACKGROUND

Severe sepsis/septic shock with severe neutropenia often leads to poor prognosis. However, it is unknown if severe neutropenia is associated with different clinical outcomes and biomarker features in severe sepsis/septic patients.

METHODS

This retrospective cohort study enrolled 141 severe sepsis/septic shock patients admitted to intensive care unit of Shanghai Children's Medical Center between January 2015 and November 2019. Patients were followed up for the development of ventilation support, the use of vasoactive drugs, continuous renal replacement therapy (CRRT) procedure, and mortality. Biomarkers that reflect the level of inflammation in severe sepsis/septic shock patients with neutropenia were compared to that in patients without neutropenia.

RESULTS

Of 141 patients enrolled, 54 patients suffered from severe sepsis/septic shock with severe neutropenia. In patients with severe sepsis/septic shock, severe neutropenia as a complication was an independent risk factor for the use of vasoactive drugs (RR 9.796; 95% CI: 3.774, 25.429; P<0.001), but not for ventilation support (RR 0.157; 95% CI: 0.06, 0.414; P<0.001), CRRT procedure (RR 1.032; 95% CI: 0.359, 2.969; P=0.953) or 28-day mortality (RR 1.405; 95% CI: 0.533, 3.708; P=0.492). Severe sepsis/septic patients with severe neutropenia had a higher plasma level of the following biomarkers: c-reaction protein (CRP) (180.5 vs. 121 mg/mL, P<0.001), procalcitonin (PCT) (12.15 vs. 2.7 ng/mL; P=0.005), interleukin (IL)-6 (316.83 vs. 55.77 pg/mL, P<0.001), IL-10 (39.165 vs. 10.09 pg/mL, P<0.001), interferon (IFN)-γ (6.155 vs. 3.71 pg/mL, P=0.016), and the percentage of regulatory T cells (Tregs) (2.7% vs. 2.09%, P=0.003). Based on the receiver operating characteristic curves, IL-10 exhibited high specificity (79.4%) in evaluating the prognosis of septic patients with neutropenia.

CONCLUSIONS

In patients with severe sepsis/septic shock, being complicated with severe neutropenia is associated with higher proportion of using vasoactive drugs, and those patients tend to have higher plasma levels of IL-6, IL-10, IFN-γ and percentage of Treg.

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.

The bone marrow niche components are adversely affected in sepsis

Multiple organ dysfunction is an important cause of death in patients with sepsis. Currently, few studies have focused on the impact of sepsis on bone marrow (BM), especially on the cell components of BM niche. In this study, we performed mouse sepsis models by intraperitoneal injection of LPS and cecal ligation and puncture (CLP). The changes of niche major components in the mouse BM among vascular structures, mesenchymal stem cells and Treg cells were observed and analyzed. The results showed that pathological changes in BM was earlier and more prominent than in other organs, and various cell components of the BM niche changed significantly, of which vascular endothelial cells increased transiently with vascular remodeling and the regulatory T cells decreased over a long period of time. These results indicated that the components of the BM niche underwent series of adaptive changes in sepsis.

Glycolytic and lipid oxidative metabolic programs are essential for freshly-isolated regulatory T cells in mice with sepsis

Freshly-isolated Treg cells showed metabolic reprogramming in mice with sepsis, mainly manifested by increased glycolysis and fatty acid oxidation pathways.

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.

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.

T cells and their immunometabolism: A novel way to understanding sepsis immunopathogenesis and future therapeutics

Sepsis has always been considered as a big challenge for pharmaceutical companies in terms of discovering and designing new therapeutics. The pathogenesis of sepsis involves aberrant activation of innate immune cells (i.e. macrophages, neutrophils etc.) at early stages. However, a stage of immunosuppression is also observed during sepsis even in the patients who have recovered from it. This stage of immunosuppression is observed due to the loss of conventional (i.e. CD4⁺, CD8⁺) T cells, Th17 cells and an upregulation of regulatory T cells (Tregs). This process also impacts metabolic processes controlling immune cell metabolism called immunometabolism. The present review is focused on the T cell-mediated immune response, their immunometabolism and targeting T cell immunometabolism during sepsis as future therapeutic approach. The first part of the manuscripts describes an impact of sepsis on conventional T cells, Th17 cells and Tregs along with their impact on sepsis. The subsequent section further describes the immunometabolism of these cells (CD4⁺, CD8⁺, Th17, and Tregs) under normal conditions and during sepsis-induced immunosuppression. The article ends with the therapeutic targeting of T cell immunometabolism (both conventional T cells and Tregs) during sepsis as a future immunomodulatory approach for its management.

Sepsis increases perioperative metastases in a murine model

Background

Cancer surgery can promote tumour metastases and worsen prognosis, however, the effect of perioperative complications on metastatic disease remains unclear. In this study we sought to evaluate the effect of common perioperative complications including perioperative blood loss, hypothermia, and sepsis on tumour metastases in a murine model.

Methods

Prior to surgery, pulmonary metastases were established by intravenous challenge of CT26LacZ colon cancer cells in BALB/c mice. Surgical stress was generated through partial hepatectomy (PH) or left nephrectomy (LN). Sepsis was induced by puncturing the cecum to express stool into the abdomen. Hemorrhagic shock was induced by removal of 30% of total blood volume (i.e. stage 3 hemorrhage) via the saphenous vein. Hypothermia was induced by removing the heating apparatus during surgery and lowering core body temperatures to 30 °C. Lung tumour burden was quantified 3 days following surgery.

Results

Surgically stressed mice subjected to stage 3 hemorrhage or hypothermia did not show an additional increase in lung tumour burden. In contrast, surgically stressed mice subjected to intraoperative sepsis demonstrated an additional 2-fold increase in the number of tumour metastases. Furthermore, natural killer (NK) cell function, as assessed by YAC-1 tumour cell lysis, was significantly attenuated in surgically stressed mice subjected to intraoperative sepsis. Both NK cell-mediated cytotoxic function and lung tumour burden were improved with perioperative administration of polyI:C, which is a toll-like receptor (TLR)-3 ligand.

Conclusions

Perioperative sepsis alone, but not hemorrhage or hypothermia, enhances the prometastatic effect of surgery in murine models of cancer. Understanding the cellular mechanisms underlying perioperative immune suppression will facilitate the development of immunomodulation strategies that can attenuate metastatic disease.

Toll-like receptor 4 deficiency increases resistance in sepsis-induced immune dysfunction

Sepsis constitutes a serious life-threatening syndrome associated with complications of deregulated inflammatory response against endotoxin/lipopolysaccharide (LPS)-mediated severe infection. Toll-like receptor 4 (TLR4) plays a critical role in the activation of innate immunity through recognition of LPS. However, the impact of TLR4 signaling on the development of sepsis-induced immune dysfunction remains unclear. The aim of this study was to investigate the effect of TLR4 on regulatory T cells (Tregs) and its potential mechanism. To simulate sepsis, male C57BL/6 (wild-type) and C57BL/10ScNJNJU (TLR4^-/-) mice were subjected to cecal ligation and puncture (CLP). After 24h, pro- and anti-inflammatory cytokine secretion, neutrophil and macrophage lung and liver infiltration were assessed to evaluate the sepsis-induced inflammatory response. The quantity and apoptotic rate of Tregs were measured. The expression of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and forkhead/winged helix transcription factor p3 (Foxp3) were analyzed. Cytokine (i.e., TNF-α, IL-2, IL-10, and IL-4) secretion by Tregs in the cell suspensions and the suppressive activity on CD4⁺CD25^- T cell proliferation were also determined in vitro. At 24h after the CLP procedure, the wild-type mice exhibited increased Treg levels and expression, and secreted inflammatory factors in the serum were markedly overproduced. However, the TLR4^-/- mice attenuated the increased Treg expression and inflammatory factor overproduction. These results indicate that in a model of post-septic mice, TLR4 deficiency improves immune paralysis by attenuating Treg activity and restoring a pro-inflammatory cytokine balance. Thus, modulation of the TLR4 activity may be useful in preventing immune dysfunction in sepsis.

Enteric immunity, the gut microbiome, and sepsis: Rethinking the germ theory of disease

Sepsis is a poorly understood syndrome of systemic inflammation responsible for hundreds of thousands of deaths every year. The integrity of the gut epithelium and competence of adaptive immune responses are notoriously compromised during sepsis, and the prevalent assumption in the scientific and medical community is that intestinal commensals have a detrimental role in the systemic inflammation and susceptibility to nosocomial infections seen in critically ill, septic patients. However, breakthroughs in the last decade provide strong credence to the idea that our mucosal microbiome plays an essential role in adaptive immunity, where a human host and its prokaryotic colonists seem to exist in a carefully negotiated armistice with compromises and benefits that go both ways. In this review, we re-examine the notion that intestinal contents are the driving force of critical illness. An overview of the interaction between the microbiome and the immune system is provided, with a special focus on the impact of commensals in priming and the careful balance between normal intestinal flora and pathogenic organisms residing in the gut microbiome. Based on the data in hand, we hypothesize that sepsis induces imbalances in microbial populations residing in the gut, along with compromises in epithelial integrity. As a result, normal antigen sampling becomes impaired, and proliferative cues are intermixed with inhibitory signals. This situates the microbiome, the gut, and its complex immune network of cells and bacteria, at the center of aberrant immune responses during and after sepsis.

The Involvement of Danger-Associated Molecular Patterns in the Development of Immunoparalysis in Cardiac Arrest Patients

OBJECTIVES

After cardiac arrest, patients are highly vulnerable toward infections, possibly due to a suppressed state of the immune system called "immunoparalysis." We investigated if immunoparalysis develops following cardiac arrest and whether the release of danger-associated molecular patterns could be involved.

DESIGN

Observational study.

SETTING

ICU of a university medical center.

PATIENTS

Fourteen post-cardiac arrest patients treated with mild therapeutic hypothermia for 24 hours and 11 control subjects.

MEASUREMENTS AND MAIN RESULTS

Plasma cytokines showed highest levels within 24 hours after cardiac arrest and decreased during the next 2 days. By contrast, ex vivo production of cytokines interleukin-6, tumor necrosis factor-α, and interleukin-10 by lipopolysaccharide-stimulated leukocytes was severely impaired compared with control subjects, with most profound effects observed at day 0, and only partially recovering afterward. Compared with incubation at 37°C, incubation at 32°C resulted in higher interleukin-6 and lower interleukin-10 production by lipopolysaccharide-stimulated leukocytes of control subjects, but not of patients. Plasma nuclear DNA, used as a marker for general danger-associated molecular pattern release, and the specific danger-associated molecular patterns (EN-RAGE and heat shock protein 70) were substantially higher in patients at days 0 and 1 compared with control subjects. Furthermore, plasma heat shock protein 70 levels were negatively correlated with ex vivo production of inflammatory mediators interleukin-6, tumor necrosis factor-α, and interleukin-10. Extracellular newly identified receptor for advanced glycation end products-binding protein levels only showed a significant negative correlation with ex vivo production of interleukin-6 and tumor necrosis factor-α and a borderline significant inverse correlation with interleukin-10. No significant correlations were observed between plasma nuclear DNA levels and ex vivo cytokine production.

INTERVENTIONS

None.

CONCLUSIONS

Release of danger-associated molecular patterns during the first days after cardiac arrest is associated with the development of immunoparalysis. This could explain the increased susceptibility toward infections in cardiac arrest patients.

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.

New insights into the resolution of inflammation

The goal of treating chronic inflammatory diseases must be to inhibit persistent inflammation and restore tissue function. To achieve this we need to improve our understanding of the pathways that drive inflammation as well as those that bring about its resolution. In particular, resolution of inflammation is driven by a complex set of mediators that regulate cellular events required to clear inflammatory cells from sites of injury or infection and restore homeostasis. Indeed, it may be argued that dysfunctional resolution may underpin the aetiology of some chronic inflammatory disease and that a novel goal in treating such diseases is to develop drugs based on the mode of endogenous pro-resolution factors in order to drive on-going inflammation down a pro-resolution pathway. And while we are improving our understanding of the resolution of acute and chronic inflammation, much remains to be discovered. Here we will discuss the key endogenous checkpoints necessary for mounting an effective yet limited inflammatory response and the crucial biochemical pathways necessary to prevent its persistence and trigger its resolution. In doing so, we will provide an update on what is known about resolution of acute inflammation, in particular its link with adaptive immunity.

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.

Urinary trypsin inhibitor attenuated inflammatory response of patients undergoing cardiopulmonary bypass by inducing activated Treg cells

The urinary trypsin inhibitor (ulinastatin) is used in the clinic to prevent inflammatory responses in patients undergoing cardiopulmonary bypass (CPB); however, the anti-inflammatory mechanism is unclear. In the current study, we recruited 40 patients undergoing selective cardiac valve replacement surgery; and these patients were randomly divided into two groups (ulinastatin group [UG] and control group [CG]). We collected peripheral blood preoperatively, at the end of CPB, and postoperative days 1 and 3 and analyzed the kinetic changes in regulatory T (Treg) cell subsets. There was no statistically significant difference in the number of CD4(+) T cells between the two groups. The number of CD4(+)CD25(+) Treg cells, especially the suppressive activated Treg (aTreg) subset, was higher in the UG than the CG 1 and 3 days postoperatively. Thus, ulinastatin alleviated the inflammatory response during CPB by inducing the expansion of aTreg cells.

Proresolving lipid mediators and mechanisms in the resolution of acute inflammation

Inflammatory responses, like all biological cascades, are shaped by a delicate balance between positive and negative feedback loops. It is now clear that in addition to positive and negative checkpoints, the inflammatory cascade rather unexpectedly boasts an additional checkpoint, a family of chemicals that actively promote resolution and tissue repair without compromising host defense. Indeed, the resolution phase of inflammation is just as actively orchestrated and carefully choreographed as its induction and inhibition. In this review, we explore the immunological consequences of omega-3-derived specialized proresolving mediators (SPMs) and discuss their place within what is currently understood of the role of the arachidonic acid-derived prostaglandins, lipoxins, and their natural C15-epimers. We propose that treatment of inflammation should not be restricted to the use of inhibitors of the acute cascade (antagonism) but broadened to take account of the enormous therapeutic potential of inducers (agonists) of the resolution phase of inflammation.

Serial changes of CD4+CD25+FoxP3+ regulatory T cell in canine model of sepsis induced by endotoxin

Regulatory T cells (Tregs) suppress the immune system and maintain the homeostasis of the immune system in healthy dogs. In septic patients, the percentage of circulating Tregs is increasing, which may cause the sepsis-induced immunosuppression. This study was performed to investigate the changes of the percentage of Tregs in total lymphocytes of the peripheral blood in the experimental canine endotoxemia model. The animals injected with a high dose lipopolysaccharide (LPS) induced severe leukopenia followed by leukocytosis, but the total lymphocytes number was relatively consistent. As a result of flow cytometric analysis, the percentage of Tregs in total lymphocytes of the peripheral blood was 8.45 ± 1.30% (day 0), and it temporarily decreased 2.54 ± 1.16% (day 1) and increased continuously until the end of the experiment (14.34 ± 4.10% on day 3 and 25.70 ± 7.39% on day 7), respectively. This study provides basic information in physiologic and immunologic changes in Tregs in dogs with sepsis model.

Pathways mediating resolution of inflammation: when enough is too much

Patients with critical illness, and in particular sepsis, are now recognized to undergo unifying, pathogenic disturbances of immune function. Whilst scientific and therapeutic focus has traditionally been on understanding and modulating the initial pro-inflammatory limb, recent years have witnessed a refocusing on the development and importance of immunosuppressive 'anti-inflammatory' pathways. Several mechanisms are known to drive this phenomenon; however, no overriding conceptual framework justifies them. In this article we review the contribution of pro-resolution pathways to this phenotype, describing the observed immune alterations in terms of either a failure of resolution of inflammation or the persistence of pro-resolution processes causing inappropriate 'injurious resolution'-a novel hypothesis. The dysregulation of key processes in critical illness, including apoptosis of infiltrating neutrophils and their efferocytosis by macrophages, are discussed, along with the emerging role of specialized cell subtypes Gr1(+) CD11b(+) myeloid-derived suppressor cells and CD4(+) CD25(+) FoxP3(+) T-regulatory cells.

The changing immune system in sepsis: is individualized immuno-modulatory therapy the answer?

Sepsis remains the leading cause of death in most intensive care units. Advances in understanding the immune response to sepsis provide the opportunity to develop more effective therapies. The immune response in sepsis can be characterized by a cytokine-mediated hyper-inflammatory phase, which most patients survive, and a subsequent immune-suppressive phase. Patients fail to eradicate invading pathogens and are susceptible to opportunistic organisms in the hypo-inflammatory phase. Many mechanisms are responsible for sepsis-induced immuno-suppression, including apoptotic depletion of immune cells, increased T regulatory and myeloid-derived suppressor cells, and cellular exhaustion. Currently in clinical trial for sepsis are granulocyte macrophage colony stimulating factor and interferon gamma, immune-therapeutic agents that boost patient immunity. Immuno-adjuvants with promise in clinically relevant animal models of sepsis include anti-programmed cell death-1 and interleukin-7. The future of immune therapy in sepsis will necessitate identification of the immunologic phase using clinical and laboratory parameters as well as biomarkers of innate and adaptive immunity.

Biomarkers of sepsis

Sepsis is an unusual systemic reaction to what is sometimes an otherwise ordinary infection, and it probably represents a pattern of response by the immune system to injury. A hyper-inflammatory response is followed by an immunosuppressive phase during which multiple organ dysfunction is present and the patient is susceptible to nosocomial infection. Biomarkers to diagnose sepsis may allow early intervention which, although primarily supportive, can reduce the risk of death. Although lactate is currently the most commonly used biomarker to identify sepsis, other biomarkers may help to enhance lactate’s effectiveness; these include markers of the hyper-inflammatory phase of sepsis, such as pro-inflammatory cytokines and chemokines; proteins such as C-reactive protein and procalcitonin which are synthesized in response to infection and inflammation; and markers of neutrophil and monocyte activation. Recently, markers of the immunosuppressive phase of sepsis, such as anti-inflammatory cytokines, and alterations of the cell surface markers of monocytes and lymphocytes have been examined. Combinations of pro- and anti-inflammatory biomarkers in a multi-marker panel may help identify patients who are developing severe sepsis before organ dysfunction has advanced too far. Combined with innovative approaches to treatment that target the immunosuppressive phase, these biomarkers may help to reduce the mortality rate associated with severe sepsis which, despite advances in supportive measures, remains high.

Bench-to-bedside review: Natural killer cells in sepsis - guilty or not guilty?

Bacterial sepsis and septic shock are complex inflammatory disorders associated with a systemic inflammatory response syndrome. In the most severe cases of infection, an overzealous release of pro-inflammatory cytokines and inflammatory mediators by activated leukocytes, epithelial cells and endothelial cells, known as a 'cytokine storm', leads to deleterious effects such as organ dysfunction and even death. By the end of the 20th century, natural killer (NK) cells were for the first time identified as important players during sepsis. The role of this cell type was, however, double-edged, either 'angel' or 'devil' depending upon the bacterial infection model under study. Bacterial sensors (such as Toll-like receptors) have recently been shown to be expressed at the protein level in these cells. In addition, NK cells are important sources of interferon-γ and granulocyte-macrophage colony-stimulating factor, which are pro-inflammatory cytokines necessary to fight infection but can contribute to deleterious inflammation as well. Interestingly, an adaptative response occurs aimed to silence them, similar to the well-known phenomenon of endotoxin reprogramming.

Dendritic cell apoptosis and the pathogenesis of dengue

Dengue viruses and other members of the Flaviviridae family are emerging human pathogens. Dengue is transmitted to humans by Aedes aegypti female mosquitoes. Following infection through the bite, cells of the hematopoietic lineage, like dendritic cells, are the first targets of dengue virus infection. Dendritic cells (DCs) are key antigen presenting cells, sensing pathogens, processing and presenting the antigens to T lymphocytes, and triggering an adaptive immune response. Infection of DCs by dengue virus may induce apoptosis, impairing their ability to present antigens to T cells, and thereby contributing to dengue pathogenesis. This review focuses on general mechanisms by which dengue virus triggers apoptosis, and possible influence of DC-apoptosis on dengue disease severity.

The role of regulatory T cells in the pathogenesis of sepsis and its clinical implication

Sepsis is denoted as a complex syndrome that results from a serious infection followed by amplified and dysregulated inflammatory response. The complex immune response associated with sepsis results in a high rate of morbidity and mortality, despite substantial basic science and clinical advances. Recently, accumulating evidence have demonstrated that regulatory T cells (Tregs) play important roles in suppression of immune response, as demonstrated by the number increase and functional enhancement following the onset of severe sepsis or septic shock. This article reviews recent advances in understanding the potential role of Tregs in the pathophysiology of septic response, as well as implications in the development of novel therapeutic strategies for improving the clinical outcome of patients with severe injury and subsequent septic complications.

Reproductive immunology: current status and future directions (part I)

Extensive research work over the past couple of decades has indicated a series of intricate relations between immune and reproductive systems. A range of reproductive immunology topics including the roles of adoptive and innate immunity in infertility and pregnancy, the immune system's role in induction of labor and preterm delivery, and immuno-modulatory effects of the female sex hormones will be discussed in this and the next issue of the Journal. The implications of this research on the development of novel therapeutic approaches are also addressed.

Dendritic cell apoptosis: regulation of tolerance versus immunity

Dendritic cell (DC) apoptosis is an important event that regulates the balance between tolerance and immunity through multiple pathways, and defects in DC apoptosis can trigger autoimmunity. DC apoptosis is also associated with immunosuppression and has been observed under several pathologies and infections. Recent studies indicate that apoptotic DCs can also play an active role in induction of tolerance. This review discusses the regulatory pathways of DC apoptosis, stimuli inducing DC apoptosis, and the implications of DC apoptosis in the induction of immunosuppression and/or tolerance.

The kinetics of T regulatory cells in shock: beyond sepsis

During the past decade, there have been an increasing number of studies investigating the precise role of T regulatory cells in human disease. First recognized for their ability to prevent autoimmunity, T regulatory cells control effector CD4⁺ and CD8⁺ T lymphocytes and innate immune cells by several different suppressive mechanisms, like cell to cell contact, secretion of inhibitory cytokines and cytolysis. This suppressive function of T regulatory cells could contribute in a similar way to the profound immune dysfunction seen in critical illness whether the latter is due to sepsis or severe injury.

Experimental evidence on the immunopathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease for which an autoimmune pathogenesis is supported by clinical and experimental data, including the presence of autoantibodies and autoreactive T cells. The etiology remains to be determined, yet data suggest that both a susceptible genetic background and unknown environmental factors determine disease onset. Multiple infectious and chemical candidates have been proposed to trigger the disease in a genetically susceptible host, mostly by molecular mimicry. Most recently, several murine models have been reported, including genetically determined models as well as models induced by immunization with xenobiotics and bacteria.