Diminished bacterial clearance is associated with decreased IL-12 and interferon-gamma production but a sustained proinflammatory response in a murine model of postseptic immunosuppression

M1 cholinergic signaling in the brain modulates cytokine levels and splenic cell sub-phenotypes following cecal ligation and puncture

BACKGROUND

The contribution of the central nervous system to sepsis pathobiology is incompletely understood. In previous studies, administration of endotoxin to mice decreased activity of the vagus anti-inflammatory reflex. Treatment with the centrally-acting M1 muscarinic acetylcholine (ACh) receptor (M1AChR) attenuated this endotoxin-mediated change. We hypothesize that decreased M1AChR-mediated activity contributes to inflammation following cecal ligation and puncture (CLP), a mouse model of sepsis.

METHODS

In male C57Bl/6 mice, we quantified basal forebrain cholinergic activity (immunostaining), hippocampal neuronal activity, serum cytokine/chemokine levels (ELISA) and splenic cell subtypes (flow cytometry) at baseline, following CLP and following CLP in mice also treated with the M1AChR agonist xanomeline.

RESULTS

At 48 h. post-CLP, activity in basal forebrain cells expressing choline acetyltransferase (ChAT) was half of that observed at baseline. Lower activity was also noted in the hippocampus, which contains projections from ChAT-expressing basal forebrain neurons. Serum levels of TNFα, IL-1β, MIP-1α, IL-6, KC and G-CSF were higher post-CLP than at baseline. Post-CLP numbers of splenic macrophages and inflammatory monocytes, TNFα+ and ILβ+ neutrophils and ILβ+ monocytes were higher than baseline while numbers of central Dendritic Cells (cDCs), CD4+ and CD8+ T cells were lower. When, following CLP, mice were treated with xanomeline activity in basal forebrain ChAT-expressing neurons and in the hippocampus was significantly higher than in untreated animals. Post-CLP serum concentrations of TNFα, IL-1β, and MIP-1α, but not of IL-6, KC and G-CSF, were significantly lower in xanomeline-treated mice than in untreated mice. Post-CLP numbers of splenic neutrophils, macrophages, inflammatory monocytes and TNFα+ neutrophils also were lower in xanomeline-treated mice than in untreated animals. Percentages of IL-1β+ neutrophils, IL-1β+ monocytes, cDCs, CD4+ T cells and CD8+ T cells were similar in xanomeline-treated and untreated post-CLP mice.

CONCLUSION

Our findings indicate that M1AChR-mediated responses modulate CLP-induced alterations in serum levels of some, but not all, cytokines/chemokines and affected splenic immune response phenotypes.

M1 Cholinergic Signaling Modulates Cytokine Levels and Splenocyte Sub-Phenotypes Following Cecal Ligation and Puncture

Background

The contribution of the central nervous system to sepsis pathobiology is incompletely understood. In previous studies, administration of endotoxin to mice decreased activity of the vagus anti-inflammatory reflex. Treatment with the centrally-acting M1/M4 muscarinic acetylcholine (ACh) receptor (M1/M4AChR) attenuated this endotoxin-mediated change. We hypothesize that decreased M1/M4AChR-mediated activity contributes to inflammation following cecal ligation and puncture (CLP), a mouse model of sepsis.

Methods

Basal forebrain cholinergic activity (immunostaining), serum cytokine/chemokine levels (ELISA) and splenocyte subtypes (flow cytometry) were examined at baseline and following CLP in male C57BL/6 male mice.

Rersults

At 48hrs. post-CLP, activity in basal forebrain cells expressing choline acetyltransferase (ChAT) was half of that observed at baseline. Lower activity was also noted in the hippocampus, which contains projections from ChAT-expressing basal forebrain neurons. Serum levels of TNFα, IL-1β, MIP-1α, IL-6, KC and G-CSF were higher post-CLP than at baseline. Post-CLP numbers of splenic macrophages and inflammatory monocytes, TNFa+ and ILb+ neutrophils and ILb+ monocytes were higher than baseline while numbers of central Dendritic Cells (cDCs), CD4+ and CD8+ T cells were lower. When, following CLP, mice were treated with xanomeline, a central-acting M1AChR agonist, activity in basal forebrain ChAT-expressing neurons and in the hippocampus was significantly higher than in untreated animals. Post-CLP serum concentrations of TNFα, IL-1β, and MIP-1α, but not of IL-6, KC and G-CSF, were significantly lower in xanomline-treated mice than in untreated mice. Post-CLP numbers of splenic neutrophils, macrophages, inflammatory monocytes and TNFα+ neutrophils also were lower in xanomeline-treated mice than in untreated animals. The effects of CLP on percentages of IL-1β+ neutrophils, IL-1β+ monocytes, cDCs, CD4+ T cells and CD8+ T cells were similar in xanomeline - treated and untreated post-CLP mice.

Conclusion

Our findings indicate that M1/M4AChR-mediated responses modulate CLP-induced alterations in the distribution of some, but not all, leukocyte phenotypes and certain cytokines and chemokines.

Increased mortality and altered local immune response in secondary peritonitis after previous visceral operations in mice

Postoperative peritonitis is characterized by a more severe clinical course than other forms of secondary peritonitis. The pathophysiological mechanisms behind this phenomenon are incompletely understood. This study used an innovative model to investigate these mechanisms, combining the models of murine Colon Ascendens Stent Peritonitis (CASP) and Surgically induced Immune Dysfunction (SID). Moreover, the influence of the previously described anti-inflammatory reflex transmitted by the vagal nerve was characterized. SID alone, or 3 days before CASP were performed in female C57BL/6 N mice. Subdiaphragmatic vagotomy was performed six days before SID with following CASP. The immune status was assessed by FACS analysis and measurement of cytokines. Local intestinal inflammatory changes were characterized by immunohistochemistry. Mortality was increased in CASP animals previously subjected to SID. Subclinical bacteremia occurred after SID, and an immunosuppressive milieu occurred secondary to SID just before the induction of CASP. Previous SID modified the pattern of intestinal inflammation induced by CASP. Subdiaphragmatic vagotomy had no influence on sepsis mortality in our model of postoperative peritonitis. Our results indicate a surgery-induced inflammation of the small intestine and the peritoneal cavity with bacterial translocation, which led to immune dysfunction and consequently to a more severe peritonitis.

Phenylephrine impairs host defence mechanisms to infection: a combined laboratory study in mice and translational human study

BACKGROUND

Immunosuppression after surgery is associated with postoperative complications, mediated in part by catecholamines that exert anti-inflammatory effects via the β-adrenergic receptor. Phenylephrine, generally regarded as a selective α-adrenergic agonist, is frequently used to treat perioperative hypotension. However, phenylephrine may impair host defence through β-adrenergic affinity.

METHODS

Human leukocytes were stimulated with lipopolysaccharide (LPS) in the presence or absence of phenylephrine and α- and β-adrenergic antagonists. C57BL/6J male mice received continuous infusion of phenylephrine (30-50 μg kg^-1 min^-1 i.v.) or saline via micro-osmotic pumps, before LPS administration (5 mg kg_-1 i.v.) or caecal ligation and puncture (CLP). Twenty healthy males were randomised to a 5 h infusion of phenylephrine (0.5 μg kg^-1 min^-1) or saline before receiving LPS (2 ng kg^-1 i.v.).

RESULTS

In vitro, phenylephrine enhanced LPS-induced production of the anti-inflammatory cytokine interleukin (IL)-10 (maximum augmentation of 93%) while attenuating the release of pro-inflammatory mediators. These effects were reversed by pre-incubation with β-antagonists, but not α-antagonists. Plasma IL-10 levels were higher in LPS-challenged mice infused with phenylephrine, whereas pro-inflammatory mediators were reduced. Phenylephrine infusion increased bacterial counts after CLP in peritoneal fluid (+42%, P=0.0069), spleen (+59%, P=0.04), and liver (+35%, P=0.09). In healthy volunteers, phenylephrine enhanced the LPS-induced IL-10 response (+76%, P=0.0008) while attenuating plasma concentrations of pro-inflammatory mediators including IL-8 (-15%, P=0.03).

CONCLUSIONS

Phenylephrine exerts potent anti-inflammatory effects, possibly involving the β-adrenoreceptor. Phenylephrine promotes bacterial outgrowth after surgical peritonitis. Phenylephrine may therefore compromise host defence in surgical patients and increase susceptibility towards infection.

CLINICAL TRIAL REGISTRATION

NCT02675868 (Clinicaltrials.gov).

Regulatory T Cells Modulate CD4 Proliferation after Severe Trauma via IL-10

Objective: Severely injured patients frequently develop an immunological imbalance following the traumatic insult, which might result in infectious complications evoked by a persisting immunosuppression. Regulatory T cells (Tregs) maintain the immune homeostasis by suppressing proinflammatory responses, however, their functionality after trauma is unclear. Here, we characterized the role of Tregs in regulating the proliferation of CD4⁺ lymphocytes in traumatized patients (TP). Methods: Peripheral blood was obtained daily from 29 severely injured TP (Injury Severity Score, ISS ≥16) for ten days following admission to the emergency department (ED). Ten healthy volunteers (HV) served as controls. The frequency and activity of Tregs were assessed by flow cytometry. Proliferation of CD4⁺ cells was analyzed either in presence or absence of Tregs, or after blocking of either IL-10 or IL-10R1. Results: The frequencies of CD4⁺CD25^high and CD4⁺CD25⁺CD127⁻ Tregs were significantly decreased immediately upon admission of TP to the ED and during the following 10 post-injury days. Compared with HV CD4⁺ T cell proliferation in TP increased significantly upon their admission and on the following days. As expected, CD4⁺CD25⁺CD127⁻ Tregs reduced the proliferation of CD4⁺ cells in HV, nevertheless, CD4⁺ proliferation in TP was increased by Tregs. Neutralization of IL-10 as well as blocking the IL-10R1 increased further CD4⁺ T cell proliferation in Tregs-depleted cultures, thereby confirming an IL-10-mediated mechanism of IL-10-regulated CD4⁺ T cell proliferation. Neutralization of IL-10 in TP decreased CD4⁺ T cell proliferation in Tregs-depleted cultures, whereas blocking of the IL-10R1 receptor had no significant effects. Conclusions: The frequency of Tregs in the CD4⁺ T lymphocyte population is reduced after trauma; however, their inductiveness is increased. The mechanisms of deregulated influence of Tregs on CD4⁺ T cell proliferation are mediated via IL-10 but not via the IL-10R1.

Streptococcus suis 2 Transcriptional Regulator TstS Stimulates Cytokine Production and Bacteremia to Promote Streptococcal Toxic Shock-Like Syndrome

Two large-scale outbreaks of streptococcal toxic shock-like syndrome (STSLS) have revealed Streptococcus suis 2 to be a severe and evolving human pathogen. We investigated the mechanism by which S. suis 2 causes STSLS. The transcript abundance of the transcriptional regulator gene tstS was found to be upregulated during experimental infection. Compared with the wild-type 05ZY strain, a tstS deletion mutant (ΔtstS) elicited reduced cytokine secretion in macrophages. In a murine infection model, tstS deletion resulted in decreased virulence and bacterial load, and affected cytokine production. Moreover, TstS expression in the P1/7 strain of S. suis led to the induction of STSLS in the infected mice. This is noteworthy because, although it is virulent, the P1/7 strain does not normally induce STSLS. Through a microarray-based comparative transcriptomics analysis, we found that TstS regulates multiple metabolism-related genes and several virulence-related genes associated with immune evasion.

Flt3 Ligand Treatment Attenuates T Cell Dysfunction and Improves Survival in a Murine Model of Burn Wound Sepsis

INTRODUCTION

Sepsis is a leading cause of death among severely burned patients. Burn injury disrupts the protective skin barrier and causes immunological dysfunction. In our previous studies, we found that burn injury and wound infection causes a significant decline in lymphocyte populations, implying adaptive immune system dysfunction. In the present study, we examined the effect of treatment with Fms-like tyrosine kinase-3 Ligand (Flt3L) on T cell phenotype and function in a model of burn wound sepsis. FLt3L is an essential cytokine required for hematopoietic progenitor cell development and expansion of both myeloid and lymphoid lineages. Flt3L has been shown to potentiate innate immune functions of dendritic cells and neutrophils during burn wound sepsis. However, the ability of Flt3L to improve T cell function during burn wound sepsis has not been previously evaluated.

METHODS

Mice underwent 35% total body surface area scald burn and were treated with Flt3L (10 μg) or vehicle daily via the intraperitoneal route starting 1 day after burn injury. On day 4 after burn injury, Pseudomonas aeruginosa was used to induce wound infection. Leukocytes in spleen and wound draining lymph nodes were characterized using flow cytometry. Bacterial clearance, organ injury, and survival were also assessed.

RESULTS

Flt3L treatment prevented the decline in splenic CD4 and CD8 T cells caused by burn injury and infection. Flt3L treatment also attenuated the decline in CD28 expression on CD4 and CD8 T cells and IFNγ production by CD8 T cells in the spleen and wound draining lymph nodes. Furthermore, Flt3L decreased the levels of programmed death ligand 1 expression on splenic dendritic cells and macrophages. Flt3 treatment improved systemic bacterial clearance, decreased liver and kidney injury, and significantly improved survival in mice with burn wound sepsis.

CONCLUSION

Burn injury and associated sepsis causes significant loss of T cells and evidence of T cell dysfunction. Flt3L attenuates T cell dysfunction and improves host resistance to burn wound sepsis in mice.

Frontline Science: Anti-PD-L1 protects against infection with common bacterial pathogens after burn injury

Burn patients are susceptible to infections due, in part, to immune dysfunction. Upregulation of programmed death-1 (PD-1) receptor on T cells and programmed cell death ligand-1 (PD-L1) on myeloid cells contribute to immune dysfunction in nonburn-related sepsis. We hypothesized that PD-1/PDL1 interactions contribute to immune dysfunction after burn injury. To determine the impact of burn injury and infection on PD-L1, PD-1 and costimulatory receptor expression by leukocytes and its relationship to T cell functions. The efficacy of anti-PD-L1 antibody was evaluated in a clinically relevant mouse model of burn injury and bacterial infection. Mice underwent 35% scald burn followed by Pseudomonas aeruginosa or Staphylococcus aureus infection on day 4 postburn. Anti-PD-L1 was administered on day 3 postburn. Numbers and phenotype of leukocytes, plasma cytokine concentrations, bacterial clearance, organ injury, and survival were assessed. Burn injury and infection with P. aeruginosa caused a significant upregulation of PD-L1 on myeloid cells, along with a decrease in T cell numbers and function, significant multiorgan injury, and decreased survival. Treatment with anti-PD-L1 antibody improved bacterial clearance, reduced organ injury, and enhanced survival during Pseudomonas burn wound infection. Furthermore, anti-PD-L1 effectively protected against multiorgan injury, and improved bacterial clearance and survival following systemic S. aureus infection after burn injury. Blockade of PD-1/PD-L1 interactions might represent a viable treatment to improve outcomes among critically ill burn-injured subjects and increased leukocyte PD-L1 expression could serve as a valuable biomarker to select appropriate patients for such treatment.

Down-regulation of MicroRNA-31 in CD4+ T Cells Contributes to Immunosuppression in Human Sepsis by Promoting TH2 Skewing

BACKGROUND

Immunosuppression has been recognized as a major cause of sepsis-related mortality. Currently, there is much interest in identifying central hubs controlling septic immunoparalysis. In this context, in this study, the authors investigate the role of microRNA-31 (miR-31) as a regulator of T cell functions.

METHODS

Primary human T cells were separated from healthy volunteers (n = 16) and from sepsis patients by magnetic beads (n = 23). Expression of mRNA/microRNA (miRNA) was determined by real-time polymerase chain reaction. Gene silencing was performed by small interfering RNA transfection, and miRNA-binding sites were validated by reporter gene assays. Effects of miR-31 or anti-miR-31 transfection were analyzed by real-time polymerase chain reaction, Western blotting, and flow cytometry.

RESULTS

Overexpression of miR-31 in stimulated CD4 T cells promoted a proinflammatory phenotype with increased levels of interferon-γ (1.63 ± 0.43; P = 0.001; means ± SD) and reduced expression of interleukin (IL)-2 (0.66 ± 0.19; P = 0.005) and IL-4 (0.80 ± 0.2; P = 0.0001). In contrast, transfection of anti-miR-31 directed cells toward a TH2 phenotype. Effects on IL-2 and IL-4 were mediated by targeting of nuclear factor-kappa B-inducing kinase and factor-inhibiting hypoxia-inducible factor-1α. Interferon-γ, however, was influenced via control of signaling lymphocytic activation molecule (SLAM)-associated protein, an essential adaptor molecule of immunomodulatory SLAM receptor signaling, which was identified as a novel target gene of miR-31. In sepsis patients, an epigenetically driven down-regulation of miR-31 was found (0.44 ± 0.25; P = 0.0001), associated with increased nuclear factor-kappa B-inducing kinase, factor-inhibiting hypoxia-inducible factor-1α, SLAM-associated protein expression, and a cytokine shift toward TH2.

CONCLUSIONS

In this study, the authors provide novel evidence of miR-31 as an emerging key posttranscriptional regulator of sepsis-associated immunosuppression. The study results contribute to a further understanding of septic immunoparalysis and provide new perspectives on miRNA-based diagnostic approaches.

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.

Interleukin-7 and anti-programmed cell death 1 antibody have differing effects to reverse sepsis-induced immunosuppression

Sepsis remains a major cause of morbidity and mortality in most intensive care units. Protracted sepsis can evolve into a state of profound immunosuppression characterized by secondary infections, frequently with opportunistic-type pathogens. Immunoadjuvant therapy is currently being evaluated as a novel treatment for patients with sepsis. Two of the most promising immunoadjuvants are interleukin-7 (IL-7) and anti-programmed cell death 1 antibody (anti-PD-1). Both IL-7 and anti-PD-1 have been reported to boost host immunity and improve outcomes in patients with viral infections and cancer. The purpose of this study was to define the immunological mechanisms of action of IL-7 and anti-PD-1 in the two-hit sepsis model of cecal ligation and puncture followed by Candida albicans. In addition, we examined whether combined treatment with IL-7 and anti-PD-1 provided any additive beneficial effects in reversing immune dysfunction. The present findings demonstrated that IL-7 and anti-PD-1 had differing effects on innate and adaptive immune functions. Compared with anti-PD-1, IL-7 increased lymphocyte proliferation; expression of lymphocyte adhesion molecules, lymphocyte function-associated antigen 1, and very late antigen-4; interferon-γ production; and CD28 expression on splenic CD8 T cells. In contrast, anti-PD-1 seemed to have a greater effect on major histocompatibility complex class II expression on splenic macrophages and dendritic cells than IL-7. Combined treatment with IL-7 and anti-PD-1 produced additive effects on CD28 expression, lymphocyte proliferation, and splenic secretion of interferon-γ. In conclusion, the present study shows differences in immunomodulatory actions between IL-7 and anti-PD-1 and provides a potential rationale for combining IL-7 and anti-PD-1 in the therapy of sepsis.

Role of G-CSF in monophosphoryl lipid A-mediated augmentation of neutrophil functions after burn injury

Infection is the leading cause of death in severely burned patients that survive the acute phase of injury. Neutrophils are the first line of defense against infections, but hospitalized burn patients frequently cannot mount an appropriate innate response to infection. Thus, immune therapeutic approaches aimed at improving neutrophil functions after burn injury may be beneficial. Prophylactic treatment with the TLR4 agonist monophosphoryl lipid A is known to augment resistance to infection by enhancing neutrophil recruitment and facilitating bacterial clearance. This study aimed to define mechanisms by which monophosphoryl lipid A treatment improves bacterial clearance and survival in a model of burn-wound sepsis. Burn-injured mice were treated with monophosphoryl lipid A or vehicle, and neutrophil mobilization was evaluated in the presence or absence of Pseudomonas aeruginosa infection. Monophosphoryl lipid A treatment induced significant mobilization of neutrophils from the bone marrow into the blood and sites of infection. Neutrophil mobilization was associated with decreased bone marrow neutrophil CXCR4 expression and increased plasma G-CSF concentrations. Neutralization of G-CSF before monophosphoryl lipid A administration blocked monophosphoryl lipid A-induced expansion of bone marrow myeloid progenitors and mobilization of neutrophils into the blood and their recruitment to the site of infection. G-CSF neutralization ablated the enhanced bacterial clearance and survival benefit endowed by monophosphoryl lipid A in burn-wound-infected mice. Our findings provide convincing evidence that monophosphoryl lipid A-induced G-CSF facilitates early expansion, mobilization, and recruitment of neutrophils to the site of infection after burn injury, allowing for a robust immune response to infection.

Adjuvants and myeloid-derived suppressor cells: enemies or allies in therapeutic cancer vaccination

Adjuvants are a critical but largely overlooked and poorly understood component included in vaccine formulations to stimulate and modulate the desired immune responses to an antigen. However, unlike in the protective infectious disease vaccines, adjuvants for cancer vaccines also need to overcome the effect of tumor-induced suppressive immune populations circulating in tumor-bearing individuals. Myeloid-derived suppressor cells (MDSC) are considered to be one of the key immunosuppressive populations that inhibit tumor-specific T cell responses in cancer patients. This review focuses on the different signals for the activation of the immune system induced by adjuvants, and the close relationship to the mechanisms of recruitment and activation of MDSC. This work explores the possibility that a cancer vaccine adjuvant may either strengthen or weaken the effect of tumor-induced MDSC, and the crucial need to address this in present and future cancer vaccines.

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.

The effect of ghrelin upon the early immune response in lean and obese mice during sepsis

Introduction

It is well established that obesity-related hormones can have modulatory effects associated with the immune response. Ghrelin, a hormone mainly derived from endocrine cells of the gastric mucosa, regulates appetite, energy expenditure and body weight counteracting leptin, a hormone mainly derived from adipocytes. Additionally, receptors of both have been detected on immune cells and demonstrated an immune regulatory function during sepsis.

Methods

In the present study, the effect of peripheral ghrelin administration on early immune response and survival was investigated with lean mice and mice with diet-induced obesity using cecal ligation and puncture to induce sepsis.

Results

In the obese group, we found that ghrelin treatment improved survival, ameliorated hypothermia, and increased hyperleptinemia as compared to the lean controls. We also observed that ghrelin treatment divergently regulated serum IL-1ß and TNF-α concentrations in both lean and obese septic mice. Ghrelin treatment initially decreased but later resulted in increased bacteriaemia in lean mice while having no impact upon obese mice. Similarly, ghrelin treatment increased early neutrophil oxidative burst while causing a decrease 48 hours after sepsis inducement.

Conclusion

In conclusion, as the immune response to sepsis temporally changes, ghrelin treatment differentially mediates this response. Specifically, we observed that ghrelin conferred protective effects during the early phase of sepsis, but during the later phase deteriorated immune response and outcome. These adverse effects were more pronounced upon lean mice as compared to obese mice.

Myeloid-derived suppressor cells: paradoxical roles in infection and immunity

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature suppressor cells that are generated due to aberrant myelopoiesis under pathological conditions. Although MDSCs have been recognized for more than 20 years under the guise of different monikers, these particular populations of myeloid cells gained more attention recently due to their immunosuppressive properties, which halt host immune responses to growing cancers or overwhelming infections. While MDSCs may contribute to immune homeostasis after infection or tissue injury by limiting excessive inflammatory processes, their expansion may be at the expense of pathogen elimination and thus may lead to disease persistence. Therefore, MDSCs may be either damaging or obliging to the host by attenuating, for example, antitumor or anti-infectious immune responses. In this review, we recapitulate the biological and immunological aspects of MDSCs, including their generation, distribution, trafficking and the factors involved in their activation, expansion, suppressive functions, and interplay between MDSCs and regulatory T cells, with a focus on the perspectives of infection and inflammation.

Obesity-induced hyperleptinemia improves survival and immune response in a murine model of sepsis

BACKGROUND

Obesity is a growing health problem and associated with immune dysfunction. Sepsis is defined as systemic inflammatory response syndrome that occurs during infection. Excessive inflammation combined with immune dysfunction can lead to multiorgan damage and death.

METHODS

The authors investigated the influence of a class 1 obesity (body mass index between 30 and 34.9) on immune function and outcome in sepsis and the role of leptin on the immune response. The authors used a long-term high-fat-diet feeding model (12 weeks) on C57Bl/6 mice (n = 100) and controls on standard diet (n = 140) followed by a polymicrobial sepsis induced by cecal ligation and puncture.

RESULTS

The authors show that class 1 obesity is connected to significant higher serum leptin levels (data are mean ± SEM) (5.7 ± 1.2 vs. 2.7 ± 0.2 ng/ml; n = 5; P = 0.033) and improved innate immune response followed by significant better survival rate in sepsis (71.4%, n = 10 vs. 10%, n = 14; P < 0.0001). Additional sepsis-induced increases in leptin levels stabilize body temperature and are associated with a controlled immune response in a time-dependent and protective manner. Furthermore, leptin treatment of normal-weight septic mice with relative hypoleptinemia (n = 35) also significantly stabilizes body temperature, improves cellular immune response, and reduces proinflammatory cytokine response resulting in improved survival (30%; n = 10).

CONCLUSIONS

Relative hyperleptinemia of class 1 obesity or induced by treatment is protective in sepsis. Leptin seems to play a regulatory role in the immune system in sepsis, and treatment of relative hypoleptinemia could offer a new way of an individual sepsis therapy.

Myeloid derived suppressor cells in physiological and pathological conditions: the good, the bad, and the ugly

Myeloid derived suppressor cells (MDSCs), a heterogeneous population of myeloid progenitors, are recognized as a key element in tumor escape and progression. The importance of MDSCs in human malignancies has been demonstrated in recent years, and new approaches targeting their suppressive/tolerogenic action are currently being tested in both preclinical model and clinical trials. However, emerging evidence suggests that MDSCs may play a prominent role as regulator of the physiologic, the chronic, and the pathologic immune responses. This review will focus on the biology of MDSC in light of these new findings and the possible role of this myeloid population not only in the progression of the tumor but also in its initiation.

GM3-containing nanoparticles in immunosuppressed hosts: Effect on myeloid-derived suppressor cells

Cancer vaccines to date have not broadly achieved a significant impact on the overall survival of patients. The negative effect on the immune system of the tumor itself and conventional anti-tumor treatments such as chemotherapy is, undoubtedly, a key reason for these disappointing results. Myeloid-derived suppressor cells (MDSCs) are considered a central node of the immunosuppressive network associated with tumors. These cells inhibit the effector function of natural killer and CD8⁺ T cells, expand regulatory T cells and can differentiate into tumor-associated macrophages within the tumor microenvironment. Thus, overcoming the suppressive effects of MDSCs is likely to be critical for cancer immunotherapy to generate effective anti-tumor immune responses. However, the capacity of cancer vaccines and particularly their adjuvants to overcome this inhibitory population has not been well characterized. Very small size proteoliposomes (VSSP) is a nanoparticulated adjuvant specifically designed to be formulated with vaccines used in the treatment of immunocompromised patients. This adjuvant contains immunostimulatory bacterial signals together with GM3 ganglioside. VSSP promotes dendritic cell maturation, antigen cross-presentation to CD8⁺ T cells, Th1 polarization, and enhances CD8⁺ T cell response in tumor-free mice. Currently, four cancer vaccines using VSSP as the adjuvant are in Phase I and II clinical trials. In this review, we summarize our work characterizing the unique ability of VSSP to stimulate antigen-specific CD8⁺ T cell responses in two immunocompromised scenarios; in tumor-bearing mice and during chemotherapy-induced leukopenia. Particular emphasis has been placed on the interaction of these nanoparticles with MDSCs, as well as comparison with other cancer vaccine adjuvants currently in preclinical or clinical studies.

The immunobiology of toll-like receptor 4 agonists: from endotoxin tolerance to immunoadjuvants

Lipopolysaccharide (LPS, endotoxin) is a structural component of the gram-negative outer membrane. The lipid A moiety of LPS binds to the LPS receptor complex expressed by leukocytes, endothelial cells, and parenchymal cells and is the primary component of gram-negative bacteria that is recognized by the immune system. Activation of the LPS receptor complex by native lipid A induces robust cytokine production, leukocyte activation, and inflammation, which is beneficial for clearing bacterial infections at the local level but can cause severe systemic inflammation and shock at higher challenge doses. Interestingly, prior exposure to LPS renders the host resistant to shock caused by subsequent LPS challenge, a phenomenon known as endotoxin tolerance. Treatment with lipid A has also been shown to augment the host response to infection and to serve as a potent vaccine adjuvant. However, the adverse effects associated with the pronounced inflammatory response limit the use of native lipid A as a clinical immunomodulator. More recently, analogs of lipid A have been developed that possess attenuated proinflammatory activity but retain attractive immunomodulatory properties. The lipid A analog monophosphoryl lipid A exhibits approximately 1/1,000th of the toxicity of native lipid A but retains potent immunoadjuvant activity. As such, monophosphoryl lipid A is currently used as an adjuvant in several human vaccine preparations. Because of the potency of lipid A analogs as immunoadjuvants, numerous laboratories are actively working to identify and develop new lipid A mimetics and to optimize their efficacy and safety. Based on those characteristics, lipid A analogs represent an attractive family of immunomodulators.

A disturbed interaction with accessory cells upon opportunistic infection with Pseudomonas aeruginosa contributes to an impaired IFN-γ production of NK cells in the lung during sepsis-induced immunosuppression

Impaired resistance to Pseudomonas aeruginosa-induced pneumonia after cecal ligation and puncture (CLP), a mouse model for human polymicrobial sepsis, is associated with decreased IFN-γ, but increased IL-10, levels in the lung. We investigated the so far unknown mechanisms underlying this reduced IFN-γ synthesis in CLP mice. CD11b(+) NK cells, but not T or NKT cells in the lung were impaired in IFN-γ synthesis upon challenge with Pseudomonas in vitro and in vivo after CLP. The inhibition of NK cells was independent of IL-10. IFN-γ synthesis of NK cells was only partly restored by addition of recombinant IL-12. Accessory cells including dendritic cells and alveolar macrophages were required for maximal IFN-γ secretion. But accessory cells of CLP mice suppressed the IFN-γ secretion from naive lung leukocytes. In turn, naive accessory cells were unable to restore the IFN-γ production from lung leukocytes of CLP mice. Thus, a disturbed interaction of accessory cells and NK cells is involved in the impaired IFN-γ release in response to Pseudomonas in the lung of CLP mice. Considering the importance of IFN-γ in the immune defense against bacteria the dysfunction of accessory cells and NK cells might contribute to the enhanced susceptibility to Pseudomonas after CLP.

Lipoxin A(4) promotes more complete inflammation resolution in sepsis compared to stable lipoxin A(4) analog

In sepsis, excessive inflammation may lead to organ injury or a paradoxical immunosuppressed state where the host is unable to clear preexisting infection. Resolution of inflammation is the process which restores tissue homeostasis and ensures that a chronic cycle of infection/inflammation does not occur. Lipoxin A4 (LXA4) is one of a family of lipid mediators with novel inflammation resolution activity. We compared the actions of LXA4 to the stable 15-epi-16-(para-fluorophenoxy)-lipoxin A4 methyl ester (LXA4 analog) in the cecal ligation and puncture (CLP) model of sepsis. Both LXA4 compounds (at 7 μg/kg; i.v.) reduced plasma TNFα and IL-6 concentrations compared to rats given vehicle saline. Neither treatment altered plasma IL-10 compared to CLP given saline, but LXA4 analog, increased plasma IL-10 concentrations compared to rats given LXA4. LXA4 reduced blood bacterial load but the LXA4 analog did not. LXA4 increased 8 day survival and the LXA4 analog did not have a significant effect. To examine possible mechanisms for the differences, we investigated peritoneal leukocyte gene expression of iNOS and macrophage phagocytic ability. Only LXA4 increased the percentage of phagocytic peritoneal macrophages. LXA4 reduced neutrophil gene expression of iNOS compared to CLP rats given vehicle, while the LXA4 analog did not. Our results suggest that at doses which reduced systemic inflammation, only LXA4 inhibited bacterial spread and increased survival. This difference may be due to the shorter-lived compound being able to increase macrophage phagocytosis and reduce neutrophil iNOS expression.

On the armament and appearances of human myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) have frequently been observed in patients with cancer. This heterogeneous population of myeloid cells can exert potent suppression of lymphocyte function and thereby poses a significant hurdle to natural or therapeutically induced anti-tumor immunity. On the other hand, the natural function of MDSC is not yet well understood and their role in infection, inflammation and autoimmune disease is still puzzling. Understanding MDSC biology will provide the tools necessary for therapeutic targeting of this population, but also permit exploitation of their strong tolerogenic function in the treatment of inflammatory conditions and the prevention of graft rejection.

Lipoxin a4 increases survival by decreasing systemic inflammation and bacterial load in sepsis

Sepsis is characterized by systemic inflammation with release of a large amount of inflammatory mediators. If sustained, this inflammatory response can lead to multiple organ failure and/or immunoparalysis. In the latter condition, the host may be susceptible to opportunistic infections or be unable to clear existing infections. Therefore, it is potentially beneficial to resolve inflammation by reducing inflammation without compromising host defense. We examined the effect of lipoxin A4 (LXA4), a compound with inflammatory resolution properties, in the cecal ligation and puncture (CLP) model of sepsis. Cecal ligation and puncture rats were given either saline or LXA4 (40 μg/kg, i.p.) 5 h after surgery. Lipoxin A4 administration increased 8-day survival of CLP rats, which lived longer than 48 h, and attenuated tissue injury after 8 days. Therefore, we investigated the effects of LXA4 on systemic inflammation and bacterial load 48 h after CLP sepsis. Plasma IL-6, monocyte chemotactic protein 1, and IL-10 levels were reduced in LXA4-treated rats compared with CLP rats given saline vehicle. Lipoxin A4 reduced phosphorylation of the p65 subunit of nuclear factor κB (NF-κB) at serines 536 and 468 in peritoneal macrophages, suggesting that LXA4 reduced production of proinflammatory mediators through an NF-κB-mediated mechanism. Lipoxin A4 reduced blood bacterial load and increased peritoneal macrophage number without affecting phagocytic ability, suggesting that LXA4 reduced blood bacterial load by enhancing macrophage recruitment. It also suggests that LXA4 reduced systemic inflammation and NF-κB activation without compromising host defense. Increased macrophage recruitment was in part due to a direct effect of LXA4 as LXA4 increased peritoneal macrophage recruitment in sham controls and partly due to reduced production of IL-10 as LXA4 decreased macrophage IL-10 release (a known inhibitor of macrophage migration) after CLP. The results suggest that LXA4 increased survival in sepsis by simultaneously reducing systemic inflammation as well as bacterial spread.

Cecal ligation and puncture followed by methicillin-resistant Staphylococcus aureus pneumonia increases mortality in mice and blunts production of local and systemic cytokines

Mortality in the intensive care unit frequently results from the synergistic effect of two temporally distinct infections. This study examined the pathophysiology of a new model of intra-abdominal sepsis followed by methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. Mice underwent cecal ligation and puncture (CLP) or sham laparotomy followed 3 days later by an intratracheal injection of MRSA or saline. Both CLP/saline and sham/MRSA mice had 100% survival, whereas animals with CLP followed by MRSA pneumonia had 67% 7-day survival. Animals subjected to CLP/MRSA had increased bronchoalveolar lavage concentrations of MRSA compared with sham/MRSA animals. Animals subjected to sham/MRSA pneumonia had increased bronchoalveolar lavage levels of interleukin 6 (IL-6), tumor necrosis factor α, and granulocyte colony-stimulating factor compared with those given intratracheal saline, whereas CLP/MRSA mice had a blunted local inflammatory response with markedly decreased cytokine levels. Similarly, animals subjected to CLP/saline had increased peritoneal lavage levels of IL-6 and IL-1β compared with those subjected to sham laparotomy, whereas this response was blunted in CLP/MRSA mice. Systemic cytokines were upregulated in both CLP/saline and sham/MRSA mice, and this was blunted by the combination of CLP/MRSA. In contrast, no synergistic effect on pneumonia severity, white blood cell count, or lymphocyte apoptosis was identified in CLP/MRSA mice compared with animals with either insult in isolation. These results indicate that a clinically relevant model of CLP followed by MRSA pneumonia causes higher mortality than could have been predicted from studying either infection in isolation, and this was associated with a blunted local (pulmonary and peritoneal) and systemic inflammatory response and decreased ability to clear infection.

The effect of obesity on adverse outcomes and metabolism in pediatric burn patients

Hypothesis

Obesity influences metabolism and increases the incidence of clinical complications and worsens outcomes in pediatric burn patients.

Design

Retrospective, single-center study.

Subjects

Five hundred ninety-two severely burned pediatric patients who had burns covering more than 30% of the total body surface area and who were treated between 2001 and 2008 were enrolled in this study. Patients were divided into ≥ 85th percentile (n = 277) and normal (n = 315) weight groups based on body mass index percentiles.

Results

Patients stratified below (normal) and ≥ 85^th percentile had similar age, gender distribution, and total burn size. No significant differences were detected in the incidence of sepsis (11% for obese vs. 10% for normal), the incidence of multiple organ failure (21% for obese and 16% for normal), or mortality (11% for obese vs. 8% for normal). Compared to the normal group, the ≥ 85^th percentile group had low levels of constitutive proteins (α2macroglobulin and Apolipoprotein A-1) (p < 0.05 for both) as well as high levels of triglycerides and the acute-phase protein, C-reactive protein (p < 0.05 for both) up to 60 days after injury. Patients ≥ 85^th percentile showed a significant higher loss of bone mineral density and lipolysis compared to normal individuals. Stepwise logistic regression analysis revealed that body mass index had a positive predictive value towards the maximum DENVER2 score, an index of organ failure (p < 0.001).

Conclusions

BMI ≥ 85^th percentile altered the post-burn acute phase and catabolic response but did not increase the incidence of sepsis, multiple organ failure, or mortality in pediatric burn patients. Our results suggest that impaired metabolism and an altered inflammatory response occurs already in patients starting at the 85th percentile BMI.

CLP-induced impairment of innate immune function is caused by exposure to the cecal lumenal contents and not the tissue trauma or tissue ischemia/necrosis components

When mice are subjected to a Pseudomonas aeruginosa challenge 5 days after cecal ligation and puncture (CLP), clearance of the Pseudomonas is diminished when compared to sham mice. The object of this study was to determine which component(s) of CLP contributed to the impairment of the innate immune response. Mice subjected to either trauma alone or cecal ischemia/necrosis alone did not have impaired ability to clear a subsequent Pseudomonas challenge (determined by colony-forming units (cfu's) after culture of spleen tissue). However, mice subjected to abdominal contamination with heat-killed cecal contents had reduced ability to clear the subsequent Pseudomonas challenge. In contrast to normobiotic mice, neither CLP performed in germ-free mice nor abdominal contamination of mice with cecal contents from germ-free mice adversely affected clearance of a subsequent Pseudomonas challenge. These data suggest that suppressed immune function after CLP is due to exposure to microbial ligands within the cecal lumen rather than tissue trauma, ischemia, or necrosis. However, suppression of immune function did not appear to be due to exposure to LPS as TLR4-deficient mice subject to abdominal contamination with cecal contents had diminished clearance of a Pseudomonas challenge similar to that seen in wild-type mice.

Cecal ligation and puncture-induced impairment of innate immune function does not occur in the absence of caspase-1

Mice that have been subjected to cecal ligation and puncture (CLP) have an impaired ability to clear a subsequent Pseudomonas aeruginosa challenge compared with that of sham CLP controls. We hypothesized that this outcome is dependent upon a caspase-1 mechanism and tested this hypothesis by measuring caspase-1 after CLP and by measuring clearance of a bacterial challenge in caspase-1-deficient mice after CLP. Wild-type mice subjected to CLP had increased caspase-1 activity as well as increased IL-1β and increased IL-18 production in splenocytes stimulated with heat-killed Pseudomonas and had increased plasma concentrations of IL-1β and IL-18 and impaired clearance of a P. aeruginosa challenge compared with sham controls. Healthy, uninjured caspase-1(-\-) mice did not differ from wild-type mice in their ability to clear a Pseudomonas challenge. However, unlike wild-type mice, caspase-1(-/-) mice subjected to CLP had no impairment of bacterial clearance of the Pseudomonas challenge, suggesting that caspase-1 induction after CLP played a role in impairment of bacterial clearance. This was further substantiated by the use of a specific caspase-1 inhibitor, Ac-YVAD-CMK. Wild-type mice treated with Ac-YVAD-CMK (10 mg/kg s.c. twice daily, initiated at time of CLP) did not have impaired clearance of a Pseudomonas challenge compared with that of sham mice and had significantly improved bacterial clearance compared with that of untreated CLP mice. Increased caspase-1 expression and activity after CLP injury appears to contribute to diminished innate immune function.

Dysregulated cytokine expression by CD4+ T cells from post-septic mice modulates both Th1 and Th2-mediated granulomatous lung inflammation

Previous epidemiological studies in humans and experimental studies in animals indicate that survivors of severe sepsis exhibit deficiencies in the activation and effector function of immune cells. In particular, CD4+ T lymphocytes can exhibit reduced proliferative capacity and improper cytokine responses following sepsis. To further investigate the cell-intrinsic defects of CD4+ T cells following sepsis, splenic CD4+ T cells from sham surgery and post-septic mice were transferred into lymphopenic mice. These recipient mice were then subjected to both TH1-(purified protein derivative) and TH2-(Schistosoma mansoni egg antigen) driven models of granulomatous lung inflammation. Post-septic CD4+ T cells mediated smaller TH1 and larger TH2 lung granulomas as compared to mice receiving CD4+ T cells from sham surgery donors. However, cytokine production by lymph node cells in antigen restimulation assays indicated increased pan-specific cytokine expression by post-septic CD4+ T cell recipient mice in both TH1 and TH2 granuloma models. These include increased production of T_H2 cytokines in TH1 inflammation, and increased production of T_H1 cytokines in TH2 inflammation. These results suggest that cell-intrinsic defects in CD4+ T cell effector function can have deleterious effects on inflammatory processes post-sepsis, due to a defect in the proper regulation of TH-specific cytokine expression.

The pathogenesis of sepsis

Sepsis is a serious clinical condition that represents a patient's response to a severe infection and has a very high mortality rate. Normal immune and physiologic responses eradicate pathogens, and the pathophysiology of sepsis is due to the inappropriate regulation of these normal reactions. In an ideal scenario, the first pathogen contact with the inflammatory system should eliminate the microbe and quickly return the host to homeostasis. The septic response may accelerate due to continued activation of neutrophils and macrophages/monocytes. Upregulation of lymphocyte costimulatory molecules and rapid lymphocyte apoptosis, delayed apoptosis of neutrophils, and enhanced necrosis of cells/tissues also contribute to the pathogenesis of sepsis. The coagulation system is closely tied to the inflammatory response, with cross talk between the two systems driving the dysregulated response. Biomarkers may be used to help diagnose patients with sepsis, and they may also help to identify patients who would benefit from immunomodulatory therapies.

Experimentally approaching the ICU: monitoring outcome-based responses in the two-hit mouse model of posttraumatic sepsis

To simulate and monitor the evolution of posttraumatic sepsis in mice, we combined a two-hit model of trauma/hemorrhage (TH) followed by polymicrobial sepsis with repetitive blood sampling. Anesthetized mice underwent femur fracture/sublethal hemorrhage and cecal ligation and puncture (CLP) 48 h later. To monitor outcome-dependent changes in circulating cells/biomarkers, mice were sampled daily (facial vein) for 7 days and retrospectively divided into either dead (DIE) or surviving (SUR) by post-CLP day 7. Prior to CLP, AST was 3-fold higher in DIE, while all other post-TH changes were similar between groups. There was a significant post-CLP intergroup separation. In SUR, RBC and Hb were lower, platelets and neutrophils higher, and lymphocytes mixed compared to DIE. In DIE, all organ function markers except glucose (decrease) were few folds higher compared to SUR. In summary, the combination of daily monitoring with an adequate two-hit model simulates the ICU setting, allows insight into outcome-based responses, and can identify biomarkers indicative of death in the acute posttraumatic sepsis in mice.

Modulation of dendritic cell differentiation in the bone marrow mediates sustained immunosuppression after polymicrobial sepsis

Murine polymicrobial sepsis is associated with a sustained reduction of dendritic cell (DC) numbers in lymphoid organs and with a dysfunction of DC that is considered to mediate the chronic susceptibility of post-septic mice to secondary infections. We investigated whether polymicrobial sepsis triggered an altered de novo formation and/or differentiation of DC in the bone marrow. BrdU labeling experiments indicated that polymicrobial sepsis did not affect the formation of splenic DC. DC that differentiated from bone marrow (bone marrow-derived DC [BMDC]) of post-septic mice released enhanced levels of IL-10 but did not show an altered phenotype in comparison with BMDC from sham mice. Adoptive transfer experiments of BMDC into naive mice revealed that BMDC from post-septic mice impaired Th1 priming but not Th cell expansion and suppressed the innate immune defense mechanisms against Pseudomonas bacteria in the lung. Accordingly, BMDC from post-septic mice inhibited the release of IFN-γ from NK cells that are critical for the protection against Pseudomonas. Additionally, sepsis was associated with a loss of resident DC in the bone marrow. Depletion of resident DC from bone marrow of sham mice led to the differentiation of BMDC that were impaired in Th1 priming similar to BMDC from post-septic mice. Thus, in response to polymicrobial sepsis, DC precursor cells in the bone marrow developed into regulatory DC that impaired Th1 priming and NK cell activity and mediated immunosuppression. The absence of resident DC in the bone marrow after sepsis might have contributed to the modulation of DC differentiation.

A paradoxical role for myeloid-derived suppressor cells in sepsis and trauma

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of immature myeloid cells whose numbers dramatically increase in chronic and acute inflammatory diseases, including cancer, autoimmune disease, trauma, burns and sepsis. Studied originally in cancer, these cells are potently immunosuppressive, particularly in their ability to suppress antigen-specific CD8(+) and CD4(+) T-cell activation through multiple mechanisms, including depletion of extracellular arginine, nitrosylation of regulatory proteins, and secretion of interleukin 10, prostaglandins and other immunosuppressive mediators. However, additional properties of these cells, including increased reactive oxygen species and inflammatory cytokine production, as well as their universal expansion in nearly all inflammatory conditions, suggest that MDSCs may be more of a normal component of the inflammatory response ("emergency myelopoiesis") than simply a pathological response to a growing tumor. Recent evocative data even suggest that the expansion of MDSCs in acute inflammatory processes, such as burns and sepsis, plays a beneficial role in the host by increasing immune surveillance and innate immune responses. Although clinical efforts are currently underway to suppress MDSC numbers and function in cancer to improve antineoplastic responses, such approaches may not be desirable or beneficial in other clinical conditions in which immune surveillance and antimicrobial activities are required.

CNS leptin action modulates immune response and survival in sepsis

Sepsis describes a complex clinical syndrome that results from an infection, setting off a cascade of systemic inflammatory responses that can lead to multiple organ failure and death. Leptin is a 16 kDa adipokine that, among its multiple known effects, is involved in regulating immune function. Here we demonstrate that leptin deficiency in ob/ob mice leads to higher mortality and more severe organ damage in a standard model of sepsis in mice [cecal ligation and puncture (CLP)]. Moreover, systemic leptin replacement improved the immune response to CLP. Based on the molecular mechanisms of leptin regulation of energy metabolism and reproductive function, we hypothesized that leptin acts in the CNS to efficiently coordinate peripheral immune defense in sepsis. We now report that leptin signaling in the brain increases survival during sepsis in leptin-deficient as well as in wild-type mice and that endogenous CNS leptin action is required for an adequate systemic immune response. These findings reveal the existence of a relevant neuroendocrine control of systemic immune defense and suggest a possible therapeutic potential for leptin analogs in infectious disease.

Impaired CD4+ T-cell proliferation and effector function correlates with repressive histone methylation events in a mouse model of severe sepsis

Immunosuppression following severe sepsis remains a significant human health concern, as long-term morbidity and mortality rates of patients who have recovered from life-threatening septic shock remain poor. Mouse models of severe sepsis indicate this immunosuppression may be partly due to alterations in myeloid cell function; however, the effect of severe sepsis on subsequent CD4(+) T-cell responses remains unclear. In the present study, CD4(+) T cells from mice subjected to an experimental model of severe sepsis (cecal ligation and puncture (CLP)) were analyzed in vitro. CD4(+)CD62L(+) T cells from CLP mice exhibited reduced proliferative capacity and altered gene expression. Additionally, CD4(+)CD62L(+) T cells from CLP mice exhibit dysregulated cytokine production after in vitro skewing with exogenous cytokines, indicating a decreased capability of these cells to commit to either the T(H)1 or T(H)2 lineage. Repressive histone methylation marks were also evident at promoter regions for the T(H)1 cytokine IFN-gamma and the T(H)2 transcription factor GATA-3 in naïve CD4(+) T cells from CLP mice. These results provide evidence that CD4(+) T-cell subsets from post-septic mice exhibit defects in activation and effector function, possibly due to chromatin remodeling proximal to genes involved in cytokine production or gene transcription.

Characterization and modulation of the immunosuppressive phase of sepsis

Sepsis continues to cause significant morbidity and mortality in critically ill patients. Studies of patients and animal models have revealed that changes in the immune response during sepsis play a decisive role in the outcome. Using a clinically relevant two-hit model of sepsis, i.e., cecal ligation and puncture (CLP) followed by the induction of Pseudomonas aeruginosa pneumonia, we characterized the host immune response. Second, AS101 [ammonium trichloro(dioxoethylene-o,o')tellurate], a compound that blocks interleukin 10 (IL-10), a key mediator of immunosuppression in sepsis, was tested for its ability to reverse immunoparalysis and improve survival. Mice subjected to pneumonia following CLP had different survival rates depending upon the timing of the secondary injury. Animals challenged with P. aeruginosa at 4 days post-CLP had approximately 40% survival, whereas animals challenged at 7 days had 85% survival. This improvement in survival was associated with decreased lymphocyte apoptosis, restoration of innate cell populations, increased proinflammatory cytokines, and restoration of gamma interferon (IFN-gamma) production by stimulated splenocytes. These animals also showed significantly less P. aeruginosa growth from blood and bronchoalveolar lavage fluid. Importantly, AS101 improved survival after secondary injury 4 days following CLP. This increased survival was associated with many of the same findings observed in the 7-day group, i.e., restoration of IFN-gamma production, increased proinflammatory cytokines, and decreased bacterial growth. Collectively, these studies demonstrate that immunosuppression following initial septic insult increases susceptibility to secondary infection. However, by 7 days post-CLP, the host's immune system has recovered sufficiently to mount an effective immune response. Modulation of the immunosuppressive phase of sepsis may aid in the development of new therapeutic strategies.

Dendritic cells modulate lung response to Pseudomonas aeruginosa in a murine model of sepsis-induced immune dysfunction

Host infection by pathogens triggers an innate immune response leading to a systemic inflammatory response, often followed by an immune dysfunction which can favor the emergence of secondary infections. Dendritic cells (DCs) link innate and adaptive immunity and may be centrally involved in the regulation of sepsis-induced immune dysfunction. We assessed the contribution of DCs to lung defense in a murine model of sublethal polymicrobial sepsis (cecal ligature and puncture, CLP). In this model, bone marrow-derived DCs (BMDCs) retained an immature phenotype, associated with decreased capacity of IL-12p70 release and impaired priming of T cell lymphocytes. Eight days after CLP surgery, we induced a secondary pulmonary infection through intratracheal instillation of 5 x 10(6) CFUs of Pseudomonas aeruginosa. Whereas all sham-operated mice survived, 80% of post-CLP mice died after secondary pneumonia. Post-CLP mice exhibited marked lung damage with early recruitment of neutrophils, cytokine imbalance with decreased IL-12p70 production, and increased IL-10 release, but no defective bacterial lung clearance, while systemic bacterial dissemination was almost constant. Concomitant intrapulmonary administration of exogenous BMDCs into post-CLP mice challenged with P. aeruginosa dramatically improved survival. BMDCs did not improve bacterial lung clearance, but delayed neutrophil recruitment, strongly attenuated the early peak of TNF-alpha and restored an adequate Il-12p70/IL-10 balance in post-CLP mice. Thus, adoptive transfer of BMDCs reversed sepsis-induced immune dysfunction in a relevant model of secondary P. aeruginosa pneumonia. Unexpectedly, the mechanism of action of BMDCs did not involve enhanced antibacterial activity, but occurred by dampening the pulmonary inflammatory response.

CD4-expressing cells are early mediators of the innate immune system during sepsis

It is well established that the immune response to sepsis is mediated by leukocytes associated with the innate immune system. However, there is an emerging view that T lymphocytes can also mediate this response. Here, we observed a significant depletion of both CD4 and CD8 T cells in human patients after blunt trauma. To determine what effect the loss of these cells may have during a subsequent infection, we obtained CD4- and CD8-deficient mice and subjected them to cecal ligation and puncture (CLP). We observed that CD4 knockout (KO) mice showed increased CLP-induced mortality compared with CD8-deficient and wild-type (WT) mice especially within the first 30 h of injury. CD4 KO mice also exhibited significantly increased IL-6 concentrations after the CLP. The CD4 KO mice had an increased concentration of bacteremia as compared with WT mice. Antibiotic treatment decreased mortality in the CD4 KO mice as compared with no changes in the wild mice after CLP. Neutrophils isolated from septic CD4 KO mice showed decreased spontaneous oxidative burst compared with neutrophils taken from septic controls. We examined the role of IFN-gamma by using mice deficient in this cytokine and found these mice to have significantly higher mortality as compared with WT mice. Finally, we detected a 2-fold increase in CD11b+ cells that exhibited intracellular IFN-gamma staining in the peritoneum of WT mice after CLP. The data suggest that CD4+ cells may facilitate the early clearance of bacteria by regulating neutrophils function possibly through an IFN-gamma-dependent mechanism.

"Host tissue damage" signal ATP impairs IL-12 and IFNgamma secretion in LPS stimulated whole human blood

OBJECTIVE

Critical illness is associated with tissue damage, inflammation and the development of immune dysfunction. Leukocyte reprogramming occurs leading to insufficient production of pro-inflammatory cytokines upon subsequent stimulation. Cellular nucleotides released during tissue damage act via purinergic receptors to modulate immune function. We hypothesized that extracellular nucleotides in concentrations similar to those found near injured and ischemic tissues will modulate cytokine secretion.

DESIGN AND PARTICIPANTS

Bench study in 28 healthy human volunteers using standardized lipopolysaccharide (LPS) stimulated ex vivo whole blood cultures (ILCS).

SETTING

The Nepean Hospital Laboratories, University of Sydney.

INTERVENTIONS

Nucleotides ATP, ADP and other P2 purinergic receptor agonists ATPgammaS, BzATP, UTP and P1 agonist CV1808 were injected into the ILCS, and cultured for 6, 12 and 24 h as indicated.

MEASUREMENTS AND RESULTS

ATP (100 muM) reduced the LPS stimulated secretion of TNFalpha at 6 and 12 h, as well as IL-12(p70) and IFNgamma at 24 h of incubation. ADP, ATPgammaS, BzATP, and CV1808, but not UTP displayed IL-12(p70) and IFNgamma reducing effect similar to ATP. Higher ATP concentration (500 muM) had even more pronounced immunosuppressive effect. Nucleotides had variable effect on stimulated IL-10 secretion.

CONCLUSIONS

ATP and ADP at high-micromolar concentrations reduce secretion of the main Th1 cytokines TNFalpha, IL-12(p70) and IFNgamma in LPS stimulated human blood. As immune dysfunction associated with critical illness is characterized by decreased TNFalpha, IL-12 and IFNgamma production by leukocytes, extracellular nucleotides might contribute to its pathogenesis [corrected]

Neutrophil depletion causes a fatal defect in murine pulmonary Staphylococcus aureus clearance

BACKGROUND

Staphylococcus aureus is the most common cause of healthcare-associated pneumonia. Despite the significant morbidity and mortality associated with the disease, animal models of S. aureus pneumonia are rare.

MATERIALS AND METHODS

We examined the pathogenicity of four different strains of S. aureus (both methicillin-sensitive and -resistant as well as Panton-Valentine leukocidin-positive and -negative) in four strains of immunocompetent inbred and outbred mice (FVB/N, C57Bl/6, BALB/c, ND4; n = 148). The immunological basis for the development of murine S. aureus pneumonia was then determined by selectively depleting neutrophils, lymphocytes, or pulmonary macrophages prior to the onset of infection. An additional cohort of animals was rendered immunosuppressed by induction of abdominal sepsis via cecal ligation and puncture 2, 4, or 7 d prior to the onset of pneumonia.

RESULTS

Nearly all immunocompetent mice survived, regardless of which strain of S. aureus was used or which strain of mouse was infected. Among animals with immune depletion or prior immunosuppression, survival was decreased only following neutrophil depletion (26% versus 90% alive at 7 d, P < 0.0001). Compared to immunocompetent animals, neutrophil-depleted mice with S. aureus pneumonia had delayed pulmonary bacterial clearance at 16 and 40 h but had no difference in levels of bacteremia. Neutrophil-depleted mice also had elevated levels of pulmonary monocyte chemotactic protein-1 (822 pg/mL versus 150 pg/mL, P < 0.05). In contrast, pulmonary histological appearance was similar in both groups as was dry/wet lung weight.

CONCLUSIONS

These results suggest that neutrophils play a critical role in the host response to S. aureus pneumonia, and the survival differences observed in neutrophil-depleted mice are associated with alterations in bacterial clearance and pulmonary cytokine response.

Innate immunity: a cutaneous perspective

The first responsibility for protection against microbial infection rests on the normal function of the innate immune system. This system establishes an antimicrobial barrier, recognizes attempts to breach this barrier, and responds rapidly to danger, all based on an innate defense system. Here, we review this system as it applies to mammalian skin, highlighting how a physical, cellular, and chemical barrier is formed to resist infection. When challenged, the diverse cellular components of the skin recognize the nature of the challenge and respond with an appropriate antimicrobial program including the release of antimicrobial peptides and, when necessary, recruitment and coordination with adaptive immune responses. Recent insights into these processes have advanced the understanding of disease pathogenesis and provided new therapeutic options for a variety of skin diseases.

Maternal serum soluble CD30 is increased in pregnancies complicated with acute pyelonephritis

OBJECTIVES

Normal pregnancy is characterized by activation of the innate immunity and suppression of the adaptive limb of the immune response. However, pregnant women are more susceptible to the effects of infection and microbial products than non-pregnant women. CD30 is a member of the tumor necrosis factor receptor superfamily and is preferentially expressed by activated T cells producing Th2-type cytokines. Its soluble form (sCD30) is proposed to be an index of Th2 immune response. High serum concentrations of sCD30 have been found in the acute phase of viral infections, such as HIV-1 and hepatitis B. There is, however, conflicting evidence about serum sCD30 concentration in patients with bacterial infections. The objective of this study was to determine whether there are changes in the serum concentration of sCD30 in pregnant women with pyelonephritis.

METHODS

This cross-sectional study included normal pregnant women (N = 89) and pregnant women with pyelonephritis (N = 41). Maternal serum concentration of sCD30 was measured by a specific and sensitive enzyme-linked immunoassay. Non-parametric tests were used for comparisons. A p value <0.05 was considered statistically significant.

RESULTS

(1) Pregnant women with pyelonephritis had a significantly higher median serum concentration of sCD30 than those with a normal pregnancy (median 44.3 U/mL, range 16-352.5 vs. median 29.7 U/mL, range 12.2-313.2, respectively; p < 0.001), and (2) No significant differences were found in the median maternal serum concentration of sCD30 between pregnant women with pyelonephritis who had a positive blood culture compared to those with a negative blood culture (median 47.7 U/mL, range 17.1-118.8 vs. median 42.6 U/mL, range 16-352.5, respectively; p = 0.86).

CONCLUSIONS

Acute pyelonephritis during pregnancy is associated with a higher maternal serum concentration of sCD30 than normal pregnancy. This finding is novel and suggests that pregnant women with pyelonephritis may have a complex immune state in which there is activation of some components of what is considered a Th2 immune response.

Signal transducer and activator of transcription 4 (STAT4), but not IL-12 contributes to Pseudomonas aeruginosa-induced lung inflammation in mice

Pseudomonas aeruginosa is a major opportunistic pathogen in immune-compromised individuals and cystic fibrosis patients. This organism stimulates a complex inflammatory response in the lung, including production of various cytokines and chemokines. The specific contribution of these mediators in the host defense against this bacterium has yet to be fully characterized. Interleukin-12 (IL-12) is commonly known as a master regulator of innate and adaptive immunity. IL-12 induces its biological effects through its associated intracellular signaling molecule, the signal transducer and activator of transcription 4 (STAT4). To examine a specific role of IL-12 and STAT4 in P. aeruginosa lung infection in mice, STAT4-deficient (STAT4-/-) and IL-12 p40-deficient (IL-12 p40-/-) mice were infected with P. aeruginosa intranasally. Interestingly, STAT4-/- mice, but not IL-12 p40-/- mice after 24h infection showed impaired production of the pro-inflammatory cytokines tumor necrosis factor, interleukin-1beta, and macrophage-inflammatory protein-2. However, neither STAT4 nor IL-12 p40 deficiency significantly affected INFgamma production or bacterial clearance compared to wild-type mice. Similarly, neutrophil recruitment was not affected in the STAT4-/- and IL-12 p40-/- mice. These results suggest that STAT4 contributes to P. aeruginosa-induced inflammation, but it is not essential for bacterial clearance. Although IL-12 is essential for the host defense against various pathogens, this cytokine is likely not a major player in the host response to P. aeruginosa lung infection.

The innate immune response to secondary peritonitis

Secondary peritonitis continues to cause high morbidity and mortality despite improvements in medical and surgical therapy. This review combines data from published literature, focusing on molecular patterns of inflammation in pathophysiology and prognosis during peritonitis. Orchestration of the innate immune response is essential. To clear the microbial infection, activation and attraction of leukocytes are essential and beneficial, just like the expression of inflammatory cytokines. Exaggeration of these inflammatory systems leads to tissue damage and organ failure. Nonsurvivors have increased proinflammation, complement activation, coagulation, and chemotaxis. In these patients, anti-inflammatory systems are decreased in blood and lungs, whereas the abdominal compartment shows decreased neutrophil activation and decreased or stationary chemokine and cytokine levels. A later down-regulation of proinflammatory mediators with concomitant overexpression of anti-inflammatory mediators leads to immunoparalysis and failure to clear residual bacterial load, resulting in the occurrence of superimposed infections. Thus, in patients with adverse outcome, the inflammatory reaction is no longer contained within the abdomen, and the inflammatory response has shifted to other compartments. For the understanding of the host response to secondary peritonitis, it is essential to realize that the defense systems presumably are expressed differently and, in part, autonomously in different compartments.

Gammadelta T cells mitigate the organ injury and mortality of sepsis

Sepsis is a difficult condition to treat and is associated with a high mortality rate. Sepsis is known to cause a marked depletion of lymphocytes, although the function of different lymphocyte subsets in the response to sepsis is unclear. gammadelta T cells are found largely in epithelial-rich tissues, and previous studies of gammadelta T cells in models of sepsis have yielded divergent results. In the present study, we examined the function of gammadelta T cells during sepsis in mice using cecal ligation and puncture (CLP). Mice deficient in gammadelta T cells had decreased survival times and increased tissue damage after CLP compared with wild-type mice. Furthermore, bacterial load was increased in gammadelta T cell-deficient mice, yet antibiotic treatment did not change mortality. Additionally, we found that recruitment of neutrophils and myeloid suppressor cells to the site of infection was diminished in gammadelta T cell-deficient mice. Finally, we found that circulating levels of IFN-gamma were increased, and systemic levels of IL-10 were decreased in gammadelta T cell-deficient mice after CLP compared with wild-type mice. gammadelta T cell-deficient mice also had increased intestinal permeability after CLP compared with wild-type mice. Neutralization of IFN-gamma abrogated the increase in intestinal permeability in gammadelta T cell-deficient mice. The intestines taken from gammadelta T cell-deficient mice had decreased myeloperoxidase yet had increased tissue damage as compared with wild-type mice. Collectively, our data suggest that gammadelta T cells modulate the response to sepsis and may be a potential therapeutic target.

Effects of intra-abdominal administration of recombinant tissue plasminogen activator on coagulation, fibrinolysis and inflammatory responses in experimental polymicrobial peritonitis

Peritonitis represents a procoagulant state because of activated coagulation and inhibited fibrinolysis. Intra-abdominal fibrin deposition-entrapping bacteria-prevents bacterial spread but impairs bacterial clearance. Activating intra-abdominal fibrinolysis by recombinant tissue-type plasminogen activator (r-tPA) early during peritonitis may enhance bacterial clearance and reduce inflammation. This study examines effects of abdominal r-tPA lavage on local and distant coagulation, fibrinolysis, and inflammatory responses in experimental polymicrobial peritonitis. Twenty-four hours after cecal ligation and puncture, mice were exposed to therapeutic abdominal lavage with varying doses of r-tPA or saline (controls). Coagulation, fibrinolysis, and inflammation were assessed in abdominal, systemic, and pulmonary compartments (n = 6 per group per time point). Survival was assessed during 96 h (n = 16 per group). Highest-dose (2 mg/mL) r-tPA lavage caused immediate death. High-dose (0.5 mg/mL) r-tPA lavage increased fibrinolysis, demonstrated by low abdominal plasminogen activator inhibitor 1 levels and elevated pulmonary tPA levels, resulting in reduced abdominal bacterial load, chemokine levels, leukocyte influx, and thrombin generation, along with less pulmonary fibrin depositions and organ damage on histological examination (P < 0.05 vs. saline lavage). Low-dose (0.05 mg/mL) r-tPA lavage showed hardly any effect compared with saline lavage. Adversely, abdominal and plasma interleukin (IL) 12 were elevated, whereas IL-10 levels were decreased after high-dose r-tPA lavage (P < 0.05 vs. saline). Survival rate was not affected by any dose of r-tPA lavage compared with saline lavage. Delayed local stimulation of fibrinolysis by peritoneal r-tPA lavage enhanced intra-abdominal bacterial clearance and reduced intra- and extra-abdominal coagulation responses in a dose-dependent manner. Survival rate was unaffected likely due to adverse changes in IL-12 and IL-10 levels.