Immune depression in polymicrobial sepsis: the role of necrotic (injured) tissue and endotoxin

invariant Natural Killer T Cells Modulate the Peritoneal Macrophage Response to Polymicrobial Sepsis

INTRODUCTION

A dysregulated immune system is a major driver of the mortality and long-term morbidity from sepsis. With respect to macrophages, it has been shown that phenotypic changes are critical to effector function in response to acute infections, including intra-abdominal sepsis. Invariant natural killer T cells (iNKT cells) have emerged as potential central regulators of the immune response to a variety of infectious insults. Specifically, various iNKT cell:macrophage interactions have been noted across a spectrum of diseases, including acute events such as sepsis. However, the potential for iNKT cells to affect peritoneal macrophages during an abdominal septic event is as yet unknown.

METHODS

Cecal ligation and puncture (CLP) was performed in both wild type (WT) and invariant natural killer T cell knockout (iNKT-/-) mice. 24 h following CLP or sham operation, peritoneal macrophages were collected for analysis. Analysis of macrophage phenotype and function was undertaken to include analysis of bactericidal activity and cytokine or superoxide production.

RESULTS

Within iNKT-/- mice, a greater degree of intraperitoneal macrophages in response to the sepsis was noted. Compared to WT mice, within iNKT-/- mice, CLP did induce an increase in CD86+ and CD206+, but no difference in CD11b+. Unlike WT mice, intra-abdominal sepsis within iNKT-/- mice induced an increase in Ly6C-int (5.2% versus 14.9%; P < 0.05) and a decrease in Ly6C-high on peritoneal macrophages. Unlike phagocytosis, iNKT cells did not affect macrophage bactericidal activity. Although iNKT cells did not affect interleukin-6 production, iNKT cells did affect IL-10 production and both nitrite and superoxide production from peritoneal macrophages.

CONCLUSIONS

The observations indicate that iNKT cells affect specific phenotypic and functional aspects of peritoneal macrophages during polymicrobial sepsis. Given that pharmacologic agents that affect iNKT cell functioning are currently in clinical trial, these findings may have the potential for translation to critically ill surgical patients with abdominal sepsis.

Of mice and men: Laboratory murine models for recapitulating the immunosuppression of human sepsis

Prolonged immunosuppression is increasingly recognized as the major cause of late phase and long-term mortality in sepsis. Numerous murine models with different paradigms, such as lipopolysaccharide injection, bacterial inoculation, and barrier disruption, have been used to explore the pathogenesis of immunosuppression in sepsis or to test the efficacy of potential therapeutic agents. Nonetheless, the reproducibility and translational value of such models are often questioned, owing to a highly heterogeneric, complex, and dynamic nature of immunopathology in human sepsis, which cannot be consistently and stably recapitulated in mice. Despite of the inherent discrepancies that exist between mice and humans, we can increase the feasibility of murine models by minimizing inconsistency and increasing their clinical relevance. In this mini review, we summarize the current knowledge of murine models that are most commonly used to investigate sepsis-induced immunopathology, highlighting their strengths and limitations in mimicking the dysregulated immune response encountered in human sepsis. We also propose potential directions for refining murine sepsis models, such as reducing experimental inconsistencies, increasing the clinical relevance, and enhancing immunological similarities between mice and humans; such modifications may optimize the value of murine models in meeting research and translational demands when applied in studies of sepsis-induced immunosuppression.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Extracellular DNA-A Danger Signal Triggering Immunothrombosis

Clotting and inflammation are effective danger response patterns positively selected by evolution to limit fatal bleeding and pathogen invasion upon traumatic injuries. As a trade-off, thrombotic, and thromboembolic events complicate severe forms of infectious and non-infectious states of acute and chronic inflammation, i.e., immunothrombosis. Factors linked to thrombosis and inflammation include mediators released by platelet granules, complement, and lipid mediators and certain integrins. Extracellular deoxyribonucleic acid (DNA) was a previously unrecognized cellular component in the blood, which elicits profound proinflammatory and prothrombotic effects. Pathogens trigger the release of extracellular DNA together with other pathogen-associated molecular patterns. Dying cells in the inflamed or infected tissue release extracellular DNA together with other danger associated molecular pattern (DAMPs). Neutrophils release DNA by forming neutrophil extracellular traps (NETs) during infection, trauma or other forms of vascular injury. Fluorescence tissue imaging localized extracellular DNA to sites of injury and to intravascular thrombi. Functional studies using deoxyribonuclease (DNase)-deficient mouse strains or recombinant DNase show that extracellular DNA contributes to the process of immunothrombosis. Here, we review rodent models of immunothrombosis and the evolving evidence for extracellular DNA as a driver of immunothrombosis and discuss challenges and prospects for extracellular DNA as a potential therapeutic target.

Effects of End-Tidal Carbon Dioxide-Guided Fluid Resuscitation on Outcomes in a Cecal Ligation and Puncture Induced Rat Model of Sepsis

Cecal ligation and puncture (CLP) was used to cause severe sepsis in male Sprague-Dawley rats. There are four groups in this study: sham (n = 5), CLP (n = 10), end-tidal carbon dioxide (ETCO2) (n = 10), and mean arterial pressure (MAP) (n = 10). In ETCO2 group, fluid resuscitation (FR) began when ETCO2 at most 25 mmHg. In MAP group, FR began when MAP at most 100 mmHg. Electrocardiogram, aortic pressure, core temperature, and ETCO2 values were recorded at baseline, 2, 4, 6, 8, 10, and 12 h post-CLP. Lactate level, cardiac output (CO), perfused small vessel density (PSVD), and microvascular flow index (MFI) were assessed at the same time points as above. The results showed that MAP, CO, and ETCO2 gradually decreased after CLP. After FR, MAP, ETCO2, and CO in the ETCO2 group increased compared with the MAP group 12 h after CLP (all P < 0.05). Lactate level remains high in MAP group while decreasing in the ETCO2 group 8 h post-CLP. Both PSVD and MFI deteriorated after CLP in CLP group, though significantly improved in the ETCO2 group 8 h post-CLP. The average survival time in the ETCO2 group was significantly greater than MAP group (14.95 ± 3.90 h vs. 11.15 ± 1.76 h; t = 2.804, P = 0.012). Moreover, ETCO2 showed a negative correlation with lactic acid levels and a positive correlation with CO, PSVD, and MFI. In conclusion, ETCO2 can guide FR implement and improve outcomes of severe sepsis in CLP-inducted rat model. ETCO2 might be a potential index to guiding early FR in severe sepsis.

Cannabinoid Receptor 2 Modulates Neutrophil Recruitment in a Murine Model of Endotoxemia

The endocannabinoid system consists of endogenous lipid mediators and cannabinoid receptors (CB) 1 and 2. It has previously been demonstrated that activation of the leukocyte-expressed CB₂ has anti-inflammatory effects in vivo. Here, we report its role under baseline conditions and in a model of low-dose endotoxemia by comparing CB₂ knockout to littermate control mice. CB₂-deficient mice displayed significantly more neutrophils and fewer monocytes in the bone marrow under steady state. In initial validation experiments, administration of 1 mg/kg LPS to male C57BL/6J mice was shown to transiently upregulate systemic proinflammatory mediators (peaked at 2 hours) and mobilise bone marrow neutrophils and monocytes into circulation. In CB₂ knockout mice, the level of the metalloproteinase MMP-9 was significantly elevated by 2 hours and we also observed augmented recruitment of neutrophils to the spleen in addition to increased levels of Ccl2, Ccl3, Cxcl10, and Il6. Collectively, our data show that the absence of CB₂ receptor increases the levels of innate immune cell populations in the bone marrow under steady state. Furthermore, during an acute systemic inflammatory insult, we observe a highly reproducible and site-specific increase in neutrophil recruitment and proinflammatory chemokine expression in the spleen of CB₂ knockout mice.

EGCG induces G-CSF expression and neutrophilia in experimental sepsis

A major green tea component, epigallocatechin-3-gallate (EGCG), has been proven protective against lethal sepsis in experimental setting, but its protective mechanisms remain incompletely understood. Here, we provide evidence to support EGCG's capacities in stimulating G-CSF production and neutrophilia in vivo. In an animal model of sepsis, EGCG significantly elevated peritoneal levels of G-CSF and several chemokines (e.g., MCP-1/CCL2 and MIP-1γ/CCL9), and consequently increased peritoneal neutrophil numbers (neutrophilia) at a late stage. In vitro, EGCG divergently affected HMGB1-mediated production of several chemokines: reducing CXCL15 and RANTES/CCL5, but elevating G-CSF and MIP-1α/CCL3 production by peritoneal macrophages. Similarly, it significantly induced the expression and secretion of G-CSF and MIP-1α/CCL3 in human peripheral blood mononuclear cells. Based on our preliminary data, it may be important to search for anti-inflammatory and G-CSF-stimulating agents for the clinical management of inflammatory diseases.

Intestine-Derived Matrix Metalloproteinase-8 Is a Critical Mediator of Polymicrobial Peritonitis

OBJECTIVE

Inhibition of matrix metalloproteinase-8 improves survival following cecal ligation and puncture in mice, making it a potential therapeutic target. In the current study, we expand our understanding of the role of matrix metalloproteinase-8 in sepsis by using an adoptive transfer approach and alternative sepsis models.

DESIGN

We used three different sepsis models: cecal ligation and puncture, cecal slurry, and intestinal implantation. In our first model, adoptive transfer experiments were followed by cecal ligation and puncture to test the hypothesis that matrix metalloproteinase-8-containing myeloid cells are a critical factor in sepsis following cecal ligation and puncture. Our second model, cecal slurry, used intraperitoneal injections of cecal contents to induce polymicrobial peritonitis without tissue compromise in the recipient. Our third model, intestinal implantation, involved ligating and puncturing a cecum from a donor, and then removing the cecum and placing it into the recipient's peritoneal cavity. Clinically, blood samples were drawn from pediatric patients within 24 hours of meeting criteria for septic shock.

SETTING

Basic science laboratory.

SUBJECTS

Wild type and genetically modified mice.

INTERVENTIONS

Experimental models of sepsis.

MEASUREMENTS AND MAIN RESULTS

In our adoptive transfer experiments, matrix metalloproteinase-8 null mice receiving wild-type marrow had a survival advantage when compared with wild-type mice receiving matrix metalloproteinase-8 null marrow, suggesting that matrix metalloproteinase-8-containing myeloid cells are not a critical factor in sepsis following cecal ligation and puncture. In our cecal slurry model, no survival advantage was seen among matrix metalloproteinase-8 null mice. Our third model, intestinal implantation, found that mice receiving matrix metalloproteinase-8 null intestine had a survival advantage when compared with mice receiving wild-type intestine, regardless of recipient genotype. Clinically, median matrix metalloproteinase-8 serum concentrations were higher in patients with sepsis and primary intestinal pathology than in septic patients without primary intestinal pathology.

CONCLUSIONS

Intestine-derived matrix metalloproteinase-8 is a critical component of septic peritonitis secondary to intestinal compromise.

Contribution of programmed cell death receptor (PD)-1 to Kupffer cell dysfunction in murine polymicrobial sepsis

Recent studies suggest that coinhibitory receptors appear to be important in contributing sepsis-induced immunosuppression. Our laboratory reported that mice deficient in programmed cell death receptor (PD)-1 have increased bacterial clearance and improved survival in experimental sepsis induced by cecal ligation and puncture (CLP). In response to infection, the liver clears the blood of bacteria and produces cytokines. Kupffer cells, the resident macrophages in the liver, are strategically situated to perform the above functions. However, it is not known if PD-1 expression on Kupffer cells is altered by septic stimuli, let alone if PD-1 ligation contributes to the altered microbial handling seen. Here we report that PD-1 is significantly upregulated on Kupffer cells during sepsis. PD-1-deficient septic mouse Kupffer cells displayed markedly enhanced phagocytosis and restoration of the expression of major histocompatibility complex II and CD86, but reduced CD80 expression compared with septic wild-type (WT) mouse Kupffer cells. In response to ex vivo LPS stimulation, the cytokine productive capacity of Kupffer cells derived from PD-1-/- CLP mice exhibited a marked, albeit partial, restoration of the release of IL-6, IL-12, IL-1β, monocyte chemoattractant protein-1, and IL-10 compared with septic WT mouse Kupffer cells. In addition, PD-1 gene deficiency decreased LPS-induced apoptosis of septic Kupffer cells, as indicated by decreased levels of cleaved caspase-3 and reduced terminal deoxynucleotidyl transferase dUTP nick end-labeling-positive cells. Exploring the signal pathways involved, we found that, after ex vivo LPS stimulation, septic PD-1-/- mouse Kupffer cells exhibited an increased Akt phosphorylation and a reduced p38 phosphorylation compared with septic WT mouse Kupffer cells. Together, these results indicate that PD-1 appears to play an important role in regulating the development of Kupffer cell dysfunction seen in sepsis.

Differential Paradigms in Animal Models of Sepsis

Sepsis is a serious clinical problem involving complex mechanisms which requires better understanding and insight. Animal models of sepsis have played a major role in providing insight into the complex pathophysiology of sepsis. There have been various animal models of sepsis with different paradigms. Endotoxin, bacterial infusion, cecal ligation and puncture, and colon ascendens stent peritonitis models are the commonly practiced methods at present. Each of these models has their own advantages and also confounding factors. We have discussed the underlying mechanisms regulating each of these models along with possible reasons why each model failed to translate into the clinic. In animal models, the timing of development of the hemodynamic phases and the varied cytokine patterns could not accurately resemble the progression of clinical sepsis. More often, the exuberant and transient pro-inflammatory cytokine response is only focused in most models. Immunosuppression and apoptosis in the later phase of sepsis have been found to cause more damage than the initial acute phase of sepsis. Likewise, better understanding of the existing models of sepsis could help us create a more relevant model which could provide solution to the currently failed clinical trials in sepsis.

Intestinal trefoil factor increased the Bcl-2 level in a necrotizingenterocolitis neonate rat model

BACKGROUND/AIM

The aim of this study was to investigate the therapeutic effect of intestinal trefoil factor (ITF) on necrotizing enterocolitis (NEC) by observing the pathological changes and detecting the protein level differences in Caspase-3, Bax, and Bcl-2 in an NEC neonate rat model.

MATERIALS AND METHODS

A Wistar rat model of NEC was established and 30 one-day-old neonate Wistar rats were randomly divided into three groups including a normal control (group A), NEC rats treated with 0.2 ml physiological saline through intraperitoneal (i.p.) injection (group B), and NEC rats treated with 0.2 mg ITF by i.p injection (group C).

RESULTS

Compared with group B, there were statistically significant differences in Caspase-3, Bax, and Bcl-2 levels in groups A and C(P < 0.05). Moreover, there was a significant difference in the Bcl-2 level between groups A and B (P < 0.05).

CONCLUSION

ITF alleviated injury of the intestinal tract in neonate rats with NEC and this mechanism was possibly related to a reduction in the expression of Caspase-3 and Bax and the increase in Bcl-2 expression.

Sepsis induces incomplete M2 phenotype polarization in peritoneal exudate cells in mice

Background

Macrophages can differentiate into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes upon exposure to a pathogen or a cytokine microenvironment. However, M1/M2 macrophage polarization in polymicrobial sepsis has not been fully characterized.

Methods

The polarity of peritoneal exudate (PE) cells from mice that had undergone cecal ligation and puncture (CLP) and the response of those cells to lipopolysaccharide (LPS) in terms of cytokine and chemokine expression were examined.

Results

PE cells from CLP mice demonstrated a shift toward the M2 phenotype in terms of marker enzyme expression. In addition, the CLP-derived PE cells showed apparent unresponsiveness to LPS stimulation with regard to expression of pro-inflammatory cytokines such as TNF-α, while the expression of anti-inflammatory cytokines such as IL-10 was induced. Nevertheless, the CLP-PE cells failed to express M2 chemokines including chemokine (C-C motif) ligand 17 (CCL17), CCL22, and CCL24, all of which are important for T cell recruitment.

Conclusions

The results suggested that a shift of naïve monocytes/macrophages to the M2 phenotype, along with the lack of M2 chemokine expression in septic monocytes/macrophages, might be responsible for immunosuppression after sepsis.

Electronic supplementary material

The online version of this article (doi:10.1186/s40560-015-0124-1) contains supplementary material, which is available to authorized users.

Multifaceted role of β-arrestins in inflammation and disease

Arrestins are intracellular scaffolding proteins known to regulate a range of biochemical processes including G-protein coupled receptor (GPCR) desensitization, signal attenuation, receptor turnover and downstream signaling cascades. Their roles in regulation of signaling network have lately been extended to receptors outside of the GPCR family, demonstrating their roles as important scaffolding proteins in various physiological processes including proliferation, differentiation, and apoptosis. Recent studies have demonstrated a critical role for arrestins in immunological processes including key functions in inflammatory signaling pathways. In this review, we provide a comprehensive analysis of the different functions of the arrestin family of proteins especially related to immunity and inflammatory diseases.

Predicting disease severity of necrotizing enterocolitis: how to identify infants for future novel therapies

Necrotizing enterocolitis (NEC) remains a very devastating problem within the very low birth weight neonatal population. Several experimental therapies are being tested in animal models and soon may be ready for human trials. Despite this progress, we currently have no way to identify infants who would be optimal targets for therapy. Specifically, we are unable to predict which infants will progress to the more severe Bell's stage of disease that may necessitate surgery. Ideally, an algorithm could be constructed that would encompass multiple neonatal and maternal risk factors as well as potential biologic markers of disease so that these infants could be identified in a more timely fashion. This review summarizes the known risk factors and biomarkers of disease in hopes of stimulating clinical research to identify such an “early warning” NEC algorithm.

Upregulation of GRAIL is associated with impaired CD4 T cell proliferation in sepsis

The loss of numbers and functionality of CD4 T cells is observed in sepsis; however, the mechanism remains elusive. Gene related to anergy in lymphocytes (GRAIL) is critical for the impairment of CD4 T cell proliferation. We therefore sought to examine the role of GRAIL in CD4 T cell proliferation during sepsis. Sepsis was induced in 10-wk-old male C57BL/6 mice by cecal ligation and puncture. Splenocytes were isolated and subjected to flow cytometry to determine CD4 T cell contents. CD4 T cell proliferation was assessed by CFSE staining, and the expression of GRAIL in splenocytes was measured by immunohistochemistry, real-time PCR, and flow cytometry. The expressions of IL-2 and early growth response-2 were determined by real-time PCR. As compared with shams, the numbers of CD4 T cells were significantly reduced in spleens. Septic CD4 T cells were less efficient in proliferation than shams. The IL-2 expression was significantly reduced, whereas the GRAIL expression was significantly increased in septic mice splenocytes as compared with shams. The small interfering RNA-mediated knockdown of GRAIL expression re-established the CD4 T cell proliferation ability ex vivo. Similarly, the treatment with recombinant murine IL-2 to the septic CD4 T cells restored their proliferation ability by downregulating GRAIL expression. Our findings reveal a novel association of the increased GRAIL expression with impaired CD4 T cell proliferation, implicating an emerging therapeutic tool in sepsis.

The Methanol Extract of Azadirachta indica A. Juss Leaf Protects Mice Against Lethal Endotoxemia and Sepsis

In the present study, the inhibitory effect of neem leaf extract (NLE) on lipopolysaccaride (LPS)-induced nitric oxide (NO) and tumor necrosis factor-α (TNF-α) production was examined both in vitro and in vivo. In vitro study revealed that NLE treatment (100 μg/ml) inhibits LPS (100 ng/ml)-induced NO production by 96% and TNF-α production by 32%. The reduction in NO production is probably conferred by the complete suppression of inducible nitric oxide synthase (iNOS) expression. Interestingly, in vivo NLE significantly improved the survival rate of mice in an experimental sepsis model. Administration of NLE (100 mg/kg) 24 h before LPS treatment (20 mg/kg) improved the survival rate of mice by 60%. The inhibition of plasma NO and TNF-α production by NLE is likely to account for the improved survival of mice. Our results suggest that NLE may present a promising avenue in the development of therapeutic agents for the treatment of inflammatory diseases.

Carbenoxolone blocks endotoxin-induced protein kinase R (PKR) activation and high mobility group box 1 (HMGB1) release

The pathogen- and damage-associated molecular patterns (for example, bacterial endotoxin and adenosine 5'-triphosphate [ATP]) activate the double-stranded RNA-activated protein kinase R (PKR) to trigger the inflammasome-dependent high mobility group box 1 (HMGB1) release. Extracellular ATP contributes to the inflammasome activation through binding to the plasma membrane purinergic P2X7 receptor (P2X7R), triggering the opening of P2X7R channels and the pannexin-1 (panx-1) hemichannels permeable for larger molecules up to 900 daltons. It was previously unknown whether panx-1 channel blockers can abrogate lipopolysaccharide (LPS)-induced PKR activation and HMGB1 release in innate immune cells. Here we demonstrated that a major gancao (licorice) component (glycyrrhizin, or glycyrrhizic acid) derivative, carbenoxolone (CBX), dose dependently abrogated LPS-induced HMGB1 release in macrophage cultures with an estimated IC50 ≈ 5 μmol/L. In an animal model of polymicrobial sepsis (induced by cecal ligation and puncture [CLP]), repetitive CBX administration beginning 24 h after CLP led to a significant reduction of circulating and peritoneal HMGB1 levels, and promoted a significant increase in animal survival rates. As did P2X7R antagonists (for example, oxidized ATP, oATP), CBX also effectively attenuated LPS-induced P2X7R/panx-1 channel activation (as judged by Lucifer Yellow dye uptake) and PKR phosphorylation in primary peritoneal macrophages. Collectively, these results suggested that CBX blocks LPS-induced HMGB1 release possibly through impairing PKR activation, supporting the involvement of PKR in the regulation of HMGB1 release.

Gene dosage-dependent negative regulatory role of β-arrestin-2 in polymicrobial infection-induced inflammation

β-arrestin-2 (β-arr2) is a scaffolding protein of the arrestin family with a wide variety of cellular functions. Recent studies have demonstrated differential roles for β-arr2 in inflammation following endotoxemia and cecal ligation and puncture (CLP) models of sepsis. Because CLP-induced inflammation involves response to fecal contents and necrotic cecum in addition to microbial challenge, in this study, we examined the role of β-arr2 in an exclusively polymicrobial infection (PMI) model. In addition, we examined the role of gene dosage of β-arr2 in polymicrobial sepsis. Our studies demonstrate that β-arr2 is a negative regulator of systemic inflammation in response to polymicrobial infection and that one allele is sufficient for this process. Our results further reveal that loss of β-arr2 leads to increased neutrophil sequestration and overt inflammation specifically in the lungs following polymicrobial infection. Consistent with this, specific NF-κB and mitogen-activated protein kinase (MAPK) signaling pathways were differentially activated in the β-arr2 knockout (KO) mice lungs compared to the wild type (WT) following PMI. Associated with enhanced inflammation in the KO mice, PMI-induced mortality was also significantly higher in KO mice than in WT mice. To understand the differential role of β-arr2 in different sepsis models, we used cell culture systems to evaluate inflammatory cytokine production following endotoxin and polymicrobial stimulation. Our results demonstrate cell-type- as well as stimulus-specific roles for β-arr2 in inflammation. Taken together, our results reveal a negative regulatory role for β-arr2 in polymicrobial infection-induced inflammation and further demonstrate that one allele of β-arr2 is sufficient to mediate most of these effects.

Lung microenvironment contributes to the resistance of alveolar macrophages to develop tolerance to endotoxin*

OBJECTIVE

Endotoxin tolerance corresponds to reprogramming of mononuclear phagocytes after iterative encounters with toll-like receptor agonists aimed to dampen the inflammatory response. We investigated why this phenomenon cannot be observed with murine alveolar macrophages.

DESIGN

Animal study.

SETTING

Research institution laboratory.

SUBJECTS

rag2-/-, rag2γc-/-, cd3ε-/-, µ-/-, il-15-/-, Jα18-/-, ifnγr-/-, il-18r-/-, and wild-type mice.

INTERVENTIONS

Alveolar macrophages were harvested from untreated mice or after injection of endotoxin. Alveolar macrophages were activated in vitro with endotoxin (lipopolysaccharide), and tumor necrosis factor production was monitored.

MEASUREMENTS AND MAIN RESULTS

In contrast to monocytes or peritoneal macrophages, alveolar macrophages did not display endotoxin tolerance in an ex vivo model after injection of endotoxin. An in vivo systemic inhibition of granulocyte-macrophage colony-stimulating factor or interferon-γ allowed the induction of alveolar macrophage endotoxin tolerance, which was also observed in interferon-γ receptor-deficient mice. Using mice missing different leukocyte subsets and adoptive cell transfers, we demonstrated the involvement of B lymphocytes in interferon-γ production within the lung microenvironment and in the prevention of alveolar macrophage endotoxin tolerance. Furthermore, we demonstrated the importance of interleukin-18 in preventing alveolar macrophage endotoxin tolerance through studies of interleukin-18 messenger RNA expression in il-18r-/- mice and injection of interleukin-18 in rag2-/- and µ-/- mice.

CONCLUSIONS

Our results support the conclusion that at homeostasis in the lungs, constitutive expression of granulocyte-macrophage colony-stimulating factor, interleukin-18, interferon-γ and possibly interleukin-15, and a cross-talk between B lymphocytes and alveolar macrophages create a microenvironment specific to the lungs that prevents alveolar macrophages from becoming tolerant to endotoxin.

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: the gold standard model for polymicrobial sepsis?

Sepsis is a serious medical condition characterized by dysregulated systemic inflammatory responses followed by immunosuppression. To study the pathophysiology of sepsis, diverse animal models have been developed. Polymicrobial sepsis induced by cecal ligation and puncture (CLP) is the most frequently used model because it closely resembles the progression and characteristics of human sepsis. Here we summarize the role of several immune components in the pathogenesis of sepsis induced by CLP. However, several therapies proposed on the basis of promising results obtained by CLP could not be translated to the clinic. This demonstrates that experimental sepsis models do not completely mimic human sepsis. We propose several strategies to narrow the gap between experimental sepsis models and clinical sepsis, including targeting factors that contribute to the immunosuppressive phase of sepsis, and reproducing the heterogeneity of human patients.

Aging-related hyperinflammation in endotoxemia is mediated by the alpha2A-adrenoceptor and CD14/TLR4 pathways

AIMS

Sepsis is a major cause of morbidity and mortality in the elderly population. In prior studies, we have shown that in vivo, the inflammatory response in aged animals is exaggerated as compared to young animals and that this response likely accounts for the increased morbidity and mortality. Part of this uncontrolled inflammatory response in sepsis is due to the innate immune response. However, recent studies have shown that the pathogenesis of sepsis is much more complex. The adrenergic autonomic nervous system is now thought to play a key role in modulating the inflammatory response in sepsis. In this study, we hypothesize that not only is the innate immune response enhanced in response to lipopolysaccharide (LPS) in aged animals, but that the adrenergic nervous system also plays a role in the release of excess inflammatory cytokines.

MAIN METHODS

Male Fischer-344 rats (young: 3 months; aged: 24 months) were used. Endotoxemia was induced by intravenous injection of lipopolysaccharide (LPS, 15 mg/kg BW). Splenic tissues were harvested and mRNA and protein were extracted. The protein expression of CD14 and TLR4, key mediators of LPS in the innate response, as well as alpha-2A adrenergic receptor (alpha(2A)-AR) and phosphodiesterase 4D (PDE4D), as the means by which the autonomic nervous system exerts its effects were analyzed.

KEY FINDINGS

Splenic tissue concentrations of alpha(2A)-AR, PDE4D, CD14, and TLR4 were significantly increased in septic aged rats as compared to aged sham rats and septic young rats. The increased expression of alpha(2A)-AR in septic aged rats was further confirmed by immunohistochemical staining of splenic tissues.

SIGNIFICANCE

These data support the hypothesis that not only is the innate immune response increased in aged animals during sepsis, but that there is also an upregulated response of the adrenergic autonomic nervous system that contributes to excess proinflammatory cytokine release.

Present status and perspectives of stem cell-based therapies for gastrointestinal diseases

In recent years the interest in stem cell-based therapies for gastrointestinal injury has been increasing continuously. From the clinical point of view, transplantation of bone marrow derived stem cells may represent an alternative therapy for gastrointestinal injury, such as radioactive injury, inflammatory bowel disease, and other refractory gastrointestinal tract injury. There were several reports indicated that bone marrow derived stem cells located in the injured gastrointestinal tract and contributed to its regeneration by differentiating into functional epithelia cells or infusing with the gastrointestinal stem cells. Although the concept of cell-based therapy for various diseases of the gastrointestinal is widely accepted, the practical approach in humans remains difficult. Here we discussed the recent published data on clinical and experimental bone marrow stem cell transplantation and the possible role of stem cells in gastrointestinal tissue repair.

The role of hepatic invariant NKT cells in systemic/local inflammation and mortality during polymicrobial septic shock

NKT cells have been described as innate regulatory cells because of their rapid response to conserved glycolipids presented on CD1d via their invariant TCR. However, little is known about the contribution of the hepatic NKT cell to the development of a local and/or systemic immune response to acute septic challenge (cecal ligation and puncture (CLP)). We found not only that mice deficient in invariant NKT cells (Jalpha18(-/-)) had a marked attenuation in CLP-induced mortality, but also exhibited an oblation of the systemic inflammatory response (with little effect on splenic/peritoneal immune responsiveness). Flow cytometric data indicated that following CLP, there was a marked decline in the percentage of CD3(+)alpha-galactosylceramide CD1d tetramer(+) cells in the mouse C57BL/6J and BALB/c liver nonparenchymal cell population. This was associated with the marked activation of these cells (increased expression of CD69 and CD25) as well as a rise in the frequency of NKT cells positive for both Th1 and Th2 intracellular cytokines. In this respect, when mice were pretreated in vivo with anti-CD1d-blocking Ab, we observed not only that this inhibited the systemic rise of IL-6 and IL-10 levels in septic mice and improved overall septic survival, but that the CLP-induced changes in liver macrophage IL-6 and IL-10 expressions were inversely effected by this treatment. Together, these findings suggest that the activation of hepatic invariant NKT cells plays a critical role in regulating the innate immune/systemic inflammatory response and survival in a model of acute septic shock.

Fucoidan extracted from Fucus evanescens brown algae corrects immunity and hemostasis disorders in experimental endotoxemia

Fucoidan extracted from brown algae (Fucus evanescens) was used for correction of immunity and hemostasis disorders in experimental endotoxemia induced by injection of LPS. Fucoidan reduced the elevated levels of proinflammatory cytokines (TNF-alpha, IL-1, IL-6) and partially arrested hypercoagulation phenomena, thus improving animal resistance to LPS.

Proestrus female rats are more resistant to right ventricular pressure overload

Multiple studies of left ventricular dysfunction suggest that females may be more resistant to ischemia or endotoxemia. However, sex differences in right ventricular (RV) responses to pressure overload and/or endotoxemia have not been elucidated. We hypothesized that females would maintain better RV function during acute pressure overload (APO), endotoxemia, or a simultaneous insult from both processes. Age-matched male and proestrus female Sprague-Dawley rats were given an intraperitoneal injection of either phosphate buffered saline or LPS. Six hours after injection, hearts were removed by median sternotomy and isolated via Langendorff. End-diastolic pressures were sequentially elevated past physiologic levels by increasing the volume of a latex balloon that was inserted into the RV. Male RV function was depressed to a greater degree after APO injury compared with that in females (developed pressure: male, 44.97 mmHg vs. female, 58.23 mmHg). Interestingly though, at a physiologic end-diastolic pressure of 5 mmHg, endotoxic males and females maintained equivalent RV function. However, with concurrent endotoxic insult and APO, RV function was better maintained in males as compared with that in females (developed pressure: male, 59% of control versus female, 41% of control). Furthermore, tissue levels of IL-1 and IL-6, but not IL-10, were increased after endotoxin exposure but did not differ based on sex. Through this study, we have shown that sex differences exist in RV dysfunction, and that different cardiac insults diversely affect myocardial function. Understanding these differences may allow for the implementation of novel therapeutic treatment options that are designed to attenuate RV cardiovascular collapse.

Stem cells as a potential future treatment of pediatric intestinal disorders

All surgical disciplines encounter planned and unplanned ischemic events that may ultimately lead to cellular dysfunction and death. Stem cell therapy has shown promise for the treatment of a variety of ischemic and inflammatory disorders where tissue damage has occurred. As stem cells have proven beneficial in many disease processes, important opportunities in the future treatment of gastrointestinal disorders may exist. Therefore, this article will serve to review the different types of stem cells that may be applicable to the treatment of gastrointestinal disorders, review the mechanisms suggesting that stem cells may work for these conditions, discuss current practices for harvesting and purifying stem cells, and provide a concise summary of a few of the pediatric intestinal disorders that could be treated with cellular therapy.

Ulinastatin alone does not reduce caspase 3-mediated apoptosis in protease-positive Aeromonas hydrophilia-induced sepsis

BACKGROUND/PURPOSE

To evaluate the effect of ulinastatin, a protease inhibitor, on survival and apoptosis in protease-positive Aeromonas hydrophilia (PPAH)-induced sepsis.

METHODS

Thirty mice were randomly allocated to receive intraperitoneal injection of either phosphate buffered saline (PBS) (control mice, n = 10) or PPAH (PPAH mice, n = 20). After 30 minutes, control mice received an additional intraperitoneal PBS injection, 10 PPAH mice received intraperitoneal PBS injection (non-treated PPAH mice), and the remaining 10 PPAH mice received an intraperitoneal injection of ulinastatin (ulinastatin-treated PPAH mice).

RESULTS

Survival at 24 hours was 100% in control mice, and 35% (p < 0.05) in PPAH mice; the survival rate in non-treated and ulinastatin-treated PPAH mice were 30% and 40% (p > 0.05), respectively. The thymus weight (mg) decreased significantly in PPAH mice (51.1 +/- 14.9) compared to control mice (69.7 +/- 14.4; p < 0.001); there was no difference between ulinastatin-treated (52 +/- 13.9; p > 0.05) and non-treated PPAH mice (50.4 +/- 16). The thymus gland cell count reduced significantly in PPAH mice (8.1 +/- 4.7 x 10(7)) compared to control mice (12.8 +/- 6.6 x 10(7); p < 0.01), and immunofluorescence analysis demonstrated that the reduced cells were mostly CD4+ CD8+, in contrast to the increase in CD4+ CD8- cells. There was no difference in cell count between ulinastatin-treated (8.7 +/- 4.9 x 10(7)) and non-treated PPAH mice (7.4 +/- 4.6 x 10(7); p > 0.05). Caspase 3-mediated apoptosis was not detectable in control mice in contrast to the pronounced manifestation in PPAH mice.

CONCLUSION

PPAH-induced sepsis has a high mortality that is related to lymphocyte apoptosis. Ulinastatin alone does not significantly reduce caspase 3-mediated lymphocyte apoptosis.

Activation of individual tumor necrosis factor receptors differentially affects stem cell growth factor and cytokine production

Necrotizing enterocolitis (NEC) is an emergency of the newborn that often requires surgery. Growth factors from stem cells may aid in decreasing intestinal damage while also promoting restitution. We hypothesized that 1) TNF, LPS, or hypoxia would alter bone marrow mesenchymal stem cell (BMSC) TNF, IGF-1, IL-6, and VEGF production, and 2) TNF receptor type 1 (TNFR1) or type 2 (TNFR2) ablation would result in changes to the patterns of cytokines and growth factors produced. BMSCs were harvested from female wild-type (WT), TNFR1 knockout (KO), and TNFR2KO mice. Cells were stimulated with TNF, LPS, or hypoxia. After 24 h, cell supernatants were assayed via ELISA. Production of TNF and IGF-1 was decreased in both knockouts compared with WT regardless of the stimulus utilized, whereas IL-6 and VEGF levels appeared to be cooperatively regulated by both the activated TNF receptor and the initial stimulus. IL-6 was increased compared with WT in both knockouts following TNF stimulation but was significantly decreased with LPS. Compared with WT, hypoxia increased IL-6 in TNFR1KO but not TNFR2KO cells. TNF stimulation decreased VEGF in TNFR2KO cells, whereas TNFR1 ablation resulted in no change in VEGF compared with WT. TNFR1 ablation resulted in a decrease in VEGF following LPS stimulation compared with WT; no change was noted in TNFR2KO cells. With hypoxia, TNFR1KO cells expressed more VEGF compared with WT, whereas no difference was noted between WT and TNFR2KO cells. TNF receptor ablation modifies BMSC cytokine production. Identifying the proper stimulus and signaling cascades for the production of desired growth factors may be beneficial in maximizing the therapeutic potential of stem cells.

Chronic sepsis mortality characterized by an individualized inflammatory response

Late mortality in septic patients often exceeds the lethality occurring in acute sepsis, yet the immunoinflammatory alterations preceding chronic sepsis mortality are not well defined. We studied plasma cytokine concentrations preceding late septic deaths (days 6-28) in a murine model of sepsis induced by polymicrobial peritonitis. The late prelethal inflammatory response varied from a virtually nonexistent response in three of 14 to a mixed response in eight of 14 mice to the concurrent presence of nearly all measured cytokines, both proinflammatory and anti-inflammatory in three of 14 mice. In responding mice a consistent prelethal surge of plasma MIP-2 (1.6 vs 0.12 ng/ml in survivors; mean values), MCP-1 (2.0 vs 1.3 ng/ml), soluble TNF receptor type I (2.5 vs 0.66 ng/ml), and the IL-1 receptor antagonist (74.5 vs 3.3 ng/ml) was present, although there were infrequent increases in IL-6 (1.9 vs 0.03 ng/ml) and IL-10 (0.12 vs 0.04 ng/ml). For high mobility group box 1, late mortality was signaled by its decrease in plasma levels (591 vs 864 ng/ml). These results demonstrate that impeding mortality in the chronic phase of sepsis may be accurately predicted by plasma biomarkers, providing a mechanistic basis for individualized therapy. The pattern of late prelethal responses suggest that the systemic inflammatory response syndrome to compensatory anti-inflammatory response syndrome transition paradigm fails to follow a simple linear pattern.

In vivo observation of mesenteric leukocyte-endothelial interactions after cecal ligation/puncture and surgical sepsis source control

PURPOSE

Cecal ligation and puncture (CLP) has been used as a useful model for the induction of polymicrobial sepsis. Necrotic tissue resection and peritoneal lavage (REL) are the surgical procedures for controlling perforated appendicitis. The aim of this study was to evaluate leukocyte-endothelial interactions in the rat mesentery in vivo after CLP and REL.

METHODS

Thirty-seven male Wistar rats (250-300 g) underwent laparotomy and were randomly assigned to the following groups: 1) SHAM; 2) CLP: animals submitted to CLP, 3) CLP+REL: animals submitted to CLP and REL. Mesenteric leukocyte-endothelial interactions were studied by intravital microscopy assessed once in each animal (3-5 postcapillary venules, 15-25 microm diameter) 24 hours after intervention. Follow-up was performed in all animals; this included analysis of glycemia, lactate, hematocrit, white blood cell count as well as a functional score that was the sum of scoring on the following parameters: alertness, mobility, piloerection, diarrhea, encrusted eyes, and dirty nose and tail.

RESULTS

None of the animals showed significant changes in body weight (265 +/- 20 g) or in hematocrit levels (46% +/- 2%) during the experimental protocol. Compared to SHAM animals, CLP animals showed an increased number of rolling (2x), adherent, and migrating leukocytes (7x) in the mesenteric microcirculation, an increase in blood glucose (136 +/- 8 mg/dL), lactate (3.58 +/- 0.94 mmol/L), white cell count (23,570 +/- 4,991 cells/mm(3)) and functional alterations (score 11 +/- 1), characterized by impaired alertness and mobility, and presence of piloerection, diarrhea, encrusted eyes, and dirty nose and tail. The REL procedure normalized the number of rolling, adherent, and migrated leukocytes in the mesentery; glycemia; lactate; and white blood cell count. The REL procedure also improved the functional score (7 +/- 1).

CONCLUSION

Local and systemic inflammation was induced by CLP, while REL completely overcame the inflammatory process.

A cardiovascular drug rescues mice from lethal sepsis by selectively attenuating a late-acting proinflammatory mediator, high mobility group box 1

The pathogenesis of sepsis is mediated in part by bacterial endotoxin, which stimulates macrophages/monocytes to sequentially release early (e.g., TNF, IL-1, and IFN-gamma) and late (e.g., high mobility group box 1 (HMGB1) protein) proinflammatory cytokines. The recent discovery of HMGB1 as a late mediator of lethal sepsis has prompted investigation for development of new experimental therapeutics. We found that many steroidal drugs (such as dexamethasone and cortisone) and nonsteroidal anti-inflammatory drugs (such as aspirin, ibuprofen, and indomethacin) failed to influence endotoxin-induced HMGB1 release even at superpharmacological concentrations (up to 10-25 microM). However, several steroid-like pigments (tanshinone I, tanshinone IIA, and cryptotanshinone) of a popular Chinese herb, Danshen (Salvia miltiorrhiza), dose dependently attenuated endotoxin-induced HMGB1 release in macrophage/monocyte cultures. A water-soluble tanshinone IIA sodium sulfonate derivative (TSNIIA-SS), which has been widely used as a Chinese medicine for patients with cardiovascular disorders, selectively abrogated endotoxin-induced HMGB1 cytoplasmic translocation and release in a glucocorticoid receptor-independent manner. Administration of TSNIIA-SS significantly protected mice against lethal endotoxemia and rescued mice from lethal sepsis even when the first dose was given 24 h after the onset of sepsis. The therapeutic effects were partly attributable to attenuation of systemic accumulation of HMGB1 (but not TNF and NO) and improvement of cardiovascular physiologic parameters (e.g., decrease in total peripheral vascular resistance and increase in cardiac stroke volume) in septic animals. Taken together, these data re-enforce the pathogenic role of HMGB1 in lethal sepsis, and support a therapeutic potential for TSNIIA-SS in the treatment of human sepsis.

Beneficial Versus Detrimental Effects of Neutrophils Are Determined by the Nature of the Insult

BACKGROUND

Neutrophils are thought to play pivotal roles in eliminating pathogens, and they have also been implicated in end organ dysfunction associated with systemic inflammatory response syndrome (SIRS). Because modulating neutrophil survival and function has been proposed as a therapy for sepsis, it remains critical to determine under which circumstances modulating neutrophil function is efficacious. The aim of this study was to investigate whether sustaining the presence of neutrophils activated by hemorrhagic shock (HEM) would be disadvantageous during subsequent sepsis, ie, inflammation plus infection, or systemic inflammation without infection.

STUDY DESIGN

Transgenic mice, overexpressing the antiapoptotic protein Bcl-2 in a myeloid restricted fashion (Bcl-2(my)), and controls (C57) were subjected to HEM, followed 24 hours thereafter either by cecal ligation and puncture to induce sepsis, or by intraperitoneal injection of lipopolysaccharide to induce SIRS. Lung injury was assessed by bronchoalveolar lavage fluid protein and histology. Lung, plasma, and liver cytokines were quantified through CBA or ELISA.

RESULTS

In sepsis, Bcl-2(my) had increased lung neutrophil and lower lung bacteria counts compared with C57. This translated into a marked early survival benefit for Bcl-2(my). There were no differences between Bcl-2(my) and C57 with respect to the degree of lung injury or lung and plasma cytokines. In contrast, in SIRS, Bcl-2(my) exhibited markedly increased acute lung injury and lung and plasma cytokines when compared with C57. Bcl-2(my) also had a profound survival disadvantage.

CONCLUSIONS

Whether effects of prolonged survival of hemorrhage-primed neutrophils are beneficial or detrimental is determined by the nature of the second insult. During sepsis, prolonging neutrophil survival is beneficial, enhancing antimicrobial activity. Alternatively, during inflammation without infection, increased organ damage by long-lived neutrophils is detrimental.

Glucose-6-phosphate dehydrogenase deficiency and the inflammatory response to endotoxin and polymicrobial sepsis*

OBJECTIVE

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common human genetic polymorphism. The deficiency protects against malaria but was shown to worsen the clinical course after severe trauma. This study tested whether the deficiency is associated with altered cytokine responses in vitro and in vivo and affects survival after endotoxemia or polymicrobial sepsis (cecal ligation and puncture).

DESIGN

Genotyping of animals was carried out using a novel and improved allele-specific polymerase chain reaction assay. Macrophage and splenocyte responses in vitro and ex vivo were compared using gene array analyses and enzyme-linked immunosorbent assays and flow cytometry under both baseline and lipopolysaccharide-stimulated conditions. Endotoxemia- or sepsis-induced mortality was compared under a variety of treatment and resuscitation protocols.

SETTINGS

Medical school research laboratories.

SUBJECTS

Litter mates of wild-type and G6PD-mutant mice that display a degree of G6PD deficiency similar to that observed in the African-type human deficiency (20% of normal).

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide in vivo (lipopolysaccharide from Escherichia coli, 10-35 mg/kg body weight intraperitoneally) resulted in greater interleukin-1beta, interleukin-6, and interleukin-10 levels in serum and peritoneal lavage in G6PD-deficient mice compared with wild type. Prevailing doses of lipopolysaccharide in vivo increased mortality in G6PD-deficient animals (40-70%) as compared with wild type (5-40%). In contrast, mortality after cecal ligation and puncture-induced sepsis was similar in G6PD-deficient and wild-type animals either in saline-resuscitated or antibiotic-treated animals. Splenic and blood phagocytes from septic G6PD-deficient and wild-type animals displayed attenuated ex vivo lipopolysaccharide responsiveness.

CONCLUSIONS

This study demonstrates that G6PD deficiency augments cytokine responses after inflammatory challenges. The deficiency is disadvantageous as reflected in increased mortality after hyperinflammation caused by acute endotoxemia. However, the deficiency may not manifest worsened survival after the immunosuppressed condition associated with severe sepsis.

Pulmonary cytomegalovirus reactivation causes pathology in immunocompetent mice

OBJECTIVE

Cytomegalovirus (CMV) is a ubiquitous herpes virus that persists in the host in a latent state following primary infection. We have recently observed that CMV reactivates in lungs of critically ill surgical patients and that this reactivation can be triggered by bacterial sepsis. Although CMV is a known pathogen in immunosuppressed transplant patients, it is unknown whether reactivated CMV is a pathogen in immunocompetent hosts. Using an animal model of latency/reactivation, we studied the pathobiology of CMV reactivation in the immunocompetent host.

DESIGN

Laboratory study.

SETTING

University laboratory.

SUBJECTS

Cohorts of immunocompetent BALB/c mice with or without latent murine CMV (MCMV+/MCMV-).

INTERVENTIONS

Mice underwent cecal ligation and puncture. Lung tissue homogenates were evaluated after cecal ligation and puncture for tumor necrosis factor-alpha, interleukin-1beta, neutrophil chemokine KC, and macrophage inflammatory protein-2 messenger RNA by polymerase chain reaction and real-time quantitative reverse transcription-polymerase chain reaction. Because pulmonary tumor necrosis factor-alpha expression is known to cause pulmonary fibrosis, trichrome-stained sections of lung tissues were analyzed using image analysis to quantitate pulmonary fibrosis. In a second experiment, a cohort of MCMV+ mice received ganciclovir (10 mg/kg/day subcutaneously) following cecal ligation and puncture. Tumor necrosis factor-alpha messenger RNA and pulmonary fibrosis were evaluated as described previously.

MEASUREMENTS AND MAIN RESULTS

All MCMV+ mice had CMV reactivation beginning 2 wks after cecal ligation and puncture. Following reactivation, these mice had abnormal tumor necrosis factor-alpha, interleukin-1beta, neutrophil chemokine KC, and macrophage inflammatory protein-2 messenger RNA expression compared with controls. Image analysis showed that MCMV+ mice had significantly increased pulmonary fibrosis compared with MCMV- mice 3 wks after cecal ligation and puncture. Ganciclovir treatment following cecal ligation and puncture prevented MCMV reactivation. Furthermore, ganciclovir-treated mice did not demonstrate abnormal pulmonary expression of tumor necrosis factor-alpha messenger RNA. Finally, ganciclovir treatment prevented pulmonary fibrosis following MCMV reactivation.

CONCLUSIONS

This study shows that CMV reactivation causes abnormal tumor necrosis factor-alpha expression, and that following CMV reactivation, immunocompetent mice have abnormal pulmonary fibrosis. Ganciclovir blocks MCMV reactivation, thus preventing abnormal tumor necrosis factor-alpha expression and pulmonary fibrosis. These data may explain a mechanism by which critically ill surgical patients develop fibroproliferative acute respiratory distress syndrome. These data suggest that human studies using antiviral agents during critical illness are warranted.

The aqueous extract of a popular herbal nutrient supplement, Angelica sinensis, protects mice against lethal endotoxemia and sepsis

Despite recent advances in antibiotic therapy and intensive care, sepsis remains a widespread problem in critically ill patients. The high mortality from sepsis is in part mediated by bacterial endotoxin, which stimulates macrophages/monocytes to sequentially release early (e.g., tumor necrosis factor, interleukin-1, and interferon-gamma) and late [e.g., high mobility group box 1 protein (HMGB1)] proinflammatory cytokines. Our discovery of HMGB1 as a late mediator of lethal systemic inflammation has initiated a new field of investigation for the development of experimental therapeutics. A popular Chinese herb, Angelica sinensis (also known as Dang Gui or Dong Quai) has been used traditionally for treating women with gynecological disorders (such as dysmenorrheal and hot flashes). Here we examined the effect of Angelica sinensis extract on endotoxin-induced HMGB1 release in vitro, and explored its therapeutic potential in animal models of lethal endotoxemia and sepsis [induced by cecal ligation and puncture (CLP)] in vivo. We demonstrated that a low-molecular-weight (<10 kDa) fraction of A. sinensis extract significantly attenuated endotoxin-induced HMGB1 release in part through interfering with its cytoplasmic translocation in macrophage cultures. Prophylactic administration of an aqueous extract of A. sinensis significantly attenuated systemic HMGB1 accumulation in vivo, and conferred a dose-dependent protection against lethal endotoxemia. Furthermore, delayed administration of A. sinensis extract beginning 24 h after CLP attenuated systemic HMGB1 accumulation, and significantly rescued mice from lethal sepsis. Taken together, these data suggest that A. sinensis contains water-soluble components that exert protective effects against lethal endotoxemia and experimental sepsis in part by attenuating systemic accumulation of a late proinflammatory cytokine, HMGB1.

Animal models of sepsis: setting the stage

Sepsis is a state of disrupted inflammatory homeostasis that is often initiated by infection. The development and progression of sepsis is multi-factorial, and affects the cardiovascular, immunological and endocrine systems of the body. The complexity of sepsis makes the clinical study of sepsis and sepsis therapeutics difficult. Animal models have been developed in an effort to create reproducible systems for studying sepsis pathogenesis and preliminary testing of potential therapeutic agents. However, demonstrated benefit from a therapeutic agent in animal models has rarely been translated into success in human clinical trials. This review summarizes the common animal sepsis models and highlights how results of recent human clinical trials might affect their use.

The effects of repeated endotoxin exposure on rat brain metabolites as measured by ex vivo 1HMRS

Abnormalities in brain chemistry induced by acute or chronic treatment with LPS were studied in the rat model. Ex vivo brain metabolites were measured using proton magnetic resonance spectroscopy, whereas serum corticosterone levels were determined using radioimmunoassay. We observed increased lactate levels in all measured brain regions and decreased choline in the hypothalamus after chronic LPS treatment. Acute LPS treatment led to an elevation of corticosterone, whereas chronic LPS treatment led to attenuation of the HPA response. These findings suggest that chronic inflammation induced by LPS could lead to cell loss/dysfunction, and hence, desensitization of the HPA axis, particularly in the hypothalamus.

Pulmonary contusion causes impairment of macrophage and lymphocyte immune functions and increases mortality associated with a subsequent septic challenge*

OBJECTIVE AND DESIGN

Pulmonary contusion is frequently followed by acute respiratory distress syndrome, pneumonia, and sepsis. However, immunologic alterations of circulating and resident immune cell populations contributing to the posttraumatic immunosuppression are poorly understood. We therefore characterized the influence of pulmonary contusion on peripheral blood mononuclear cells, peritoneal macrophages, splenocytes, and splenic macrophages. To address the significance of the immunosuppression associated with lung contusion, we investigated how the consecutive addition of moderate or severe sepsis affected survival after blunt chest trauma.

SUBJECTS

Male C3H/HeN mice (n = 10 per group) were anesthetized and subjected to chest trauma or sham procedure.

MEASUREMENTS

The cytokine release of cultured peripheral blood mononuclear cells, peritoneal macrophages, splenocytes, and splenic macrophages and plasma levels of tumor necrosis factor-alpha and interleukin-6 from those animals were quantified. Sepsis was induced via cecal ligation and puncture 24 hrs after lung contusion.

MAIN RESULTS

Two hours after blunt chest trauma, plasma tumor necrosis factor-alpha and interleukin-6 were markedly increased, as was peripheral blood mononuclear cell cytokine production, lung myeloperoxidase activity, and lung chemokine concentrations. At 24 hrs and, in part, already at 2 hrs, cytokine release from peritoneal macrophages, splenic macrophages, and splenocytes was significantly suppressed. Furthermore, pulmonary contusion when followed by moderate sepsis significantly diminished survival rate when compared with chest trauma or moderate sepsis alone.

CONCLUSIONS

These results indicate that pulmonary contusion causes severe immunodysfunction of splenocytes, macrophages, and monocytes in different local compartments and systemically. Moreover, this immunosuppression is associated with an increased susceptibility to infectious complications, which results in a decreased survival rate if blunt chest trauma is followed by a septic insult.

Sepsis associated with immunosuppressive medications: an evidence-based review

OBJECTIVE

In 2003, critical care and infectious disease experts representing 11 international organizations developed management guidelines for sepsis associated with immunosuppressive medications that would be of practical use for the bedside clinician, under the auspices of the Surviving Sepsis Campaign, an international effort to increase awareness and improve outcome in severe sepsis.

DESIGN

The process included a modified Delphi method, a consensus conference, several subsequent smaller meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee.

METHODS

The modified Delphi methodology used for grading recommendations built on a 2001 publication sponsored by the International Sepsis Forum. We undertook a systematic review of the literature graded along five levels to create recommendation grades from A to E, with A being the highest grade. Pediatric considerations to contrast adult and pediatric management are in the article by Parker et al. on p. S591.

CONCLUSION

Immunosuppressed patients, by definition, are susceptible to a wider spectrum of infectious agents than immunologically normal patients and, thus, require a broader spectrum antimicrobial regimen when they present with sepsis or septic shock. Special expertise managing immunosuppressed patient populations is needed to predict and establish the correct diagnosis and to choose appropriate empiric and specific agents and maximize the likelihood that patients will survive these microbial challenges.

Activation of acid sphingomyelinase and its inhibition by the nitric oxide/cyclic guanosine 3',5'-monophosphate pathway: key events in Escherichia coli-elicited apoptosis of dendritic cells

Depletion of dendritic cells (DCs) via apoptosis contributes to sepsis-induced immune suppression. The mechanisms leading to DC apoptosis during sepsis are not known. In this study we report that immature DCs undergo apoptosis when treated with high numbers of Escherichia coli. This effect was mimicked by high concentrations of LPS. Apoptosis was accompanied by generation of ceramide through activation of acid sphingomyelinase (A-SMase), was prevented by inhibitors of this enzyme, and was restored by exogenous ceramide. Compared with immature DCs, mature DCs expressed significantly reduced levels of A-SMase, did not generate ceramide in response to E. coli or LPS, and were insensitive to E. coli- and LPS-triggered apoptosis. However, sensitivity to apoptosis was restored by addition of exogenous A-SMase or ceramide. Furthermore, inhibition of A-SMase activation and ceramide generation was found to be the mechanism through which the immune-modulating messenger NO protects immature DCs from the apoptogenic effects of E. coli and LPS. NO acted through formation of cGMP and stimulation of the cGMP-dependent protein kinase. The relevance of A-SMase and its inhibition by NO/cGMP were confirmed in a mouse model of LPS-induced sepsis. DC apoptosis was significantly higher in inducible NO synthase-deficient mice than in wild-type animals and was significantly reduced by treatment ex vivo with NO, cGMP, or the A-SMase inhibitor imipramine. Thus, A-SMase plays a central role in E. coli/LPS-induced DC apoptosis and its inhibition by NO, and it might be a target of new therapeutic approaches to sepsis.

Bacterial endotoxin stimulates macrophages to release HMGB1 partly through CD14- and TNF-dependent mechanisms

Bacterial endotoxin [lipopolysaccharide (LPS)] stimulates macrophages to sequentially release early [tumor necrosis factor (TNF)] and late [high mobility group box 1 (HMGB1)] proinflammatory cytokines. The requirement of CD14 and mitogen-activated protein kinases [MAPK; e.g., p38 and extracellular signal-regulated kinase (ERK)1/2] for endotoxin-induced TNF production has been demonstrated previously, but little is known about their involvement in endotoxin-mediated HMGB1 release. Here, we demonstrated that genetic disruption of CD14 expression abrogated LPS-induced TNF production but only partially attenuated LPS-induced HMGB1 release in cultures of primary murine peritoneal macrophages. Pharmacological suppression of p38 or ERK1/2 MAPK with specific inhibitors (SB203580, SB202190, U0126, or PD98059) significantly attenuated LPS-induced TNF production but failed to inhibit LPS-induced HMGB1 release. Consistently, an endogenous, immunosuppressive molecule, spermine, failed to inhibit LPS-induced activation of p38 MAPK and yet, still significantly attenuated LPS-mediated HMGB1 release. Direct suppression of TNF activity with neutralizing antibodies or genetic disruption of TNF expression partially attenuated HMGB1 release from macrophages induced by LPS at lower concentrations (e.g., 10 ng/ml). Taken together, these data suggest that LPS stimulates macrophages to release HMGB1 partly through CD14- and TNF-dependent mechanisms.

Evaluation of protein C and other biomarkers as predictors of mortality in a rat cecal ligation and puncture model of sepsis

OBJECTIVE

To evaluate protein C and other factors associated with the septic response as predictors of mortality in a clinically relevant animal model of sepsis.

DESIGN

Laboratory investigation.

SETTING

Eli Lilly and Company discovery research laboratory.

SUBJECTS

Forty female Sprague Dawley rats weighing 245-265 g.

INTERVENTIONS

Polyethylene catheters were surgically implanted into the femoral vein and sepsis was induced by cecal ligation and puncture (CLP). A solution of 5% dextrose in 0.9 % saline was continuously infused via femoral catheters immediately following surgery. Blood sampling was done before surgery and at 6 and 20 hrs after surgery. Rats were then monitored for survival out to 4 days.

MEASUREMENTS AND MAIN RESULTS

Blood collections were used to measure blood glucose, bacteremia, plasma protein C, D-dimer, hormones, chemokines, cytokines, and myoglobin (as a marker of organ damage). Mortality was categorized into three groups: early death (before 30 hrs post-CLP), late death (after 30 hrs post-CLP), and survivors (96 hrs post-CLP). Compared with survivors, early death rats had statistically significant differences in 30 variables indicative of severe inflammation, coagulopathy, and muscle damage including less bacterial clearance, hypoglycemia, lower plasma protein C, higher plasma D dimer, higher plasma cytokine/ chemokines, and higher plasma myoglobin concentrations. Twenty variables had a moderate to strong correlation with time of death. Receiver operator characteristic curves generated from a simple logistic regression model indicated that KC and macrophage inflammatory protein-2, rodent homologues of the human growth related oncogene CXC chemokine family, and protein C were the best predictors of mortality in this model.

CONCLUSIONS

The data from this study indicate that an early decrease in protein C concentration predicts poor outcome in a rat sepsis model. The data further indicate that increases in the CXC chemokines macrophage inflammatory protein-2 and KC precede poor outcome.

Advances in Sepsis Therapy

During the past 3 years new insights have been gained into the fundamental elements that underlie the pathogenesis of sepsis, and after years of frustrating failures, progress in the basic understanding of sepsis has translated into successful new therapies. These new treatment strategies have significantly improved the outcome of patients experiencing the puzzling syndrome of severe sepsis. More effective supportive therapies with early, goal-oriented therapy including volume resuscitation, catecholamine therapy and transfusion improve the chances for survival in septic shock. Novel endocrine management with hydrocortisone replacement therapy for relative adrenal insufficiency in septic shock patients and strict blood glucose control provide a survival advantage in critically ill patients. Administering appropriate antimicrobial therapy, nutritional support and ventilation protocols with low tidal volumes have now been shown to benefit septic patients. Finally, human recombinant activated protein C (drotrecogin alfa), which ameliorates sepsis-induced disseminated intravascular coagulation and exerts several other favourable effects on endothelial cells, has been shown to reduce mortality in patients with severe sepsis. On the basis of newly discovered pathophysiological mechanisms of sepsis, several other adjuvant therapies for sepsis are in various stages of preclinical and clinical development. Individualised and optimal supportive care with efforts to reverse the precipitating cause of sepsis remains the mainstay of therapy for severe sepsis. How these new and often expensive regimens will fit into the standard treatment approach to sepsis remains to be defined by future clinical investigations.

Sepsis-induced changes in macrophage co-stimulatory molecule expression: CD86 as a regulator of anti-inflammatory IL-10 response

BACKGROUND

Sepsis remains a substantial risk after surgery or other trauma. Macrophage dysfunction, as a component of immune suppression seen during trauma and sepsis, appears to be one of the contributing factors to morbidity and mortality. However, whereas it is known that the ability of macrophages to present antigen and express major histocompatibility complex MHC class II molecules is decreased during sepsis, it is not known to what extent this is associated with the loss of co-stimulatory receptor expression. Our objectives in this study were, therefore, to determine if the expression of co-stimulatory molecules, such as CD40, CD80, or CD86, on peritoneal/splenic/liver macrophages were altered by sepsis (cecal ligation [CL] and puncture [CLP] or necrotic tissue injury (CL) alone; and to establish the contribution of such changes to the response to septic challenge using mice that are deficient in these receptors.

METHODS

To address our first objective, male C3H/HeN mice were subjected to CLP, CL, or sham (n = four to six mice/group), and the adherent macrophages were isolated from the peritoneum, spleen, or liver at 24 h post-insult. The macrophages were then analyzed by flow cytometry for their ex vivo expression of CD40, CD80, CD86, and/or MHC II.

RESULTS

The expression of CD86 and MHC II, but not CD40 or CD80, were significantly decreased on peritoneal macrophages after the onset of sepsis or CL alone. In addition, CD40 expression was significantly increased in Kupffer cells after sepsis. Alternatively, splenic macrophages from septic or CL mice did not show changes in the expression of CD80, CD86, or CD40. To the degree that the loss of CD86 expression might contribute to the changes reported in macrophage function in septic mice, we subsequently examined the effects of CLP on CD86 -/- mice. Interestingly, we found that, unlike the background controls, neither the serum IL-10 concentrations nor the IL-10 release capacity of peritoneal macrophages from septic CD86 -/- mice were increased.

CONCLUSION

Together, these data suggest a potential role for the co-stimulatory receptor CD86/B7-2 beyond that of simply promoting competent antigen presentation to T-cells, but also as a regulator of the anti-inflammatory IL-10 response. Such a role may implicate the latter response in the development of sepsis-induced immune dysfunction.

Inhibition of CD1d activation suppresses septic mortality: a role for NK-T cells in septic immune dysfunction

BACKGROUND

Studies indicate that following septic insult there is development of generalized immune dysfunction in T cells, B cells and phagocytes, which is thought to contribute to morbidity and mortality. Specifically, there is a shift in the lymphocytes of septic animals toward an increased release of Th2 cytokines. NK-T cells have been shown to contribute to propagation of the Th2 response. The influence of NK-T cells on the immune response to septic challenge is poorly understood. In this study, we examine whether NK-T cells contribute to the immune dysfunction seen following the onset of polymicrobial sepsis, as produced by cecal ligation and puncture (CLP).

MATERIALS AND METHODS

Male 129S1/SvImJ mice were pretreated with either rat IgG (isotypic control) or monoclonal antibody to CD1d (clone 1B1) (0.5 mg), which blocks signaling/antigen presentation via the CD1d cell surface receptor, thereby, ablating the activation and differentiation of the NK-T cells. Septic survival with and without anti-CD1d (CLP/CD1d) pretreatment was assessed. Mice sacrificed 24 h after CLP were assessed for change in splenic %NK-T cell (via flourescense activated cell sector) and for splenic, hepatic, and lymphoid/macrophage production of pro-inflammatory or anti-inflammatory cytokines (via enzyme-linked immunosorbent assay).

RESULTS

Administration of anti-CD1d reduced septic mortality 35% at 6-10 d (n = 23 mice/group) (P <.05). There was a consistent increase in the %CD3(+) NK1.1(+) cell population (NK-T cells) in septic mice (1.706%), which was markedly suppressed by pretreatment with anti-CD1d (0.592%). IL-6 and IL-10 levels were suppressed by anti-CD1d in the spleen and blood.

CONCLUSIONS

Together these findings imply not only that NK-T cells may play a role in mediating the immune suppression seen in bacterial sepsis, but that inhibition of their activation promotes survival to septic challenge.

Mechanisms of immune resolution

Initially after injury, the innate/proinflammatory and some aspects of the acquired immune response are up-regulated to maintain a defense against foreign pathogens, clear tissue debris present at the wound site, and orchestrate aspects of tissue remodeling, cell proliferation and angiogenic process, associated with the wound response. However, for proper wound healing to progress, this initial inflammatory response has to be regulated or shut down so as to allow for the reestablishment of matrix, recellularization, and tissue remodeling. Inability to properly resolve the extent of innate/acquired response at a site of injury can lead to poor wound healing, immune suppression, and recurrent infectious episodes. This review attempts to summarize information on regulatory mechanisms that are thought to be involved in controlling/resolving innate or acquired immune responses so as to provide a framework for use in thinking about the impact these processes and their manipulation may have on wound healing and its potential management.