CC chemokine receptor 2 regulates leukocyte recruitment and IL-10 production during acute polymicrobial sepsis

Indole-3-carbinol attenuates lipopolysaccharide-induced acute respiratory distress syndrome through activation of AhR: role of CCR2+ monocyte activation and recruitment in the regulation of CXCR2+ neutrophils in the lungs

Introduction

Indole-3-carbinol (I3C) is found in cruciferous vegetables and used as a dietary supplement. It is known to act as a ligand for aryl hydrocarbon receptor (AhR). In the current study, we investigated the role of AhR and the ability of I3C to attenuate LPS-induced Acute Respiratory Distress Syndrome (ARDS).

Methods

To that end, we induced ARDS in wild-type C57BL/6 mice, Ccr2gfp/gfp KI/KO mice (mice deficient in the CCR2 receptor), and LyZcreAhRfl/fl mice (mice deficient in the AhR on myeloid linage cells). Additionally, mice were treated with I3C (65 mg/kg) or vehicle to investigate its efficacy to treat ARDS.

Results

I3C decreased the neutrophils expressing CXCR2, a receptor associated with neutrophil recruitment in the lungs. In addition, LPS-exposed mice treated with I3C revealed downregulation of CCR2+ monocytes in the lungs and lowered CCL2 (MCP-1) protein levels in serum and bronchoalveolar lavage fluid. Loss of CCR2 on monocytes blocked the recruitment of CXCR2+ neutrophils and decreased the total number of immune cells in the lungs during ARDS. In addition, loss of the AhR on myeloid linage cells ablated I3C-mediated attenuation of CXCR2+ neutrophils and CCR2+ monocytes in the lungs from ARDS animals. Interestingly, scRNASeq showed that in macrophage/monocyte cell clusters of LPS-exposed mice, I3C reduced the expression of CXCL2 and CXCL3, which bind to CXCR2 and are involved in neutrophil recruitment to the disease site.

Discussion

These findings suggest that CCR2+ monocytes are involved in the migration and recruitment of CXCR2+ neutrophils during ARDS, and the AhR ligand, I3C, can suppress ARDS through the regulation of immune cell trafficking.

Characterization of Chemotaxis-Associated Gene Dysregulation in Myeloid Cell Populations in the Lungs during Lipopolysaccharide-Mediated Acute Lung Injury

During endotoxin-induced acute lung injury (ALI), immune cell recruitment resulting from chemotaxis is mediated by CXC and CC chemokines and their receptors. In this study, we investigated the role of chemokines and their receptors in the regulation of myeloid cell populations in the circulation and the lungs of C57BL/6J mice exhibiting LPS-mediated ALI using single-cell RNA sequencing. During ALI, there was an increase in the myeloid cells, M1 macrophages, monocytes, neutrophils, and other granulocytes, whereas there was a decrease in the residential alveolar macrophages and M2 macrophages. Interestingly, LPS triggered the upregulation of CCL3, CCL4, CXCL2/3, and CXCL10 genes associated with cellular migration of various subsets of macrophages, neutrophils, and granulocytes. Furthermore, there was an increase in the frequency of myeloid cells expressing CCR1, CCR3, CCR5, and CXCR2 receptors during ALI. MicroRNA sequencing studies of vehicle versus LPS groups identified several dysregulated microRNAs targeting the upregulated chemokine genes. This study suggests that chemokine ligand-receptors interactions are responsible for myeloid cell heterogenicity and cellular recruitment to the lungs during ALI. The single-cell transcriptomics allowed for an in-depth assessment and characterization of myeloid cells involved in immune cell trafficking during ALI.

Advances in Rodent Experimental Models of Sepsis

In the development of therapeutic strategies for human diseases, preclinical experimental models have a key role. However, the preclinical immunomodulatory therapies developed using rodent sepsis were not successful in human clinical trials. Sepsis is characterized by a dysregulated inflammation and redox imbalance triggered by infection. Human sepsis is simulated in experimental models using methods that trigger inflammation or infection in the host animals, most often mice or rats. It remains unknown whether the characteristics of the host species, the methods used to induce sepsis, or the molecular processes focused upon need to be revisited in the development of treatment methods that will succeed in human clinical trials. Our goal in this review is to provide a survey of existing experimental models of sepsis, including the use of humanized mice and dirty mice, and to show how these models reflect the clinical course of sepsis. We will discuss the strengths and limitations of these models and present recent advances in this subject area. We maintain that rodent models continue to have an irreplaceable role in studies toward discovering treatment methods for human sepsis.

Neutrophil chemoattractant receptors in health and disease: double-edged swords

Neutrophils are frontline cells of the innate immune system. These effector leukocytes are equipped with intriguing antimicrobial machinery and consequently display high cytotoxic potential. Accurate neutrophil recruitment is essential to combat microbes and to restore homeostasis, for inflammation modulation and resolution, wound healing and tissue repair. After fulfilling the appropriate effector functions, however, dampening neutrophil activation and infiltration is crucial to prevent damage to the host. In humans, chemoattractant molecules can be categorized into four biochemical families, i.e., chemotactic lipids, formyl peptides, complement anaphylatoxins and chemokines. They are critically involved in the tight regulation of neutrophil bone marrow storage and egress and in spatial and temporal neutrophil trafficking between organs. Chemoattractants function by activating dedicated heptahelical G protein-coupled receptors (GPCRs). In addition, emerging evidence suggests an important role for atypical chemoattractant receptors (ACKRs) that do not couple to G proteins in fine-tuning neutrophil migratory and functional responses. The expression levels of chemoattractant receptors are dependent on the level of neutrophil maturation and state of activation, with a pivotal modulatory role for the (inflammatory) environment. Here, we provide an overview of chemoattractant receptors expressed by neutrophils in health and disease. Depending on the (patho)physiological context, specific chemoattractant receptors may be up- or downregulated on distinct neutrophil subsets with beneficial or detrimental consequences, thus opening new windows for the identification of disease biomarkers and potential drug targets.

Progranulin Plays a Central Role in Host Defense during Sepsis by Promoting Macrophage Recruitment

RATIONALE

Progranulin, a widely expressed protein, has multiple physiological functions. The functional role of progranulin in the host response to sepsis remains unknown.

OBJECTIVES

To assess the role of progranulin in the host response to sepsis.

METHODS

Effects of progranulin on host response to sepsis were determined.

MEASUREMENTS AND MAIN RESULTS

Progranulin concentrations were significantly elevated in adult (n = 74) and pediatric (n = 26) patients with sepsis relative to corresponding healthy adult (n = 36) and pediatric (n = 17) control subjects, respectively. By using a low-lethality model of nonsevere sepsis, we observed that progranulin deficiency not only increased mortality but also decreased bacterial clearance during sepsis. The decreased host defense to sepsis in progranulin-deficient mice was associated with reduced macrophage recruitment, with correspondingly impaired chemokine CC receptor ligand 2 (CCL2) production in peritoneal lavages during the early phase of sepsis. Progranulin derived from hematopoietic cells contributed to host defense in sepsis. Therapeutic administration of recombinant progranulin not only rescued impaired host defense in progranulin-deficient mice after nonsevere sepsis but also protected wild-type mice against a high-lethality model of severe sepsis. Progranulin-mediated protection against sepsis was closely linked to improved peritoneal macrophage recruitment. In addition, CCL2 treatment of progranulin-deficient mice improved survival and decreased peritoneal bacterial loads during sepsis, at least in part through promotion of peritoneal macrophage recruitment.

CONCLUSIONS

This proof-of-concept study supports a central role of progranulin-dependent macrophage recruitment in host defense to sepsis, opening new opportunities to host-directed therapeutic strategy that manipulate host immune response in the treatment of sepsis.

CCR-2 neutralization augments murine fresh BMC activation by Staphylococcus aureus via two distinct mechanisms: at the level of ROS production and cytokine response

CCR-2 signaling regulates recruitment of monocytes from the bone marrow into the bloodstream and then to sites of infection. We sought to determine whether CCL-2/CCR-2 signaling is involved in the killing of Staphylococcus aureus by murine bone marrow cells (BMCs). The intermittent link of reactive oxygen species (ROS)-NF-κB/p38-MAPK-mediated CCL-2 production in CCR-2 signaling prompted us to determine whether neutralization of CCR-2 augments the response of murine fresh BMCs (FBMCs) after S. aureus infection. It was observed that anti-CCR-2 Ab-treated FBMCs released fewer ROS on encountering S. aureus infection than CCR-2 non-neutralized FBMCs, also correlating with reduced killing of S. aureus in CCR-2 neutralized FBMCs. Staphylococcal catalase and SOD were also found to play a role in protecting S. aureus from the ROS-mediated killing of FBMC. S. aureus infection of CCR-2 intact FBMCs pre-treated with either NF-κB or p-38-MAPK blocker induced less CCL-2, suggesting that NF-κB or p-38-MAPK is required for CCL-2 production by FBMCs. Moreover, blocking of CCR-2 along with NF-κB or p-38-MAPK resulted in elevated CCL-2 production and reduced CCR-2 expression. Inhibition of CCR-2 impairs the response of murine BMCs to S. aureus infection by attenuation ROS production and modulating the cytokine response.

Murine macrophage response from peritoneal cavity requires signals mediated by chemokine receptor CCR-2 during Staphylococcus aureus infection

C-C chemokine receptor-2 (CCR-2) is a cognate receptor for monocyte chemotactic protein-1 (MCP-1), and recent studies revealed that MCP-1-CCR-2 signaling is involved in several inflammatory diseases characterized by macrophage infiltration. Currently, there is no study on the involvement of CCR-2 in the killing of S. aureus by macrophages of Swiss albino mice, and its substantial role in host defense against S. aureus infection in murine macrophages is still unclear. Therefore, the present study was aimed to investigate the functional and interactive role of CCR-2 and MCP-1 in regulating peritoneal macrophage responses with respect to acute S. aureus infection. We found that phagocytosis of S. aureus can serve as an important stimulus for MCP-1 production by peritoneal macrophages, which is dependent directly or indirectly on cytokines, reactive oxygen species and nitric oxide. Neutralization of CCR-2 in macrophages leads to increased production of IL-10 and decreased production of IFN-γ and IL-6. In CCR-2 blocked macrophages, pretreatment with specific blocker of NF-κB or p38-MAPK causes elevation in MCP-1 level and subsequent downregulation of CCR-2 itself. We speculate that CCR-2 is involved in S. aureus-induced MCP-1 production via NF-κB or p38-MAPK signaling. We also hypothesized that unnaturally high level of MCP-1 that build up upon CCR-2 neutralization might allow promiscuous binding to one or more other chemokine receptors, a situation that would not occur in CCR-2 non-neutralized condition. This may be the plausible explanation for such observed Th-2 response in CCR-2 blocked macrophages infected with S. aureus in the present study.

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.

S-adenosylmethionine mediates inhibition of inflammatory response and changes in DNA methylation in human macrophages

S-adenosylmethionine (SAM), the unique methyl donor in DNA methylation, has been shown to lower lipopolysaccharide (LPS)-induced expression of the proinflammatory cytokine TNF-α and increase the expression of the anti-inflammatory cytokine IL-10 in macrophages. The aim of this study was to assess whether epigenetic mechanisms mediate the anti-inflammatory effects of SAM. Human monocytic THP1 cells were differentiated into macrophages and treated with 0, 500, or 1,000 μmol/l SAM for 24 h, followed by stimulation with LPS. TNFα and IL-10 expression levels were measured by real-time PCR, cellular concentrations of SAM and S-adenosylhomocysteine (SAH), a metabolite of SAM, were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and DNA methylation was measured with LC-MS/MS and microarrays. Relative to control (0 μmol/l SAM), treatment with 500 μmol/l SAM caused a significant decrease in TNF-α expression (-45%, P < 0.05) and increase in IL-10 expression (+77%, P < 0.05). Treatment with 1,000 μmol/l SAM yielded no significant additional benefits. Relative to control, 500 μmol/l SAM increased cellular SAM concentrations twofold without changes in SAH, and 1,000 μmol/l SAM increased cellular SAM sixfold and SAH fourfold. Global DNA methylation increased 7% with 500 μmol/l SAM compared with control. Following treatment with 500 μmol/l SAM, DNA methylation microarray analysis identified 765 differentially methylated regions associated with 918 genes. Pathway analysis of these genes identified a biological network associated with cardiovascular disease, including a subset of genes that were differentially hypomethylated and whose expression levels were altered by SAM. Our data indicate that SAM modulates the expression of inflammatory genes in association with changes in specific gene promoter DNA methylation.

Cutting edge: Divergent cell-specific functions of MyD88 for inflammatory responses and organ injury in septic peritonitis

Although global MyD88 deficiency attenuates lethal inflammation in sepsis, cell-specific functions of MyD88 remain largely unknown. Using mice with selective expression of MyD88 in myeloid cells (Myd88(MYEL)), we show that, during polymicrobial septic peritonitis, both myeloid and nonmyeloid cells contribute to systemic inflammation, whereas myeloid cell MyD88 was sufficient to fully establish the peritoneal cytokine response. Importantly, Myd88(MYEL) mice developed markedly aggravated liver injury that was linked to impaired upregulation of cellular inhibitor of apoptosis protein 2 and an excessive production of TNF-α. Upregulation of inducible cAMP early repressor (ICER), a known transcriptional repressor of the Tnfa gene, was impaired in Myd88(MYEL) mice. Moreover, Myd88(MYEL) mice showed enhanced transcription of the Tnfa gene and an excessive production of CCL3, which is also negatively regulated by ICER, but they had normal levels of CXCL1, which is expressed in an ICER-independent manner. Together, these findings suggest a novel protective role for nonmyeloid cell MyD88 in attenuating liver injury during septic peritonitis.

The dynamics of the early inflammatory response in double-hit burn and sepsis animal models

Severe burn trauma is generally associated with bacterial infections, which causes a more persistent inflammatory response with an ongoing hypermetabolic and catabolic state. This complex biological response, mediated by chemokines and cytokines, can be more severe when excessive interactions between the mediators take place. In this study, the early inflammatory response following the cecum ligation and puncture (CLP) or its corresponding control treatment (sham-CLP or SCLP) in burn (B) male rats was analyzed by measuring 23 different cytokines and chemokines. Cytokines and chemokines, including MCP-1, IP-10, leptin, TNF-α, MIP-1α, IL-18, GMCSF, RANTES and GCSF were significantly altered in both B+CLP and B+SCLP groups. IL-10 and IL-6 were significantly up-regulated in the B+CLP group when compared to the B+SCLP group. Down regulation of leptin and IP-10 concentrations were found to be related to surgery and/or infection. IL-18 and MCP-1 were elevated in all groups including previously published single injury models receiving similar treatments. In this study, insult-specific mediators with their characteristic temporal patterns were elucidated in double hit models.

Comparison of the cytokine and chemokine dynamics of the early inflammatory response in models of burn injury and infection

The inflammatory response, and its subsequent resolution, are the result of a very complex cascade of events originating at the site of injury or infection. When the response is severe and persistent, Systemic Inflammatory Response Syndrome can set in, which is associated with a severely debilitating systemic hypercatabolic state. This complex behavior, mediated by cytokines and chemokines, needs to be further explored to better understand its systems properties and potentially identify multiple targets that could be addressed simultaneously. In this context, short term responses of serum cytokines and chemokines were analyzed in two types of insults: rats receiving a "sterile" cutaneous dorsal burn on 20% of the total body surface area (TBSA); rats receiving a cecum ligation and puncture treatment (CLP) to induce infection. Considering the temporal variability observed in the baseline corresponding to the control group, the concept of area under the curve (AUC) was explored to assess the dynamic responses of cytokines and chemokines. MCP-1, GROK/KC, IL-12, IL-18 and IL-10 were observed in both burn and CLP groups. While IL-10 concentration was only increased in the burn group, Eotaxin was only elevated in CLP group. It was also observed that Leptin and IP-1 concentrations were decreased in both CLP and sham-CLP groups. The link between the circulating protein mediators and putative transcription factors regulating the cytokine/chemokine gene expression was explored by searching the promoter regions of cytokine/chemokine genes in order to characterize and differentiate the inflammatory responses based on the dynamic data. Integrating multiple sources together with the bioinformatics tools identified mediators sensitive to type and extent of injury, and provided putative regulatory mechanisms. This is essential to gain a better understanding for the important regulatory points that can be used to modulate the inflammatory state at molecular level.

Improved host defense against septic peritonitis in mice lacking MyD88 and TRIF is linked to a normal interferon response

The signaling adapters MyD88 and TRIF are engaged by TLRs and/or receptors of the IL-1 family and are considered important for innate immune responses that combat bacterial infections. Here, the consequences of a combined MyD88 and TRIF deficiency for the innate immune response against severe septic peritonitis was examined. We demonstrate that Myd88(-/-);Trif(Lps2/Lps2) mice had markedly reduced bacterial numbers in the peritoneal cavity and peripheral blood, indicating that bacterial clearance in this model is improved in the absence of MyD88/TRIF signals. Survival of Myd88(-/-); Trif(Lps2/Lps2) mice was improved significantly. The lack of MyD88/TRIF signaling prevented the excessive production of inflammatory cytokines and of IL-10. In contrast, Ifng mRNA was expressed at WT levels, and induction of Ifnb mRNA was reduced only by one-half. Consistent with these findings, numerous IFN-regulated genes, including p47 and p65 GTPases, as well as CXCL10, were expressed in a MyD88/TRIF-independent manner. In support of the in vivo data, Myd88(-/-); Trif(Lps2/Lps2) macrophages stimulated with live intestinal bacteria produced normal amounts of CXCL10. The production of p47 GTPases and CXCL10 in septic peritonitis was found to be dependent on the presence of IFNAR1, but not IFN-γ, indicating a normal induction of the type I IFN response in Myd88(-/-);Trif(Lps2/Lps2) mice, despite attenuated IFN-β production. Together, these results provide evidence that in severe septic peritonitis, the absence of MyD88 and TRIF balances the innate immune response in a favorable manner by attenuating deleterious responses such as excessive cytokine release, while leaving intact protective IFN responses.

Innate immunity signaling pathways: links between immunonutrition and responses to sepsis

Septic infections in patients treated in intensive care units show the highest mortality rates. Despite advances in treatment methods, there is still no therapy available to efficiently reduce the excessive inflammatory response, which can increase the risk of multiple organ failure. One of the ways to discover new, more efficient treatment methods involves regulating the mechanisms of inflammatory response to a massive infection. Toll-like receptors (TLRs) that recognize pathogen-associated molecular patterns play a significant role in innate antibacterial and inflammatory responses. The regulatory impact of immunonutrition on TLR expression in septic patients seems to be a promising research direction. This paper presents the main mechanisms for the innate immune response to lipopolysaccharide, based on the research results for both TLR-dependent and independent signaling pathways. Special emphasis was put on the research results for the TLR-dependent immune response and the anti-bacterial/anti-inflammatory response after applying immunonutrition with increased concentrations of glutamine and unsaturated fatty acids.

Innate immunity of the liver microcirculation

The liver is a complex organ with a unique microcirculation and both synthetic and immune functions. Innate immune responses have been studied in response to single inflammatory mediators and several clinically relevant models of infection and injury. While standard histological techniques have been used in many models, the liver microcirculation is also amenable to in vivo examination using epifluorescent, confocal and transillumination intravital microscopy. These techniques have begun to clarify not only the molecular mechanisms but also the specific cell populations involved in the liver inflammation. In this review, we discuss the cells and mediators involved in hepatic innate immunity in simple and complex models of injury and infection, and present the view that the liver microcirculation utilizes non-classical pathways for leukocyte recruitment.

Animal models of sepsis

In this review, we start with a general discussion of relevant factors that can determine the validity of a sepsis animal model. We briefly review some of the currently used animal models of sepsis (small animal models and large animal models). We discuss the clinical relevance of animal models in sepsis research today and address potential reasons for the apparent underperformance of animal models in predicting therapeutic success of novel drugs in clinical trials.

CCR2 promotes hepatic fibrosis in mice

Chemokines and chemokine receptors contribute to the migration of hepatic stellate cells (HSCs) and Kupffer cells, two key cell types in fibrogenesis. Here, we investigate the role of CCR2, the receptor for monocyte chemoattractant protein (MCP)-1, MCP-2, and MCP-3, in hepatic fibrosis. Hepatic CCR2, MCP-1, MCP-2, and MCP-3 messenger RNA expression was increased after bile duct ligation (BDL). Both Kupffer cells and HSCs, but not hepatocytes, expressed CCR2. BDL- and CCl(4)-induced fibrosis was markedly reduced in CCR2(-/-) mice as assessed through collagen deposition, alpha-smooth muscle actin expression, and hepatic hydroxyproline content. We generated CCR2 chimeric mice by the combination of clodronate, irradiation, and bone marrow (BM) transplantation allowing full reconstitution of Kupffer cells, but not HSCs, with BM cells. Chimeric mice containing wild-type BM displayed increased macrophage recruitment, whereas chimeric mice containing CCR2(-/-) BM showed less macrophage recruitment at 5 days after BDL. Although CCR2 expressed in the BM enhanced macrophage recruitment in early phases of injury, CCR2 expression on resident liver cells including HSCs, but not on the BM, was required for fibrogenic responses in chronic fibrosis models. In vitro experiments demonstrated that HSCs deficient in CCR2(-/-) or its downstream mediator p47phox(-/-) did not display extracellular signal-regulated kinase and AKT phosphorylation, chemotaxis, or reactive oxygen species production in response to MCP-1, MCP-2, and MCP-3.

CONCLUSION

Our results indicate that CCR2 promotes HSC chemotaxis and the development of hepatic fibrosis.

CCR2 promotes hepatic fibrosis in mice

Chemokines and chemokine receptors contribute to the migration of hepatic stellate cells (HSCs) and Kupffer cells, two key cell types in fibrogenesis. Here, we investigate the role of CCR2, the receptor for monocyte chemoattractant protein (MCP)-1, MCP-2, and MCP-3, in hepatic fibrosis. Hepatic CCR2, MCP-1, MCP-2, and MCP-3 messenger RNA expression was increased after bile duct ligation (BDL). Both Kupffer cells and HSCs, but not hepatocytes, expressed CCR2. BDL- and CCl(4)-induced fibrosis was markedly reduced in CCR2(-/-) mice as assessed through collagen deposition, alpha-smooth muscle actin expression, and hepatic hydroxyproline content. We generated CCR2 chimeric mice by the combination of clodronate, irradiation, and bone marrow (BM) transplantation allowing full reconstitution of Kupffer cells, but not HSCs, with BM cells. Chimeric mice containing wild-type BM displayed increased macrophage recruitment, whereas chimeric mice containing CCR2(-/-) BM showed less macrophage recruitment at 5 days after BDL. Although CCR2 expressed in the BM enhanced macrophage recruitment in early phases of injury, CCR2 expression on resident liver cells including HSCs, but not on the BM, was required for fibrogenic responses in chronic fibrosis models. In vitro experiments demonstrated that HSCs deficient in CCR2(-/-) or its downstream mediator p47phox(-/-) did not display extracellular signal-regulated kinase and AKT phosphorylation, chemotaxis, or reactive oxygen species production in response to MCP-1, MCP-2, and MCP-3.

CONCLUSION

Our results indicate that CCR2 promotes HSC chemotaxis and the development of hepatic fibrosis.

Blockade of CD137 signaling counteracts polymicrobial sepsis induced by cecal ligation and puncture

Sepsis, a leading cause of death worldwide, involves proinflammatory responses and inefficient bacterial clearance. Previously, we have shown that CD137 (4-1BB), a member of the tumor necrosis factor receptor superfamily, plays critical roles in eradicating infective Listeria monocytogenes, a gram-positive bacterium, and that stimulation of CD137 protects mice from sepsis-induced death. In this study, we unexpectedly found that CD137 activation aggravated polymicrobial sepsis due to mixed gram-positive and gram-negative bacterial infection induced by cecal ligation and puncture (CLP). CD137-deficient (CD137(-/-)) mice showed significantly lower mortality than CD137-sufficient (CD137(+/+)) mice in the CLP model. Administration of an agonistic anti-CD137 monoclonal antibody (MAb) to CD137(+/+) mice decreased their survival in this infection model, while administration of a blocking anti-CD137 ligand MAb (TKS-1) to such mice increased their survival. CD137(-/-) mice and TKS-1-treated CD137(+/+) mice had lower levels of chemokines/proinflammatory cytokines (monocyte chemoattractant protein 1, interleukin-6 [IL-6], tumor necrosis factor alpha, IL-12) and an anti-inflammatory cytokine (IL-10), exhibited improved bacterial clearance in the peritoneum, liver, and blood, and had greater numbers of infiltrated peritoneal neutrophils and macrophages in the CLP model than control mice. Our data suggest that CD137 activation aggravates polymicrobial sepsis induced by CLP.

Mesenchymal stromal cell-derived CCL2 suppresses plasma cell immunoglobulin production via STAT3 inactivation and PAX5 induction

We demonstrate that the secretome of mesenchymal stromal cells (MSCs) suppresses plasma cell (PC) immunoglobulin (Ig) production, induces plasmablast proliferation, and leads to interleukin-10-mediated blockade in vitro. We found that these effects are the result of MSC-derived CC chemokine ligands CCL2 and CCL7. More specifically, MSCs further processed these CC chemokines by the activity of matrix metalloproteinases (MMPs), leading to the generation of proteolytically processed antagonistic CCL2 variant. Neutralizing CCL2 or inhibiting MMP enzymatic activity abolished the PC-suppressive effect of MSCs. We also observed that MMP-processed CCL2 suppresses signal transducer and activator of transcription 3 (STAT3) activation in PC. As a result, the transcription factor PAX5 is induced, thus explaining the inhibition of Ig synthesis. The absence of inhibitory effects by MSC on the humoral response of CCR2(-/-) mice to xenoantigen suggests that MMP-cleaved CCL2/CCR2 interaction as well as downstream phosphatase activity is necessary for antagonistic effect. We tested syngeneic MSCs in hemophilic B6 mice with predeveloped antihuman factor VIII (hFVIII) antibodies and demonstrated a robust decrease in hFVIII-specific IgG levels. Thus, MSCs may play a role in modulating Ig production by PCs via MMP processing of CCL2 and may represent an appealing cell therapy approach for pathologic humoral responses.

Ron receptor tyrosine kinase-dependent hepatic neutrophil recruitment and survival benefit in a murine model of bacterial peritonitis

OBJECTIVE

To determine whether Ron receptor tyrosine kinase signaling affects the in vivo response to bacterial peritonitis.

DESIGN

Experimental study.

SETTING

University laboratory.

SUBJECTS

Male mice 8-11 wks of age (22-28 g).

INTERVENTIONS

A genetic approach comparing wild-type mice to mice with a targeted deletion of the Ron tyrosine kinase signaling domain (TK-/-) was undertaken to determine the influence of Ron receptor in the in vivo response to a well-characterized model of bacterial peritonitis and sepsis induced by cecal ligation and puncture.

MEASUREMENTS AND MAIN RESULTS

Several clinical (i.e., survival curves, blood and tissue bacterial burdens, and neutrophil oxidative burst), morphologic (i.e., liver histology and leukocyte trafficking), and biochemical variables (i.e., serum aminotransferases and select serum cytokine and chemokine levels) important for assessing inflammatory responses to bacterial infection were assessed in mice following cecal ligation and puncture. Ron TK-/- mice had a significant decrease in survival time compared with controls, and this was associated with a significant increase in bacterial colony-forming units found in the blood and several end-organs. Moreover, this increased bacterial load was associated with increased liver necrosis and serum alanine aminotransferase levels. Neutrophils isolated from TK-/- mice exhibited decreased spontaneous oxidative burst capacity ex vivo, and by intravital microscopy, a reduced level of neutrophil migration to and translocation within the liver was observed. Loss of Ron signaling resulted in significantly reduced production of serum monocyte chemoattractant protein-1 and interleukin-6 levels following cecal ligation and puncture, and peritoneal macrophage isolated from TK-/- mice exhibited blunted production of monocyte chemoattractant protein-1, interleukin-6, and macrophage inflammatory protein-2 following stimulation with endotoxin ex vivo.

CONCLUSIONS

Ron signaling negatively regulates the response to polymicrobial infection by regulating the activation and recruitment of inflammatory cells necessary for clearing a systemic bacterial burden. This effect may be regulated in part through the Ron-dependent, macrophage-mediated production of cytokines and chemokines, namely monocyte chemoattractant protein-1, interleukin-6, and macrophage inflammatory protein-2, important for neutrophil mobilization.

Inhibition of interleukin-22 attenuates bacterial load and organ failure during acute polymicrobial sepsis

Interleukin-22 (IL-22) is a recently discovered proinflammatory cytokine, structurally related to IL-10. Since IL-22 is induced by lipopolysaccharide in vivo, we studied the role of IL-22 in a model of polymicrobial peritonitis. Quantitative real-time reverse transcription-PCR analysis showed marked induction of IL-22 and IL-22 receptor in spleen and kidney during the course of sepsis. The biological activity of IL-22 is modulated by IL-22-binding protein (IL-22BP), which is considered a natural antagonist of IL-22. To further analyze the role of IL-22 during septic peritonitis, mice were treated with recombinant IL-22BP generated as Fcgamma2a fusion protein. IL-22BP-Fc completely blocked IL-22-induced STAT3 activation in hepatocytes in vitro. Treatment of mice with IL-22BP-Fc 4 h before sepsis induction led to enhanced accumulation of neutrophils and mononuclear phagocytes and a reduced bacterial load at the site of infection. In addition, IL-22 blockade led to an enhanced bacterial clearance in liver and kidney and reduced kidney injury. These results imply an important proinflammatory role of IL-22 during septic peritonitis, contributing to bacterial spread and organ failure. IL-22 therefore appears to play an important role in the regulation of inflammatory processes in vivo.

Age- and gender-related differences of the immune function in a murine model of hemorrhagic shock: IL-10 restores immunodepression in aged females without reduction of mortality

INTRODUCTION

Interleukin-10 (IL-10) treatment has been shown to have beneficial effects on the immune function after hemorrhagic shock and to improve survival after subsequent sepsis in young male mice, but not in young females. Although it was demonstrated that the immune function under these conditions is reversed with age, it remains unclear whether the observed gender-related effect of IL-10 treatment continues to exist in aged mice.

MATERIALS AND METHODS

Aged male and female CBA/J mice (18-19 months) were subjected to hemorrhage (35 +/- 5 mmHg for 90 min) or sham operation. At resuscitation, each received either 10-microg recombinant murine (rm)IL-10 or placebo i.p. At 48 h after resuscitation, either the mice were killed and the plasma, splenic macrophages (sM phi), and splenocytes were harvested or polymicrobial sepsis was induced by cecal ligation and puncture (CLP). After CLP, either survival over 10 days was determined or, 4 h after CLP, tissues were again harvested and cytokine-released in vitro were assessed by enzyme-linked immunosorbent assay.

RESULTS

Early IL-10 treatment restored depressed proinflammatory immune response (TNF-alpha, IL-1 beta) and Th1 response of splenocytes in aged females after hemorrhage, whereas having no effects or having suppressive effects in aged males. Subsequent sepsis combined with placebo treatment led to a significant suppression of proinflammatory cytokine release of sM phi and a significant increase of Th2 response in both males and females associated with high mortality (80-100%, respectively) after CLP. These effects were not influenced by early rmIL-10 treatment.

CONCLUSION

After hemorrhage, early rmIL-10 treatment restored immune function in aged females, but not in males. However, in contrast to young mice, rmIL-10 treatment had no effect on survival and immune function after CLP in aged mice.

INCREASED SUSCEPTIBILITY TO SEPTIC AND ENDOTOXIC SHOCK IN MONOCYTE CHEMOATTRACTANT PROTEIN 1/CC CHEMOKINE LIGAND 2-DEFICIENT MICE CORRELATES WITH REDUCED INTERLEUKIN 10 AND ENHANCED MACROPHAGE MIGRATION INHIBITORY FACTOR PRODUCTION

The chemokine monocyte chemoattractant protein 1/CC chemokine ligand 2 (MCP-1/CCL2) is a potent chemoattractant of mononuclear cells and a regulatory mediator involved in a variety of inflammatory diseases. In the present study, we demonstrate that mcp-1/ccl2-deficient mice are more susceptible to systemic inflammatory response syndrome induced by lipopolysaccharide and to polymicrobial sepsis induced by cecum ligation and puncture (CLP) when compared with wild-type mice. Interestingly, in the CLP model, mcp-1/ccl2-deficient mice efficiently cleared the bacteria despite an impaired recruitment of leukocytes, especially mononuclear cells. The increased lethality rate in these models correlates with an impaired production of interleukin (IL) 10 in vivo. Furthermore, macrophages from mcp-1/ccl2-deficient mice activated with lipopolysaccharide also produced lower amounts of IL-10 and similar tumor necrosis factor compared with wild-type mice. We observed a drastic increase in the amounts of macrophage migration inhibitory factor at 6 and 24 h after CLP in mcp-1/ccl2-deficient mice. These results indicate that endogenous MCP-1/CCL2 positively regulates IL-10 but negatively controls macrophage migration inhibitory factor during peritoneal sepsis, thus suggesting an important immunomodulatory role for MCP-1/CCL2 in controlling the balance between proinflammatory and anti-inflammatory factors in sepsis.

Type I IFN Modulates Host Defense and Late Hyperinflammation in Septic Peritonitis

TLRs are considered important for the control of immune responses during endotoxic shock or polymicrobial sepsis. Signaling by TLRs may proceed through the adapter proteins MyD88 or TIR domain-containing adaptor inducinng IFN-beta. Both pathways can lead to the production of type I IFNs (IFN-alphabeta). In the present study, the role of the type I IFN pathway for host defense and immune pathology in sepsis was investigated using a model of mixed bacterial peritonitis. Systemic levels of IFN-alphabeta protein were markedly elevated during septic peritonitis. More detailed analyses revealed production of IFN-beta, but not IFN-alpha subtypes, and identified CD11b+ CD11c- macrophage-like cells as major producers of IFN-beta. The results further demonstrate that in IFN-alphabeta receptor I chain (IFNARI)-deficient mice, the early recruitment of neutrophils to the infected peritoneal cavity was augmented, most likely due to an increased local production of MCP-1 and leukotriene B4. In the absence of IFNARI, peritoneal neutrophils also exhibited enhanced production of reactive oxygen intermediates and elevated expression of Mac-1. Conversely, administration of recombinant IFN-beta resulted in reduced leukotriene B4 levels and decreased peritoneal neutrophil recruitment and activation. Analysis of the cytokine response to septic peritonitis revealed that IFNARI deficiency strongly attenuated late, but not early, hyperinflammation. In accordance with these findings, bacterial clearance and overall survival of IFNARI(-/-) mice were improved. Therefore, the present study reveals critical functions of the type I IFN pathway during severe mixed bacterial infections leading to sepsis. The results suggest that type I IFN exerts predominantly adverse effects under these conditions.

Preprotachykinin-A Gene Products Are Key Mediators of Lung Injury in Polymicrobial Sepsis

Preprotachykinin-A (PPT-A) gene products substance P and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products in lung injury in sepsis, polymicrobial sepsis was induced by cecal ligation and puncture in PPT-A gene-deficient mice (PPT-A(-/-)) and the wild-type control mice (PPT-A(+/+)). PPT-A gene deletion significantly protected against mortality, delayed the onset of lethality, and improved the long-term survival following cecal ligation and puncture-induced sepsis. PPT-A(-/-) mice also had significantly attenuated inflammation and damage in the lungs. The data suggest that deletion of the PPT-A gene may have contributed to the disruption in recruitment of inflammatory cells resulting in protection against tissue damage, as in these mice the sepsis-associated increase in chemokine levels is significantly attenuated.

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.