The role of macrophage 1 antigen in polymicrobial sepsis

Macrophage-1 antigen exacerbates histone-induced acute lung injury and promotes neutrophil extracellular trap formation

Acute lung injury (ALI), which occurs in association with sepsis, trauma, and coronavirus disease 2019 (COVID-19), is a serious clinical condition with high mortality. Excessive platelet-leukocyte aggregate (PLA) formation promotes neutrophil extracellular trap (NET) release and thrombosis, which are involved in various diseases, including ALI. Macrophage-1 antigen (Mac-1, CD11b/CD18), which is expressed on the surface of leukocytes, is known to promote NET formation. This study aimed to elucidate the role of Mac-1 in extracellular histone-induced ALI. Exogenous histones were administered to Mac-1-deficient mice and wild-type (WT) mice with or without neutrophil or platelet depletion, and several parameters were investigated 1 h after histone injection. Depletion of neutrophils or platelets improved survival time and macroscopic and microscopic properties of lung tissues, and decreased platelet-leukocyte formation and plasma myeloperoxidase levels. These improvements were also observed in Mac-1-/- mice. NET formation in Mac-1-/- bone marrow neutrophils (BMNs) was significantly lower than that in WT BMNs. In conclusion, our findings suggest that Mac-1 is associated with exacerbation of histone-induced ALI and the promotion of NET formation in the presence of activated platelets.

αDβ2 as a novel target of experimental polymicrobial sepsis

Since sepsis was defined three decades ago, it has been a target of intensive study. However, there is no specific sepsis treatment available, with its high mortality and morbidity. αDβ2 (CD11d/CD18) is one of the four β2 integrin members. Its role in sepsis has been limitedly studied. Using an experimental polymicrobial sepsis model, we found that the deficiency of αDβ2 was associated with less lung injury and better outcome, which was in sharp contrast to other β2 integrin member αLβ2 (CD11a/CD18), and αMβ2 (CD11b/CD18). This phenotype was supported by a reduction of bacterial loads in αDβ2 knockout mice. Further analysis showed that the deficiency of αDβ2 led to a reduction of neutrophil cell death as well as an increase in neutrophil phagocytosis in both murine and human systems. Our data showed a unique role of αDβ2 among the β2 integrin members, which would serve as a potential target to improve the outcome of sepsis.

Isoflurane attenuates sepsis-associated lung injury

Acute lung injury is one of major complications associated with sepsis, responsible for morbidity and mortality. Patients who suffer from acute lung injury often require respiratory support under sedations, and it would be important to know the role of sedatives in lung injury. We examined volatile anesthetic isoflurane, which is commonly used in surgical setting, but also used as an alternative sedative in intensive care settings in European countries and Canada. We found that isoflurane exposure attenuated neutrophil recruitment to the lungs in mice suffering from experimental polymicrobial abdominal sepsis. We found that isoflurane attenuated one of major neutrophil chemoattractants LTB4 mediated response via its receptor BLT1 in neutrophils. Furthermore, we have shown that isoflurane directly bound to BLT1 by a competition assay using newly developed labeled BLT1 antagonist, suggesting that isoflurane would be a BLT1 antagonist.

Irrigation of peritoneal cavity with cold atmospheric plasma treated solution effectively reduces microbial load in rat acute peritonitis model

Accurate and timely diagnosis of appendicitis in children can be challenging, which leads to delayed admittance or misdiagnosis that may cause perforation. Surgical management involves the elimination of the focus (appendectomy) and the reduction of the contamination with peritoneal irrigation to prevent sepsis. However, the validity of conventional irrigation methods is being debated, and novel methods are needed. In the present study, the use of cold plasma treated saline solution as an intraperitoneal irrigation solution for the management of acute peritonitis was investigated. Chemical and in vitro microbiological assessments of the plasma-treated solution were performed to determine the appropriate plasma treatment time to be used in in-vivo experiments. To induce acute peritonitis in rats, the cecal ligation and perforation (CLP) model was used. Sixty rats were divided into six groups, namely, sham operation, plasma irrigation, CLP, dry cleaning after CLP, saline irrigation after CLP, and plasma-treated saline irrigation after CLP group. The total antioxidant and oxidant status, oxidative stress index, microbiological, and pathological evaluations were performed. Findings indicated that plasma-treated saline contains reactive species, and irrigation with plasma-treated saline can effectively inactivate intraperitoneal contamination and prevent sepsis with no short-term local and/or systemic toxicity.

CD11c regulates hematopoietic stem and progenitor cells under stress

β2 integrins are well-known leukocyte adhesion molecules consisting of 4 members: CD11a-d. Their known biological functions range widely from leukocyte recruitment, phagocytosis, to immunological synapse formation, but the studies have been primarily focused on CD11a and CD11b. CD11c is 1 of the 4 members and is extremely homologous to CD11b. It has been well known as a dendritic cell marker, but the characterization of its function has been limited. We found that CD11c was expressed on the short-term hematopoietic stem cells and multipotent progenitor cells. The lack of CD11c did not affect the number of hematopoietic stem and progenitor cells (HSPCs) in healthy CD11c knockout mice. Different from other β2 integrin members, however, CD11c deficiency was associated with increased apoptosis and significant loss of HSPCs in sepsis and bone marrow transplantation. Although integrins are generally known for their overlapping and redundant roles, we showed that CD11c had a distinct role of regulating the expansion of HSPCs under stress. This study shows that CD11c, a well-known dendritic cell marker, is expressed on HSPCs and serves as their functional regulator. CD11c deficiency leads to the loss of HSPCs via apoptosis in sepsis and bone marrow transplantation.

Frontline Science: The expression of integrin αD β2 (CD11d/CD18) on neutrophils orchestrates the defense mechanism against endotoxemia and sepsis

Neutrophil-macrophage interplay is a fine-tuning mechanism that regulates the innate immune response during infection and inflammation. Cell surface receptors play an essential role in neutrophil and macrophage functions. The same receptor can provide different outcomes within diverse leukocyte subsets in different inflammatory conditions. Understanding the variety of responses mediated by one receptor is critical for the development of anti-inflammatory treatments. In this study, we evaluated the role of a leukocyte adhesive receptor, integrin αD β2 , in the development of acute inflammation. αD β2 is mostly expressed on macrophages and contributes to the development of chronic inflammation. In contrast, we found that αD -knockout dramatically increases mortality in the cecal ligation and puncture sepsis model and LPS-induced endotoxemia. This pathologic outcome of αD -deficient mice is associated with a reduced number of monocyte-derived macrophages and an increased number of neutrophils in their lungs. However, the tracking of adoptively transferred fluorescently labeled wild-type (WT) and αD-/- monocytes in WT mice during endotoxemia demonstrated only a moderate difference between the recruitment of these two subsets. Moreover, the rescue experiment, using i.v. injection of WT monocytes to αD -deficient mice followed by LPS challenge, showed only slightly reduced mortality. Surprisingly, the injection of WT neutrophils to the bloodstream of αD-/- mice markedly increased migration of monocyte-derived macrophage to lungs and dramatically improves survival. αD -deficient neutrophils demonstrate increased necrosis/pyroptosis. αD β2 -mediated macrophage accumulation in the lungs promotes efferocytosis that reduced mortality. Hence, integrin αD β2 implements a complex defense mechanism during endotoxemia, which is mediated by macrophages via a neutrophil-dependent pathway.

Surgical Site Infections and Perioperative Optimization of Host Immunity by Selection of Anesthetics

Surgical site infections are significant health care issues, and efforts to mitigate their occurrence have been ongoing worldwide, mainly focusing to reduce the spillage of microbes to the otherwise sterile tissues. Optimization of host immunity has been also recognized including temperature regulation (normothermia), adequate oxygenation, and glucose management. A number of papers have described the role of anesthetics in host immunity. The role of anesthetics in postoperative outcomes including surgical site infections has been also studied. We will review the current literature and propose the importance of anesthetic selection to potentially mitigate surgical site infections.

Complement Receptors and Their Role in Leukocyte Recruitment and Phagocytosis

The complement system is deeply embedded in our physiology and immunity. Complement activation generates a multitude of molecules that converge simultaneously on the opsonization of a target for phagocytosis and activation of the immune system via soluble anaphylatoxins. This response is used to control microorganisms and to remove dead cells, but also plays a major role in stimulating the adaptive immune response and the regeneration of injured tissues. Many of these effects inherently depend on complement receptors expressed on leukocytes and parenchymal cells, which, by recognizing complement-derived molecules, promote leukocyte recruitment, phagocytosis of microorganisms and clearance of immune complexes. Here, the plethora of information on the role of complement receptors will be reviewed, including an analysis of how this functionally and structurally diverse group of molecules acts jointly to exert the full extent of complement regulation of homeostasis.

The Functional Crosstalk between Myeloid-Derived Suppressor Cells and Regulatory T Cells within the Immunosuppressive Tumor Microenvironment

Simple Summary

Immunotherapy improved the therapeutic landscape for patients with advanced cancer diseases. However, many patients do not benefit from immunotherapy. The bidirectional crosstalk between myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) contributes to immune evasion, limiting the success of immunotherapy by checkpoint inhibitors. This review aims to outline the current knowledge of the role and the immunosuppressive properties of MDSC and Treg within the tumor microenvironment (TME). Furthermore, we will discuss the importance of the functional crosstalk between MDSC and Treg for immunosuppression, issuing particularly the role of cell adhesion molecules. Lastly, we will depict the impact of this interaction for cancer research and discuss several strategies aimed to target these pathways for tumor therapy.

Abstract

Immune checkpoint inhibitors (ICI) have led to profound and durable tumor regression in some patients with metastatic cancer diseases. However, many patients still do not derive benefit from immunotherapy. Here, the accumulation of immunosuppressive cell populations within the tumor microenvironment (TME), such as myeloid-derived suppressor cells (MDSC), tumor-associated macrophages (TAM), and regulatory T cells (Treg), contributes to the development of immune resistance. MDSC and Treg expand systematically in tumor patients and inhibit T cell activation and T effector cell function. Numerous studies have shown that the immunosuppressive mechanisms exerted by those inhibitory cell populations comprise soluble immunomodulatory mediators and receptor interactions. The latter are also required for the crosstalk of MDSC and Treg, raising questions about the relevance of cell–cell contacts for the establishment of their inhibitory properties. This review aims to outline the current knowledge on the crosstalk between these two cell populations, issuing particularly the potential role of cell adhesion molecules. In this regard, we further discuss the relevance of β2 integrins, which are essential for the differentiation and function of leukocytes as well as for MDSC–Treg interaction. Lastly, we aim to describe the impact of such bidirectional crosstalk for basic and applied cancer research and discuss how the targeting of these pathways might pave the way for future approaches in immunotherapy.

The effect of anesthetics on toll like receptor 9

Toll like receptors (TLRs) are critical receptors to respond to danger signals, and their functions are relevant in the perioperative period. We previously reported that volatile anesthetics directly bound to TLR2 and TLR4 and attenuated their functions. Given that TLR9 can respond to mitochondrial DNA, a danger signal that is released upon tissue injury, we examined the role of anesthetics on TLR9 function. Our reporter assay showed that volatile anesthetics isoflurane and sevoflurane increased the activation of TLR9, while propofol attenuated it. TLR9 activation occurs via its dimerization. The dimerization is facilitated by unmethylated cytosine-phosphate-guanine (CpG) DNA as well as DNA containing cytosine at the second position from 5'-end (5'-xCx DNA). Our structural analysis using photoactivable anesthetics and rigid docking simulation showed that isoflurane and sevoflurane bound to both TLR9 dimer interface and 5'-xCx DNA binding site. Propofol bound to the TLR9 antagonist binding site. This is the first illustration that anesthetics can affect the binding of nucleic acids to their receptor. This study sets the foundation for the effect of anesthetics on TLR9 and will pave the way for future studies to determine the significance of such interactions in the clinical setting.

Volatile Anesthetic Sevoflurane Attenuates Toll-Like Receptor 1/2 Activation

BACKGROUND

Although immunomodulatory effects of anesthetics have been increasingly recognized, their underlying molecular mechanisms are not completely understood. Toll-like receptors (TLRs) are one of the major receptors to recognize invading pathogens and danger signals from damaged host tissues to initiate immune responses. Among the TLR family, TLR2 and TLR4 recognize a wide range of ligands and are considered to be important players in perioperative pathophysiology. Based on our recent finding that volatile anesthetics modulate TLR4 function, we tested our hypothesis that they would also modulate TLR2 function.

METHODS

The effect of anesthetics isoflurane, sevoflurane, propofol, and dexmedetomidine on TLR2 activation was examined by reporter assays. An anesthetic that affected the activation was subjected to in silico rigid docking simulation on TLR2. To test our prediction that sevoflurane and a TLR1/TLR2 ligand Pam3CSK4 would compete for the same pocket of TLR2, we performed Pam3CSK4 competitive binding assay to TLR2 using HEK cells stably transfected with TLR2 (HEK-TLR2) with or without sevoflurane. We examined the effect of different anesthetics on the functions of human neutrophils stimulated with TLR2 ligands. Kruskal-Wallis test and Mann-Whitney U test were used for statistical analysis.

RESULTS

We observed that the attenuation of TLR1/TLR2 activation was seen on sevoflurane exposure but not on isoflurane, propofol, or dexmedetomidine exposure. The attenuation of TLR2/TLR6 activation was not seen in any of the anesthetics tested. The rigid docking simulation predicted that sevoflurane and Pam3CSK4 bound to the same pocket of TLR1/TLR2 complex. The binding of Pam3CSK4 to HEK-TLR2 cells was impaired in the presence of sevoflurane, indicating that sevoflurane and Pam3CSK4 competed for the pocket, as predicted in silico. The stimulation of neutrophils with Pam3CSK4 induced L-selection shedding but did not affect phagocytosis and reactive oxygen species production. L-selectin shedding from neutrophils was attenuated only by sevoflurane, consistent with the result of our reporter assays.

CONCLUSIONS

We found that TLR1/TLR2 activation was attenuated by sevoflurane, but we found no evidence for attenuation by isoflurane, propofol, or dexmedetomidine at clinically relevant concentrations. Our structural analysis and competition assay supported that sevoflurane directly bound to TLR2 at the interphase of the TLR1/TLR2 complex. Sevoflurane attenuated neutrophil L-selectin shedding, an important step for neutrophil migration.

Phagocytosis-Inflammation Crosstalk in Sepsis: New Avenues for Therapeutic Intervention

Phagocytosis is a complex process by which cells within most organ systems remove pathogens and cell debris. Phagocytosis is usually followed by inflammatory pathway activation, which promotes pathogen elimination and inhibits pathogen growth. Delayed pathogen elimination is the first step in sepsis development and a key factor in sepsis resolution. Phagocytosis thus has an important role during sepsis and likely contributes to all of its clinical stages. However, only a few studies have specifically explored and characterized phagocytic activity during sepsis. Here, we describe the phagocytic processes that occur as part of the immune response preceding sepsis onset and identify the elements of phagocytosis that might constitute a predictive marker of sepsis outcomes. First, we detail the key features of phagocytosis, including the main receptors and signaling hallmarks associated with different phagocytic processes. We then discuss how the initial events of phagosome formation and cytoskeletal remodeling might be associated with known sepsis features, such as a cytokine-driven hyperinflammatory response and immunosuppression. Finally, we highlight the unresolved mechanisms of sepsis development and progression and the need for cross-disciplinary approaches to link the clinical complexity of the disease with basic cellular and molecular mechanisms.

Role of β2 Integrins in Neutrophils and Sepsis

Sepsis remains medically challenging, with high morbidity and mortality. A novel intervention is urgently needed in the absence of specific, targeted therapy. Neutrophils act as double-edged swords in sepsis; they can help to eradicate microbes, but they also contribute to tissue injury. β2 integrins are critical adhesion molecules that regulate a number of neutrophil functions. β2 integrins consist of four members, namely, αLβ2, αMβ2, αXβ2, and αDβ2. Here, we review the role of each β2 integrin in neutrophils and sepsis and consider future direction for therapeutic intervention.

Exploiting species specificity to understand the tropism of a human-specific toxin

Many pathogens produce virulence factors that are specific toward their natural host. Clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) isolates are highly adapted to humans and produce an array of human-specific virulence factors. One such factor is LukAB, a recently identified pore-forming toxin that targets human phagocytes by binding to the integrin component CD11b. LukAB exhibits strong tropism toward human, but not murine, CD11b. Here, phylogenetics and biochemical studies lead to the identification of an 11-residue domain required for the specificity of LukAB toward human CD11b, which is sufficient to render murine CD11b compatible with toxin binding. CRISPR-mediated gene editing was used to replace this domain, resulting in a "humanized" mouse. In vivo studies revealed that the humanized mice exhibit enhanced susceptibility to MRSA bloodstream infection, a phenotype mediated by LukAB. Thus, these studies establish LukAB as an important toxin for MRSA bacteremia and describe a new mouse model to study MRSA pathobiology.

β2 Integrins-Multi-Functional Leukocyte Receptors in Health and Disease

β2 integrins are heterodimeric surface receptors composed of a variable α (CD11a-CD11d) and a constant β (CD18) subunit and are specifically expressed by leukocytes. The α subunit defines the individual functional properties of the corresponding β2 integrin, but all β2 integrins show functional overlap. They mediate adhesion to other cells and to components of the extracellular matrix (ECM), orchestrate uptake of extracellular material like complement-opsonized pathogens, control cytoskeletal organization, and modulate cell signaling. This review aims to delineate the tremendous role of β2 integrins for immune functions as exemplified by the phenotype of LAD-I (leukocyte adhesion deficiency 1) patients that suffer from strong recurrent infections. These immune defects have been largely attributed to impaired migratory and phagocytic properties of polymorphonuclear granulocytes. The molecular base for this inherited disease is a functional impairment of β2 integrins due to mutations within the CD18 gene. LAD-I patients are also predisposed for autoimmune diseases. In agreement, polymorphisms within the CD11b gene have been associated with autoimmunity. Consequently, β2 integrins have received growing interest as targets in the treatment of autoimmune diseases. Moreover, β2 integrin activity on leukocytes has been implicated in tumor development.

The volatile anesthetic sevoflurane reduces neutrophil apoptosis via Fas death domain-Fas-associated death domain interaction

Sepsis remains a significant health care burden, with high morbidities and mortalities. Patients with sepsis often require general anesthesia for procedures and imaging studies. Knowing that anesthetic drugs can pose immunomodulatory effects, it would be critical to understand the impact of anesthetics on sepsis pathophysiology. The volatile anesthetic sevoflurane is a common general anesthetic derived from ether as a prototype. Using a murine sepsis model induced by cecal ligation and puncture surgery, we examined the impact of sevoflurane on sepsis outcome. Different from volatile anesthetic isoflurane, sevoflurane exposure significantly improved the outcome of septic mice. This was associated with less apoptosis in the spleen. Because splenic apoptosis was largely attributed to the apoptosis of neutrophils, we examined the effect of sevoflurane on FasL-induced neutrophil apoptosis. Sevoflurane exposure significantly attenuated apoptosis. Sevoflurane did not affect the binding of FasL to the extracellular domain of Fas receptor. Instead, in silico analysis suggested that sevoflurane would bind to the interphase between Fas death domain (DD) and Fas-associated DD (FADD). The effect of sevoflurane on Fas DD-FADD interaction was examined using fluorescence resonance energy transfer (FRET). Sevoflurane attenuated FRET efficiency, indicating that sevoflurane hindered the interaction between Fas DD and FADD. The predicted sevoflurane binding site is known to play a significant role in Fas DD-FADD interaction, supporting our in vitro and in vivo apoptosis results.-Koutsogiannaki, S., Hou, L., Babazada, H., Okuno, T., Blazon-Brown, N., Soriano, S. G., Yokomizo, T., Yuki, K. The volatile anesthetic sevoflurane reduces neutrophil apoptosis via Fas death domain-Fas-associated death domain interaction.

Leukadherin-1-Mediated Activation of CD11b Inhibits LPS-Induced Pro-inflammatory Response in Macrophages and Protects Mice Against Endotoxic Shock by Blocking LPS-TLR4 Interaction

Dysregulation of macrophage has been demonstrated to contribute to aberrant immune responses and inflammatory diseases. CD11b, expressed on macrophages, plays a critical role in regulating pathogen recognition, phagocytosis, and cell survival. In the present study, we explored the effect of leukadherin-1 (LA1), an agonist of CD11b, on regulating LPS-induced pro-inflammatory response in macrophages and endotoxic shock. Intriguingly, we found that LA1 could significantly reduce mortalities of mice and alleviated pathological injury of liver and lung in endotoxic shock. In vivo studies showed that LA1-induced activation of CD11b significantly inhibited the LPS-induced pro-inflammatory response in macrophages of mice. Moreover, LA1-induced activation of CD11b significantly inhibited LPS/IFN-γ-induced pro-inflammatory response in macrophages by inhibiting MAPKs and NF-κB signaling pathways in vitro. Furthermore, the mice injected with LA1-treated BMDMs showed fewer pathological lesions than those injected with vehicle-treated BMDMs in endotoxic shock. In addition, we found that activation of TLR4 by LPS could endocytose CD11b and activation of CD11b by LA1 could endocytose TLR4 in vitro and in vivo, subsequently blocking the binding of LPS with TLR4. Based on these findings, we concluded that LA1-induced activation of CD11b negatively regulates LPS-induced pro-inflammatory response in macrophages and subsequently protects mice from endotoxin shock by partially blocking LPS-TLR4 interaction. Our study provides a new insight into the role of CD11b in the pathogenesis of inflammatory diseases.

Leukadherin-1-Mediated Activation of CD11b Inhibits LPS-Induced Pro-inflammatory Response in Macrophages and Protects Mice Against Endotoxic Shock by Blocking LPS-TLR4 Interaction

Dysregulation of macrophage has been demonstrated to contribute to aberrant immune responses and inflammatory diseases. CD11b, expressed on macrophages, plays a critical role in regulating pathogen recognition, phagocytosis, and cell survival. In the present study, we explored the effect of leukadherin-1 (LA1), an agonist of CD11b, on regulating LPS-induced pro-inflammatory response in macrophages and endotoxic shock. Intriguingly, we found that LA1 could significantly reduce mortalities of mice and alleviated pathological injury of liver and lung in endotoxic shock. In vivo studies showed that LA1-induced activation of CD11b significantly inhibited the LPS-induced pro-inflammatory response in macrophages of mice. Moreover, LA1-induced activation of CD11b significantly inhibited LPS/IFN-γ-induced pro-inflammatory response in macrophages by inhibiting MAPKs and NF-κB signaling pathways in vitro. Furthermore, the mice injected with LA1-treated BMDMs showed fewer pathological lesions than those injected with vehicle-treated BMDMs in endotoxic shock. In addition, we found that activation of TLR4 by LPS could endocytose CD11b and activation of CD11b by LA1 could endocytose TLR4 in vitro and in vivo, subsequently blocking the binding of LPS with TLR4. Based on these findings, we concluded that LA1-induced activation of CD11b negatively regulates LPS-induced pro-inflammatory response in macrophages and subsequently protects mice from endotoxin shock by partially blocking LPS-TLR4 interaction. Our study provides a new insight into the role of CD11b in the pathogenesis of inflammatory diseases.

Poly(I:C) Priming Exacerbates Cecal Ligation and Puncture-Induced Polymicrobial Sepsis in Mice

Sepsis continues to be a major healthcare issue with one of the highest mortality rates in intensive care units. Toll-like receptors are pattern recognition receptors that are intricately involved in the pathogenesis of sepsis. TLR3 is a major receptor for double-stranded RNA and is largely associated with immunity to viral infection. In this study, we examined the role of TLR3 priming in the immunopathology of sepsis using cecal-ligation and puncture (CLP) model of sepsis in mice. Mice injected with vehicle or poly(I:C) were subjected to sham or CLP surgery and various parameters of sepsis, including mortality, inflammation, and bacterial clearance were assessed. Poly(I:C) pre-treatment significantly enhanced mortality in mice subjected to CLP. Consistent with this, inflammatory cytokines including TNFα, IL-12p40, IFNγ, and MCP-1 were enhanced both systemically and locally in the poly(I:C)-treated group compared to the vehicle control. In addition, bacterial load was significantly higher in the poly(I:C)-treated septic mice. These changes were associated with reduced macrophage activation (but not neutrophils) in the peritoneal cavity of poly(I:C) pre-treated mice compared to vehicle pre-treatment. Together our results demonstrate that poly(I:C) priming in sepsis is likely to be detrimental to the host due to effects on systemic inflammatory cytokines and bacterial clearance.

Cell-Derived Nanoparticles are Endogenous Modulators of Sepsis With Therapeutic Potential

Cell-derived nanoparticles (CDNPs) containing cytosolic proteins and RNAs/DNAs can be isolated from stressed eukaryotic cells. Previously, CDNPs isolated from cultured cells exerted immunomodulatory activities in different infections. Here, we sought to elucidate the role of CDNPs using a murine model of cecal ligation and puncture (CLP). We hypothesized that CDNPs influence the immune response at the site of infection, where severe cellular stress occurs. We observed early CDNP accumulation in the peritoneum after 4 h and continued CDNP presence 24 h after CLP. To determine whether CDNPs influence the host response to sepsis, we isolated CDNPs from a murine fibroblast cell line stressed by nutrient-deprivation, and injected them into septic mice. CDNP-treated mice demonstrated decreased peritoneal interleukin 6 levels and an approximately 2-log lower bacterial load compared with control mice 24 h after CLP. Additionally, a 20% CFU reduction was observed when incubating CDNPs with Pseudomona aeroginosa, indicating that CDNPs are bactericidal. To identify CDNP-responsive cells, CFSE-labeled CDNPs were injected into mice at the time of CLP. We observed that CDNPs were preferentially ingested by F4/80 macrophages, and to a lesser degree, associated with inflammatory monocytes and neutrophils. Strikingly, CDNP-ingesting cells demonstrated elevated CD11b and MHCII expression compared with control cells. Altogether, our data indicate that CDNPs enhance the immune response at the site of infection and promote bacterial clearance, by direct bacterial killing and increasing phagocyte activation. Thus, CDNPs represent a novel, unexplored endogenous sepsis modulator with therapeutic potential.

CD11b Activity Modulates Pathogenesis of Lupus Nephritis

Lupus nephritis (LN) is a common complication of systemic lupus erythematosus (SLE) with unclear etiology and limited treatment options. Immune cell infiltration into the kidneys, a hallmark of LN, triggers tissue damage and proteinuria. CD11b, the α-chain of integrin receptor CD11b/CD18 (also known as α_Mβ2, Mac-1, and CR3), is highly expressed on the surface of innate immune cells, including macrophages and neutrophils. Genetic variants in the human ITGAM gene, which encodes for CD11b, are strongly associated with susceptibility to SLE, LN, and other complications of SLE. CD11b modulates several key biological functions in innate immune cells, including cell adhesion, migration, and phagocytosis. CD11b also modulates other signaling pathways in these cells, such as the Toll-like receptor signaling pathways, that mediate generation of type I interferons, a key proinflammatory cytokine and circulating biomarker in SLE and LN patients. However, how variants in ITGAM gene contribute to disease pathogenesis has not been completely established. Here, we provide an overview of CD11b modulated mechanisms and the functional consequences of the genetic variants that can drive disease pathogenesis. We also present recent insights from studies after pharmacological activation of CD11b. These studies offer novel mechanisms for development of therapeutics for LN, SLE and other autoimmune diseases.

A ligand-specific blockade of the integrin Mac-1 selectively targets pathologic inflammation while maintaining protective host-defense

Integrin-based therapeutics have garnered considerable interest in the medical treatment of inflammation. Integrins mediate the fast recruitment of monocytes and neutrophils to the site of inflammation, but are also required for host defense, limiting their therapeutic use. Here, we report a novel monoclonal antibody, anti-M7, that specifically blocks the interaction of the integrin Mac-1 with its pro-inflammatory ligand CD40L, while not interfering with alternative ligands. Anti-M7 selectively reduces leukocyte recruitment in vitro and in vivo. In contrast, conventional anti-Mac-1 therapy is not specific and blocks a broad repertoire of integrin functionality, inhibits phagocytosis, promotes apoptosis, and fuels a cytokine storm in vivo. Whereas conventional anti-integrin therapy potentiates bacterial sepsis, bacteremia, and mortality, a ligand-specific intervention with anti-M7 is protective. These findings deepen our understanding of ligand-specific integrin functions and open a path for a new field of ligand-targeted anti-integrin therapy to prevent inflammatory conditions.

From the Cover: Prolonged Exposure to Volatile Anesthetic Isoflurane Worsens the Outcome of Polymicrobial Abdominal Sepsis

Sepsis continues to result in high morbidity and mortality. General anesthesia is often administered to septic patients, but the impacts of general anesthesia on host defense are not well understood. General anesthesia can be given by volatile and intravenous anesthetics. Our previous in vitro study showed that volatile anesthetic isoflurane directly inhibits leukocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1), critical adhesion molecules on leukocytes. Thus, the role of isoflurane exposure on in vivo LFA-1 and Mac-1 function was examined using polymicrobial abdominal sepsis model in mice. As a comparison, intravenous anesthetic propofol was given to a group of mice. Wild type, LFA-1, Mac-1, and adhesion molecule-1 knockout mice were used. Following the induction of polymicrobial abdominal sepsis by cecal ligation and puncture, groups of mice were exposed to isoflurane for either 2 or 6 h, or to propofol for 6 h, and their outcomes were examined. Bacterial loads in tissues and blood, neutrophil recruitment to the peritoneal cavity and phagocytosis were studied. Six hours of isoflurane exposure worsened the outcome of abdominal sepsis (P < .0001) with higher bacterial loads in tissues, but 2 h of isoflurane or 6 h of propofol exposure did not. Isoflurane impaired neutrophil recruitment to the abdominal cavity by inhibiting LFA-1 function. Isoflurane also impaired bacterial phagocytosis via complement receptors including Mac-1. In conclusion, prolonged isoflurane exposure worsened the outcome of experimental polymicrobial abdominal sepsis and was associated with impaired neutrophil recruitment and bacterial phagocytosis via reduced LFA-1 and Mac-1 function.

CD11b activation suppresses TLR-dependent inflammation and autoimmunity in systemic lupus erythematosus

Genetic variations in the ITGAM gene (encoding CD11b) strongly associate with risk for systemic lupus erythematosus (SLE). Here we have shown that 3 nonsynonymous ITGAM variants that produce defective CD11b associate with elevated levels of type I interferon (IFN-I) in lupus, suggesting a direct link between reduced CD11b activity and the chronically increased inflammatory status in patients. Treatment with the small-molecule CD11b agonist LA1 led to partial integrin activation, reduced IFN-I responses in WT but not CD11b-deficient mice, and protected lupus-prone MRL/Lpr mice from end-organ injury. CD11b activation reduced TLR-dependent proinflammatory signaling in leukocytes and suppressed IFN-I signaling via an AKT/FOXO3/IFN regulatory factor 3/7 pathway. TLR-stimulated macrophages from CD11B SNP carriers showed increased basal expression of IFN regulatory factor 7 (IRF7) and IFN-β, as well as increased nuclear exclusion of FOXO3, which was suppressed by LA1-dependent activation of CD11b. This suggests that pharmacologic activation of CD11b could be a potential mechanism for developing SLE therapeutics.

The many faces of Mac-1 in autoimmune disease

Mac-1 (CD11b/CD18) is a β2 integrin classically regarded as a pro-inflammatory molecule because of its ability to promote phagocyte cytotoxic functions and enhance the function of several effector molecules such as FcγR, uPAR, and CD14. Nevertheless, recent reports have revealed that Mac-1 also plays significant immunoregulatory roles, and genetic variants in ITGAM, the gene that encodes CD11b, confer risk for the autoimmune disease systemic lupus erythematosus (SLE). This has renewed interest in the physiological roles of this integrin and raised new questions on how its seemingly opposing biological functions may be regulated. Here, we provide an overview of the CD18 integrins and how their activation may be regulated as this may shed light on how the opposing roles of Mac-1 may be elicited. We then discuss studies that exemplify Mac-1's pro-inflammatory versus regulatory roles particularly in the context of IgG immune complex-mediated inflammation. This includes a detailed examination of molecular mechanisms that could explain the risk-conferring effect of rs1143679, a single nucleotide non-synonymous Mac-1 polymorphism associated with SLE.

Detecting the Hidden Properties of Immunological Data and Predicting the Mortality Risks of Infectious Syndromes

BACKGROUND

To extract more information, the properties of infectious disease data, including hidden relationships, could be considered. Here, blood leukocyte data were explored to elucidate whether hidden information, if uncovered, could forecast mortality.

METHODS

Three sets of individuals (n = 132) were investigated, from whom blood leukocyte profiles and microbial tests were conducted (i) cross-sectional analyses performed at admission (before bacteriological tests were completed) from two groups of hospital patients, randomly selected at different time periods, who met septic criteria [confirmed infection and at least three systemic inflammatory response syndrome (SIRS) criteria] but lacked chronic conditions (study I, n = 36; and study II, n = 69); (ii) a similar group, tested over 3 days (n = 7); and (iii) non-infected, SIRS-negative individuals, tested once (n = 20). The data were analyzed by (i) a method that creates complex data combinations, which, based on graphic patterns, partitions the data into subsets and (ii) an approach that does not partition the data. Admission data from SIRS+/infection+ patients were related to 30-day, in-hospital mortality.

RESULTS

The non-partitioning approach was not informative: in both study I and study II, the leukocyte data intervals of non-survivors and survivors overlapped. In contrast, the combinatorial method distinguished two subsets that, later, showed twofold (or larger) differences in mortality. While the two subsets did not differ in gender, age, microbial species, or antimicrobial resistance, they revealed different immune profiles. Non-infected, SIRS-negative individuals did not express the high-mortality profile. Longitudinal data from septic patients displayed the pattern associated with the highest mortality within the first 24 h post-admission. Suggesting inflammation coexisted with immunosuppression, one high-mortality sub-subset displayed high neutrophil/lymphocyte ratio values and low lymphocyte percents. A second high-mortality subset showed monocyte-mediated deficiencies. Numerous within- and between-subset comparisons revealed statistically significantly different immune profiles.

CONCLUSION

While the analysis of non-partitioned data can result in information loss, complex (combinatorial) data structures can uncover hidden patterns, which guide data partitioning into subsets that differ in mortality rates and immune profiles. Such information can facilitate diagnostics, monitoring of disease dynamics, and evaluation of subset-specific, patient-specific therapies.

Analysis of circulating plasmacytoid dendritic cells during the course of sepsis

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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