Control of leukocyte rolling velocity in TNF-alpha-induced inflammation by LFA-1 and Mac-1

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.

Novel Functions of Integrins as Receptors of CD154: Their Role in Inflammation and Apoptosis

CD154, an inflammatory mediator also known as CD40 ligand, has been identified as a novel binding partner for some members of the integrin family. The αIIbβ3, specifically expressed on platelets, was the first integrin to be described as a receptor for CD154 after CD40. Its interaction with soluble CD154 (sCD154) highly contributes to thrombus formation and stability. Identifying αIIbβ3 opened the door for investigating other integrins as partners of CD154. The αMβ2 expressed on myeloid cells was shown capable of binding CD154 and contributing as such to cell activation, adhesion, and release of proinflammatory mediators. In parallel, α5β1 communicates with sCD154, inducing pro-inflammatory responses. Additional pathogenic effects involving apoptosis-preventing functions were exhibited by the CD154–α5β1 dyad in T cells, conferring a role for such interaction in the survival of malignant cells, as well as the persistence of autoreactive T cells. More recently, CD154 receptors integrated two new integrin members, αvβ3 and α4β1, with little known as to their biological significance in this context. This article provides an overview of the novel role of integrins as receptors of CD154 and as critical players in pro-inflammatory and apoptotic responses.

Nanoparticle Properties Influence Transendothelial Migration of Monocytes

Nanoparticle-based delivery of therapeutics to the brain has had limited clinical impact due to challenges crossing the blood-brain barrier (BBB). Certain cells, such as monocytes, possess the ability to migrate across the BBB, making them attractive candidates for cell-based brain delivery strategies. In this work, we explore nanoparticle design parameters that impact both monocyte association and monocyte-mediated BBB transport. We use electrohydrodynamic jetting to prepare nanoparticles of varying sizes, compositions, and elasticity to address their impact on uptake by THP-1 monocytes and permeation across the BBB. An in vitro human BBB model is developed using human cerebral microvascular endothelial cells (hCMEC/D3) for the assessment of migration. We compare monocyte uptake of both polymeric and synthetic protein nanoparticles (SPNPs) of various sizes, as well as their effect on cell migration. SPNPs (human serum albumin/HSA or human transferrin/TF) are shown to promote increased monocyte-mediated transport across the BBB over polymeric nanoparticles. TF SPNPs (200 nm) associate readily, with an average uptake of 138 particles/cell. Nanoparticle loading is shown to influence the migration of THP-1 monocytes. The migration of monocytes loaded with 200 nm TF and 200 nm HSA SPNPs was 2.3-fold and 2.1-fold higher than that of an untreated control. RNA-seq analysis after TF SPNP treatment suggests that the upregulation of several migration genes may be implicated in increased monocyte migration (ex. integrin subunits α M and α L). Integrin β 2 chain combines with either integrin subunit α M chain or integrin subunit α L chain to form macrophage antigen 1 and lymphocyte function-associated antigen 1 integrins. Both products play a pivotal role in the transendothelial migration cascade. Our findings highlight the potential of SPNPs as drug and/or gene delivery platforms for monocyte-mediated BBB transport, especially where conventional polymer nanoparticles are ineffective or otherwise not desirable.

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.

Where the Action Is-Leukocyte Recruitment in Atherosclerosis

Atherosclerosis is the leading cause of death worldwide and leukocyte recruitment is a key element of this phenomenon, thus allowing immune cells to enter the arterial wall. There, in concert with accumulating lipids, the invading leukocytes trigger a plethora of inflammatory responses which promote the influx of additional leukocytes and lead to the continued growth of atherosclerotic plaques. The recruitment process follows a precise scheme of tethering, rolling, firm arrest, crawling and transmigration and involves multiple cellular and subcellular players. This review aims to provide a comprehensive up-to-date insight into the process of leukocyte recruitment relevant to atherosclerosis, each from the perspective of endothelial cells, monocytes and macrophages, neutrophils, T lymphocytes and platelets. In addition, therapeutic options targeting leukocyte recruitment into atherosclerotic lesions-or potentially arising from the growing body of insights into its precise mechanisms-are highlighted.

Association of Promoter Methylation and Expression of Inflammatory Genes IL-6 and TNF-α with the Risk of Coronary Artery Disease in Diabetic and Obese Subjects among Asian Indians

The inflammatory cytokines such as interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) are considered as the most important contributors to the endothelial dysfunction in subjects with type 2 diabetes mellitus (T2DM) and obesity. The hypomethylation of CpG sites in the promoter region of the IL-6 and TNF-α have shown to be associated with the increased expression of IL-6 and TNF-α. However, there are no studies on the methylation and expression of IL-6 and TNF-α with the risk of coronary artery disease (CAD) in subjects with T2DM and obesity in Asian Indians. Hence, the present study was aimed to investigate whether the IL-6, TNF-α promoter methylation and expression in blood leukocyte DNA is associated with the risk of CAD in diabetic and obese subjects in Asian Indians. For this study, we recruited 574 subjects which includes, 207 angiographically confirmed CAD patients, 100 T2DM patients, 82 obese subjects and 185 healthy controls. The methylation status of IL-6 and TNF-α gene loci was determined by methylation specific PCR (MPCR) and gene expression was determined by qPCR. We found significant hypomethylation of IL-6 in CAD and T2DM subjects (OR 1.98 95% CI: 1.32-2.97, p = 0.001, OR: 2.23 95% CI:1.34-3.76, p = 0.001, respectively). Further, a significant increase in the expression of IL-6 in CAD and T2DM subjects (fold change: 26.39 & 14.7, p = 0.0001) compared to the control subjects was observed. A significant increase in the hypomethylation of TNF-α in CAD, T2DM and obese subjects was observed as compared to the control (OR: 2.04 95% CI: 1.36-3.05, p = 0.0005, OR: 1.81 95% CI 1.10-2.96, p = 0.01, and OR: 2.1 95% CI 1.24-3.57, p = 0.007, respectively).We also found an increased expression of TNF-α in CAD, T2DM and obese subjects as compared to controls. In addition, presence of low folate, and hyperhomocysteinemia was observed in the present study, may be the contributing factors for the hypomethylation of IL-6 and TNF-α and oxidative stress. In conclusion, increased expression of IL-6 and TNF-α due to hypomethylation in T2DM and obese individuals may contribute to CAD risk in these subjects. The presence of hyperhomocysteinemia and increased oxidative risk may enhance the CAD risk further.

Molecular Insights Into Neutrophil Biology From the Zebrafish Perspective: Lessons From CD18 Deficiency

Neutrophils are key players in innate immunity and originate from the bone marrow of the adult mammalian organism. In mammals, mature neutrophils are released from the bone marrow into the peripheral blood where they circulate until their recruitment to sites of inflammation in a multistep adhesion cascade. Here, adhesion molecules of the β₂ integrin family (CD11/CD18) are critically required for the initial neutrophil adhesion to the inflamed endothelium and several post-adhesion steps allowing their extravasation into the inflamed tissue. Within the mammalian tissue, interstitial neutrophil migration can occur widely independent of β₂ integrins. This is in sharp contrast to neutrophil recruitment in zebrafish larvae (Danio rerio) where neutrophils originate from the caudal hematopoietic tissue and mainly migrate interstitially to sites of lesion upon the early onset of inflammation. However, neutrophils extravasate from the circulation to the inflamed tissue in zebrafish larvae at later-time points. Although zebrafish larvae are a widely accepted model system to analyze neutrophil trafficking in vivo, the functional impact of β₂ integrins for neutrophil trafficking during acute inflammation is completely unknown in this model. In this study, we generated zebrafish with a genetic deletion of CD18, the β subunit of β₂ integrins, using CRISPR/Cas9 technology. Sequence alignments demonstrated a high similarity of the amino acid sequences between zebrafish and human CD18 especially in the functionally relevant I-like domain. In addition, the cytoplasmic domain of CD18 harbors two highly conserved NXXF motifs suggesting that zebrafish CD18 may share functional properties of human CD18. Accordingly, CD18 knock-out (KO) zebrafish larvae displayed the key symptoms of patients suffering from leukocyte adhesion deficiency (LAD) type I due to defects in ITGB2, the gene for CD18. Importantly, CD18 KO zebrafish larvae showed reduced neutrophil trafficking to sites of sterile inflammation despite the fact that an increased number of neutrophils was detectable in the circulation. By demonstrating the functional importance of CD18 for neutrophil trafficking in zebrafish larvae, our findings shed new light on neutrophil biology in vertebrates and introduce a new model organism for studying LAD type I.

Intercellular Adhesion Molecule-1-Induced Posttraumatic Brain Injury Neuropathology in the Prefrontal Cortex and Hippocampus Leads to Sensorimotor Function Deficits and Psychological Stress

Intercellular adhesion molecule-1 (ICAM-1) promotes adhesion and transmigration of circulating leukocytes across the blood-brain barrier (BBB). Traumatic brain injury (TBI) causes transmigrated immunocompetent cells to release mediators [function-associated antigen (LFA)-1 and macrophage-1 antigen (Mac-1)] that stimulate glial and endothelial cells to express ICAM-1 and release cytokines, sustaining neuroinflammation and neurodegeneration. Although a strong correlation exists between TBI-mediated inflammation and impairment in functional outcome following brain trauma, the role of ICAM-1 in impairing functional outcome by inducing neuroinflammation and neurodegeneration after TBI remains inconclusive. The experimental TBI was induced in vivo by fluid percussion injury (FPI; 10 and 20 psi) in wild-type (WT) and ICAM-1-/- mice and in vitro by stretch injury (3 psi) in brain endothelial cells. We manipulate ICAM-1 pharmacologically and genetically and conducted several biochemical analyses to gain insight into the mechanisms underlying ICAM-1-mediated neuroinflammation and performed rotarod, grid-walk, sucrose preference, and light-dark tests to assess functional outcome. TBI-induced ICAM-1-mediated neuroinflammation and cell death occur via LFA-1 or Mac-1 signaling pathways that rely on oxidative stress, matrix metalloproteinase (MMP), and vascular endothelial growth factor (VEGF) pathways. The deletion or blocking of ICAM-1 resulted in a better outcome in attenuating neuroinflammation and cell death as marked by the markers such as NF-kB, IL-1β, TNF-α, cleaved-caspase-3 (cl-caspase-3), Annexin V, and by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and Trypan blue staining. ICAM-1 deletion in TBI improves sensorimotor, depression, and anxiety-like behavior with significant upregulation of norepinephrine (NE), dopamine (DA) D1 receptor (DAD1R), serotonin (5-HT)1AR, and neuropeptide Y (NPY). This study could establish the significance of ICAM-1 as a novel therapeutic target against the pathophysiology to establish functional recovery after TBI.

The Role of Biodegradable Poly-(L-lactide)-Based Polymers in Blood Cell Activation and Platelet-Monocyte Interaction

The main purpose of new stent technologies is to overcome unfavorable material-related incompatibilities by producing bio- and hemo-compatible polymers with anti-inflammatory and anti-thrombogenic properties. In this context, wettability is an important surface property, which has a major impact on the biological response of blood cells. However, the influence of local hemodynamic changes also influences blood cell activation. Therefore, we investigated biodegradable polymers with different wettability to identify possible aspects for a better prediction of blood compatibility. We applied shear rates of 100 s⁻¹ and 1500 s⁻¹ and assessed platelet and monocyte activation as well as the formation of CD62P+ monocyte-bound platelets via flow cytometry. Aggregation of circulating platelets induced by collagen was assessed by light transmission aggregometry. Via live cell imaging, leukocytes were tracked on biomaterial surfaces to assess their average velocity. Monocyte adhesion on biomaterials was determined by fluorescence microscopy. In response to low shear rates of 100 s⁻¹, activation of circulating platelets and monocytes as well as the formation of CD62P+ monocyte-bound platelets corresponded to the wettability of the underlying material with the most favorable conditions on more hydrophilic surfaces. Under high shear rates, however, blood compatibility cannot only be predicted by the concept of wettability. We assume that the mechanisms of blood cell-polymer interactions do not allow for a rule-of-thumb prediction of the blood compatibility of a material, which makes extensive in vitro testing mandatory.

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.

Inhibition of BRD4 Reduces Neutrophil Activation and Adhesion to the Vascular Endothelium Following Ischemia Reperfusion Injury

Renal ischemia reperfusion injury (IRI) is associated with inflammation, including neutrophil infiltration that exacerbates the initial ischemic insult. The molecular pathways involved are poorly characterized and there is currently no treatment. We performed an in silico analysis demonstrating changes in NFκB-mediated gene expression in early renal IRI. We then evaluated NFκB-blockade with a BRD4 inhibitor on neutrophil adhesion to endothelial cells in vitro, and tested BRD4 inhibition in an in vivo IRI model. BRD4 inhibition attenuated neutrophil adhesion to activated endothelial cells. In vivo, IRI led to increased expression of cytokines and adhesion molecules at 6 h post-IRI with sustained up-regulated expression to 48 h post-IRI. These effects were attenuated, in part, with BRD4 inhibition. Absolute neutrophil counts increased significantly in the bone marrow, blood, and kidney 24 h post-IRI. Activated neutrophils increased in the blood and kidney at 6 h post-IRI and remained elevated in the kidney until 48 h post-IRI. BRD4 inhibition reduced both total and activated neutrophil counts in the kidney. IRI-induced tubular injury correlated with neutrophil accumulation and was reduced by BRD4 inhibition. In summary, BRD4 inhibition has important systemic and renal effects on neutrophils, and these effects are associated with reduced renal injury.

Effect of CARD9 Deficiency on Neutrophil-Mediated Host Defense against Pulmonary Infection with Streptococcus pneumoniae

Streptococcus pneumoniae is a major causative bacterium of community-acquired pneumonia. Dendritic cell-associated C-type lectin-2 (dectin-2), one of the C-type lectin receptors (CLRs), was previously reported to play a pivotal role in host defense against pneumococcal infection through regulating phagocytosis by neutrophils while not being involved in neutrophil accumulation. In the present study, to elucidate the possible contribution of other CLRs to neutrophil accumulation, we examined the role of caspase recruitment domain-containing protein 9 (CARD9), a common adaptor molecule for signal transduction triggered by CLRs, in neutrophilic inflammatory response against pneumococcal infection. Wild-type (WT), CARD9 knockout (KO), and dectin-2 KO mice were infected intratracheally with pneumococcus, and the infected lungs were histopathologically analyzed to assess neutrophil accumulation at 24 h postinfection. Bronchoalveolar lavage fluids (BALFs) were collected at the same time point to count the neutrophils and assess the production of inflammatory cytokines and chemokines. Neutrophil accumulation was significantly decreased in CARD9 KO mice, but not in dectin-2 KO mice. Tumor necrosis factor alpha (TNF-α), keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) production in BALFs were also attenuated in CARD9 KO mice, but not in dectin-2 KO mice. Production of TNF-α and KC by alveolar macrophages stimulated with pneumococcal culture supernatants was significantly attenuated in CARD9 KO mice, but not in dectin-2 KO mice, compared to that in each group's respective control mice. In addition, pneumococcus-infected CARD9 KO mice showed larger bacterial burdens in the lungs than did WT mice. These data indicate that CARD9 is required for neutrophil migration after pneumococcal infection, as well as inflammatory cytokine and chemokine production by alveolar macrophages, and suggest that a CLR distinct from dectin-2 may be involved in this response.

GSK3 modulation in acute lung injury, myocarditis and polycystic kidney disease-related aneurysm

GSK3 are involved in different physical and pathological conditions and inflammatory regulated by macrophages contribute to significant mechanism. Infection stimuli may modulate GSK3 activity and influence host cell adaption, immune cells infiltration or cytokine expressions. To further address the role of GSK3 modulation in macrophages, the signal transduction of three major organs challenged by endotoxin, virus and genetic inherited factors are briefly introduced (lung injury, myocarditis and autosomal dominant polycystic kidney disease). As a result of pro-inflammatory and anti-inflammatory functions of GSK3 in different microenvironments and stages of macrophages (M1/M2), the rational resolution should be considered by adequately GSK3.

The Role and Impact of Extracellular Vesicles in the Modulation and Delivery of Cytokines during Autoimmunity

Cytokines and extracellular vesicles are two methods of initiating and maintaining cellular crosstalk. The role of cytokines in the initiation, progression, and resolution of inflammation has been well studied and more so, their pathophysiological role in the development of autoimmune disease. In recent years, the impact of extracellular vesicles on the progression of autoimmunity has become more widely appreciated. In this review, we discuss the mechanisms that allow extracellular vesicles of various sources to modulate cytokine production, and release, and how extracellular vesicles might be involved in the direct delivery and modulation of cytokine levels. Moreover, we explore what challenges are faced by current therapies and the promising future for extracellular vesicles as therapeutic agents in conditions driven by immune dysregulation.

Dipeptidase-1 Is an Adhesion Receptor for Neutrophil Recruitment in Lungs and Liver

A hallmark feature of inflammation is the orchestrated recruitment of neutrophils from the bloodstream into inflamed tissue. Although selectins and integrins mediate recruitment in many tissues, they have a minimal role in the lungs and liver. Exploiting an unbiased in vivo functional screen, we identified a lung and liver homing peptide that functionally abrogates neutrophil recruitment to these organs. Using biochemical, genetic, and confocal intravital imaging approaches, we identified dipeptidase-1 (DPEP1) as the target and established its role as a physical adhesion receptor for neutrophil sequestration independent of its enzymatic activity. Importantly, genetic ablation or functional peptide blocking of DPEP1 significantly reduced neutrophil recruitment to the lungs and liver and provided improved survival in models of endotoxemia. Our data establish DPEP1 as a major adhesion receptor on the lung and liver endothelium and identify a therapeutic target for neutrophil-driven inflammatory diseases of the lungs.

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.

Neutrophil extracellular trap-microparticle complexes trigger neutrophil recruitment via high-mobility group protein 1 (HMGB1)-toll-like receptors(TLR2)/TLR4 signalling

BACKGROUND AND PURPOSE

Recent data suggest that neutrophil extracellular traps (NETs) form aggregates with microparticles (MPs) upon activation of neutrophils although the functional role of NET-MP complexes remain elusive. The objective of this study was to examine the role of NET-MP aggregates in leukocyte recruitment in vivo.

EXPERIMENTAL APPROACH

PMA stimulation of murine bone marrow neutrophils generated NET-MP complexes and pretreatment with caspase and calpain inhibitors resulted in the formation of NETs depleted of MPs. Leukocyte-endothelium interactions were studied by using intravital microscopy of the mouse cremaster microcirculation.

KEY RESULTS

Intrascrotal injection of NET-MP aggregates dose-dependently increased leukocyte recruitment. In contrast, leukocyte responses were markedly reduced after administration of NETs depleted of MPs. Neutrophil depletion abolished intravascular and extravascular leukocytes in response to challenge with NET-MP complexes. Electron microscopy revealed that NET-associated MPs express HMGB1. Notably, immunoneutralization of HMGB1 markedly decreased NET-MP complex-induced neutrophil accumulation. Moreover, inhibition of TLR2 and TLR4 significantly reduced neutrophil recruitment in response to NET-MP aggregates.

CONCLUSIONS AND IMPLICATIONS

These data show that NET-MP complexes are potent inducers of neutrophil recruitment, which is dependent on HMGB1 expressed on MPs and mediated via TLR2 and TLR4. Blocking MP binding to NETs or downstream inhibition of the HMGB1-TLR2/TLR4 axis might provide useful targets to attenuating NET-dependent tissue damage in acute inflammation.

Microvascular Mechanisms of Polyphosphate-Induced Neutrophil-Endothelial Cell Interactions in vivo

BACKGROUND

Polyphosphates (PolyPs) have been reported to exert pro-inflammatory effects. However, the molecular mechanisms regulating PolyP-provoked tissue accumulation of leukocytes are not known. The aim of the present investigation was to determine the role of specific adhesion molecules in PolyP-mediated leukocyte recruitment.

METHODS

PolyPs and TNF-α were intrascrotally administered, and anti-P-selectin, anti-E-selectin, anti-P-selectin glycoprotein ligand-1 (PSGL-1), anti-membrane-activated complex-1 (Mac-1), anti-lymphocyte function antigen-1 (LFA-1), and neutrophil depletion antibodies were injected intravenously or intraperitoneally. Intravital microscopy of the mouse cremaster microcirculation was used to examine leukocyte-endothelium interactions and recruitment in vivo.

RESULTS

Intrascrotal injection of PolyPs increased leukocyte accumulation. Depletion of neutrophils abolished PolyP-induced leukocyte-endothelium interactions, indicating that neutrophils were the main leukocyte subtype responding to PolyP challenge. Immunoneutralization of P-selectin and PSGL-1 abolished PolyP-provoked neutrophil rolling, adhesion, and emigration. Moreover, immunoneutralization of Mac-1 and LFA-1 had no impact on neutrophil rolling but markedly reduced neutrophil adhesion and emigration evoked by PolyPs.

CONCLUSION

These results suggest that P-selectin and PSGL-1 exert important roles in PolyP-induced inflammatory cell recruitment by mediating neutrophil rolling. In addition, our data show that Mac-1 and LFA-1 are necessary for supporting PolyP-triggered firm adhesion of neutrophils to microvascular endothelium. These novel findings define specific molecules as potential targets for pharmacological intervention in PolyP-dependent inflammatory diseases.

Differentiation of neutrophil-like HL-60 cells strongly impacts their rolling on surfaces with various adhesive properties under a pressing force

BACKGROUND

HL-60 cells have been used in in vitro experiments of neutrophils rolling. They lose uniform spherical appearance and enhance deformability by differentiation to neutrophil-like cells, which would affect their rolling characteristics.

OBJECTIVE

We investigate the influence of differentiation and coating of target substrate on the fundamental rolling characteristics of the cells under a constant pressing force which mimics the pressing force to the vessel wall by erythrocytes in vivo.

METHODS

Motions of undifferentiated and differentiated HL-60 cells on plain or MPC-polymer-coated flat glass substrate were compared using a homemade inclined centrifuge microscope system.

RESULTS

Most of the cells alternated between stop and go during the motion. The differentiation resulted in a high temporal ratio of the non-moving state and low mean velocity during the moving state, together with a high suppression performance of cell adhesion by the polymer. It was also suggested that the cells were mostly rolling but that the coating probably induced an infrequent slip on the substrate to stabilize the cells motion.

CONCLUSIONS

Differentiation strongly affects adhesivity of HL-60 cells but less affects the mean velocity. Our findings also demonstrate the importance of the pressing force and advantage of the present system with respect to classical flow chambers.

The ITIM Domain-Containing NK Receptor Ly49Q Impacts Pulmonary Infection by Mediating Neutrophil Functions

Pulmonary infection is a frequent pathology associated with excessive neutrophil infiltration. Ly49Q, an ITIM domain-bearing receptor expressed on different leukocytes, has been recently reported to impact neutrophil migration and polarization. Utilizing a murine model of Klebsiella pneumoniae-induced pulmonary infection in combination with additional in vivo and in vitro assays, we show that Ly49Q is critically involved in different steps of the leukocyte adhesion cascade. Ly49Q deficiency is associated with a reduced rolling velocity, impaired crawling capacity, and diminished transmigration. We show that overactivation of the neutrophil β₂ integrins Mac-1 and LFA-1 is responsible for increased adhesion and reduced neutrophil transmigration, resulting in a strongly impaired immune defense against pulmonary infection. Structure function analysis in vitro and in vivo demonstrated that different domains of Ly49Q are important for its function. In summary, Ly49Q regulates integrin activation and neutrophil recruitment and is required for an adequate immune response in pulmonary infection.

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.

Non-identical twins: Different faces of CR3 and CR4 in myeloid and lymphoid cells of mice and men

Integrins are cell membrane receptors that are involved in essential physiological and serious pathological processes. Their main role is to ensure a closely regulated link between the extracellular matrix and the intracellular cytoskeletal network enabling cells to react to environmental stimuli. Complement receptor type 3 (CR3, αMβ₂, CD11b/CD18) and type 4 (CR4, αXβ₂, CD11c/CD18) are members of the β₂-integrin family expressed on most white blood cells. Both receptors bind multiple ligands like iC3b, ICAM, fibrinogen or LPS. β₂-integrins are accepted to play important roles in cellular adhesion, migration, phagocytosis, ECM rearrangement and inflammation. Several pathological conditions are linked to the impaired functions of these receptors. CR3 and CR4 are generally thought to mediate overlapping functions in monocytes, macrophages and dendritic cells, therefore the potential distinctive role of these receptors has not been investigated so far in satisfactory details. Lately it has become clear that a functional segregation has evolved between the two receptors regarding phagocytosis, cellular adhesion and podosome formation. In addition to their tasks on myeloid cells, the expression and function of CR3 and CR4 on lymphocytes have also gained interest recently. The picture is further complicated by the fact that while these β₂-integrins are expressed by immune cells both in mice and humans, there are significant differences in their expression level, functions and the pathological consequences of genetic defects. Here we aim to summarize our current knowledge on CR3 and CR4 and highlight the functional differences between these receptors, involving their expression in myeloid and lymphoid cells of both men and mice.

Loss of mDia1 causes neutropenia via attenuated CD11b endocytosis and increased neutrophil adhesion to the endothelium

Formin protein mDia1 is involved in actin polymerization and plays important roles in the migration and adhesion of hematopoietic cells. The mDia1 encoding gene is located on chromosome 5q, which is commonly deleted in patients with del(5q) myelodysplastic syndromes (MDSs). We previously reported that mice with mDia1 deficiency developed neutropenia that closely mimics MDS. However, the mechanism of neutropenia in these mice and patients with del(5q) MDS remains incompletely defined. Here, we reveal that mDia1 knockout mice show cell-autonomously increased CD11b expression on neutrophils in the peripheral blood and bone marrow. The level of CD11b was also higher in patients with del(5q) MDS compared with normal individuals. Mechanistically, loss of mDia1 significantly attenuated the endocytosis of CD11b on neutrophils, which led to an increased number of neutrophils adhering to the blood vessels in mDia1 knockout mice. Administration of CD11b antibody to mDia1 knockout mice reduced the adhesion of neutrophils to the vessels and rescued neutropenia. Our study reveals the role of mDia1 deficiency in the upregulation of CD11b on neutrophils, which leads to their increased binding to the blood vessels. These results may provide important clues for the pathogenesis of neutropenia in patients with del(5q) MDS.

CD40L and Its Receptors in Atherothrombosis-An Update

CD40L (CD154), a member of the tumor necrosis factor superfamily, is a co-stimulatory molecule that was first discovered on activated T cells. Beyond its fundamental role in adaptive immunity-ligation of CD40L to its receptor CD40 is a prerequisite for B cell activation and antibody production-evidence from more than two decades has expanded our understanding of CD40L as a powerful modulator of inflammatory pathways. Although inhibition of CD40L with neutralizing antibodies has induced life-threatening side effects in clinical trials, the discovery of cell-specific effects and novel receptors with distinct functional consequences has opened a new path for therapies that specifically target detrimental properties of CD40L. Here, we carefully evaluate the signaling network of CD40L by gene enrichment analysis and its cell-specific expression, and thoroughly discuss its role in cardiovascular pathologies with a specific emphasis on atherosclerotic and thrombotic disease.

Age Increases Monocyte Adhesion on Collagen

Adhesion of monocytes to micro-injuries on arterial walls is an important early step in the occurrence and development of degenerative atherosclerotic lesions. At these injuries, collagen is exposed to the blood stream. We are interested whether age influences monocyte adhesion to collagen under flow, and hence influences the susceptibility to arteriosclerotic lesions. Therefore, we studied adhesion and rolling of human peripheral blood monocytes from old and young individuals on collagen type I coated surface under shear flow. We find that firm adhesion of monocytes to collagen type I is elevated in old individuals. Pre-stimulation by lipopolysaccharide increases the firm adhesion of monocytes homogeneously in older individuals, but heterogeneously in young individuals. Blocking integrin α_x showed that adhesion of monocytes to collagen type I is specific to the main collagen binding integrin α_xβ₂. Surprisingly, we find no significant age-dependent difference in gene expression of integrin α_x or integrin β₂. However, if all integrins are activated from the outside, no differences exist between the age groups. Altered integrin activation therefore causes the increased adhesion. Our results show that the basal increase in integrin activation in monocytes from old individuals increases monocyte adhesion to collagen and therefore the risk for arteriosclerotic plaques.

NET-producing CD16high CD62Ldim neutrophils migrate to tumor sites and predict improved survival in patients with HNSCC

The concept of functional neutrophil subsets is new and their clinical significance in malignancies is unknown. Our study investigated the role of CD16^dim CD62L^high , CD16^high CD62L^high and CD16^high CD62L^dim neutrophil subsets in head and neck squamous cell carcinoma (HNSCC) patients. These neutrophil subsets may play different roles in immune-related activity in cancer, based on their profile, activation state and migration ability within a tumor site, which may be important in predicting cancer prognoses. Tumor biopsies and blood were obtained from newly diagnosed untreated HNSCC patients and healthy controls. Neutrophil subsets and their phenotype were characterized using flow cytometry. Isolated granulocytes were assessed for anti-tumor immune functions. Compared to controls HNSCC patients exhibited increased CD16^high CD62L^dim neutrophils in blood; this subset displayed a distinct phenotypes with high expression of CD11b and CD18. This subset was prone to migrate into the tumor facilitated by tumor-derived IL-8. Furthermore, IL-8 was also found to activate neutrophils and thereby promoting subset transition. Various assays demonstrated that activated CD16^high CD62L^dim neutrophils inhibited migration, proliferation and induced apoptosis of FaDu cancer cells. Neutrophil elastase detected in activated CD16^high CD62L^dim neutrophils and tumor biopsies suggested that CD16^high CD62L^dim neutrophils impart anti-tumoral activity via neutrophil extracellular traps. Furthermore, increased fraction of CD16^high CD62L^dim neutrophils was shown to correlate with an increased survival rate. Our study demonstrates the clinical relevance of the CD16^high CD62L^dim neutrophil subset, providing evidence for its increased migration capacity, its anti-tumor activity including increased NET formation and finally its correlation with increased survival in HNSCC patients.

Neuroanatomy and Physiology of Brain Dysfunction in Sepsis

Sepsis-associated encephalopathy (SAE), a complication of sepsis, is often complicated by acute and long-term brain dysfunction. SAE is associated with electroencephalogram pattern changes and abnormal neuroimaging findings. The major processes involved are neuroinflammation, circulatory dysfunction, and excitotoxicity. Neuroinflammation and microcirculatory alterations are diffuse, whereas excitotoxicity might occur in more specific structures involved in the response to stress and the control of vital functions. A dysfunction of the brainstem, amygdala, and hippocampus might account for the increased mortality, psychological disorders, and cognitive impairment. This review summarizes clinical and paraclinical features of SAE and describes its mechanisms at cellular and structural levels.

Inflammation, but not recruitment, of adipose tissue macrophages requires signalling through Mac-1 (CD11b/CD18) in diet-induced obesity (DIO)

Cell accumulation is a prerequisite for adipose tissue inflammation. The leukocyte integrin Mac-1 (CD11b/CD18, α_Mβ₂) is a classic adhesion receptor critically regulating inflammatory cell recruitment. Here, we tested the hypothesis that a genetic deficiency and a therapeutic modulation of Mac-1 regulate adipose tissue inflammation in a mouse model of diet-induced obesity (DIO). C57Bl6/J mice genetically deficient (Mac-1^-/-) or competent for Mac-1 (WT) consumed a high fat diet for 20 weeks. Surprisingly, Mac-1^-/- mice presented with increased diet-induced weight gain, decreased insulin sensitivity in skeletal muscle and in the liver in insulin-clamps, insulin secretion deficiency and elevated glucose levels in fasting animals, and dyslipidaemia. Unexpectedly, accumulation of adipose tissue macrophages (ATMs) was unaffected, while gene expression indicated less inflamed adipose tissue and macrophages in Mac-1^-/- mice. In contrast, inflammatory gene expression at distant locations, such as in skeletal muscle, was not changed. Treatment of ATMs with an agonistic anti-Mac-1 antibody, M1/70, induced pro-inflammatory genes in cell culture. In vivo, treatment with M1/70 induced a hyper-inflammatory phenotype with increased expression of IL-6 and MCP-1, whereas accumulation of ATMs did not change. Finally, inhibition of Mac-1's adhesive interaction to CD40L by the peptide inhibitor cM7 did not affect myeloid cell accumulation in adipose tissue. We present the surprising finding that adhesive properties of the leukocyte integrin Mac-1 are not required for macrophage accumulation in adipose tissue. Instead, Mac-1 modulates inflammatory gene expression in macrophages. These findings question the net effect of integrin blockade in cardio-metabolic disease.

Leukocyte arrest: Biomechanics and molecular mechanisms of β2 integrin activation

Integrins are a group of heterodimeric transmembrane receptors that play essential roles in cell-cell and cell-matrix interaction. Integrins are important in many physiological processes and diseases. Integrins acquire affinity to their ligand by undergoing molecular conformational changes called activation. Here we review the molecular biomechanics during conformational changes of integrins, integrin functions in leukocyte biorheology (adhesive functions during rolling and arrest) and molecules involved in integrin activation.

Moesin regulates neutrophil rolling velocity in vivo

During inflammation, the selectin-induced slow rolling of neutrophils on venules cooperates with chemokine signaling to mediate neutrophil recruitment into tissues. Previous studies identified P-selectin glycoprotein ligand-1 (PSGL-1) and CD44 as E-selectin ligands that activate integrins to induce slow rolling. We show here that in TNF-α-treated cremaster muscle venules, slow leukocyte rolling was impaired in mice deficient in moesin, a member of the ezrin-radixin-moesin (ERM) family. Accordingly, neutrophil recruitment in a peritonitis model was decreased in moesin-deficient mice when chemokine signaling was blocked with pertussis toxin. These results suggest that moesin contributes to the slow rolling and subsequent recruitment of neutrophils during inflammation.

Effect of salvianolic acid B on TNF-α induced cerebral microcirculatory changes in a micro-invasive mouse model

PURPOSE

To investigate the effects of salvianolic acid B (SAB) on tumor necrosis factor a (TNF-α) induced alterations of cerebral microcirculation with a bone-abrading model.

METHODS

The influences of craniotomy model and bone-abrading model on cerebral microcirculation were compared. The bone-abrading method was used to detect the effects of intracerebroventricular application of 40 μg/kg·bw TNF-α on cerebral venular leakage of fluorescein isothiocyanate (FITC)- albulmin and the rolling and adhesion of leukocytes on venules with fluorescence tracer rhodamine 6G. The therapeutical effects of SAB on TNF-α induced microcirculatory alteration were observed, with continuous intravenous injection of 5 mg/kg·h SAB starting at 20 min before or 20 min after TNF-α administration, respectively. The expressions of CD11b/CD18 and CD62L in leukocytes were measured with flow cytometry. Immunohistochemical staining was also used to detect E-selectin and ICAM-1 expression in endothelial cells.

RESULTS

Compared with craniotomy method, the bone-abrading method preserved a higher erythrocyte velocity in cerebral venules and more opening capillaries. TNF-α intervention only caused responses of vascular hyperpermeability and leukocyte rolling on venular walls, without leukocyte adhesion and other hemodynamic changes. Pre- or post-SAB treatment attenuated those responses and suppressed the enhanced expressions of CD11b/CD18 and CD62L in leukocytes and E-selectin and ICAM-1 in endothelial cells induced by TNF-α.

CONCLUSIONS

The pre- and post-applications of SAB during TNF-α stimulation could suppress adhesive molecular expression and subsequently attenuate the increase of cerebral vascular permeability and leukocyte rolling.

Adhesive Mechanisms of Histone-Induced Neutrophil-Endothelium Interactions in the Muscle Microcirculation

BACKGROUND

Extracellular histones released during cell damage have the capacity to cause tissue injury associated with increased leukocyte accumulation. However, the molecular mechanisms regulating histone-induced leukocyte recruitment remain elusive. The objective of this study was to examine the role of adhesion molecules in histone-dependent leukocyte accumulation by use of intravital microscopy of the mouse cremaster microcirculation.

METHODS

Histone 3 and TNF-α were intrascrotally administered, and anti-P-selectin, anti-P-selectin glycoprotein ligand-1 (PSGL-1), anti-membrane-activated complex-1 (Mac-1), anti-lymphocyte function antigen-1 (LFA-1) antibody and neutrophil depletion antibody were injected intravenously or intraperitoneally.

RESULTS

Intrascrotal injection of histone 3 dose-dependently increased leukocyte recruitment. Neutrophil depletion abolished intravascular and extravascular leukocytes after histone 3 challenge, suggesting that neutrophils were the dominating leukocyte subtype responding to histone stimulation. Pretreatment with an anti-P-selectin and an anti-PSGL-1 antibody abolished histone-stimulated neutrophil rolling, adhesion and emigration. When the anti-P-selectin or the anti-PSGL-1 antibody was administrated after histone 3 stimulation, neutrophil rolling was reduced, whereas the number of firmly adherent and emigrated neutrophils were unchanged, suggesting that the inhibitory effect of blocking P-selectin and PSGL-1 on neutrophil adhesion and recruitment was due to the reduction in neutrophil rolling. Moreover, pretreatment with antibodies against Mac-1 and LFA-1 had no effect of neutrophil rolling but abolished adhesion and emigration evoked by histone 3. Thus, our data demonstrate that P-selectin and PSGL-1 play an important role in histone-induced inflammatory cell recruitment by mediating neutrophil rolling as a precondition for histone-provoked firm adhesion and emigration in vivo. Moreover, we conclude that both Mac-1 and LFA-1 are critical in supporting histone-provoked firm adhesion of neutrophils to endothelial cells.

CONCLUSION

These novel findings define specific selectins and integrins as potential targets for pharmacological intervention in histone-dependent inflammatory diseases.

Quantitative Glycoproteomic Analysis Identifies Platelet-Induced Increase of Monocyte Adhesion via the Up-Regulation of Very Late Antigen 5

Physiological stimuli, such as thrombin, or pathological stimuli, such as lysophosphatidic acid (LPA), activate platelets circulating in blood. Once activated, platelets bind to monocytes via P-selectin-PSGL-1 interactions but also release the stored contents of their granules. These platelet releasates, in addition to direct platelet binding, activate monocytes and facilitate their recruitment to atherosclerotic sites. Consequently, understanding the changes platelet releasates induce in monocyte membrane proteins is critical. We studied the glyco-proteome changes of THP-1 monocytic cells affected by LPA- or thrombin-induced platelet releasates. We employed lectin affinity chromatography combined with filter aided sample preparation to achieve high glyco- and membrane protein and protein sequence coverage. Using stable isotope labeling by amino acids in cell culture, we quantified 1715 proteins, including 852 membrane and 500 glycoproteins, identifying the up-regulation of multiple proteins involved in monocyte extracellular matrix binding and transendothelial migration. Flow cytometry indicated expression changes of integrin α5, integrin β1, PECAM-1, and PSGL-1. The observed increase in monocyte adhesion to fibronectin was determined to be mediated by the up-regulation of very late antigen 5 via a P-selectin-PSGL-1 independent mechanism. This novel aspect could be validated on CD14+ human primary monocytes, highlighting the benefits of the improved enrichment method regarding high membrane protein coverage and reliable quantification.

The role of macrophage 1 antigen in polymicrobial sepsis

PURPOSE

Macrophage 1 antigen (Mac-1, CD11bCD18) is a leukocyte adhesion molecule that is involved in many functions including leukocyte recruitment, phagocytosis, and neutrophil apoptosis. The previous report of mild polymicrobial, abdominal sepsis showed that the administration of anti-CD11b-blocking antibody administration attenuated lung injury without any survival benefit. Here we tested the impact of Mac-1 deficiency in severe polymicrobial abdominal sepsis model.

METHODS

Polymicrobial sepsis was studied using cecal ligation and puncture model in wild-type (WT) or Mac-1-deficient (CD11b knockout [KO]) mice, and their outcomes were examined. Bacterial tissue load and the recruitment of neutrophils to the abdominal cavity were assessed. In vitro bacterial killing assay was performed. Serum cytokine levels were measured using multiarray. Apoptosis of spleen tissues was assessed using Western blot analysis and immunohistochemistry (cleaved caspase 3 and TUNEL staining). In addition, in vitro apoptosis assay was performed using primary splenocytes from both WT and KO mice. The recruitment of neutrophils to lung was assessed by measuring myeloperoxidase activity.

RESULTS

Macrophage 1 antigen deficiency significantly decreased survival (survival percentage WT 43.5% vs. KO 13.0%; P = 0.0038) with higher bacterial load in blood and more severe systemic inflammation. Knockout mice demonstrated higher apoptosis both in vivo and in vitro. The recruitment of neutrophils to lung was not different between WT and KO mice.

CONCLUSIONS

Macrophage 1 antigen deficiency was associated with poorer outcomes, more bacterial load, systemic inflammation, and splenic apoptosis. However, Mac-1 deficiency did not attenuate neutrophil recruitment to lung.

Extracellular MRP8/14 is a regulator of β2 integrin-dependent neutrophil slow rolling and adhesion

Myeloid-related proteins (MRPs) 8 and 14 are cytosolic proteins secreted from myeloid cells as proinflammatory mediators. Currently, the functional role of circulating extracellular MRP8/14 is unclear. Our present study identifies extracellular MRP8/14 as an autocrine player in the leukocyte adhesion cascade. We show that E-selectin–PSGL-1 interaction during neutrophil rolling triggers Mrp8/14 secretion. Released MRP8/14 in turn activates a TLR4-mediated, Rap1-GTPase-dependent pathway of rapid β2 integrin activation in neutrophils. This extracellular activation loop reduces leukocyte rolling velocity and stimulates adhesion. Thus, we identify Mrp8/14 and TLR4 as important modulators of the leukocyte recruitment cascade during inflammation in vivo.

MRP8/14 are actively secreted by myeloid cells during inflammation. Here the authors show that MRP8/14 play an important role in leukocyte recruitment to the inflammatory site, triggering an autocrine cascade that promotes neutrophil adhesion to the endothelium.

Differential effects of volatile anesthetics on leukocyte integrin macrophage-1 antigen

Macrophage-1 antigen (Mac-1, αMβ2) is a leukocyte adhesion molecule that plays a significant role in leukocyte crawling and phagocytosis, and is homologous to its sister protein leukocyte function-associated antigen-1 (LFA-1, αLβ2). The authors have previously demonstrated that volatile anesthetics isoflurane and sevoflurane bound to and inhibited LFA-1. Here, the hypothesis tested was that isoflurane and sevoflurane would inhibit Mac-1. A binding assay of Mac-1 to its ligand inter-cellular adhesion molecule-1 (ICAM-1) using V-bottom plates was established. The effect of isoflurane and sevoflurane on Mac-1 was examined using this ICAM-1 binding assay and by probing exposure of activation-sensitive epitopes. The docking program Glide was used to predict anesthetic binding site(s) on Mac-1. The functional role of this predicted binding site was then assessed by introducing point mutations in this region. Lastly, the effect of anesthetic on activating mutants was evaluated. The results indicated that isoflurane inhibited binding of Mac-1 to ICAM-1, but sevoflurane did not. Isoflurane also attenuated the exposure of the activation-sensitive epitopes. The docking simulation predicted the isoflurane binding site to be at the cavity underneath the α7 helix of the ligand binding domain (the αM I domain). Point mutants at this predicted binding site contained both activating and deactivating mutants, suggesting its functional significance. The binding of activating mutants αM-Y267A β2-WT and αM-L312A β2-WT to ICAM-1 was not affected by isoflurane, but binding of another activating mutant αM-WT β2-L132A was inhibited supporting the binding of isoflurane to this cavity. The conclusion reached from these findings was that isoflurane inhibited Mac-1 binding to ICAM-1 by binding to the cavity underneath the α7 helix of the αM I domain, but sevoflurane did not. Thus, because these common clinical volatile anesthetics demonstrated different effects on Mac-1, this implied their effects on the immune system might differ.

Deficiency of both L-selectin and ICAM-1 exacerbates imiquimod-induced psoriasis-like skin inflammation through increased infiltration of antigen presenting cells

To assess the role of inter-cellular adhesion molecule (ICAM)-1 and L-selectin in psoriasis pathogenic process, we examined the psoriasiform skin inflammation triggered by imiquimod, a toll-like receptor 7/8 agonist, in mice lacking ICAM-1 (ICAM-1(-/-)), L-selectin (L-selectin(-/-)), or both (L-selectin/ICAM-1(-/-)). Disease severity was significantly reduced in ICAM-1(-/-) and L-selectin(-/-) mice compared with wild type mice, while it was exacerbated in L-selectin/ICAM-1(-/-) mice. Cutaneous interleukin (IL)-17A, IL-23, and tumor necrosis factor (TNF)-α expression was increased in L-selectin/ICAM-1(-/-) mice compared with wild type mice. Furthermore, only L-selectin/ICAM-1(-/-) mice was refractory to anti-TNF-α antibody treatment. The skin lesion from L-selectin/ICAM-1(-/-) mice showed augmented E-selectin expression compared with ICAM-1(-/-) and L-selectin(-/-) mice, and augmented E-selectin ligand-1 expression compared with wild type mice. The current study demonstrates that although ICAM-1 and L-selectin regulate psoriasiform inflammation, deleting both L-selectin and ICAM-1 simultaneously would rather induce refractory skin inflammation, due to compensatory up-regulation of other adhesion molecules.

Leukocyte integrins: role in leukocyte recruitment and as therapeutic targets in inflammatory disease

Infection or sterile inflammation triggers site-specific attraction of leukocytes. Leukocyte recruitment is a process comprising several steps orchestrated by adhesion molecules, chemokines, cytokines and endogenous regulatory molecules. Distinct adhesive interactions between endothelial cells and leukocytes and signaling mechanisms contribute to the temporal and spatial fine-tuning of the leukocyte adhesion cascade. Central players in the leukocyte adhesion cascade include the leukocyte adhesion receptors of the β2-integrin family, such as the αLβ2 and αMβ2 integrins, or of the β1-integrin family, such as the α4β1-integrin. Given the central involvement of leukocyte recruitment in different inflammatory and autoimmune diseases, the leukocyte adhesion cascade in general, and leukocyte integrins in particular, represent key therapeutic targets. In this context, the present review focuses on the role of leukocyte integrins in the leukocyte adhesion cascade. Experimental evidence that has implicated leukocyte integrins as targets in animal models of inflammatory disorders, such as experimental autoimmune encephalomyelitis, psoriasis, inflammatory bone loss and inflammatory bowel disease as well as preclinical and clinical therapeutic applications of antibodies that target leukocyte integrins in various inflammatory disorders are presented. Finally, we review recent findings on endogenous inhibitors that modify leukocyte integrin function, which could emerge as promising therapeutic targets.

Leukocyte mimetic polysaccharide microparticles tracked in vivo on activated endothelium and in abdominal aortic aneurysm

We have developed injectable microparticles functionalized with fucoidan, in which sulfated groups mimic the anchor sites of P-selectin glycoprotein ligand-1 (PSGL-1), one of the principal receptors supporting leukocyte adhesion. These targeted microparticles were combined with a fluorescent dye and a T2(∗) magnetic resonance imaging (MRI) contrast agent, and then tracked in vivo with small animal imaging methods. Microparticles of 2.5μm were obtained by a water-in-oil emulsification combined with a cross-linking process of polysaccharide dextran, fluorescein isothiocyanate dextran, pullulan and fucoidan mixed with ultrasmall superparamagnetic particles of iron oxide. Fluorescent intravital microscopy observation revealed dynamic adsorption and a leukocyte-like behaviour of fucoidan-functionalized microparticles on a calcium ionophore induced an activated endothelial layer of a mouse mesentery vessel. We observed 20times more adherent microparticles on the activated endothelium area after the injection of functionalized microparticles compared to non-functionalized microparticles (197±11 vs. 10±2). This imaging tool was then applied to rats presenting an elastase perfusion model of abdominal aortic aneurysm (AAA) and 7.4T in vivo MRI was performed. Visual analysis of T2(∗)-weighted MR images showed a significant contrast enhancement on the inner wall of the aneurysm from 30min to 2h after the injection. Histological analysis of AAA cryosections revealed microparticles localized inside the aneurysm wall, in the same areas in which immunostaining shows P-selectin expression. The developed leukocyte mimetic imaging tool could therefore be relevant for molecular imaging of vascular diseases and for monitoring biologically active areas prone to rupture in AAA.

Emodin improves lipopolysaccharide-induced microcirculatory disturbance in rat mesentery

OBJECTIVE

Sepsis is a systemic inflammatory response syndrome. Emodin is a major ingredient of Rheum Palmatum, a Chinese herb that is widely used in China for treatment of endotoxemia-related diseases. This study intended to examine the effect of Emodin on LPS-induced rat mesenteric microcirculatory disturbance and the underlying mechanisms.

METHODS

The male Wistar rats received LPS (5 mg/kg/hr) for 90 min, with or without administration of Emodin (10 mg/kg/hr) by enema 30 min before (pre-treatment) or after (post-treatment) LPS infusion, and the dynamics of mesenteric microcirculation were determined by inverted intravital microscopy. Expression of adhesion molecules and TLR4, NF-κB p65, ICAM-1, MPO, and AP-1 in mesentery tissue was evaluated by flow cytometry and Western-blot, respectively.

RESULTS

Pre or post-treatment with Emodin significantly ameliorated LPS-induced leukocyte emigration, reactive oxygen species production and albumin leakage, and the expression of TLR4, NF-κB p65, ICAM-1, MPO and AP-1 in mesentery.

CONCLUSIONS

These results demonstrate the beneficial role of Emodin in attenuating the LPS-induced microcirculatory disturbance, and support the use of Emodin for patients with endotoxemia.

Decreased plasma levels of soluble CD18 link leukocyte infiltration with disease activity in spondyloarthritis

INTRODUCTION

Spondyloarthritis (SpA) comprises a group of diseases often associated with HLA-B27 and characterized by inflammation of the entheses and joints of the axial skeleton. The inflammatory process in SpA is presumably driven by innate immune cells but is still poorly understood. Thus, new tools for monitoring and treating inflammation are needed. The family of CD18 integrins is pivotal in guiding leukocytes to sites of inflammation, and CD18 hypomorphic mice develop a disease resembling SpA. Previously, we demonstrated that altered soluble CD18 (sCD18) complexes in the blood and synovial fluid of patients with arthritis have anti-inflammatory functions. Here, we study the mechanisms for these alterations and their association with SpA disease activity.

METHODS

Plasma levels of sCD18 in a study population with 84 patients with SpA and matched healthy controls were analyzed with a time-resolved immunoflourometric assay (TRIFMA). Binding of sCD18 to endothelial cells and fibroblast-like synoviocytes (FLSs) was studied with confocal microscopy. Shedding of CD18 from peripheral blood mononuclear cells (PBMCs) was studied with flow cytometry and TRIFMA.

RESULTS

Plasma levels of sCD18 were decreased in patients with SpA compared with healthy volunteers (P <0.001), and the lowest levels were in the HLA-B27-positive subgroup (P <0.05). In a multiple regression model, the sCD18 levels exhibited an inverse correlation with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (P <0.05), the level of morning stiffness (P <0.05), the Bath Ankylosing Spondilitis Metrology Index (P <0.05), the physician global assessment score (P <0.01), and the sacroiliac magnetic resonance imaging activity score (P <0.05). The mechanisms for these changes could be simulated in vitro. First, sCD18 in plasma adhered to inflammation-induced intercellular adhesion molecule 1 (ICAM-1) on endothelial cells and FLS, indicating increased consumption. Second, CD18 shedding from SpA PBMCs correlated inversely with the BASDAI (P <0.05), suggesting insufficient generation. CD18 was shed primarily from intermediate CD14⁺⁺ CD16⁺ monocytes, supporting the view that alterations in innate immunity can regulate the inflammatory processes in SpA.

CONCLUSIONS

Taken together, the failure of patients with SpA to maintain adequate sCD18 levels may reflect insufficient CD18 shedding from monocytes to counterbalance the capture of sCD18 complexes to inflammation-induced ICAM-1. This could increase the availability of ICAM-1 molecules on the endothelium and in the synovium, facilitating leukocyte migration to the entheses and joints and aggregating disease activity.

New paradigms in inflammatory signaling in vascular endothelial cells

Inflammation is a basic cellular process in innate and adaptive immunity. Vascular endothelial cells play an important role in the initiation, amplification, and resolution of the inflammatory response. Deregulated inflammatory response is implicated in a variety of cardiovascular diseases such as atherosclerosis, obesity, diabetes, and hypertension. Recent studies have made significant progresses in the understanding of the complex molecular pathways that mediate the pro- and anti-inflammatory signaling in endothelial cells (ECs). Specifically, a number of macromolecular complexes termed as signalosomes have been identified to integrate the proinflammatory signaling from the membrane receptors to key transcription factors such as nuclear factor-κB (NF-κB). Inflammasomes are associated with the pattern-recognition receptors such as Toll-like receptors (TLRs), nucleotide-binding oligomerization-domain (NOD)-like receptors (NLRs) to mediate innate immunity responses. Emerging evidence has also revealed that noncoding microRNAs constitute a new class of intra- and intercellular signaling molecules to modulate inflammation in ECs. Thus this article will briefly summarize these new mechanisms with a special emphasis in the context of cardiovascular diseases.

Distinct binding affinities of Mac-1 and LFA-1 in neutrophil activation

Macrophage-1 Ag (Mac-1) and lymphocyte function-associated Ag-1 (LFA-1), two β2 integrins expressed on neutrophils (PMNs), mediate PMN recruitment cascade by binding to intercellular adhesive molecule 1. Distinct functions of LFA-1-initiating PMN slow rolling and firm adhesion but Mac-1-mediating cell crawling are assumed to be governed by the differences in their binding affinities and kinetic rates. In this study, we applied an adhesion frequency approach to compare their kinetics in the quiescent and activated states using three molecular systems, constitutively expressed receptors on PMNs, wild-type and high-affinity (HA) full-length constructs transfected on 293T cells, and wild-type and HA recombinant extracellular constructs. Data indicate that the difference in binding affinity between Mac-1 and LFA-1 is on-rate dominated with slightly or moderately varied off-rate. This finding was further confirmed when both β2 integrins were activated by chemokines (fMLF or IL-8), divalent cations (Mg(2+) or Mn(2+)), or disulfide bond lockage on an HA state. Structural analyses reveal that such the kinetics difference is likely attributed to the distinct conformations at the interface of Mac-1 or LFA-1 and intercellular adhesive molecule 1. This work furthers the understandings in the kinetic differences between Mac-1 and LFA-1 and in their biological correlations with molecular activation and structural bases.

Extracellular protein disulfide isomerase regulates ligand-binding activity of αMβ2 integrin and neutrophil recruitment during vascular inflammation

β2 integrins play a crucial role during neutrophil recruitment into the site of vascular inflammation. However, it remains unknown how ligand-binding activity of the integrin is regulated. Using fluorescence intravital microscopy in mice generated by crossing protein disulfide isomerase (PDI) floxed mice with lysozyme-Cre transgenic mice, we demonstrate that neutrophil PDI is required for neutrophil adhesion and crawling during tumor necrosis factor-α-induced vascular inflammation in vivo. Rescue experiments show that the isomerase activity of extracellular PDI is critical for its regulatory effect on neutrophil recruitment. Studies with blocking anti-PDI antibodies and αLβ2 or αMβ2 null mice suggest that extracellular PDI regulates αMβ2 integrin-mediated adhesive function of neutrophils during vascular inflammation. Consistently, we show that neutrophil surface PDI is important for αMβ2 integrin-mediated adhesion of human neutrophils under shear and static conditions and for binding of soluble fibrinogen to activated αMβ2 integrin. Confocal microscopy and biochemical studies reveal that neutrophil surface PDI interacts with αMβ2 integrin in lipid rafts of stimulated neutrophils and regulates αMβ2 integrin clustering, presumably by changing the redox state of the integrin. Thus, our results provide the first evidence that extracellular PDI could be a novel therapeutic target for preventing and treating inappropriate neutrophil sequestration.

Sepsis-induced leukocyte adhesion in the pulmonary microvasculature in vivo is mediated by CD11a and CD11b

Leukocyte accumulation is a rate-limiting step in inflammatory lung injury. The aim of this study was to define the role of CD11a/CD18 and CD11b/CD18 in sepsis-induced leukocyte rolling and adhesion in lung arterioles, capillaries and venules in male C57BL/6 mice using intravital fluorescence microscopy. Cecal ligation and puncture (CLP) markedly increased leukocyte rolling in arterioles and venules but not in capillaries in the lung. Immunoneutralization of CD11a, but not CD11b, decreased CLP-provoked leukocyte rolling in lung arterioles. Inhibition of CD11a or CD11b abolished CLP-induced arteriolar and venular leukocyte adhesion. Immunoneutralization of CD11a and CD11b reduced sepsis-induced leukocyte sequestration in pulmonary capillaries. Moreover, blocking CD11a or CD11b function improved microvascular blood flow in the lung of CLP animals. Considered together, our novel findings show that CD11a and CD11b mediate leukocyte adhesion in both arterioles and venules as well as trapping in capillaries in the lung. In addition, our data demonstrate that CD11a but not CD11b supports leukocyte rolling in pulmonary arterioles. Thus, these findings elucidate the molecular mechanisms behind leukocyte-endothelium interactions in the lung during systemic inflammation.

Multiphoton imaging reveals a new leukocyte recruitment paradigm in the glomerulus

In contrast with many capillary beds, the glomerulus readily supports leukocyte recruitment. However, little is known regarding the actions of leukocytes following their recruitment to glomeruli. We used multiphoton confocal microscopy to examine leukocyte behavior in the glomerular microvasculature. In normal glomeruli, neutrophils and monocytes were retained in capillaries for several minutes, remaining static or migrating intravascularly. Induction of glomerular inflammation resulted in an increase in the duration of retention of static and migratory leukocytes. In response to immune complex deposition, both static and migratory neutrophils generated oxidants in inflamed glomeruli via a Mac-1-dependent mechanism. Our results describe a new paradigm for glomerular inflammation, suggesting that the major effect of acute inflammation is to increase the duration of leukocyte retention in the glomerulus. Moreover, these findings describe a previously unknown form of multicellular intravascular patrolling that involves both monocytes and neutrophils, which may underlie the susceptibility of the glomerulus to inflammation.

Novel α2β1 integrin inhibitors reveal that integrin binding to collagen under shear stress conditions does not require receptor preactivation

The interaction between α2β1 integrin (GPIa/IIa, VLA-2) and vascular collagen is one of the initiating events in thrombus formation. Here, we describe two structurally similar sulfonamide derivatives, BTT-3033 and BTT-3034, and show that, under static conditions, they have an almost identical effect on α2-expressing CHO cell adhesion to collagen I, but only BTT-3033 blocks platelet attachment under flow (90 dynes/cm(2)). Differential scanning fluorimetry showed that both molecules bind to the α2I domain of the recombinant α2 subunit. To further study integrin binding mechanism(s) of the two sulfonamides, we created an α2 Y285F mutant containing a substitution near the metal ion-dependent adhesion site motif in the α2I domain. The action of BTT-3033, unlike that of BTT-3034, was dependent on Tyr-285. In static conditions BTT-3034, but not BTT-3033, inhibited collagen binding by an α2 variant carrying a conformationally activating E318W mutation. Conversely, in under flow conditions (90 dynes/cm(2)) BTT-3033, but not BTT-3034, inhibited collagen binding by an α2 variant expressing E336A loss-of-function mutation. Thus, the binding sites for BTT-3033 and BTT-3034 are differentially available in distinct integrin conformations. Therefore, these sulfonamides can be used to study the biological role of different functional stages of α2β1. Furthermore, only the inhibitor that recognized the non-activated conformation of α2β1 integrin under shear stress conditions effectively blocked platelet adhesion, suggesting that the initial interaction between integrin and collagen takes place prior to receptor activation.