Arrest chemokines

GPI Is a Prognostic Biomarker and Correlates With Immune Infiltrates in Lung Adenocarcinoma

Background

Glucose-6-phosphate isomerase (GPI) plays an important role in glycolysis and gluconeogenesis. However, the role of GPI in lung adenocarcinoma (LUAD) remains unclear.

Methods

All original data were downloaded from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases and integrated via R 3.2.2. GPI expression was explored with TCGA, GEO, and Oncomine databases. Immunohistochemistry staining was used to analyze GPI expression in clinical specimens. The correlations between GPI and cancer immune characteristics were analyzed via the TIMER and TISIDB databases. GPI-specific siRNAs were used to verify the role of GPI expression on cell proliferation and cell cycle distribution.

Results

In general, GPI is predominantly overexpressed and has reference value in the diagnosis and prognostic estimation of LUAD. Upregulated GPI was associated with poorer overall survival, clinical stage, N stage, and primary therapy outcome in LUAD. Mechanistically, we identified a hub gene that included a total of 56 GPI-related genes, which were tightly associated with the cell cycle pathway in LUAD patients. Knockdown of GPI induced cell proliferation inhibition and cell cycle arrest. GPI expression was positively correlated with infiltrating levels of Th2 cells and regulatory T cells (Tregs); in contrast, GPI expression was negatively correlated with infiltrating levels of CD8⁺ T cells, central memory T cells, dendritic cells, macrophages, mast cells, and eosinophils. GPI was negatively correlated with the expression of immunostimulators, such as CD40L, IL6R, and TMEM173, in LUAD.

Conclusion

GPI may play an important role in the cell cycle and can be used as a prognostic biomarker for determining the prognosis and immune infiltration in LUAD.

CCR7 signalosomes are preassembled on tips of lymphocyte microvilli in proximity to LFA-1

Leukocyte microvilli are elastic actin-rich projections implicated in rapid sensing and penetration across glycocalyx barriers. Microvilli are critical for the capture and arrest of flowing lymphocytes by high endothelial venules, the main lymph node portal vessels. T lymphocyte arrest involves subsecond activation of the integrin LFA-1 by the G-protein-coupled receptor CCR7 and its endothelial-displayed ligands, the chemokines CCL21 and CCL19. The topographical distribution of CCR7 and of LFA-1 in relation to lymphocyte microvilli has never been elucidated. We applied the recently developed microvillar cartography imaging technique to determine the topographical distribution of CCR7 and LFA-1 with respect to microvilli on peripheral blood T lymphocytes. We found that CCR7 is clustered on the tips of T cell microvilli. The vast majority of LFA-1 molecules were found on the cell body, likely assembled in macroclusters, but a subset of LFA-1, 5% of the total, were found scattered within 20 nm from the CCR7 clusters, implicating these LFA-1 molecules as targets for inside-out activation signals transmitted within a fraction of a second by chemokine-bound CCR7. Indeed, RhoA, the key GTPase involved in rapid LFA-1 affinity triggering by CCR7, was also found to be clustered near CCR7. In addition, we observed that the tyrosine kinase JAK2 controls CCR7-mediated LFA-1 affinity triggering and is also highly enriched on tips of microvilli. We propose that tips of lymphocyte microvilli are novel signalosomes for subsecond CCR7-mediated inside-out signaling to neighboring LFA-1 molecules, a critical checkpoint in LFA-1-mediated lymphocyte arrest on high endothelial venules.

Metabolic and behavioral features of acute hyperpurinergia and the maternal immune activation mouse model of autism spectrum disorder

Since 2012, studies in mice, rats, and humans have suggested that abnormalities in purinergic signaling may be a final common pathway for many genetic and environmental causes of autism spectrum disorder (ASD). The current study in mice was conducted to characterize the bioenergetic, metabolomic, breathomic, and behavioral features of acute hyperpurinergia triggered by systemic injection of the purinergic agonist and danger signal, extracellular ATP (eATP). Responses were studied in C57BL/6J mice in the maternal immune activation (MIA) model and controls. Basal metabolic rates and locomotor activity were measured in CLAMS cages. Plasma metabolomics measured 401 metabolites. Breathomics measured 98 volatile organic compounds. Intraperitoneal eATP dropped basal metabolic rate measured by whole body oxygen consumption by 74% ± 6% (mean ± SEM) and rectal temperature by 6.2˚ ± 0.3˚C in 30 minutes. Over 200 metabolites from 37 different biochemical pathways where changed. Breathomics showed an increase in exhaled carbon monoxide, dimethylsulfide, and isoprene. Metabolomics revealed an acute increase in lactate, citrate, purines, urea, dopamine, eicosanoids, microbiome metabolites, oxidized glutathione, thiamine, niacinamide, and pyridoxic acid, and decreased folate-methylation-1-carbon intermediates, amino acids, short and medium chain acyl-carnitines, phospholipids, ceramides, sphingomyelins, cholesterol, bile acids, and vitamin D similar to some children with ASD. MIA animals were hypersensitive to postnatal exposure to eATP or poly(IC), which produced a rebound increase in body temperature that lasted several weeks before returning to baseline. Acute hyperpurinergia produced metabolic and behavioral changes in mice. The behaviors and metabolic changes produced by ATP injection were associated with mitochondrial functional changes that were profound but reversible.

The Multitasking Potential of Alarmins and Atypical Chemokines

When the human genome was sequenced, it came as a surprise that it contains “only” 21,306 protein-coding genes. However, complexity and diversity are multiplied by alternative splicing, non-protein-coding transcripts, or post-translational modifications (PTMs) on proteome level. Here, we discuss how the multi-tasking potential of proteins can substantially enhance the complexity of the proteome further, while at the same time offering mechanisms for the fine-regulation of cell responses. Discoveries over the past two decades have led to the identification of “surprising” and previously unrecognized functionalities of long known cytokines, inflammatory mediators, and intracellular proteins that have established novel molecular networks in physiology, inflammation, and cardiovascular disease. In this mini-review, we focus on alarmins and atypical chemokines such as high-mobility group box protein-1 (HMGB-1) and macrophage migration-inhibitory factor (MIF)-type proteins that are prototypical examples of these classes, featuring a remarkable multitasking potential that allows for an elaborate fine-tuning of molecular networks in the extra- and intracellular space that may eventually give rise to novel “task”-based precision medicine intervention strategies.

Spatio-temporal regulation of concurrent developmental processes by generic signaling downstream of chemokine receptors

Chemokines are secreted proteins that regulate a range of processes in eukaryotic organisms. Interestingly, different chemokine receptors control distinct biological processes, and the same receptor can direct different cellular responses, but the basis for this phenomenon is not known. To understand this property of chemokine signaling, we examined the function of the chemokine receptors Cxcr4a, Cxcr4b, Ccr7, Ccr9 in the context of diverse processes in embryonic development in zebrafish. Our results reveal that the specific response to chemokine signaling is dictated by cell-type-specific chemokine receptor signal interpretation modules (CRIM) rather than by chemokine-receptor-specific signals. Thus, a generic signal provided by different receptors leads to discrete responses that depend on the specific identity of the cell that receives the signal. We present the implications of employing generic signals in different contexts such as gastrulation, axis specification and single-cell migration.

Fibroblast growth factor 23 actions in inflammation: a key factor in CKD outcomes

During chronic kidney disease (CKD), bone mineral metabolism is disturbed owing in part to the endogenous hormone fibroblast growth factor 23 (FGF23). Elevated FGF23 levels are seen in CKD patients. Current research has demonstrated that FGF23 directly modulates the immune response and host defense to bacterial infections. FGF23 also impairs the activation and recruitment of neutrophils, which are the main immune effector cells required for host defense against bacterial infections. In addition, while FGF23 levels reduce leukocyte recruitment and functions, inflammatory conditions may also-in a reverse fashion-contribute to elevated FGF23 levels in the circulation. In this context, altered hypoxia inducible factor 1α signaling and iron metabolism may contribute to intact FGF23 (iFGF23) production. This review examines evidence on the role of FGF23 in inflammation, immune cell function and recruitment as well as the regulation of FGF23 during inflammation and the clinical implications of this process for the immune system in individuals with CKD. Clinical observations and laboratory investigations indicate an important role of FGF23 in directly modulating leukocyte activation and recruitment behavior with consequences on host defense against bacterial infections. This novel observation may in part explain the increased infectious risk among patients with CKD. However, studies of FGF23 neutralization also revealed increased mortality after sustained administration over several weeks in rats. Thus, therapeutic interventions targeting FGF23 must be carefully evaluated.

Exercise Inhibits the Effects of Smoke-Induced COPD Involving Modulation of STAT3

PURPOSE

Evaluate the participation of STAT3 in the effects of aerobic exercise (AE) in a model of smoke-induced COPD.

METHODS

C57Bl/6 male mice were divided into control, Exe, COPD, and COPD+Exe groups. Smoke were administered during 90 days. Treadmill aerobic training begun on day 61 until day 90. Pulmonary inflammation, systemic inflammation, the level of lung emphysema, and the airway remodeling were evaluated. Analysis of integral and phosphorylated expression of STAT3 by airway epithelial cells, peribronchial leukocytes, and parenchymal leukocytes was performed.

RESULTS

AE inhibited smoke-induced accumulation of total cells (p < 0.001), lymphocytes (p < 0.001), and neutrophils (p < 0.001) in BAL, as well as BAL levels of IL-1β (p < 0.001), CXCL1 (p < 0.001), IL-17 (p < 0.001), and TNF-α (p < 0.05), while increased the levels of IL-10 (p < 0.001). AE also inhibited smoke-induced increases in total leukocytes (p < 0.001), neutrophils (p < 0.05), lymphocytes (p < 0.001), and monocytes (p < 0.01) in blood, as well as serum levels of IL-1β (p < 0.01), CXCL1 (p < 0.01), IL-17 (p < 0.05), and TNF-α (p < 0.01), while increased the levels of IL-10 (p < 0.001). AE reduced smoke-induced emphysema (p < 0.001) and collagen fiber accumulation in the airways (p < 0.001). AE reduced smoke-induced STAT3 and phospho-STAT3 expression in airway epithelial cells (p < 0.001), peribronchial leukocytes (p < 0.001), and parenchymal leukocytes (p < 0.001).

CONCLUSIONS

AE reduces smoke-induced COPD phenotype involving STAT3.

How neutrophils resist shear stress at blood vessel walls: molecular mechanisms, subcellular structures, and cell-cell interactions

Neutrophils are the first cells arriving at sites of tissue injury or infection to combat invading pathogens. Successful neutrophil recruitment to sites of inflammation highly depends on specific molecular mechanisms, fine-tuning the received information into signaling pathways and converting them into well-described recruitment steps. This review highlights the impact of vascular flow conditions on neutrophil recruitment and the multitude of mechanisms developed to enable this sophisticated process under wall shear stress conditions. The recruitment process underlies a complex interplay between adhesion and signaling molecules, as well as chemokines, in which neutrophils developed specific mechanisms to travel to sites of lesion in low and high shear stress conditions. Rolling, as the first step in the recruitment process, highly depends on endothelial selectins and their ligands on neutrophils, inducting of intracellular signaling and subsequently activating β₂ integrins, enabling adhesion and postadhesion events. In addition, subcellular structures, such as microvilli, tethers, and slings allow the cell to arrest, even under high wall shear stress. Thereby, microvilli that are pulled out from the cell body form tethers that develop into slings upon their detachment from the substrate. In addition to the above-described primary capture, secondary capture of neutrophils via neutrophil-neutrophil or neutrophil-platelet interaction promotes the process of neutrophil recruitment to sites of lesion. Thus, precise mechanisms based on a complex molecular interplay, subcellular structures, and cell-cell interactions turn the delicate process of neutrophil trafficking during flow into a robust response allowing effective neutrophil accumulation at sites of injury.

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.

FGF23 signaling impairs neutrophil recruitment and host defense during CKD

Chronic kidney disease (CKD) has been associated with impaired host response and increased susceptibility to infections. Leukocyte recruitment during inflammation must be tightly regulated to protect the host against pathogens. FGF23 levels are increased in blood during CKD, and levels of this hormone have been associated with a variety of adverse effects in CKD patients. Here, we have shown that CKD impairs leukocyte recruitment into inflamed tissue and host defense in mice and humans. FGF23 neutralization during CKD in murine models restored leukocyte recruitment and host defense. Intravital microscopy of animals with chronic kidney failure showed that FGF23 inhibits chemokine-activated leukocyte arrest on the endothelium, and downregulation of FGF receptor 2 (FGFR2) on PMNs rescued host defense in these mice. In vitro, FGF23 inhibited PMN adhesion, arrest under flow, and transendothelial migration. Mechanistically, FGF23 binding to FGFR2 counteracted selectin- and chemokine-triggered β2 integrin activation on PMNs by activating protein kinase A (PKA) and inhibiting activation of the small GTPase Rap1. Moreover, knockdown of PKA abolished the inhibitory effect of FGF23 on integrin activation. Together, our data reveal that FGF23 acts directly on PMNs and dampens host defense by direct interference with chemokine signaling and integrin activation.

Phylogeny and evolution of plant macrophage migration inhibitory factor/D-dopachrome tautomerase-like proteins

Background

The human (Homo sapiens) chemokine-like protein macrophage migration inhibitory factor (HsMIF) is a pivotal mediator of inflammatory, infectious and immune diseases including septic shock, colitis, malaria, rheumatoid arthritis, and atherosclerosis, as well as tumorigenesis. HsMIF has been found to exhibit several sequential and three-dimensional sequence motifs that in addition to its receptor binding sites include catalytic sites for oxidoreductase and tautomerase activity, which provide this 12.5 kDa protein with a remarkable functional complexity. A human MIF paralog, D-dopachrome tautomerase (HsDDT), has been identified, but its physiological relevance is incompletely understood. MIF/DDT-like proteins have been described in animals, protists and bacteria. Although based on sequence data banks the presence of MIF/DDT-like proteins has also been recognized in the model plant species Arabidopsis thaliana, details on these plant proteins have not been reported.

Results

To broaden the understanding of the biological role of these proteins across kingdoms we performed a comprehensive in silico analysis of plant MIF/DDT-like (MDL) genes/proteins. We found that the A. thaliana genome harbors three MDL genes, of which two are chiefly constitutively expressed in aerial plant organs, while the third gene shows stress-inducible transcript accumulation. The product of the latter gene likely localizes to peroxisomes. Structure prediction suggests that all three Arabidopsis proteins resemble the secondary and tertiary structure of human MIF. MIF-like proteins are found in all species across the plant kingdom, with an increasing family complexity towards evolutionarily advanced plant taxa. Plant MDL proteins are predicted to lack oxidoreductase activity, but possibly share tautomerase activity with human MIF/DDT.

Conclusions

Peroxisome localization seems to be a specific feature of a subset of MIF/DDT orthologs found in dicotyledonous plant species, which together with its stress-inducible gene expression might point to convergent evolution in higher plants and vertebrates towards neofunctionalization of MIF/MDL proteins in stress response pathways including innate immunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0337-x) contains supplementary material, which is available to authorized users.

Leukocyte traffic blockade as a therapeutic strategy in inflammatory bowel disease

Dysregulated recruitment of leukocytes into the intestine is a characteristic feature of IBD. Several families of molecules regulate the influx of these cells into sites of inflammation within the gastrointestinal tract. Pharmacological blockade of interactions between molecules that mediate the formation of stable bonds (integrins) and their endothelial ligands has already shown clinical efficacy. Antibodies that target participant molecules have been approved by the US Federal Drug Administration for use in Crohn's, multiple sclerosis (MS) (i.e. natalizumab) and psoriasis (i.e. efalizumab). A more recent additional family of drugs, which might also interfere with lymphocyte traffic (i.e. sphingosine-1- phosphate receptor agonists: fingolimod) is in clinical use for MS and just recently entered the clinical trial stage for ulcerative colitis. In the present review we discuss basic aspects of clinically relevant molecules and compile the clinical studies that support the targeting of specific steps of the leukocyte adhesion cascade for therapeutic purposes in IBD.

Increased serum adipokines implicate chronic inflammation in the pathogenesis of overactive bladder syndrome refractory to antimuscarinic therapy

OBJECTIVES

Recent studies have shown that chronic inflammation is involved in overactive bladder (OAB) syndrome. OAB could be a subtype of neurogenic inflammation. This pilot study investigated serum adipokine levels in patients with OAB refractory to antimuscarinic therapy.

METHODS

Thirty consecutive patients with OAB-dry (n = 16) or OAB-wet (n = 14) refractory to previous antimuscarinic treatment were prospectively enrolled in this study, a group of 26 normal subjects without lower urinary tract symptoms served as controls. Concentrations of serum C-reactive protein (CRP), nerve growth factor (NGF), and adipokines including interleukins ([IL], IL-1β, IL-6, IL-8), tumor necrosis factor (TNF)-α, monocyte chemotactic protein (MCP)-1, insulin, and leptin were quantified using a bead-based human serum adipokine panel B kit. Data were analyzed using the LX 200 platform. Patients were further classified as having dry or wet OAB and having medical diseases or not. The serum CRP, NGF, and adipokine levels were compared between OAB patients and the controls, and between OAB subgroups.

RESULTS

The serum concentrations of CRP, NGF, IL-1β, IL-6, IL-8, and TNF-α in OAB-dry and OAB-wet patients were significantly higher than among the controls. There was no significant difference in adipokine levels between OAB-dry and OAB-wet, or between OAB patients with and without medical diseases. Serum CRP and NGF levels were significantly higher only in OAB-wet or OAB patients with medical diseases than among controls. The MCP-1 levels, on the other hand, were significantly higher in OAB-dry or OAB patients with disease, than the controls.

CONCLUSIONS

Both OAB-dry and OAB-wet patients showed increased serum CRP, NGF, and adipokine levels compared with the controls, suggesting chronic inflammation of the bladder involving both peripheral and central mechanisms in all OAB patients refractory to antimuscarinic therapy. The increased serum adipokine levels were not relevant to medical diseases.

Distinct functions of chemokine receptor axes in the atherogenic mobilization and recruitment of classical monocytes

We used a novel approach of cytostatically induced leucocyte depletion and subsequent reconstitution with leucocytes deprived of classical (inflammatory/Gr1^hi) or non-classical (resident/Gr1^lo) monocytes to dissect their differential role in atheroprogression under high-fat diet (HFD). Apolipoprotein E-deficient (Apoe^−/−) mice lacking classical but not non-classical monocytes displayed reduced lesion size and macrophage and apoptotic cell content. Conversely, HFD induced a selective expansion of classical monocytes in blood and bone marrow. Increased CXCL1 levels accompanied by higher expression of its receptor CXCR2 on classical monocytes and inhibition of monocytosis by CXCL1-neutralization indicated a preferential role for the CXCL1/CXCR2 axis in mobilizing classical monocytes during hypercholesterolemia. Studies correlating circulating and lesional classical monocytes in gene-deficient Apoe^−/− mice, adoptive transfer of gene-deficient cells and pharmacological modulation during intravital microscopy of the carotid artery revealed a crucial function of CCR1 and CCR5 but not CCR2 or CX₃CR1 in classical monocyte recruitment to atherosclerotic vessels. Collectively, these data establish the impact of classical monocytes on atheroprogression, identify a sequential role of CXCL1 in their mobilization and CCR1/CCR5 in their recruitment.

Neutrophil-derived cathelicidin promotes adhesion of classical monocytes

RATIONALE

The leukocyte response in acute inflammation is characterized by an initial recruitment of neutrophils preceding a second wave of monocytes. Neutrophil-derived granule proteins were suggested to hold an important role in this cellular switch. The exact mechanisms by which neutrophils mediate these processes are only partially understood.

OBJECTIVE

To investigate the role of neutrophils and their granule contents in the adhesion of monocyte subpopulations in acute inflammation.

METHODS AND RESULTS

Here, we show that neutrophil-derived cathelicidins (human: LL37, mouse: CRAMP) induce adhesion of classical monocytes but not of nonclassical monocytes in the mouse cremaster muscle and in in vitro flow chamber assays. CRAMP is released from emigrated neutrophils and then transported across the endothelium, where it is presented to rolling leukocytes. Endothelial-bound cathelicidin activates formyl-peptide receptor 2 on classical monocytes, resulting in monocytic β1- and β2-integrin conformational change toward an extended, active conformation that allows for adhesion to their respective ligands, vascular cell adhesion molecule 1 and intercellular adhesion molecule 1.

CONCLUSIONS

These data elucidate a novel mechanism of neutrophil-mediated monocyte recruitment, which could be targeted in conditions where recruitment of classical monocytes plays an unfavorable role.

Tissue-specific neutrophil recruitment into the lung, liver, and kidney

The recruitment of immune cells is crucial for the development of inflammatory processes. The classical recruitment cascade of neutrophils into inflamed tissues is well understood and consists of capturing, rolling, slow rolling, arrest, postadhesion strengthening, crawling, and transmigration. While this commonly agreed paradigm might be applicable to most peripheral tissues, recruitment mechanisms may substantially vary in different organs such as the lung, liver, and kidney. These organs are highly specialized tissues with unique cell populations and structural organization, which enables them to fulfill their individual functions. The published research over the last decade has shed some light on organ-specific mechanisms of neutrophil recruitment and helped to generate a deeper understanding of the specific recruitment mechanisms involved in this process. The aim of this review is to highlight current concepts of tissue-specific differences and similarities of neutrophil recruitment into the lung, liver, and kidney.

Cardiopulmonary bypass during cardiac surgery modulates systemic inflammation by affecting different steps of the leukocyte recruitment cascade

Background

It is known that the use of a cardiopulmonary bypass (CPB) during cardiac surgery leads to leukocyte activation and may, among other causes, induce organ dysfunction due to increased leukocyte recruitment into different organs. Leukocyte extravasation occurs in a cascade-like fashion, including capturing, rolling, adhesion, and transmigration. However, the molecular mechanisms of increased leukocyte recruitment caused by CPB are not known. This clinical study was undertaken in order to investigate which steps of the leukocyte recruitment cascade are affected by the systemic inflammation during CPB.

Methods

We investigated the effects of CPB on the different steps of the leukocyte recruitment cascade in whole blood from healthy volunteers (n = 9) and patients undergoing cardiac surgery with the use of cardiopulmonary bypass (n = 7) or in off-pump coronary artery bypass-technique (OPCAB, n = 9) by using flow chamber experiments, transmigration assays, and biochemical analysis.

Results

CPB abrogated selectin-induced slow leukocyte rolling on E-selectin/ICAM-1 and P-selectin/ICAM-1. In contrast, chemokine-induced arrest and transmigration was significantly increased by CPB. Mechanistically, the abolishment of slow leukocyte rolling was due to disturbances in intracellular signaling with reduced phosphorylation of phospholipase C (PLC) γ2, Akt, and p38 MAP kinase. Furthermore, CPB induced an elevated transmigration which was caused by upregulation of Mac-1 on neutrophils.

Conclusion

These data suggest that CPB abrogates selectin-mediated slow leukocyte rolling by disturbing intracellular signaling, but that the clinically observed increased leukocyte recruitment caused by CPB is due to increased chemokine-induced arrest and transmigration. A better understanding of the underlying molecular mechanisms causing systemic inflammation after CPB may aid in the development of new therapeutic approaches.

Immune receptors involved in Streptococcus suis recognition by dendritic cells

Streptococcus suis is an important swine pathogen and an emerging zoonotic agent of septicemia and meningitis. Knowledge on host immune responses towards S. suis, and strategies used by this pathogen for subversion of these responses is scarce. The objective of this study was to identify the immune receptors involved in S. suis recognition by dendritic cells (DCs). Production of cytokines and expression of co-stimulatory molecules by DCs were shown to strongly rely on MyD88-dependent signaling pathways, suggesting that DCs recognize S. suis and become activated mostly through Toll-like receptor (TLR) signaling. Supporting this fact, TLR2^−/− DCs were severely impaired in the release of several cytokines and the surface expression of CD86 and MHC-II. The release of IL-12p70 and CXC10, and the expression of CD40 were found to depend on signaling by both TLR2 and TLR9. The release of IL-23 and CXCL1 were partially dependent on NOD2. Finally, despite the fact that MyD88 signaling was crucial for DC activation and maturation, MyD88-dependent pathways were not implicated in S. suis internalization by DCs. This first study on receptors involved in DC activation by S. suis suggests a major involvement of MyD88 signaling pathways, mainly (but not exclusively) through TLR2. A multimodal recognition involving a combination of different receptors seems essential for DC effective response to S. suis.

Neutrophil arrest by LFA-1 activation

Lymphocyte function-associated antigen-1 (LFA-1) is a heterodimeric integrin consisting of α_L (gene name, Itgal) and β₂ (gene name, Itgb2) subunits expressed in all leukocytes. LFA-1 is essential for neutrophil recruitment to inflamed tissue. Activation of LFA-1 by chemokines allows neutrophils and other leukocytes to undergo arrest, resulting in firm adhesion on endothelia expressing intercellular adhesion molecules (ICAMs). In mice, CXCR2 is the primary chemokine receptor involved in triggering neutrophil arrest, and it does so through “inside-out” activation of LFA-1. CXCR2 signaling induces changes in LFA-1 conformation that are coupled to affinity upregulation of the ligand-binding headpiece (extended with open I domain). Unlike naïve lymphocytes, engagement of P-selectin glycoprotein ligand-1 (PSGL-1) on neutrophils stimulates a slow rolling behavior that is mediated by LFA-1 in a distinct activation state (extended with closed I domain). How inside-out signaling cascades regulate the structure and function of LFA-1 is being studied using flow chambers, intravital microscopy, and flow cytometry for ligand and reporter antibody binding. Here, we review how LFA-1 activation is regulated by cellular signaling and ligand binding. Two FERM domain-containing proteins, talin-1 and Kindlin-3, are critical integrin co-activators and have distinct roles in the induction of LFA-1 conformational rearrangements. This review integrates these new results into existing models of LFA-1 activation.

Rap1a activation by CalDAG-GEFI and p38 MAPK is involved in E-selectin-dependent slow leukocyte rolling

Rolling leukocytes are exposed to different adhesion molecules and chemokines. Neutrophils rolling on E-selectin induce integrin αLβ2-mediated slow rolling on ICAM-1 by activating a phospholipase C (PLC)γ2-dependent and a separate PI3Kγ-dependent pathway. E-selectin-signaling cooperates with chemokine signaling to recruit neutrophils into inflamed tissues. However, the distal signaling pathway linking PLCγ2 (Plcg2) to αLβ2-activation is unknown. To identify this pathway, we used different Tat-fusion-mutants and gene-deficient mice in intravital microscopy, autoperfused flow chamber, peritonitis, and biochemical studies. We found that the small GTPase Rap1 is activated following E-selectin engagement and that blocking Rap1a in Pik3cg-/- mice by a dominant-negative Tat-fusion mutant completely abolished E-selectin-mediated slow rolling. We identified CalDAG-GEFI (Rasgrp2) and p38 MAPK as key signaling intermediates between PLCγ2 and Rap1a. Gαi-independent leukocyte adhesion to and transmigration through endothelial cells in inflamed postcapillary venules of the cremaster muscle were completely abolished in Rasgrp2-/- mice. The physiological importance of CalDAG-GEFI in E-selectin-dependent integrin activation is shown by complete inhibition of neutrophil recruitment into the inflamed peritoneal cavity of Rasgrp2-/- leukocytes treated with pertussis toxin to block Gαi-signaling. Our data demonstrate that Rap1a activation by p38 MAPK and CalDAG-GEFI is involved in E-selectin-dependent slow rolling and leukocyte recruitment.

Acute loss of renal function attenuates slow leukocyte rolling and transmigration by interfering with intracellular signaling

Acute loss of renal function reduces leukocyte recruitment into inflamed tissues, and we studied the molecular basis of this using intravital microscopy of cremaster muscle and an autoperfused flow chamber system after bilateral nephrectomy or sham operation in mice. Acute loss of renal function resulted in cessation of selectin-induced slow leukocyte rolling on E-selectin/intercellular adhesion molecule 1 (ICAM-1) and P-selectin/ICAM-1. It also reduced in vivo neutrophil extravasation (assessed by reflected light oblique transillumination) without affecting chemokine-induced arrest. This elimination of selectin-mediated slow leukocyte rolling was associated with a reduced phosphorylation of spleen tyrosine kinase, Akt, phospholipase C-γ2, and p38 MAPK. However, the levels of adhesion molecules located on the neutrophil surface were not altered. Leukocytes from critically ill patients with sepsis-induced acute kidney injury showed a significantly higher rolling velocity on E-selectin/ICAM-1- and P-selectin/ICAM-1-coated surfaces compared with patients with sepsis alone or healthy volunteers. Thus, an acute loss of renal function significantly impairs neutrophil rolling and transmigration, both in vivo and in vitro. These effects are due, in part, to decreased phosphorylation of selectin-dependent intracellular signaling pathways.

Characterization of the interactions of vMIP-II, and a dimeric variant of vMIP-II, with glycosaminoglycans

Chemokines are important immune proteins, carrying out their function by binding to glycosaminoglycans (GAGs) on the endothelial surface and to cell surface chemokine receptors. A unique viral chemokine analogue, viral macrophage inflammatory protein-II (vMIP-II), encoded by human herpesvirus-8, has garnered interest because of its ability to bind to multiple chemokine receptors, including both HIV coreceptors. In addition, vMIP-II binds to cell surface GAGs much more tightly than most human chemokines, which may be the key to its anti-inflammatory function in vivo. The goal of this work was to determine the mechanism of binding of GAG by vMIP-II. The interaction of vMIP-II with a heparin-derived disaccharide was characterized using NMR. Important binding sites were further analyzed by mutagenesis studies, in which corresponding vMIP-II mutants were tested for GAG binding ability using heparin chromatography and NMR. We found that despite having many more basic residues than some chemokines, vMIP-II shares a characteristic binding site similar to that of its human analogues, utilizing basic residues R18, R46, and R48. Interestingly, a particular mutation (Leu13Phe) caused vMIP-II to form a pH-dependent CC chemokine-type dimer as determined by analytical ultracentrifugation and NMR. To the best of our knowledge, this is the first example of engineering a naturally predominantly monomeric chemokine into a dissociable dimer by a single mutation. This dimeric vMIP-II mutant binds to heparin much more tightly than wild-type vMIP-II and provides a new model for studying the relationship between chemokine quaternary structure and various aspects of function. Structural differences between monomeric and dimeric vMIP-II upon GAG binding were characterized by NMR and molecular docking.

Dynamic regulation of ROCK in tumor cells controls CXCR4-driven adhesion events

CXCR4 is a chemokine receptor often found aberrantly expressed on metastatic tumor cells. To investigate CXCR4 signaling in tumor cell adhesion, we stably overexpressed CXCR4 in MCF7 breast tumor cells. Cell attachment assays demonstrate that stimulation of the receptor with its ligand, CXCL12, promotes adhesion of MCF7-CXCR4 cells to both extracellular matrix and endothelial ligands. To more closely mimic the conditions experienced by a circulating tumor cell, we performed the attachment assays under shear stress conditions. We found that CXCL12-induced tumor cell attachment is much more pronounced under flow. ROCK is a serine/threonine kinase associated with adhesion and metastasis, which is regulated by CXCR4 signaling. Thus, we investigated the contribution of ROCK activity during CXC12-induced adhesion events. Our results demonstrate a biphasic regulation of ROCK in response to adhesion. During the initial attachment, inhibition of ROCK activity is required. Subsequently, re-activation of ROCK activity is required for maturation of adhesion complexes and enhanced tumor cell migration. Interestingly, CXCL12 partially reduces the level of ROCK activity generated by attachment, which supports a model in which stimulation with CXCL12 regulates tumor cell adhesion events by providing an optimal level of ROCK activity for effective migration.

alpha4-Integrin antagonism with natalizumab: effects and adverse effects

Based on the results of two phase III clinical trials, the humanized recombinant monoclonal antibody natalizumab was approved for the treatment of relapsing forms of multiple sclerosis (MS). Since its initial approval in November 2004, it has been announced that six patients who received natalizumab in the context of clinical studies acquired an infection with the human polyoma virus JC and were diagnosed with progressive multifocal leukoencephalopathy (PML). Two of these individuals had a fatal outcome. Our groups recently showed that natalizumab therapy results in a reduction of CD4(+) T cells within the cerebrospinal fluid (CSF) that is ten-fold more pronounced than the reduction in the number of CD8(+) T lymphocytes. Interestingly, it appears that the effect of natalizumab on cell numbers in the CSF persists for at least 6 months after cessation of treatment. More recently, we studied the expression of major histocompatibility complex (MHC) I and II, and the number and phenotypes of leukocytes in cerebral perivascular spaces (CPVS). We observed that natalizumab therapy was associated with a significant decrease in the cell surface expression of MHC class II molecules, and the numbers of dendritic cells in CPVS. In addition, no CD4(+) T cells were detectable in this compartment. Our observations may explain the differential and prolonged effects of natalizumab therapy on different leukocyte subsets in the central nervous system. They also suggest that natalizumab treatment may result in prolonged immunosuppression in peripheral organs, and the delayed onset of adverse events.

Homing of Mesenchymal Stem Cells

SUMMARY: Mesenchymal stem cells (MSCs) are primarily fibroblast-like cells. Yet, once studied under conditions of shear stress when flowing along endothelial cells in vitro or in blood vessels, as well as in classic migration assays such as chemotaxis assays, MSCs have recently been found to function similarly to leukocytes in many ways. Firstly, MSCs express several homing receptors which are typically activated during extravasation of leukocytes. Secondly, some of these receptors are definitely functional, and required for their tissue localization in certain physiological or pathological contexts. Clinical protocols have in the last few years provided the first data on whether and how human MSCs may work in patients once delivered locally e.g. by injection, or systemically via the intra-arterial or intravenous route. Still, analysis of the ability of MSCs to activate specific homing receptors has up to now received relatively little attention. Moreover, maintenance or alterations of homing receptor expression or functions during good manufacturing practice (GMP) preparation steps, and documentation of presence and function of individual pathways on MSC preparations for clinical use are often missed. Hence, we review here mechanisms predicted to be relevant for adhesion, migration, and homing competence of MSCs. We also discuss some early data on homing of MSCs, deduced from preclinical experiments and from the few clinical studies with MSCs. Finally, we introduce some assays which could be applied to monitor preservation of the homing capacity of MSCs during GMP preparation.

The role of the chemokines MCP-1, GRO-alpha, IL-8 and their receptors in the adhesion of monocytic cells to human atherosclerotic plaques

Monocyte adhesion to the arterial endothelium and subsequent migration into the intima are central events in the pathogenesis of atherosclerosis. Previous experimental models have shown that chemokines can enhance monocyte–endothelial adhesion by activating monocyte integrins. Our study assesses the role of chemokines IL-8, MCP-1 and GRO-α, together with their monocyte receptors CCR2 and CXCR2 in monocyte adhesion to human atherosclerotic plaques. In an adhesion assay, a suspension of monocytic U937 cells was incubated with human atherosclerotic artery sections and the levels of endothelial adhesion were quantified. Adhesion performed in the presence of a monoclonal antibody to a chemokine, chemokine receptor or of an isotype matched control immunoglobulin, shows that antibodies to all chemokines tested, as well as their receptors, inhibit adhesion compared to the control immunoglobulins. Immunohistochemistry demonstrated the expression of MCP-1, GRO-α and their receptors in the endothelial cells and intima of all atherosclerotic lesions. These results suggest that all these chemokines and their receptors can play a role in the adhesion of monocytes to human atherosclerotic plaques. Furthermore, they suggest that these chemokine interactions provide potential targets for the therapy of atherosclerosis.

Cells on the run: shear-regulated integrin activation in leukocyte rolling and arrest on endothelial cells

The arrest of rolling leukocytes on various target vascular beds is mediated by specialized leukocyte integrins and their endothelial immunoglobulin superfamily (IgSF) ligands. These integrins are kept in largely inactive states and undergo in situ activation upon leukocyte-endothelial contact by both biochemical and mechanical signals from flow-derived shear forces. In vivo and in vitro studies suggest that leukocyte integrin activation involves conformational alterations through inside-out signaling followed by ligand-induced rearrangements accelerated by external forces. This activation process takes place within fractions of seconds by in situ signals transduced to the rolling leukocyte as it encounters specialized endothelial-displayed chemoattractants, collectively termed arrest chemokines. In neutrophils, selectin rolling engagements trigger intermediate affinity integrins to support reversible adhesions before chemokine-triggered arrest. Different leukocyte subsets appear to use different modalities of integrin activation during rolling and arrest at distinct endothelial sites.

Autotaxin, an ectoenzyme that produces lysophosphatidic acid, promotes the entry of lymphocytes into secondary lymphoid organs

The extracellular lysophospholipase D autotaxin (ATX) and its product, lysophosphatidic acid, have diverse functions in development and cancer, but little is known about their functions in the immune system. Here we found that ATX had high expression in the high endothelial venules of lymphoid organs and was secreted. Chemokine-activated lymphocytes expressed receptors with enhanced affinity for ATX, which provides a mechanism for targeting the secreted ATX to lymphocytes undergoing recruitment. Lysophosphatidic acid induced chemokinesis in T cells. Intravenous injection of enzymatically inactive ATX attenuated the homing of T cells to lymphoid tissues, probably through competition with endogenous ATX and exertion of a dominant negative effect. Our results support the idea of a new and general step in the homing cascade in which the ectoenzyme ATX facilitates the entry of lymphocytes into lymphoid organs.

The coordinated action of G-CSF and ELR + CXC chemokines in neutrophil mobilization during acute inflammation

In this study, we have identified a unique combinatorial effect of the chemokines KC/MIP-2 and the cytokine granulocyte colony-stimulating factor (G-CSF) with respect to the rapid mobilization of neutrophils from the bone marrow in a model of acute peritonitis. At 2 hours following an intraperitoneal injection of thioglycollate, there was a 4.5-fold increase in blood neutrophil numbers, which was inhibited 84% and 72% by prior administration of blocking mAbs against either the chemokines KC/MIP-2 or G-CSF, respectively. An intraperitoneal injection of G-CSF acted remotely to stimulate neutrophil mobilization, but did not elicit recruitment into the peritoneum. Further, in vitro G-CSF was neither chemotactic nor chemokinetic for murine neutrophils, and had no priming effect on chemotaxis stimulated by chemokines. Here, we show that, in vitro and in vivo, G-CSF induces neutrophil mobilization by disrupting their SDF-1alpha-mediated retention in the bone marrow. Using an in situ perfusion system of the mouse femoral bone marrow to directly assess mobilization, KC and G-CSF mobilized 6.8 x 10(6) and 5.4 x 10(6) neutrophils, respectively, while the infusion of KC and G-CSF together mobilized 19.5 x 10(6) neutrophils, indicating that these factors act cooperatively with respect to neutrophil mobilization.

Membranal cholesterol is not required for L-selectin adhesiveness in primary lymphocytes but controls a chemokine-induced destabilization of L-selectin rolling adhesions

Cholesterol-enriched lipid microdomains regulate L-selectin signaling, but the role of membrane cholesterol in L-selectin adhesion is unclear. Arrest chemokines are a subset of endothelial chemokines that rapidly activate leukocyte integrin adhesiveness under shear flow. In the absence of integrin ligands, these chemokines destabilize L-selectin-mediated leukocyte rolling. In the present study, we investigated how cholesterol extraction from the plasma membrane of peripheral blood T or B cells affects L-selectin adhesions and their destabilization by arrest chemokines. Unlike the Jurkat T cell line, whose L-selectin-mediated adhesion is cholesterol dependent, in primary human PBLs and in murine B cells and B cell lines, cholesterol depletion did not impair any intrinsic adhesiveness of L-selectin, consistent with low selectin partitioning into lipid rafts in these cells. However, cholesterol raft disruption impaired the ability of two arrest chemokines, CXCL12 and CXCL13, but not of a third arrest chemokine, CCL21, to destabilize L-selectin-mediated rolling of T lymphocytes. Actin capping by brief incubation with cytochalasin D impaired the ability of all three chemokines to destabilize L-selectin rolling. Blocking of the actin regulatory phosphatidylinositol lipid, phosphatidylinositol 4,5-bisphosphate, did not affect chemokine-mediated destabilization of L-selectin adhesions. Collectively, our results suggest that L-selectin adhesions are inhibited by actin-associated, cholesterol-stabilized assemblies of CXCL12- and CXCL13-binding receptors on both T and B lymphocytes. Thus, the regulation of L-selectin by cholesterol-enriched microdomains varies with the cell type as well as with the identity of the destabilizing chemokine.

Integrin modulation and signaling in leukocyte adhesion and migration

The movement of leukocytes from the blood into peripheral tissues plays a key role in immunity as well as chronic inflammatory and autoimmune diseases. The shear force of blood flow presents special challenges to leukocytes as they establish adhesion on the vascular endothelium and migrate into the underlying tissues. Integrins are a family of cell adhesion and signaling molecules, whose function can be regulated to meet these challenges. The affinity of integrins for their vascular ligands can be stimulated in subseconds by chemoattractant signaling. This aids in inducing leukocyte adhesion under flow conditions. Further, linkage of these integrins to the actin cytoskeleton also helps to establish adhesion to the endothelium under flow conditions. In the case of alpha4beta1 integrins, this linkage of the integrin to the cytoskeleton is mediated in part by the binding of paxillin to the alpha4 integrin subunit and the subsequent binding of paxillin to the cytoskeleton molecule talin. The movement of leukocytes along the vascular endothelium and in between endothelial cells requires the temporal and spatial regulation of small guanosine triphosphatases, such as Rac1. We describe mechanisms through which alpha4beta1 integrin signaling regulates appropriate Rac activation to drive leukocyte migration.

Cell-surface thioredoxin-1: possible involvement in thiol-mediated leukocyte-endothelial cell interaction through lipid rafts

Human thioredoxin-1 (hTrx) exhibits a disulfide reducing activity and was originally identified as a soluble cytokine-like factor secreted from cells of a human T-cell leukemia virus type I (HTLV-I)-transformed cell line. Recent studies have revealed that endogenous Trx plays an important role in cytoprotection against various oxidative stress-associated disorders. However, the function of exogenous Trx is still not fully understood. We report here that a cysteine-modified mutant of recombinant human Trx (rhTrx-C35S) binds to human umbilical vein endothelial cells (HUVECs) as well as stimulated T cells and rapidly enters these cells via lipid rafts. In addition, we found that endogenous Trx is expressed on the surface of HUVECs, including lipid rafts. These events suggest cell-surface Trx as a possible target of rhTrx-C35S. Furthermore, we found that anti-human Trx mouse monoclonal antibody inhibits adherence of LPS-stimulated human peripheral blood polymorphonuclear cells (PMNs) to HUVECs. This adherence was also suppressed by a recombinant human Trx (rhTrx), but not by a mutant rhTrx (rhTrx-C32S/C35S) with no reducing activity. Cell-surface Trx may be involved in the process of interaction between PMNs and HUVECs and a possible target of cysteine-modified exogenous Trx as well as wild-type exogenous Trx through redox regulation.

Pharmacological properties, toxicology and scientific rationale for the use of natalizumab (Tysabri) in inflammatory diseases

Natalizumab (Tysabri) was the first adhesion molecule antagonist to make it into clinical trial for patients with multiple sclerosis (MS) and other inflammatory disorders. Natalizumab is a humanized recombinant monoclonal antibody (MAb) that binds to the alpha (alpha)(4) chain of the alpha(4) beta (beta)(1) (very late activating antigen 4; VLA-4) and alpha(4)beta(7) integrins. The scientific rationale for natalizumab therapy is the reduction of leukocyte extravasation into peripheral tissues. Natalizumab, like other VLA-4 antagonists, may also interfere with the activation of T lymphocytes in secondary lymphoid organs and their reactivation in the central nervous system (CNS). Shortly after its approval for the treatment of relapsing-remitting MS (RR-MS), three patients who were treated with natalizumab in the setting of clinical trials developed progressive multifocal leukoencephalopathy (PML), an opportunistic infection of the brain with the polyoma virus JC. It remains to be elucidated why the use of this VLA-4 antagonist is associated with an increased incidence of PML. Natalizumab was recently reapproved for the treatment of relapsing forms of MS. In this review, we outline the scientific rationale for using natalizumab in MS and other inflammatory disorders. In addition, an overview of pharmacological properties, clinical efficacy, safety, and toxicology of natalizumab is provided.

Streptococcus suisSerotype 2, an Important Swine and Human Pathogen, Induces Strong Systemic and Cerebral Inflammatory Responses in a Mouse Model of Infection

Streptococcus suis, an important swine and human pathogen, causes septic shock and meningitis. The pathogenesis of both systemic and CNS infections caused by S. suis is poorly understood. A hematogenous model of infection in CD1 mice was developed to study the systemic release of cytokines during the septic shock phase and the proinflammatory events in the CNS associated with this pathogen. Using a liquid array system, high levels of systemic TNF-alpha, IL-6, IL-12, IFN-gamma, CCL2, CXCL1, and CCL5 were observed 24 h after infection and might be responsible for the sudden death of 20% of animals. Infected mice that survived the early sepsis later developed clinical signs of meningitis and exhibited lesions in the meninges and in numerous regions of the brain, such as the cortex, hippocampus, thalamus, hypothalamus, and corpus callosum. Bacterial Ags were found in association with microglia residing only in the affected zones. In situ hybridization combined with immunocytochemistry showed transcriptional activation of TLR2 and TLR3 as well as CD14, NF-kappaB, IL-1beta, CCL2, and TNF-alpha, mainly in myeloid cells located in affected cerebral structures. Early transcriptional activation of TLR2, CD14, and inflammatory cytokines in the choroid plexus and cells lining the brain endothelium suggests that these structures are potential entry sites for the bacteria into the CNS. Our data indicate an important role of the inflammatory response in the pathogenesis of S. suis infection in mice. This experimental model may be useful for studying the mechanisms underlying sepsis and meningitis during bacterial infection.

A LAD-III syndrome is associated with defective expression of the Rap-1 activator CalDAG-GEFI in lymphocytes, neutrophils, and platelets

Leukocyte and platelet integrins rapidly alter their affinity and adhesiveness in response to various activation (inside-out) signals. A rare leukocyte adhesion deficiency (LAD), LAD-III, is associated with severe defects in leukocyte and platelet integrin activation. We report two new LAD cases in which lymphocytes, neutrophils, and platelets share severe defects in β₁, β₂, and β₃ integrin activation. Patients were both homozygous for a splice junction mutation in their CalDAG-GEFI gene, which is a key Rap-1/2 guanine exchange factor (GEF). Both mRNA and protein levels of the GEF were diminished in LAD lymphocytes, neutrophils, and platelets. Consequently, LAD-III platelets failed to aggregate because of an impaired α_IIbβ₃ activation by key agonists. β₂ integrins on LAD-III neutrophils were unable to mediate leukocyte arrest on TNFα-stimulated endothelium, despite normal selectin-mediated rolling. In situ subsecond activation of neutrophil β₂ integrin adhesiveness by surface-bound chemoattractants and of primary T lymphocyte LFA-1 by the CXCL12 chemokine was abolished. Chemokine inside-out signals also failed to stimulate lymphocyte LFA-1 extension and high affinity epitopes. Chemokine-triggered VLA-4 adhesiveness in T lymphocytes was partially defective as well. These studies identify CalDAG-GEFI as a critical regulator of inside-out integrin activation in human T lymphocytes, neutrophils, and platelets.

Selective binding and presentation of CCL5 by discrete tissue microenvironments during renal inflammation

T cells are differentially recruited to the tubulointerstitium during renal inflammation. The selective presentation of chemokines by surface structures may in part underlie this phenomenon. In an attempt to better characterize the presentation of chemokines by tissue environments an exemplary chemokine with a well-defined structure was selected, and a binding assay for the protein on fixed archival tissue sections was developed. This article describes the selective binding of the chemokine CCL5 to renal structures. CCL5 was shown to bind to endothelial regions, interstitial extracellular matrix, tubular epithelial cells, and tubular basement membranes but rarely to glomerular structures in well-preserved kidneys. In contrast, binding of CCL5 to glomerular components was seen in renal biopsies with acute allograft glomerulitis (in which T cells accumulate in glomeruli). The N terminus mediates receptor binding, whereas two clusters of basic amino acid residues ((44)RKNR(47) and (55)KKWVR(59)) are involved in the presentation of CCL5 by extracellular structures. Mutation of either loop abrogated CCL5 binding to tissue sections. Variations of the N terminus and a mutation that prevents higher order oligomerization did not change the binding pattern. The data suggest that renal compartments differ in their capacity to present chemokines, which may help explain the differential recruitment of leukocytes during allograft injury. Both clusters of basic residues in CCL5 are necessary for sufficient binding of CCL5 to tissue sections.

Attenuated virulence of a Francisella mutant lacking the lipid A 4'-phosphatase

Francisella tularensis causes tularemia, a highly contagious disease of animals and humans, but the virulence features of F. tularensis are poorly defined. F. tularensis and the related mouse pathogen Francisella novicida synthesize unusual lipid A molecules lacking the 4'-monophosphate group typically found in the lipid A of Gram-negative bacteria. LpxF, a selective phosphatase located on the periplasmic surface of the inner membrane, removes the 4'-phosphate moiety in the late stages of F. novicida lipid A assembly. To evaluate the relevance of the 4'-phosphatase to pathogenesis, we constructed a deletion mutant of lpxF and compared its virulence with wild-type F. novicida. Intradermal injection of 10(6) wild-type but not 10(8) mutant F. novicida cells is lethal to mice. The rapid clearance of the lpxF mutant is associated with a stronger local cytokine response and a greater influx of neutrophils compared with wild-type. The F. novicida mutant was highly susceptible to the cationic antimicrobial peptide polymyxin. LpxF therefore represents a kind of virulence factor that confers a distinct lipid A phenotype, preventing Francisella from activating the host innate immune response and preventing the bactericidal actions of cationic peptides. Francisella lpxF mutants may be useful for immunization against tularemia.

Interplay between shear stress and adhesion on neutrophil locomotion

Leukocyte locomotion over the lumen of inflamed endothelial cells is a critical step, following firm adhesion, in the inflammatory response. Once firmly adherent, the cell will spread and will either undergo diapedesis through individual vascular endothelial cells or will migrate to tight junctions before extravasating to the site of injury or infection. Little is known about the mechanisms of neutrophil spreading or locomotion, or how motility is affected by the physical environment. We performed a systematic study to investigate the effect of the type of adhesive ligand and shear stress on neutrophil motility by employing a parallel-plate flow chamber with reconstituted protein surfaces of E-selectin, E-selectin/PECAM-1, and E-selectin/ICAM-1. We find that the level and type of adhesive ligand and the shear rate are intertwined in affecting several metrics of migration, such as the migration velocity, random motility, index of migration, and the percentage of cells moving in the direction of flow. On surfaces with high levels of PECAM-1, there is a near doubling in random motility at a shear rate of 180 s(-1) compared to the motility in the absence of flow. On surfaces with ICAM-1, neutrophil random motility exhibits a weaker response to shear rate, decreasing slightly when shear rate is increased from static conditions to 180 s(-1), and is only slightly higher at 1000 s(-1) than in the absence of flow. The random motility increases with increasing surface concentrations of E-selectin and PECAM-1 under static and flow conditions. Our findings illustrate that the endothelium may regulate neutrophil migration in postcapillary venules through the presentation of various adhesion ligands at sites of inflammation.

Leukocyte recruitment and vascular injury in diabetic nephropathy

Different types of activated leukocytes play a crucial role in the pathogenesis of most kidney diseases from acute to chronic stages; however, diabetic nephropathy was not considered an inflammatory disease in the past. This view is changing now because there is a growing body of evidence implicating inflammatory cells at every stage of diabetic nephropathy. Renal tissue macrophages, T cells, and neutrophils produce various reactive oxygen species, proinflammatory cytokines, metalloproteinases, and growth factors, which modulate the local response and increase inflammation within the diabetic kidney. Although the precise mechanisms that direct leukocyte homing into renal tissues are not fully identified, it has been reported that intercellular adhesion molecule-1 and the chemokines CCL2 and CX3CL1 probably are involved in leukocyte migration in diabetic nephropathy. This review focuses on the molecular mechanisms of leukocyte recruitment into the diabetic kidney and the involvement of immigrated immune cells in the damage to renal tissues.

Identifying Chemokines as Therapeutic Targets in Renal Disease: Lessons from Antagonist Studies and Knockout Mice

Chemokines, in concert with cytokines and adhesion molecules, play multiple roles in local and systemic immune responses. In the kidney, the temporal and spatial expression of chemokines correlates with local renal damage and accumulation of chemokine receptor-bearing leukocytes. Chemokines play important roles in leukocyte trafficking and blocking chemokines can effectively reduce renal leukocyte recruitment and subsequent renal damage. However, recent data indicate that blocking chemokine or chemokine receptor activity in renal disease may also exacerbate renal inflammation under certain conditions. An increasing amount of data indicates additional roles of chemokines in the regulation of innate and adaptive immune responses, which may adversively affect the outcome of interventional studies. This review summarizes available in vivo studies on the blockade of chemokines and chemokine receptors in kidney diseases, with a special focus on the therapeutic potential of anti-chemokine strategies, including potential side effects, in renal disease.

Vav GEFs are required for beta2 integrin-dependent functions of neutrophils

Integrin regulation of neutrophils is essential for appropriate adhesion and transmigration into tissues. Vav proteins are Rho family guanine nucleotide exchange factors that become tyrosine phosphorylated in response to adhesion. Using Vav1/Vav3-deficient neutrophils (Vav1/3^ko), we show that Vav proteins are required for multiple β₂ integrin-dependent functions, including sustained adhesion, spreading, and complement-mediated phagocytosis. These defects are not attributable to a lack of initial β₂ activation as Vav1/3^ko neutrophils undergo chemoattractant-induced arrest on intercellular adhesion molecule-1 under flow. Accordingly, in vivo, Vav1/3^ko leukocytes arrest on venular endothelium yet are unable to sustain adherence. Thus, Vav proteins are specifically required for stable adhesion. β₂-induced activation of Cdc42, Rac1, and RhoA is defective in Vav1/3^ko neutrophils, and phosphorylation of Pyk2, paxillin, and Akt is also significantly reduced. In contrast, Vav proteins are largely dispensable for G protein-coupled receptor–induced signaling events and chemotaxis. Thus, Vav proteins play an essential role coupling β₂ to Rho GTPases and regulating multiple integrin-induced events important in leukocyte adhesion and phagocytosis.

Cutting edge: T cells trigger CD40-dependent platelet activation and granular RANTES release: a novel pathway for immune response amplification

Platelets, in addition to exerting hemostatic activity, contribute to immunity and inflammation. The recent report that platelets express CD40 led us to hypothesize that CD40 ligand (CD40L)-positive T cells could bind to platelets, cause their activation, and trigger granular RANTES release, creating a T cell recruitment feedback loop. Platelets were cocultured with resting or activated autologous T cells and their activation was assessed by P-selectin expression. RANTES binding to endothelial cells was assessed by confocal microscopy, and its biological activity was demonstrated by a T cell adhesion assay. CD40L-positive T cells induced platelet activation through a contact-mediated, CD40-dependent pathway resulting in RANTES release, which bound to endothelial cells and mediated T cell recruitment. Soluble CD40L induced the same events via p38, but not extracellular signal-regulated kinase, phosphorylation. These results show the existence of a novel platelet-dependent pathway of immune response amplification which brings these nonimmune cells close to the level of pathogenic relevance traditionally attributed to classical immune cells.

Bench-to-bedside review: acute respiratory distress syndrome - how neutrophils migrate into the lung

Acute lung injury and its more severe form, acute respiratory distress syndrome, are major challenges in critically ill patients. Activation of circulating neutrophils and transmigration into the alveolar airspace are associated with development of acute lung injury, and inhibitors of neutrophil recruitment attenuate lung damage in many experimental models. The molecular mechanisms of neutrophil recruitment in the lung differ fundamentally from those in other tissues. Distinct signals appear to regulate neutrophil passage from the intravascular into the interstitial and alveolar compartments. Entry into the alveolar compartment is under the control of CXC chemokine receptor (CXCR)2 and its ligands (CXC chemokine ligand [CXCL]1–8). The mechanisms that govern neutrophil sequestration into the vascular compartment of the lung involve changes in the actin cytoskeleton and adhesion molecules, including selectins, β₂ integrins and intercellular adhesion molecule-1. The mechanisms of neutrophil entry into the lung interstitial space are currently unknown. This review summarizes mechanisms of neutrophil trafficking in the inflamed lung and their relevance to lung injury.