Optimal selectin-mediated rolling of leukocytes during inflammation in vivo requires intercellular adhesion molecule-1 expression

Recruitment and maturation of the coronary collateral circulation: Current understanding and perspectives in arteriogenesis

The coronary collateral circulation is a rich anastomotic network of primitive vessels which have the ability to augment in size and function through the process of arteriogenesis. In this review, we evaluate the current understandings of the molecular and cellular mechanisms by which this process occurs, specifically focussing on elevated fluid shear stress (FSS), inflammation, the redox state and gene expression along with the integrative, parallel and simultaneous process by which this occurs. The initiating step of arteriogenesis occurs following occlusion of an epicardial coronary artery, with an increase in FSS detected by mechanoreceptors within the endothelium. This must occur within a 'redox window' where an equilibrium of oxidative and reductive factors are present. These factors initially result in an inflammatory milieu, mediated by neutrophils as well as lymphocytes, with resultant activation of a number of downstream molecular pathways resulting in increased expression of proteins involved in monocyte attraction and adherence; namely vascular cell adhesion molecule 1 (VCAM-1), monocyte chemoattractant protein 1 (MCP-1) and transforming growth factor beta (TGF-β). Once monocytes and other inflammatory cells adhere to the endothelium they enter the extracellular matrix and differentiate into macrophages in an effort to create a favourable environment for vessel growth and development. Activated macrophages secrete inflammatory cytokines such as tumour necrosis factor-α (TNF-α), growth factors such as fibroblast growth factor-2 (FGF-2) and matrix metalloproteinases. Finally, vascular smooth muscle cells proliferate and switch to a contractile phenotype, resulting in an increased diameter and functionality of the collateral vessel, thereby allowing improved perfusion of the distal myocardium subtended by the occluded vessel. This simultaneously reduces FSS within the collateral vessel, inhibiting further vessel growth.

Targeting functionalized nanoparticles to activated endothelial cells under high wall shear stress

Local inflammation of the endothelium is associated with a plethora of cardiovascular diseases. Vascular-targeted carriers (VTCs) have been advocated to provide focal effective therapeutics to these disease sites. Here, we examine the design of functionalized nanoparticles (NPs) as VTCs that can specifically localize at an inflamed vessel wall under pathological levels of high shear stress, associated for example with clinical (or in vivo) conditions of vascular narrowing and arteriogenesis. To test this, carboxylated fluorescent 200 nm polystyrene particles were functionalized with ligands to activated endothelium, that is, an E-selectin binding peptide (Esbp), an anti ICAM-1 antibody, or using a combination of both. The functionalized NPs were investigated in vitro using microfluidic models lined with inflamed (TNF-α stimulated) and control endothelial cells (EC). Specifically, their adhesion was monitored under different relevant wall shear stresses (i.e., 40-300 dyne/cm2) via real-time confocal microscopy. Experiments reveal a significantly higher specific adhesion of the examined functionalized NPs to activated EC for the window of examined wall shear stresses. Moreover, particle adhesion correlated with the surface coating density whereby under high surface coating (i.e., ~10,000 molecule/particle), shear-dependent particle adhesion increased significantly. Altogether, our results show that functionalized NPs can be designed to target inflamed endothelial cells under high shear stress. Such VTCs underscore the potential for attractive avenues in targeting drugs to vasoconstriction and arteriogenesis sites.

Artery-Associated Sympathetic Innervation Drives Rhythmic Vascular Inflammation of Arteries and Veins

BACKGROUND

The incidence of acute cardiovascular complications is highly time-of-day dependent. However, the mechanisms driving rhythmicity of ischemic vascular events are unknown. Although enhanced numbers of leukocytes have been linked to an increased risk of cardiovascular complications, the role that rhythmic leukocyte adhesion plays in different vascular beds has not been studied.

METHODS

We evaluated leukocyte recruitment in vivo by using real-time multichannel fluorescence intravital microscopy of a tumor necrosis factor-α-induced acute inflammation model in both murine arterial and venous macrovasculature and microvasculature. These approaches were complemented with genetic, surgical, and pharmacological ablation of sympathetic nerves or adrenergic receptors to assess their relevance for rhythmic leukocyte adhesion. In addition, we genetically targeted the key circadian clock gene Bmal1 (also known as Arntl) in a lineage-specific manner to dissect the importance of oscillations in leukocytes and components of the vessel wall in this process.

RESULTS

In vivo quantitative imaging analyses of acute inflammation revealed a 24-hour rhythm in leukocyte recruitment to arteries and veins of the mouse macrovasculature and microvasculature. Unexpectedly, although in arteries leukocyte adhesion was highest in the morning, it peaked at night in veins. This phase shift was governed by a rhythmic microenvironment and a vessel type-specific oscillatory pattern in the expression of promigratory molecules. Differences in cell adhesion molecules and leukocyte adhesion were ablated when disrupting sympathetic nerves, demonstrating their critical role in this process and the importance of β₂-adrenergic receptor signaling. Loss of the core clock gene Bmal1 in leukocytes, endothelial cells, or arterial mural cells affected the oscillations in a vessel type-specific manner. Rhythmicity in the intravascular reactivity of adherent leukocytes resulted in increased interactions with platelets in the morning in arteries and in veins at night with a higher predisposition to acute thrombosis at different times as a consequence.

CONCLUSIONS

Together, our findings point to an important and previously unrecognized role of artery-associated sympathetic innervation in governing rhythmicity in vascular inflammation in both arteries and veins and its potential implications in the occurrence of time-of-day-dependent vessel type-specific thrombotic events.

High-mannose intercellular adhesion molecule-1 enhances CD16+ monocyte adhesion to the endothelium

Human monocytes have been classified into three distinct groups, classical (anti-inflammatory; CD14⁺/CD16^-), nonclassical (patrolling; CD14⁺/CD16⁺⁺), and intermediate (proinflammatory; CD14⁺⁺/CD16⁺). Adhesion of nonclassical/intermediate monocytes with the endothelium is important for innate immunity, and also vascular inflammatory disease. However, there is an incomplete understanding of the mechanisms that regulate CD16⁺ versus CD16^- monocyte adhesion to the inflamed endothelium. Here, we tested the hypothesis that a high-mannose (HM) N-glycoform of intercellular adhesion molecule-1 (ICAM-1) on the endothelium mediates the selective recruitment of CD16⁺ monocytes. Using TNF-α treatment of human umbilical vein endothelial cells (HUVECs), and using proximity ligation assay for detecting proximity of specific N-glycans and ICAM-1, we show that TNF-α induces HM-ICAM-1 formation on the endothelial surface in a time-dependent manner. We next measured CD16^- or CD16⁺ monocyte rolling and adhesion to TNF-α-treated HUVECs in which HM- or hybrid ICAM-1 N-glycoforms were generated using the α-mannosidase class I and II inhibitors, kifunensine and swainsonine, respectively. Expression of HM-ICAM-1 selectively enhanced CD16⁺ monocyte adhesion under flow with no effect on CD16^- monocytes noted. CD16⁺ monocyte adhesion was abrogated by blocking either HM epitopes or ICAM-1. A critical role for HM-ICAM-1 in mediating CD16⁺ monocyte rolling and adhesion was confirmed using COS-1 cells engineered to express HM or complex ICAM-1 N-glycoforms. These data suggest that HM-ICAM-1 selectively recruits nonclassical/intermediate CD16⁺ monocytes to the activated endothelium.NEW & NOTEWORTHY Monocyte subsets have been associated with cardiovascular disease, yet it is unknown how different subsets are recruited to the endothelium. This study demonstrates the formation of distinct ICAM-1 N-glycoforms in the activated endothelium and reveals a key role for high mannose ICAM-1 in mediating proinflammatory CD16⁺ monocyte adhesion. Presented data identify roles for endothelial N-glycans in recruiting specific monocyte subsets during inflammation.

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.

Influence of haplotypes, gene expression and soluble levels of L-selectin on the risk of acute coronary syndrome

BACKGROUND

L-selectin gene (SELL) is a candidate gene for the development of acute coronary syndrome (ACS) that contributes to endothelial dysfunction. The -642C>T (rs2205849) and 725C>T (rs2229569) polymorphisms have been associated with changes in gene expression, ligand affinity and increased risk of cardiovascular disease. The aim of this study was to investigate the association between the haplotypes constructed with the -642C>T and 725C>T polymorphisms of the SELL gene, the expression levels of its mRNA and the serum levels of soluble L-selectin with ACS.

METHODS

We recruited 615 individuals of Mexican origin matched by age, including 342 patients with ACS and 273 individuals without personal history of ischemic cardiopathy as control group (CG). Genotyping was performed by PCR-RFLP. The qPCR technique was used to analyze the expression of mRNA using TaqMan® UPL probes. The levels of soluble L-selectin were measured with ELISA.

RESULTS

The allele variants in both polymorphisms were over-represented in the CG compared to the ACS (OR range: 0.371-0.716, p<0.006). The CT and TT haplotypes had a protective effect against the development of ACS (OR=0.401, p<0.0001; OR=0.628, p<0.0001, respectively). SELL expression was 3.076 times higher in the ACS group compared to CG (p<0.001). The levels of soluble L-selectin were similar between ACS and CG.

CONCLUSIONS

Both polymorphisms had no effect on mRNA expression and soluble protein levels. The polymorphisms -642C>T and 725C>T of the SELL gene are protective factors against the development of ACS. There is an increased gene expression of L-selectin in ACS compared to CG in the population of Western Mexico.

Galectin-3: A Positive Regulator of Leukocyte Recruitment in the Inflamed Microcirculation

In vivo and ex vivo imaging were used to investigate the function of galectin-3 (Gal-3) during the process of leukocyte recruitment to the inflamed microcirculation. The cremasteric microcirculation of wild-type (C57BL/6), Gal-3^-/-, and CX₃CR1^gfp/+ mice were assessed by intravital microscopy after PBS, IL-1β, TNF-α, or recombinant Gal-3 treatment. These cellular responses were investigated further using flow-chamber assays, confocal microscopy, flow cytometry, PCR analysis, and proteome array. We show that mechanisms mediating leukocyte slow rolling and emigration are impaired in Gal-3^-/- mice, which could be because of impaired expression of cell adhesion molecules and an altered cell surface glycoproteome. Local (intrascrotal) administration of recombinant Gal-3 to wild-type mice resulted in a dose-dependent reduction in rolling velocity associated with increased numbers of adherent and emigrated leukocytes, ∼50% of which were Ly6G⁺ neutrophils. Intrascrotal administration of Gal-3 to CX₃CR1^gfp/+ mice confirmed that approximately equal numbers of monocytes are also recruited in response to this lectin. Exogenous Gal-3 treatment was accompanied by increased proinflammatory cytokines and chemokines within the local tissue. In conclusion, this study unveils novel biology for both exogenous and endogenous Gal-3 in promoting leukocyte recruitment during acute inflammation.

Circulating endothelial mediators in human pancreatitis-associated lung injury

OBJECTIVES

To investigate the role of endothelial cell mediators, E-selectin (ES), intercellular adhesion molecule-1 (ICAM-1), tissue factor (TF), and von Willebrand factor (vWF), in the early phase of severe acute pancreatitis (SAP) complicated with respiratory failure [pancreatitis-associated lung injury (PALI)].

PATIENTS AND METHODS

This study included 30 patients with SAP and 39 patients with PALI. Blood samples were taken from SAP and PALI patients on presenting to the hospital (day 1), and days 2, 3, 5, and 10. The relationship between blood concentrations of the studied endothelial mediators and lung function tests was analyzed.

RESULTS

PALI patients had significantly higher ES, ICAM-1, TF, and vWF blood levels than those with SAP as early as at admission and throughout the period studied. We found the highest concentration of ES on the second day, ICAM-1 and TF at admission, and vWF level on the fifth day. There were adverse correlations between ES, ICAM-1, TF, vWF concentrations, and the index of oxygenation--PaO2/FiO2 ratio (Rs=-0.385, Rs=-0.523, Rs=-0.505, Rs=-0.408, P<0.001, respectively). The most accurate prediction of PALI was provided by ICAM-1 and TF levels on the day of admission [areas under curve (AUCs): ES, 0.704; ICAM-1, 0.787; TF, 0.757; and vWF, 0.686].

CONCLUSION

Endothelium-related mediators ES, ICAM-1, TF, and vWF appear to participate in pancreatitis-associated lung injury. In SAP, the measurement of endothelial mediator levels (especially ICAM-1 and TF) may be used as an early prognostic indicator that would predict the development of respiratory failure and to monitor the severity of lung dysfunction.

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.

A crucial role of L-selectin in C protein-induced experimental polymyositis in mice

OBJECTIVE

To investigate the role of adhesion molecules in C protein-induced myositis (CIM), a murine model of polymyositis (PM).

METHODS

CIM was induced in wild-type mice, L-selectin-deficient (L-selectin(-/-) ) mice, intercellular adhesion molecule 1 (ICAM-1)-deficient (ICAM-1(-/-) ) mice, and mice deficient in both L-selectin and ICAM-1 (L-selectin(-/-) ICAM-1(-/-) mice). Myositis severity, inflammatory cell infiltration, and messenger RNA expression in the inflamed muscles were analyzed. The effect of dendritic polyglycerol sulfate, a synthetic inhibitor that suppresses the function of L-selectin and endothelial P-selectin, was also examined.

RESULTS

L-selectin(-/-) mice and L-selectin(-/-) ICAM-1(-/-) mice developed significantly less severe myositis compared to wild-type mice, while ICAM-1 deficiency did not inhibit the development of myositis. L-selectin(-/-) mice that received wild-type T cells developed myositis. Treatment with dendritic polyglycerol sulfate significantly diminished the severity of myositis in wild-type mice compared to treatment with control.

CONCLUSION

These data indicate that L-selectin plays a major role in the development of CIM, whereas ICAM-1 plays a lesser role, if any, in the development of CIM. L-selectin-targeted therapy may be a candidate for the treatment of PM.

αB-crystallin/HspB5 regulates endothelial-leukocyte interactions by enhancing NF-κB-induced up-regulation of adhesion molecules ICAM-1, VCAM-1 and E-selectin

αB-crystallin is a small heat shock protein, which has pro-angiogenic properties by increasing survival of endothelial cells and secretion of vascular endothelial growth factor A. Here we demonstrate an additional role of αB-crystallin in regulating vascular function, through enhancing tumor necrosis factor α (TNF-α) induced expression of endothelial adhesion molecules involved in leukocyte recruitment. Ectopic expression of αB-crystallin in endothelial cells increases the level of E-selectin expression in response to TNF-α, and enhances leukocyte-endothelial interaction in vitro. Conversely, TNF-α-induced expression of intercellular adhesion molecule 1, vascular cell adhesion molecule 1 and E-selectin is markedly inhibited in endothelial cells isolated from αB-crystallin-deficient mice. This is associated with elevated levels of IκB in αB-crystallin deficient cells and incomplete degradation upon TNF-α stimulation. Consistent with this, endothelial adhesion molecule expression is reduced in inflamed vessels of αB-crystallin deficient mice, and leukocyte rolling velocity is increased. Our data identify αB-crystallin as a new regulator of leukocyte recruitment, by enhancing pro-inflammatory nuclear factor κ B-signaling and endothelial adhesion molecule expression during endothelial activation.

Adhesive interaction of functionalized particles and endothelium in idealized microvascular networks

OBJECTIVE

Leukocytes play a key role in the early response to tissue injury/infection resulting from physical, chemical or biological stimuli. This process involves the initiation of the leukocyte adhesion cascade mediated by a series of interactions between receptors and ligands on the endothelium and the leukocytes. Here, we characterize the adhesion profile of functionalized particles under physiological flow conditions in an idealized synthetic microvascular network (SMN) characterized by a bifurcation. We hypothesize that differences in the level of adhesion of functionalized particles in bifurcating SMNs are dependent on the ratio of adhesion molecules on the particles as well as geometric features of the in vitro networks.

METHODS

Functionalized particles were prepared by coating their surfaces with different ratios of antibodies against ICAM-1 and E-selectin (aICAM-1:aE-selectin=100:0, 70:30, 50:50, 30:70, and 0:100). The adhesion of functionalized particles to 4h TNF-α activated human umbilical vein endothelial cells under shear flow (0.5, 2, and 4dyn/cm(2)) in bifurcating SMNs and in a parallel plate flow chamber was then quantified.

RESULTS

The level of adhesion of 50:50 aICAM-1:aE-selectin particles was significantly higher compared to other particles in the bifurcating SMNs (~1.5-4 fold higher). However, in the parallel plate flow chamber 70:30 aICAM-1:aE-selectin particles exhibited a significantly higher level of adhesion (~1.5-2.5 fold higher). Furthermore, the adhesion of particles in junction regions was about 3-18 fold higher than that in straight sections of the SMNs. As expected, in straight sections of the SMNs and in the parallel plate flow chamber particle adhesion increased with decreasing shear. However, particle adhesion did not change significantly with decreasing shear at the junction regions of SMNs for all functionalized particles.

CONCLUSION

Adhesion efficiency of functionalized particles is significantly affected by cell-adhesion molecule ratio density as well as geometric features of the vessels. Moreover, the differential adhesion patterns of particles between straight sections of bifurcating SMNs and parallel plate flow chamber, as well as straight sections and junction regions of bifurcating SMNs, indicates that adhesion profile of particles is highly dependent on the vascular geometry of the system used.

FOXO1 Up-Regulates Human L-selectin Expression Through Binding to a Consensus FOXO1 Motif

L-selectin plays important roles in lymphocyte homing and leukocyte rolling. Mounting evidence shows that it is involved in many disease entities including diabetes, ischemia/reperfusion injuries, inflammatory diseases, and tumor metastasis. Regulation of L-selectin at protein level has been well characterized. However, the regulation of human L-selectin transcription remains largely unknown. To address transcriptional regulation of L-selectin, we cloned 1088 bp 5' of the start codon ATG. Luciferase analysis of the serial 5' deletion mutants located the core promoter region at -288/-1. A major transcription initiation site was mapped at -115 by 5'RACE. Transcription factors Sp1, Ets1, Mzf1, Klf2, and Irf1 bind to and transactivate the L-selectin promoter. Significantly, FOXO1 binds to a FOXO1 motif, CCCTTTGG, at -87/-80, and transactivates the L-selectin promoter in a dose-dependent manner. Over-expression of a constitutive-active FOXO1 increased the endogenous L-selectin expression in Jurkat cells. We conclude that FOXO1 regulates L-selectin expression through targeting its promoter.

Cardiovascular benefits of habitual exercise in systemic lupus erythematosus: a review

Systemic lupus erythematosus (SLE) is an autoimmune disease with unknown etiology that usually affects women of childbearing age. Although SLE causes damage to various body tissues, including joints, skin, kidneys, heart, lungs, blood vessels, and brain, cardiovascular (CV) disease is the leading cause of mortality and morbidity in this population. Because traditional risk factors for CV disease fail to completely explain the accelerated risk in patients with SLE, the management of CV disease is exceedingly difficult. Accumulating evidence indicates that regular exercise is beneficial in improving vascular function and disease-related symptoms associated with SLE. This can be accomplished with the intensity (mild), amount (moderate), and type (a variety) of physical activity that can be performed and tolerated by most, if not all, patients with SLE. However, the common signs and symptoms of SLE, including musculoskeletal problems, CV disease, and fatigue, are factors that are known to interfere with physical activity. Accordingly, the prescription of exercise needs to be conducted carefully for this population.

Cortactin deficiency is associated with reduced neutrophil recruitment but increased vascular permeability in vivo

Cortactin is required for endothelial barrier function and leukocyte recruitment in vivo.

Neutrophil extravasation and the regulation of vascular permeability require dynamic actin rearrangements in the endothelium. In this study, we analyzed in vivo whether these processes require the function of the actin nucleation–promoting factor cortactin. Basal vascular permeability for high molecular weight substances was enhanced in cortactin-deficient mice. Despite this leakiness, neutrophil extravasation in the tumor necrosis factor–stimulated cremaster was inhibited by the loss of cortactin. The permeability defect was caused by reduced levels of activated Rap1 (Ras-related protein 1) in endothelial cells and could be rescued by activating Rap1 via the guanosine triphosphatase (GTPase) exchange factor EPAC (exchange protein directly activated by cAMP). The defect in neutrophil extravasation was caused by enhanced rolling velocity and reduced adhesion in postcapillary venules. Impaired rolling interactions were linked to contributions of β₂-integrin ligands, and firm adhesion was compromised by reduced ICAM-1 (intercellular adhesion molecule 1) clustering around neutrophils. A signaling process known to be critical for the formation of ICAM-1–enriched contact areas and for transendothelial migration, the ICAM-1–mediated activation of the GTPase RhoG was blocked in cortactin-deficient endothelial cells. Our results represent the first physiological evidence that cortactin is crucial for orchestrating the molecular events leading to proper endothelial barrier function and leukocyte recruitment in vivo.

Activity of the lipoxygenase inhibitor 1-phenyl-3-pyrazolidinone (phenidone) and derivatives on the inhibition of adhesion molecule expression on human umbilical vascular endothelial cells

Leukocyte adhesion contributes to perfusion abnormalities and tissue damage during trauma, shock or overwhelming inflammation. This study was performed to determine whether the lipoxygenase inhibitor phenidone and derivatives decrease the expression of adhesion molecules on tumor necrosis factor-alpha (TNF-alpha) stimulated endothelial cells and attenuate leukocyte-endothelial interactions under flow in vitro. TNF-alpha stimulated human umbilical venous endothelial cells (HUVECs) were incubated with phenidone, 4-methyl-phenidone, 4-4-dimethyl-phenidone, 5-methyl-phenidone, 5-phenyl-phenidone, and 5-methyl-1,(2,5-di-chloro-phenyl)-3-pyrazolidone. We tested the inhibition of adhesion molecule expression at different inhibitor concentrations before, during, and after the stimulation of HUVECs. The inhibition of endothelial cell expression on HUVECs was measured by flow cytometry. Rolling and firm adhesion of leukocytes to pretreated endothelium was examined in a parallel plate flow chamber. Phenidone inhibited the expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and endothelial-leukocyte adhesion molecule-1 on HUVECs when added prior to HUVEC stimulation. The inhibitory effect of phenidone was still observed when added simultaneously, but not when added after HUVEC stimulation. 4-4-dimethyl-phenidone and 5-phenyl-phenidone inhibited the expression of adhesion molecules more effectively than phenidone. The attenuation of leukocyte rolling under flow conditions was also significantly more effective with 4-4-dimethyl-phenidone than with phenidone. Lipoxygenase inhibitors might be of therapeutically interest for the treatment of overwhelming systemic inflammation during shock, trauma, and sepsis.

Distamycin A inhibits HMGA1-binding to the P-selectin promoter and attenuates lung and liver inflammation during murine endotoxemia

BACKGROUND

The architectural transcription factor High Mobility Group-A1 (HMGA1) binds to the minor groove of AT-rich DNA and forms transcription factor complexes ("enhanceosomes") that upregulate expression of select genes within the inflammatory cascade during critical illness syndromes such as acute lung injury (ALI). AT-rich regions of DNA surround transcription factor binding sites in genes critical for the inflammatory response. Minor groove binding drugs (MGBs), such as Distamycin A (Dist A), interfere with AT-rich region DNA binding in a sequence and conformation-specific manner, and HMGA1 is one of the few transcription factors whose binding is inhibited by MGBs.

OBJECTIVES

To determine whether MGBs exert beneficial effects during endotoxemia through attenuating tissue inflammation via interfering with HMGA1-DNA binding and modulating expression of adhesion molecules.

METHODOLOGY/PRINCIPAL FINDINGS

Administration of Dist A significantly decreased lung and liver inflammation during murine endotoxemia. In intravital microscopy studies, Dist A attenuated neutrophil-endothelial interactions in vivo following an inflammatory stimulus. Endotoxin induction of P-selectin expression in lung and liver tissue and promoter activity in endothelial cells was significantly reduced by Dist A, while E-selectin induction was not significantly affected. Moreover, Dist A disrupted formation of an inducible complex containing NF-kappaB that binds an AT-rich region of the P-selectin promoter. Transfection studies demonstrated a critical role for HMGA1 in facilitating cytokine and NF-kappaB induction of P-selectin promoter activity, and Dist A inhibited binding of HMGA1 to this AT-rich region of the P-selectin promoter in vivo.

CONCLUSIONS/SIGNIFICANCE

We describe a novel targeted approach in modulating lung and liver inflammation in vivo during murine endotoxemia through decreasing binding of HMGA1 to a distinct AT-rich region of the P-selectin promoter. These studies highlight the ability of MGBs to function as molecular tools for dissecting transcriptional mechanisms in vivo and suggest alternative treatment approaches for critical illness.

Impaired innate immune response and enhanced pathology during Citrobacter rodentium infection in mice lacking functional P-selectin

The selectin family of adhesion molecules mediates recruitment of immune cells to sites of inflammation which is critical for host resistance against infection. To characterize the role of selectins in host defence against Citrobacter rodentium infection, wild-type (WT) mice and mice lacking P-selectin glycoprotein ligand-1 (PSGL-1), P-, E- and L-selectin were infected using a Citrobacter-induced colitis model. Infected mice lacking PSGL-1 or P-selectin showed a more pronounced morbidity associated with higher bacterial load, elevated IL-12 p70, TNF-alpha, IFN-gamma, MCP-1 and IL-6 production, more severe inflammation and surprisingly higher leucocyte infiltration in the guts than WT control. Recruitment of neutrophils and macrophages and caecal inflammation were drastically reduced in infected P-selectin knockout mice receiving blocking monoclonal antibodies to ICAM-1 or LFA-1, indicating that these adhesion molecules may compensate for the loss of selectins in leucocyte recruitment. Furthermore, the adaptive immune response in mice lacking PSGL-1 or P-selectin remained functional since these infected mice were capable of eradicating the bacteria and being protected upon re-challenge with C. rodentium. These data demonstrate a definitive phenotypic impairment of innate response in mice lacking PSGL-1 or P-selectin, and suggest that these adhesion molecules are important in host innate immune response against Citrobacter infection.

The differential role of L-selectin and ICAM-1 in Th1-type and Th2-type contact hypersensitivity

Sensitization and challenge using DNFB induce contact hypersensitivity (CHS) with predominant type 1 helper (Th1) cell infiltration, whereas those using FITC generate CHS with Th2 cell infiltration. CHS results from inflammatory cell infiltration, a process that is highly regulated by the expression of multiple adhesion molecules. We attempted to determine the role of L-selectin and ICAM-1 in Th1- and Th2-type CHS induced by DNFB or FITC in mice lacking either L-selectin, ICAM-1, or both. Th1-type CHS induced by DNFB was inhibited by L-selectin and/or ICAM-1 deficiency, which was associated with reduced IFN-gamma expression. Similarly, Th2-type CHS induced by FITC was inhibited by L-selectin deficiency. However, Th2-type CHS was increased by ICAM-1 deficiency and accompanied by increased Th2 cytokine expression. Infiltration of in vitro-generated Th1 cells into the FITC-challenged skin decreased in ICAM-1-deficient mice, whereas in vitro-generated Th2 cell infiltration increased, suggesting that ICAM-1 mediates Th1 cell migration and that in the absence of ICAM-1, Th1 cell recruitment decreased, whereas relative Th2 cell migration increased. These results suggest that ICAM-1 mediates Th1 cell recruitment irrespective of DNFB or FITC and that L-selectin recruits Th1 cells in Th1-type CHS, whereas it recruits Th2 cells in Th2-type CHS.

L-selectin: role in regulating homeostasis and cutaneous inflammation

The maintenance of immune surveillance and the generation of normal immune responses are dependent on leukocyte migration to appropriate lymphoid and non-lymphoid tissues. The process of leukocyte migration occurs through complex and highly regulated interactions between the circulating leukocytes and the vascular endothelium. Multiple families of adhesion molecules as well as specific chemoattractants and their cognate receptors function to stabilize these interactions and induce migration into the tissue. L-selectin is a key adhesion molecule that regulates both the migration of leukocytes at sites of inflammation and the recirculation of lymphocytes between blood and lymphoid tissues. L-selectin-mediated lymphocyte recirculation is required for maintaining the appropriate tissue distribution of lymphocyte subpopulations including naïve and effector subsets such as regulatory T cells. In addition, L-selectin-mediated entry into peripheral lymph nodes is required for optimal induction of lymphocyte homeostatic proliferation during lymphopenia. Importantly, L-selectin has been shown to have both adhesive and signaling functions during leukocyte migration. Specifically, L-selectin is highly efficient at capturing free-flowing leukocytes from the blood and supporting subsequent fast rolling interactions along the vascular endothelium. During rolling, synergistic interactions between L-selectin and integrin functions slow leukocyte rolling velocities allowing for chemoattractant-induced activation and eventual firm adhesion of the leukocyte to the vascular endothelium. Engagement of L-selectin by ligand generates transmembrane signals leading to activation of intracellular signaling pathways, increased integrin binding affinity, and enhanced chemotaxis. L-selectin has also been shown to mediate leukocyte recruitment during chronic inflammatory and autoimmune diseases and thus is a potential therapeutic target for drug development.

Activation of PPARbeta/delta inhibits leukocyte recruitment, cell adhesion molecule expression, and chemokine release

The infiltration of PMNs into tissues is a prominent feature in inflammation. The mechanism underlying PMN recruitment depends on the release of chemotactic mediators and CAM expression on endothelial cells. The nuclear receptor PPARbeta/delta is widely expressed in many tissues, including the vascular endothelium; however, its role in acute inflammation remains unclear. Using intravital microscopy in the mouse cremasteric microcirculation, we have shown that activation of PPARbeta/delta by its selective ligand GW501516 inhibits TNF-alpha-induced leukocyte rolling flux, adhesion, and emigration in a dose-dependant manner. Moreover, GW501516 reduced the expression of adhesion molecules such as ICAM-1, VCAM-1, and E-selectin in the cremasteric postcapillary venules. Similarly, rolling and adhesion of hPMNs under physiological flow on TNF-alpha-activated HUVECs were also inhibited markedly by GW501516. These inhibitory responses of GW501516 on activated endothelium were accompanied by a reduction in TNF-alpha-induced endothelial GRO-alpha release and VCAM-1, E-selectin, and ICAM-1 mRNA expression. Taken together, our results show that PPARbeta/delta modulates acute inflammation in vivo and in vitro under flow by targeting the neutrophil-endothelial cell interaction.

CD19 regulates the development of bleomycin-induced pulmonary fibrosis in a mouse model

OBJECTIVE

The contribution of CD19 and B lymphocytes to pulmonary fibrosis is controversial. The aim of this study was to address the role of CD19 during the development of pulmonary fibrosis.

METHODS

Mice lacking or overexpressing the B cell surface molecule CD19, which is known as a positive regulator of B cell activation, were used in a model of bleomycin-induced pulmonary fibrosis. Ten or sixteen days after intratracheal injection of bleomycin, lung sections from mice were evaluated by histologic analysis. Seven days after instillation, the total leukocyte count and the number of B cells in bronchoalveolar lavage fluid (BALF) were determined, using a hemocytometer and flow cytometry. Bleomycin was also administered into selectin-deficient or intercellular adhesion molecule 1-deficient mouse strains. The level of CXCR3 expression on B cells was determined by flow cytometry.

RESULTS

CD19 deficiency significantly reduced susceptibility to intratracheal bleomycin challenge on day 16, while CD19 overexpression augmented fibrosis even on day 10. Furthermore, the survival rate and number of B cells in BALF also correlated with CD19 expression levels. The accumulation of B cells in BALF was dependent on CD19 levels, whereas there was no association with the levels of selectins or intercellular adhesion molecule 1. Additionally, CXCR3 was up-regulated in BALF B cells, while it was rarely expressed on circulating B cells. Furthermore, CD19 signaling facilitated B cell CXCR3 up-regulation in response to stimulation in vitro.

CONCLUSION

These results suggest that CD19 signaling is associated with the development of pulmonary fibrosis by controlling B cell infiltration into lung tissue, which may be associated with CXCR3 up-regulation.

Stress-induced neurogenic inflammation in murine skin skews dendritic cells towards maturation and migration: key role of intercellular adhesion molecule-1/leukocyte function-associated antigen interactions

The skin continuously serves as a biosensor of multiple exogenous stressors and integrates the resulting responses with an individual's central and peripheral endogenous response systems to perceived stress; it also acts to protect against external challenges such as wounding and infection. We have previously shown in mice that stress induces nerve growth factor- and substance P-dependent neurogenic inflammation, which includes the prominent clustering of MHC class II(+) cells. Because the contribution of dendritic cells (DCs) in response to stress is not well understood, we examined the role of DCs in neurogenic inflammation in murine skin using a well-established murine stress model. We show that sound stress increases the number of intradermal langerin(+) and CD11c(+) DCs and induces DC maturation, as indicated by the up-regulated expression of CD11c, MHC class II, and intercellular adhesion molecule-1 (ICAM-1). Blocking of ICAM-1/leukocyte function-associated antigen-1 interactions significantly abrogated the stress-induced numeric increase, maturation, and migration of dermal DCs in vivo and also reduced stress-induced keratinocyte apoptosis and endothelial cell expression of ICAM-1. In conclusion, stress exposure causes a state of immune alertness in the skin. Such adaptation processes may ensure protection from possible infections on wounding by stressors, such as attack by predators. However, present-day stressors have changed and such adaptations appear redundant and may overrun skin homeostasis by inducing immune dermatoses.

Differential roles of ICAM-1 and VCAM-1 in leukocyte-endothelial cell interactions in skin and brain of MRL/faslpr mice

MRL/fas(lpr) mice, which undergo a systemic autoimmune disease with similarities to systemic lupus erythematosus (SLE), display reduced pathology and prolonged survival if rendered deficient in ICAM-1. However, it remains unclear whether this is a result of the ability of ICAM-1 to promote the immune response or mediate leukocyte recruitment. Therefore, the aim of these studies was to compare the role of ICAM-1 in the elevated leukocyte-endothelial interactions, which affect MRL/fas(lpr) mice. Intravital microscopy was used to compare leukocyte rolling and adhesion in postcapillary venules in the dermal and cerebral (pial) microcirculations of wild-type (ICAM+/+) and ICAM-1-deficient (ICAM-1-/-) MRL/fas(lpr) mice. In the dermal microcirculation of 16-week MRL/fas(lpr) mice, leukocyte adhesion was increased relative to nondiseased MRL+/+ mice. However, this increase was abolished in ICAM-1-/- MRL/fas(lpr) mice. ICAM-1 deficiency was also associated with reduced dermal pathology. In contrast, in the pial microcirculation, the elevation in leukocyte adhesion observed in ICAM+/+ MRL/fas(lpr) mice also occurred in ICAM-1-/- MRL/fas(lpr) mice. VCAM-1 expression was detectable in both vascular beds, but higher levels were detected in the pial vasculature. Furthermore, VCAM-1 blockade significantly reduced leukocyte adhesion and rolling in the cerebral microcirculation of ICAM-1-/- MRL/fas(lpr) mice. Therefore, ICAM-1 was critical for leukocyte adhesion in the skin but not the brain, where VCAM-1 assumed the major function. Given the ongoing development of anti-adhesion molecule therapies and their potential in inflammatory diseases such as SLE, these data indicate that implementation of these therapies in SLE should take into account the potential for tissue-specific functions of adhesion molecules.

Endothelial-dependent mechanisms of leukocyte recruitment to the vascular wall

Inflammation is a fundamental process that protects organisms by removing or neutralizing injurious agents. A key event in the inflammatory response is the localized recruitment of various leukocyte subsets. Here we address the cellular and regulatory mechanisms of leukocyte recruitment to the vessel wall in cardiovascular disease and discuss our evolving understanding of the role of the vascular endothelium in this process. The vascular endothelium is the continuous single-cell lining of the cardiovascular system that forms a critical interface between the blood and its components on one side and the tissues and organs on the other. It is heterogeneous and has many synthetic and metabolic functions including secretion of platelet-derived growth factor, von Willebrand factor, prostacyclin, NO, endothelin-1, and chemokines and the expression of adhesion molecules. It also acts as a nonthrombogenic and selective permeable barrier. Endothelial cells also interact closely with the extracellular matrix and with adjacent cells including pericytes and smooth muscle cells within the vessel wall. A central question in vascular biology is the role of the endothelium in the initiation of inflammatory response, the extent of its "molecular conversations" with recruited leukocytes, and its influence on the extent and/or outcome of this response.

A role for ICAM-1 in maintenance of leukocyte-endothelial cell rolling interactions in inflamed arterioles

A key endothelial receptor in leukocyte-endothelial cell (EC) interactions is ICAM-1. ICAM-1 is constitutively expressed at low levels on vascular ECs, and its levels significantly increase following stimulation with many proinflammatory agents. This study provides evidence that in inflamed arterioles of anesthetized mice (65 mg/kg ip Nembutal), ICAM-1 mediates leukocyte rolling, in contrast to its expected role of mediating firm adhesion in venules. The number of leukocytes rolling on arteriolar ECs is decreased in ICAM-1 knockout (KO) compared with wild-type (WT) mice (KO, 6.0 +/- 0.9; WT, 12.0 +/- 1.0 leukocytes/40 s; P < 0.05), whereas the leukocyte-rolling number in venules remains unaffected (KO, 5.6 +/- 0.9; WT, 7.0 +/- 0.7 leukocytes/40 s; n = 13-15 sites). We also show that the fraction of leukocytes that is rolling on arteriolar ECs does so with a higher characteristic velocity (>70 microm/s), and, furthermore, that the distance over which rolling contacts with the arteriolar wall are maintained is ICAM-1 dependent. In ICAM-1 KO animals or in WT mice in the presence of ICAM-1-blocking antibody, leukocytes rolled significantly shorter distances over the sampled 200-microm vessel length compared with WT (68 +/- 6.7 and 55 +/- 9.4 vs. 85 +/- 12.9% total, respectively, n = 4 sites, P < 0.05). We also found evidence that in ICAM-1 KO mice, a significant fraction of leukocyte rolling and adhesive interactions with arteriolar ECs could be accounted for by upregulation of another adhesion molecule, VCAM-1, providing an important illustration of how expression of related proteins can be altered following genetic ablatement of a target molecule (in this case ICAM-1).

Phase-dependent roles of E-selectin during chronic contact hypersensitivity responses

Chronic contact hypersensitivity (CH) models induced by repeated hapten exposure exhibit chronic dermatitis and immunological abnormalities resembling atopic dermatitis. To assess the contribution of endothelial selectins (P- and E-selectins) to cutaneous chronic inflammation, chronic CH responses were assessed in mice lacking P- or E-selectin. Elicitation with oxazolone on the ears of P-selectin(-/-) mice 7 days after the sensitization induced a typical delayed-type hypersensitivity response similar to that found in wild-type mice. By contrast, a significant increase in ear swelling was observed in E-selectin(-/-) mice 36 to 48 hours after first elicitation. E-selectin(-/-) mice showed augmented P-selectin up-regulation, and administration of anti-P-selectin monoclonal antibody significantly inhibited the enhanced ear response, suggesting that the enhanced ear-swelling response in E-selectin(-/-) mice resulted from compensatory increase in P-selectin expression. In the late phase of chronic CH, acceleration of ear swelling was significantly reduced in both E- and P-selectin(-/-) mice relative to wild-type littermates. Thus, the loss of P- or E-selectin suppressed inflammatory responses during the chronic phase of the chronic models, whereas early-phase inflammatory responses were exacerbated by E-selectin blockade. Collectively, P- and E-selectins cooperatively regulate CH response, although their roles may be different depending on the phase of the reaction.

Endothelial selectins regulate skin wound healing in cooperation with L-selectin and ICAM-1

Skin wound healing is mediated by inflammatory cell infiltration that is highly regulated by various adhesion molecules. Mice lacking intercellular adhesion molecule-1 (ICAM-1) delayed skin wound healing and mice lacking both L-selectin and ICAM-1 (L-selectin/ICAM-1(-/-)) show more delayed wound healing. Deficiency of both endothelial selectins (E-selectin or P-selectin) also delays wound healing. However, the relative contribution and interaction of selectins and ICAM-1 to the wound healing remain unknown. To clarify them, repair of excisional wounds was examined in L-selectin/ICAM-1(-/-) mice, wild-type mice with both E- and P-selectin blockade, and L-selectin/ICAM-1(-/-) mice with both E- and P-selectin blockade. Wild-type mice with both E- and P-selectin blockade showed delayed wound healing that was comparable with that in L-selectin/ICAM-1(-/-) mice. Combined E- and P-selectin blockade in L-selectin/ICAM-1(-/-) mice resulted in more significant delay. Mice lacking or blocked for adhesion molecules also showed suppressed keratinocyte migration, angiogenesis, granulation tissue formation, leukocyte infiltration, and cytokine expression, including transforming growth factor-beta and interleukin-6. Application of basic fibroblast growth factor (bFGF) but not platelet-derived growth factor to the wounds significantly improved wound healing in L-selectin/ICAM-1(-/-) mice with both E- and P-selectin blockade. bFGF significantly increased the leukocyte infiltration and subsequent fibrogenic cytokine production, as well as keratinocyte migration, angiogenesis, and collagen synthesis despite the loss of four kinds of adhesion molecules. These results indicate that skin wound healing is regulated cooperatively by all selectins and ICAM-1 and may provide critical information for the therapy of skin wounds.

Intercellular Adhesion Molecule-1 Deficiency Attenuates the Development of Skin Fibrosis in Tight-Skin Mice

The tight-skin (TSK/+) mouse, a genetic model for systemic sclerosis, develops cutaneous fibrosis. Although a fibrillin 1 gene mutation and immunological abnormalities have been demonstrated, the roles of adhesion molecules have not been investigated. To directly assess roles of adhesion molecules in skin fibrosis, TSK/+ mice lacking L-selectin and/or ICAM-1 were generated. The deficiency of ICAM-1, but not L-selectin, significantly suppressed ( approximately 48%) the development of skin sclerosis in TSK/+ mice. Similarly, ICAM-1 antisense oligonucleotides inhibited skin fibrosis in TSK/+ mice. Although T cell infiltration was modest into the skin of TSK/+ mice, ICAM-1 deficiency down-regulated this migration, which is consistent with the established roles of endothelial ICAM-1 in leukocyte infiltration. In addition, altered phenotype or function of skin fibroblasts was remarkable and dependent on ICAM-1 expression in TSK/+ mice. ICAM-1 expression was augmented on TSK/+ dermal fibroblasts stimulated with IL-4. Although growth or collagen synthesis of TSK/+ fibroblasts cultured with IL-4 was up-regulated, it was suppressed by the loss or blocking of ICAM-1. Collagen expression was dependent on the strain of fibroblasts, but not on the strain of cocultured T cells. Thus, our findings indicate that ICAM-1 expression contributes to the development of skin fibrosis in TSK/+ mice, especially via ICAM-1 expressed on skin fibroblasts.

Tumor necrosis factor alpha (TNF-alpha) receptor-II is required for TNF-alpha-induced leukocyte-endothelial interaction in vivo

Tumor necrosis factor-alpha (TNF-alpha) binds to 2 distinct cell-surface receptors: TNF-alpha receptor-I (TNFR-I: p55) and TNF-alpha receptor-II (TNFR-II: p75). TNF-alpha induces leukocyte adhesion molecules on endothelial cells (ECs), which mediate 3 defined steps of the inflammatory response; namely, leukocyte rolling, firm adhesion, and transmigration. In this study, we have investigated the role of p75 in TNF-alpha-induced leukocyte adhesion molecules using cultured ECs derived from wild-type (WT), p75-null (p75-/-), or p55-null (p55-/-) mice. We observed that p75 was essential for TNF-alpha-induced E-selectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1 (ICAM-1) expression. We also investigated the putative role of p75 in inflammation in vivo using an intravital microscopic approach with a mouse cremaster muscle model. TNF-alpha-stimulated leukocyte rolling, firm adhesion to ECs, and transmigration were dramatically reduced in p75-/- mice. Transplanted WT cremaster in p75-/- mice showed a robust leukocyte rolling and firm adhesion upon TNF-alpha activation, suggesting that the impairment in EC-leukocyte interaction in p75-/- mice is due to EC dysfunction. These results demonstrate, for the first time, that endothelial p75 is essential for TNF-alpha-induced leukocyte-endothelial-cell interaction. Our findings may contribute to the identification of novel p75-targeted therapeutic approaches for inflammatory diseases.

Intracellular heterogeneity in adhesiveness of endothelium affects early steps in leukocyte adhesion

Endothelial cell junctions are thought to be preferential sites for transmigration. However, the factors that determine the site of transmigration are not well defined. Our data show that the preferential role of endothelial cell junctions is not limited to transmigration but extends to earlier steps of leukocyte recruitment, such as rolling and arrest. We used primary mouse neutrophils and mouse aortic endothelium in a flow chamber system to compare adhesive interactions near endothelial cell junctions to interactions over endothelial cell centers. We found differences in both rolling velocity and arrest frequency for neutrophils at endothelial cell junctions vs. more central areas of endothelial cells. Differences were governed by adhesion molecule interactions, not local topography. Interestingly, the role of particular adhesion molecules depended on their location on the endothelial cell surface. Although ICAM-1 stabilized and slowed rolling over central areas of the cell, it did not influence rolling velocity over endothelial cell junctions. P-selectin and VCAM-1 were more important for rolling near endothelial cell junctions than E-selectin. This demonstrates that adhesive properties of endothelial cell junctions influence early events in the adhesion cascade, which may help explain how leukocytes are localized to sites of eventual transmigration.

Regulation of local and metastatic host-mediated anti-tumour mechanisms by L-selectin and intercellular adhesion molecule-1

Malignant melanoma is often accompanied by a host response of inflammatory cell infiltration that is highly regulated by multiple adhesion molecules. To assess the role of adhesion molecules, including L-selectin and intercellular adhesion molecule-1 (ICAM-1), in this process, subcutaneous primary growth and metastasis to the lung of B16 melanoma cells not expressing L-selectin, ICAM-1 or their ligands were examined in mice lacking L-selectin, ICAM-1 or both. Primary subcutaneous growth of B16 melanoma was augmented by loss of L-selectin, ICAM-1 or both, while pulmonary metastasis was enhanced by the loss of L-selectin or combined loss of L-selectin and ICAM-1. In both situations, the combined loss of L-selectin and ICAM-1 exhibited the greatest effect. This enhancement was associated generally with a reduced accumulation of natural killer (NK) cells, CD4+ T cells and CD8+ T cells and also with a diminished release of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha but not interleukin (IL)-6. Cytotoxicity against melanoma was not defective by the absence of ICAM-1, L-selectin or both, suggesting that the enhancement of tumour growth and metastasis caused by the loss of adhesion molecules results from an impaired migration of effector cells into the tissue rather than from a suppression of the cytotoxic response. The results indicate that L-selectin and ICAM-1 contribute co-operatively to the anti-tumour reaction by regulating lymphocyte infiltration to the tumour.

In vitro characterization of leukocyte mimetic for targeting therapeutics to the endothelium using two receptors

Selectins (E- and P-selectin) and other endothelial expressed leukocyte adhesion molecules (ELAMs) are potential targets for site-specific delivery of therapeutics to the vascular endothelium due to their specific and highly regulated expression in vascular disease. It was recently shown that degradable microspheres coated with antibodies against E-selectin or other ELAMs can target inflammation in vivo. However, targeting ELAMs alone cannot differentiate between normal and diseased state, as a basal level of these LAMs are expressed on endothelium in healthy tissues. Furthermore, leukocytes usually employ two separate adhesion molecules in parallel to home to diseased tissues, and we recently quantified the advantages of a two-receptor display for the targeting of leukocyte mimetics (Eniola AO, Willcox PJ, Hammer DA. Interplay between rolling and firm adhesion elucidated with a cell-free system engineered with two distinct receptor-ligand pairs. Biophys J 2003;85:2720-31). Here, we describe a leukocyte mimetic for targeting therapeutics to the vasculature in inflammatory diseases via two receptors, selectin and intercellular cell adhesion molecule-1 (ICAM-1), where biodegradable, polymer microspheres were co-functionalized with the selectin ligand, sialyl Lewis(X) (sLe(X)), and an antibody against ICAM-1, anti-ICAM-1 (aICAM-1). These two-receptor targeted particles, at given ratios of sLe(X)/aICAM-1, firmly adhere to substrate surface in flow only when both targeting ligands can interact with their respective receptors, mimicking the multi-step in vivo leukocyte adhesion in inflammation. Thus, we have faithfully recreated the specificity and extent of leukocyte adhesion in a platform that can allow for local delivery of therapeutics.

Dynamic shifts in LFA-1 affinity regulate neutrophil rolling, arrest, and transmigration on inflamed endothelium

Polymorphonuclear leukocyte (PMN) recruitment to vascular endothelium during acute inflammation involves cooperation between selectins, G-proteins, and beta2-integrins. LFA-1 (CD11a/CD18) affinity correlates with specific adhesion functions because a shift from low to intermediate affinity supports rolling on ICAM-1, whereas high affinity is associated with shear-resistant leukocyte arrest. We imaged PMN adhesion on cytokine-inflamed endothelium in a parallel-plate flow chamber to define the dynamics of beta2-integrin function during recruitment and transmigration. After arrest on inflamed endothelium, high-affinity LFA-1 aligned along the uropod-pseudopod major axis, which was essential for efficient neutrophil polarization and subsequent transmigration. An allosteric small molecule inhibitor targeted to the I-domain stabilized LFA-1 in an intermediate-affinity conformation, which supported neutrophil rolling but inhibited cell polarization and abrogated transmigration. We conclude that a shift in LFA-1 from intermediate to high affinity during the transition from rolling to arrest provides the contact-mediated signaling and guidance necessary for PMN transmigration on inflamed endothelium.

Molecular mechanics and dynamics of leukocyte recruitment during inflammation

Discovery of new genes and proteins directly supporting leukocyte adhesion is waning, whereas there is heightened interest in the cell mechanics and receptor dynamics that lead from transient tethering via selectins to affinity shifts and adhesion strengthening through integrins. New optical tools enable real-time imaging of leukocyte rolling and arrest in parallel plate flow channels (PPFCs), and detection of single-molecule force spectroscopy provides an inner view of the intercellular adhesive contact region. Leukocyte recruitment during acute inflammation is triggered by ligation of G protein-coupled chemotactic receptors (GPCRs) and clustering of selectins. This, in turn, activates beta(2)-integrin (CD18), which facilitates cell capture and arrest in shear flow. This review provides a conceptual model for the molecular events supporting leukocyte recruitment.

I-domain of lymphocyte function-associated antigen-1 mediates rolling of polystyrene particles on ICAM-1 under flow

In their active state, beta(2)-integrins, such as LFA-1, mediate the firm arrest of leukocytes by binding intercellular adhesion molecules (ICAMs) expressed on endothelium. Although the primary function of LFA-1 is assumed to be the ability to mediate firm adhesion, recent work has shown that LFA-1 can contribute to cell tethering and rolling under hydrodynamic flow, a role previously largely attributed to the selectins. The inserted (I) domain of LFA-1 has recently been crystallized in the wild-type (wt) and locked-open conformations and has been shown to, respectively, support rolling and firm adhesion under flow when expressed in alpha(L)beta(2) heterodimers or as isolated domains on cells. Here, we report results from cell-free adhesion assays where wt I-domain-coated polystyrene particles were allowed to interact with ICAM-1-coated surfaces in shear flow. We show that wt I-domain can independently mediate the capture of particles from flow and support their rolling on ICAM-1 surfaces in a manner similar to how carbohydrate-selectin interactions mediate rolling. Adhesion is specific and blocked by appropriate antibodies. We also show that the rolling velocity of I-domain-coated particles depends on the wall shear stress in flow chamber, I-domain site density on microsphere surfaces, and ICAM-1 site density on substrate surfaces. Furthermore, we show that rolling is less sensitive to wall shear stress and ICAM-1 substrate density at high density of I-domain on the microsphere surface. Computer simulations using adhesive dynamics can recreate bead rolling dynamics and show that the mechanochemical properties of ICAM-1-I-domain interactions are similar to those of carbohydrate-selectin interactions. Understanding the biophysics of adhesion mediated by the I-domain of LFA-1 can elucidate the complex roles this integrin plays in leukocyte adhesion in inflammation.

Flow-conditioned HUVECs support clustered leukocyte adhesion by coexpressing ICAM-1 and E-selectin

Endothelial sequestration of circulating monocytes is a key event in early atherosclerosis. Hemodynamics is proposed to regulate monocyte-endothelial cell interactions by direct cell activation and establishment of flow environments that are conducive or prohibitive to cell-cell interaction. We investigated fluid shear regulation of monocyte-endothelial cell adhesion in vitro using a disturbed laminar shear system that models in vivo hemodynamics characteristic of lesion-prone vascular regions. Human endothelial cell monolayers were flow conditioned for 6 h before evaluation of monocyte adhesion under static and dynamic flow conditions. Results revealed a distinctive clustered cell pattern of monocyte adhesion that strongly resembles in vivo leukocyte adhesion in early- and late-stage atherosclerosis. Clustered monocyte cell adhesion correlated with endothelial cells coexpressing intercellular adhesion molecule-1 (ICAM-1) and E-selectin as result of a flow-induced, selective upregulation of E-selectin expression in a subset of ICAM-1-expressing cells. Clustered monocyte cell adhesion assayed under static conditions exhibited a spatial variation in size and frequency of occurrence, which demonstrates differential regulation of endothelial cell adhesiveness by the local flow environment. Dynamic adhesion studies conducted with circulating monocytes resulted in clustered cell adhesion only within the disturbed flow region, where the monocyte rate of motion is sufficiently low for cell-cell interaction. These studies provide evidence and reveal mechanisms of local hemodynamic regulation of endothelial adhesiveness and endothelial monocyte interaction that lead to localized monocyte adhesion and potentially contribute to the focal origin of arterial diseases such as atherosclerosis.

Integrins and T cell-mediated immunity

Integrin receptors mediate adhesive events that are critical for a specific and effective immune response to foreign pathogens. Integrin-dependent interactions of lymphocytes and antigen-presenting cells (APCs) to endothelium regulate the efficiency and specificity of trafficking into secondary lymphoid organs and peripheral tissue. Within these sites, integrins facilitate cell movement via interactions with the extracellular matrix, and promote and stabilize antigen-specific interactions between T lymphocytes and APCs that are critical for initiating T cell-activation events. In this review, we discuss the role of integrins in T cell-mediated immunity, with a focus on how these receptors participate in lymphocyte recirculation and T cell activation, how antigen stimulation regulates integrin activity, and how integrins define functionally unique subsets of T cells and APCs.

Avidity modulation activates adhesion under flow and requires cooperativity among adhesion receptors

An early step in activation of leukocyte adhesion is a release of integrins from cytoskeletal constraints on their diffusion, leading to rearrangement and, consequently, increased avidity. Static adhesion assays using purified ligand as a substrate have demonstrated that very low doses of cytochalasin D disconnect beta2-integrins from their cytoskeletal links, allowing rearrangement and activating adhesion. The adhesion process in blood vessels is poorly simulated by these assays, however, for two reasons: leukocyte adhesion to endothelium 1), occurs in the presence of blood flow and 2), involves the simultaneous interactions of multiple sets of adhesion molecules. We investigated the effect of cytochalasin D, at concentrations that increase integrin diffusion but do not alter leukocyte shape and surface features, on adhesion of leukocytes to endothelial cells under flow. Cytochalasin D increased the number of rolling cells, the number of firmly adherent cells, and the duration of both rolling and firm adhesion. These effects required endothelial cell expression of ICAM-1, the ligand for leukocyte beta2-integrins. The beta2-integrin-ICAM-1 interaction alone was not sufficient, however. Experiments using purified substrates demonstrated that avidity effects on activation of adhesion under flow require functional cooperativity between integrins and other adhesion receptors.

Monitoring leukocyte traffic in vivo into human delayed-type hypersensitivity reaction

Leukocyte traffic from blood to sites of inflammation has been elaborately studied in animal models and in vitro. However, to date, little understanding has accumulated on the process in humans in vivo. A noninvasive light confocal microscopy technique has enabled us to image leukocyte rolling, arrest and transmigrated cells in vivo in human tissues. In the current study, a delayed-type hypersensitivity (DTH) reaction was elicited in the lower lip of healthy, Bacille Calmette-Guerin (BCG)-vaccinated volunteers by injection of respective purified protein derivate (PPD), mimicking the classic cutaneous Mantoux reaction. Subjects were imaged with real-time confocal microscopy at baseline and 2, 4, 24 and 48 h after the injection. The number of rolling leukocytes did not increase significantly until at 48 h. Even then, rolling cells were seen in only a minority (23%) of blood vessels. The frequency of engaged blood vessels was, nevertheless, significantly greater than at baseline. As the inflammation generated with this challenge was mild, transmigrated leukocytes could be detected in the confocal microscopy only occasionally. Histology of biopsies taken immediately after imaging at 48 h showed a T cell-dominated leukocyte population at the site of the DTH reaction. We have thus developed a method to monitor noninvasively leukocyte traffic in vivo in human subjects during the classic inflammatory model of delayed-type hypersensitivity reaction.

Arteriogenesis proceeds via ICAM-1/Mac-1- mediated mechanisms

Monocyte adhesion to shear stress-activated endothelium stands as an important initial step during arteriogenesis (collateral artery growth). Using multiple approaches, we tested the hypothesis that monocyte adhesion via intercellular adhesion molecule-1 (ICAM-1) and selectin interactions is essential for adaptive arteriogenesis. Forty-eight New Zealand White rabbits received either solvent, monocyte chemoattractant protein-1 (MCP-1) alone, MCP-1 plus ICAM-mab, or MCP-1 plus an IgG2a isotype control via osmotic minipumps. After 7 days, collateral conductance was evaluated: solvent 4.01 (mL/min per 100 mm Hg), MCP-1 plus ICAM-mab 8.04 (versus solvent P=NS), and MCP-1 alone 33.11 (versus solvent P<0.05). Furthermore, the right femoral arteries of ICAM-1-/-, Mac-1-/- and mice having defective selectin interactions (FT4/7-/-) as well as their corresponding controls were ligated. One week later, perfusion ratios were determined by the use of fluorescent microspheres. FT4/7-/- mice did not show any significant difference in perfusion restoration whereas ICAM-1-/- and Mac-1-/- mice had a significant reduction in arteriogenesis as compared with matching controls (FT4/7-WT 37+/-9%, FT4/7-/- 32+/-3%, P=0.31; C57BL/6J 59+/-9%, ICAM-1-/- 36+/-8%, P<0.05; Mac-1-/- 42+/-3%, P<0.05). ICAM-1/Mac-1-mediated monocyte adhesion to the endothelium of collateral arteries is an essential step for arteriogenesis, whereas this process can proceed via selectin interaction independent mechanisms. Furthermore, in vivo treatment with monoclonal antibodies against ICAM-1 totally abolishes the stimulatory effect of MCP-1 on collateral artery growth, suggesting that the mechanism of the MCP-1-induced arteriogenesis proceeds via the localization of monocytes rather than the action of the MCP-1 molecule itself.

Mac-1, but not LFA-1, uses intercellular adhesion molecule-1 to mediate slow leukocyte rolling in TNF-alpha-induced inflammation

We have previously shown that Mac-1 and LFA-1 play a cooperative role in slow leukocyte rolling in inflamed vessels, and that, although both have a role in leukocyte adhesion, the contribution from LFA-1 exceeds that of Mac-1. In this study, we used mice deficient in ICAM-1 (ICAM-1(null)) to study the function of ICAM-1 as an endothelial ligand for Mac-1 and LFA-1. The cremaster muscles of these mice were treated with TNF-alpha and prepared for intravital microscopy. We found that the average rolling velocity in venules was not different in ICAM-1(null) mice (4.7 micro m/s) compared with wild-type mice (5.1 micro m/s). Similarly, leukocyte adhesion efficiency in ICAM-1(null) mice (0.11 +/- 0.01 mm) was similar to that in Mac-1(-/-) (0.12 +/- 0.03 mm) mice but significantly increased compared with that in LFA-1(-/-) (0.08 +/- 0.01 mm) mice and significantly reduced from that in wild type (0.26 +/- 0.04 mm). When both LFA-1 and ICAM-1 were blocked, rolling velocity increased, and adhesion efficiency and arrest decreased. However, blocking both Mac-1 and ICAM-1 had no greater effect than either blockade alone. We conclude that endothelial ICAM-1 is the main ligand responsible for slow leukocyte rolling mediated by Mac-1, but not LFA-1.

Activation des molécules d’adhésion chez les patients en choc septique

OBJECTIVE

To analyze the pattern of adhesion molecules in patients with septic shock. Data sources. - References obtained from Pubmed databank.

DATA EXTRACTION

Models of inflammation linking endothelial dysfunction, adhesion molecules and septic states were analyzed.

DATA SYNTHESIS

The endothelium has been identified as the central effector in the inflammatory response. Adhesion molecules are strongly involved in the inflammatory process by modulating the leukocyte trafficking. The most important adhesion molecules are the selectins (E-, L-, and P-selectins) and members of the immunoglobulin superfamily (intercellular adhesion molecule-1 and vascular cell adhesion molecule-1). Plasma levels of these molecules are increased in septic shock patients, which may be related to a marked activation of the endothelium. However, a dichotomous profile is observed between plasma and tissue expression. The inhibition of adhesive molecule actions could make it possible to control the inflammatory response.

Ultraviolet light exposure suppresses contact hypersensitivity by abrogating endothelial intercellular adhesion molecule-1 up-regulation at the elicitation site

Hapten sensitization through UV-exposed skin induces systemic immune suppression, which is experimentally demonstrated by inhibition of contact hypersensitivity (CHS). Although this UV-induced effect has been shown to be mediated by inhibition of the afferent phase of the CHS, the UV effects on the efferent (elicitation) phase remain unknown. In this study, UV effects on endothelial ICAM-1 expression at elicitation sites were first examined. Mice were sensitized by hapten application onto UV-exposed back skin, and ears were challenged 5 days later. ICAM-1 up-regulation at nonirradiated elicitation sites following hapten challenge was eliminated by UV exposure on sensitization sites distant from elicitation sites. To assess whether loss of the ICAM-1 up-regulation at elicitation sites contributed to UV-induced immunosuppression, we examined CHS responses in UV-exposed ICAM-1-deficient (ICAM-1(-/-)) mice that genetically lacked the ICAM-1 up-regulation. ICAM-1(-/-) mice exhibited reduced CHS responses without UV exposure, but UV exposure did not further reduce CHS responses in ICAM-1(-/-) mice. Furthermore, ICAM-1 deficiency did not affect the afferent limb, because ICAM-1(-/-) mice had normal generation of hapten-specific suppressor and effector T cells. This UV-induced immunosuppression was associated with a lack of TNF-alpha production after Ag challenge at elicitation sites. Local TNF-alpha injection before elicitation abrogated the UV-induced CHS inhibition with increased endothelial ICAM-1 expression. TNF-alpha production at elicitation sites was down-regulated by IL-10, a possible mediator produced by hapten-specific suppressor T cells that are generated by UV exposure. These results indicate that UV exposure inhibits CHS by abrogating up-regulation of endothelial ICAM-1 expression after Ag challenge at elicitation sites.

High-temporal-resolution analysis demonstrates that ICAM-1 stabilizes WEHI 274.1 monocytic cell rolling on endothelium

Leukocyte rolling, adhesion, and migration on vascular endothelium involve several sets of adhesion molecules that interact simultaneously. Each of these receptor-ligand pairs may play multiple roles. We examined the role of ICAM-1 in adhesive interactions with mouse aortic endothelial cells (MAECs) in an in vitro flow system. Average rolling velocity of the monocytic cell line WEHI 274.1 was increased on ICAM-1-deficient MAECs compared with wild-type MAECs, both with and without TNF-alpha stimulation. High-temporal-resolution analysis provided insights into the underlying basis for these differences. Without TNF-alpha stimulation, average rolling velocity was slower on wild-type than on ICAM-1-deficient endothelium because of brief (<1 s) pauses. On TNF-alpha-stimulated ICAM-1-deficient endothelium, cells rolled faster because of transient accelerations, producing "jerky" rolling. Firm adhesion to ICAM-1-deficient MAECs was significantly reduced compared with wild-type MAECs, although the number of rolling cells was similar. These results demonstrate directly that ICAM-1 affects rolling velocity by stabilizing leukocyte rolling.

The effects of fresh frozen plasma on neutrophil-endothelial interactions

Leukocyte adhesion to endothelial cells contributes to microcirculatory disturbances during severe shock syndromes. Whereas certain plasma expanders inhibit leukocyte adhesion, contaminants of plasma protein solutions upregulate endothelial cell adhesion molecules in certain cases. We performed this study to determine whether fresh frozen plasma (FFP) affects neutrophil-endothelial interactions in cocultures of neutrophils and human umbilical vein endothelial cells (HUVEC) in vitro. HUVEC (n = 9) were incubated with either 20% FFP or 20% serum in medium for 6 h. Expression of E-selectin, intercellular adhesion molecule 1, and vascular cell adhesion molecule-1 was induced by tumor necrosis factor alpha (0.5 ng/mL for 4 h) and measured by flow cytometry. Neutrophil adhesion was examined in a parallel plate flow chamber in which isolated neutrophils were perfused over pretreated HUVEC under postcapillary flow conditions. Incubation with FFP decreased E-selectin and intercellular adhesion molecule 1 on activated HUVEC by 28% and 22%, respectively (P < or = 0.01; analysis of covariance). Consequently, neutrophil adhesion decreased by 20%-41% in FFP-treated cocultures (n = 4; P < or = 0.01; paired Student's t-test). We conclude that FFP attenuates the inflammatory response of endothelial cells with regard to neutrophil-endothelial interactions. Because the composition of patients' plasma is affected not only by transfusion, but more frequently by shock treatment with IV fluids, plasma dilution in critically ill patients could be important.

IMPLICATIONS

During shock, fluid administration leads to a massive dilution of plasma. Apart from maintaining hemodynamics, this might affect tissue damage by influencing leukocyte accumulation in the microvasculature. Using endothelial cells, isolated neutrophils, and a parallel plate flow chamber, we studied the effects of fresh frozen plasma on neutrophil-endothelial interactions.

Chemokine induction of integrin adhesiveness on rolling and arrested leukocytes local signaling events or global stepwise activation?

The arrest of rolling leukocytes on target endothelium is predominantly mediated by integrins, which pre-exist in largely inactive states on circulating immune cells and need to be activated in situ. These adhesion receptors acquire high avidity upon encounter with endothelial-displayed chemokines or chemoattractants, which are ligands to specific G protein-coupled receptors (GPCRs) on the leukocyte surface. In order to arrest, the leukocyte must constantly integrate endothelial-based signals as it moves along the vessel wall. It is unclear whether the chemokine signal is locally transmitted at the endothelial contact zone or whether the rolling leukocyte accumulates successive chemokine signals to reach a threshold global activation. Recent in vitro and in vivo data suggest that the induction of high integrin avidity by endothelial chemokine-transduced G(i)-signals is a general mechanism that has evolved to locally enhance integrin avidity to ligand within subseconds at restricted leukocyte-endothelial contacts. In addition, a second specialized mechanism, involving stepwise signals integrated by selectin ligands on rolling cells, seems to activate integrins on the entire leukocyte surface. This GPCR-independent and much slower pathway (10(1)-10(2) seconds) is transmitted through rolling engagements of neutrophils, primarily on E-selectin. We propose that these two mechanisms are differentially used by distinct leukocyte subsets at various vascular beds, providing much larger combinatorial diversity of integrin activation on rolling leukocytes than previously predicted.

Relative contributions of selectins and intercellular adhesion molecule-1 to tissue injury induced by immune complex deposition

Immune complex-induced tissue injury is mediated by inflammatory cell infiltration that is highly regulated by multiple adhesion molecules. To assess the relative contribution of adhesion molecules, including selectins and ICAM-1, in this pathogenetic process, the cutaneous passive Arthus reaction was examined in mice lacking E-selectin, P-selectin, or both L-selectin and ICAM-1 with anti-P- or E-selectin mAbs. Edema and hemorrhage were significantly reduced in P-selectin(-/-) mice compared with wild-type mice while they were not inhibited in E-selectin(-/-) mice. Combined E- and P-selectin blockade resulted in more significant reduction relative to L-selectin/ICAM-1(-/-) as well as P-selectin(-/-) mice. Remarkably, both E- and P-selectin blockade in L-selectin/ICAM-1(-/-) mice completely abrogated edema and hemorrhage. The inhibited edema and hemorrhage paralleled reduced infiltration of neutrophils and mast cells that expressed significant levels of P-selectin glycoprotein ligand-1. Similarly reduced infiltration of neutrophils and mast cells was observed in the peritoneal Arthus reaction and was associated partly with the decreased production of tumor necrosis factor-alpha and interleukin-6. The results of this study indicate that both endothelial selectins contribute predominantly to the Arthus reaction by regulating mast cell and neutrophil infiltration and that the full development of the Arthus reaction is mediated cooperatively by all selectins and ICAM-1.