Leukocyte-inspired biodegradable particles that selectively and avidly adhere to inflamed endothelium in vitro and in vivo

We exploited leukocyte-endothelial cell adhesion chemistry to generate biodegradable particles that exhibit highly selective accumulation on inflamed endothelium in vitro and in vivo. Leukocyte-endothelial cell adhesive particles exhibit up to 15-fold higher adhesion to inflamed endothelium, relative to noninflamed endothelium, under in vitro flow conditions similar to that present in blood vessels, a 6-fold higher adhesion to cytokine inflamed endothelium relative to non-cytokine-treated endothelium in vivo, and a 10-fold enhancement in adhesion to trauma-induced inflamed endothelium in vivo due to the addition of a targeting ligand. The leukocyte-inspired particles have adhesion efficiencies similar to that of leukocytes and were shown to target each of the major inducible endothelial cell adhesion molecules (E-selectin, P-selectin, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1) that are up-regulated at sites of pathological inflammation. The potential for targeted drug delivery to inflamed endothelium has significant implications for the improved treatment of an array of pathologies, including cardiovascular disease, arthritis, inflammatory bowel disease, and cancer.

Dual roles of sialyl Lewis X oligosaccharides in tumor metastasis and rejection by natural killer cells

Aberrant expression of cell surface carbohydrates such as sialyl Lewis X is associated with tumor formation and metastasis. In order to determine the roles of sialyl Lewis X in tumor metastasis, mouse melanoma B16-F1 cells were stably transfected with alpha1, 3-fucosyltransferase III to express sialyl Lewis X structures. The transfected B16-F1 cells, B16-FTIII, were separated by cell sorting into three different groups based on the expression levels of sialyl Lewis X. When these transfected cells were injected into tail veins of C57BL/6 mice, B16-FTIII.M cells expressing moderate amounts of sialyl Lewis X in poly-N-acetyllactosamines produced large numbers of lung tumor nodules. Surprisingly, B16-FTIII.H cells expressing the highest amount of sialyl Lewis X in shorter N-glycans died in lung blood vessels, producing as few lung nodules as B16-FTIII.N cells which lack sialyl Lewis X. In contrast, B16-FIII.H cells formed more tumors in beige mice and NK cell-depleted C57BL/6 mice than did B16-FTIII.M cells. B16-FTIII.H cells bound to E-selectin better than did B16-FTIII.M cells, but both cells grew at the same rate. These results indicate that excessive expression of sialyl Lewis X in tumor cells leads to rejection by NK cells rather than tumor formation facilitated by attachment to endothelial cells.

Soluble E-selectin in cardiovascular disease and its risk factors. A review of the literature

The initial steps in the pathogenesis of atherosclerosis involve changes to the vascular endothelium, which produces numerous substances involved in the regulation and maintenance of vascular integrity and the homeostasis of the coagulation/fibrinolysis system. A further change in endothelial physiology is an increase in the surface expression of cell adhesion molecules, such as E-selectin, which regulate adhesive interactions between certain blood cells and endothelium. As E-selectin is only expressed on activated endothelium, it therefore provides an opportunity to study pathophysiological aspects of this cell in cardiovascular and other disease. However, a soluble form of E selectin (i.e. sE-selectin) can be found in the plasma. This review will focus on sE-selectin, and its potential role in the pathogenesis of cardiovascular disease as raised levels have been found in hypertension, diabetes and hyperlipidemia, although its association in established atherosclerosis disease and its value as a prognostic factor is more controversial.

Importance of E-selectin for firm leukocyte adhesion in vivo

Leukocyte adhesion under flow is preferentially mediated by the selectins. In this study we used intravital microscopy to investigate whether E-selectin may promote firm leukocyte adhesion in vivo. E-Selectin is expressed by endothelial cells activated with tumor necrosis factor-alpha (TNF-alpha) and causes slow leukocyte rolling. Microinjection of formyl-methionyl-leucyl-phenylalanine (fMLP) or macrophage inflammatory protein-2 (MIP-2) next to a venule of the TNF-alpha-treated mouse cremaster muscle significantly increased the number of adherent leukocytes. In gene-targeted mice homozygous for a null mutation in the E-selectin gene or in wild-type mice treated with an E-selectin monoclonal antibody (mAb), this response was significantly attenuated (by >80%). No such defect was seen in intercellular adhesion molecule-1 (ICAM-1)-deficient mice. E-Selectin-null mice showed more rapid leukocyte rolling than wild-type or ICAM-1-deficient mice, resulting in significantly shortened leukocyte transit times through venules. Topical application of fMLP onto the whole cremaster muscle generated the same number of adherent leukocytes in wild-type and E-selectin-deficient mice. We conclude that slow leukocyte rolling through E-selectin results in long transit times, which are essential for efficient leukocyte adhesion in response to a local chemotactic stimulus.

Rho GTPases and Leukocyte Adhesion Receptor Expression and Function in Endothelial Cells

Rho family GTPases are key signal transducers that regulate cell adhesion and migration and a variety of other cellular responses, including changes in gene expression. In this review, we discuss how Rho GTPases regulate signaling by endothelial cell receptors involved in leukocyte extravasation. First, Rho GTPases affect the expression of some leukocyte adhesion molecules on endothelial cells, such as intracellular adhesion molecule-1 and E-selectin, that can be induced by proinflammatory mediators, hypoxia, or shear stress. Second, Rho GTPases are activated by engagement of several leukocyte adhesion receptors and contribute to both early morphological changes and subsequent alterations in gene expression. Rho GTPases are therefore candidate targets for inhibiting leukocyte transendothelial migration in heart disease and chronic inflammatory disorders.

Essential role of neutrophils in germ cell-specific apoptosis following ischemia/reperfusion injury of the mouse testis

This study investigates the role of neutrophils in ischemia-induced aspermatogenesis in the mouse. Previous studies in the rat have demonstrated that ischemia-inducing testicular torsion followed by torsion repair and reperfusion resulted in germ cell-specific apoptosis. This was correlated with an increase in neutrophil adhesion to subtunical venules, an increase in reactive oxygen species, and increased expression of several apoptosis-associated molecules. In the present investigation, wild-type C57BL/6 mice were subjected to various degrees and duration of testicular torsion. A torsion of 720 degrees for 2 h caused disruption of the seminiferous epithelium and significantly reduced testis weight and daily sperm production. An immunohistochemical method specific for apoptotic nuclei indicated that these effects were due to germ cell-specific apoptosis. An increase in myeloperoxidase (MPO) activity and an increase in the number of neutrophils adhering to testicular subtunical venules after torsion repair/reperfusion demonstrated an increase in neutrophil recruitment to the testis. In contrast, E-selectin knockout mice and wild-type mice rendered neutropenic showed a significant decrease in neutrophil recruitment as evidenced by MPO activity and microscopic examination of subtunical venules. Importantly, germ cell-specific apoptosis was also reduced. Thus, germ cell-specific apoptosis is observed after ischemia/reperfusion of the murine testis, and this apoptosis is directly linked to the recruitment of neutrophils to subtunical venules. Endothelial cell adhesion molecules, particularly E-selectin, play an important role in mediating this pathology.

Increased monocyte adhesion to aortic endothelium in rats with hyperhomocysteinemia: role of chemokine and adhesion molecules

OBJECTIVE

The stimulatory effect of homocysteine (Hcy) on monocyte chemoattractant protein (MCP)-1 expression in vitro has been suggested to play an important role in Hcy-mediated atherosclerosis. We investigated whether such a stimulatory effect occurs in vivo, leading to monocyte adhesion to the endothelium.

METHODS AND RESULTS

Sprague-Dawley rats were divided into 4 groups. Hyperhomocysteinemia was induced in 1 group of rats after 4 weeks of a high-methionine diet (serum Hcy levels were 4- to 5-fold higher than levels in control rats). The number of ED-1-positive cells present on the surface of aortic endothelium was significantly elevated in hyperhomocysteinemic rats. There was a significant increase in the expression of MCP-1, vascular cell adhesion molecule-1 (VCAM-1), and E-selectin in the endothelium. Antibodies recognizing MCP-1, VCAM-1, or E-selectin could abolish the enhanced monocyte binding to the aortic endothelium of hyperhomocysteinemic rats. Endothelium-dependent aortic relaxation was impaired in hyperhomocysteinemic rats.

CONCLUSIONS

These results suggest that in the absence of other known risk factors, hyperhomocysteinemia stimulates the expression of MCP-1, VCAM-1, and E-selectin in vivo, leading to increased monocyte adhesion to the aortic endothelium. Such an effect may contribute significantly to the development of atherosclerosis by facilitating monocyte/macrophage infiltration into the arterial wall.

Role of tumor endothelium in CD4+ CD25+ regulatory T cell infiltration of human pancreatic carcinoma

BACKGROUND

Regulatory T (Treg) cells have been detected in human carcinomas and may play a role in preventing the rejection of malignant cells.

METHODS

We quantified Treg cells and the expression of the addressins and the respective ligands that attract them in blood and in human pancreatic tumors and adjacent nonmalignant tissues from 47 patients. The capacity of Treg cells to adhere to and transmigrate through autologous endothelial cells was tested in vitro using spheroid adhesion assays and in vivo using a xenotransplant NOD/SCID model and in the presence and absence of antibodies to addressins. All statistical tests were two-sided.

RESULTS

More Treg cells infiltrated pancreatic carcinomas than adjacent nonmalignant pancreatic tissues (120 cells per mm2 versus 80 cells per mm2, difference = 40 cells per mm2, 95% confidence interval [CI] = 21.2 cells per mm2 to 52.1 cells per mm2; P<.001). In contrast to conventional CD4+ T cells, more blood-derived Treg cells adhered to (1.0% versus 5.2%, difference = 4.2%, 95% CI = 2.7% to 5.6%; P<.001) and transmigrated through (3332 cells versus 4976 cells, difference = 1644 cells, 95% CI = 708 cells to 2580 cells; P = .008) autologous tumor-derived endothelial cells in vitro and in vivo (458 cells versus 605 cells, difference = 147 cells, 95% CI = 50.8 to 237.2 cells; P = .04). Tumor-derived endothelial cells expressed higher levels of addressins--including mucosal adressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1), CD62-E, and CD166--than endothelial cells from normal tissue. Experiments using antibodies to addressins showed that transmigration was mediated by interactions of addressins, including MAdCAM-1, VCAM-1, CD62-E, and CD166 with their respective ligands, beta7 integrin, CD62L, and CD166, which were expressed specifically on Treg cells.

CONCLUSIONS

Tumor-induced expression of addressins on the surface of endothelial cells allows a selective transmigration of Treg cells from peripheral blood to tumor tissues.

Shear-dependent capping of L-selectin and P-selectin glycoprotein ligand 1 by E-selectin signals activation of high-avidity beta2-integrin on neutrophils

Two adhesive events critical to efficient recruitment of neutrophils at vascular sites of inflammation are up-regulation of endothelial selectins that bind sialyl Lewis(x) ligands and activation of beta(2)-integrins that support neutrophil arrest by binding ICAM-1. We have previously reported that neutrophils rolling on E-selectin are sufficient for signaling cell arrest through beta(2)-integrin binding of ICAM-1 in a process dependent upon ligation of L-selectin and P-selectin glycoprotein ligand 1 (PSGL-1). Unresolved are the spatial and temporal events that occur as E-selectin binds to human neutrophils and dynamically signals the transition from neutrophil rolling to arrest. Here we show that binding of E-selectin to sialyl Lewis(x) on L-selectin and PSGL-1 drives their colocalization into membrane caps at the trailing edge of neutrophils rolling on HUVECs and on an L-cell monolayer coexpressing E-selectin and ICAM-1. Likewise, binding of recombinant E-selectin to PMNs in suspension also elicited coclustering of L-selectin and PSGL-1 that was signaled via mitogen-activated protein kinase. Binding of recombinant E-selectin signaled activation of beta(2)-integrin to high-avidity clusters and elicited efficient neutrophil capture of beta(2)-integrin ligands in shear flow. Inhibition of p38 and p42/44 mitogen-activated protein kinase blocked the cocapping of L-selectin and PSGL-1 and the subsequent clustering of high-affinity beta(2)-integrin. Taken together, the data suggest that E-selectin is unique among selectins in its capacity for clustering sialylated ligands and transducing signals leading to neutrophil arrest in shear flow.

Determining force dependence of two-dimensional receptor-ligand binding affinity by centrifugation

Analyses of receptor-ligand interactions are important to the understanding of cellular adhesion. Traditional methods of measuring the three-dimensional (3D) dissociation constant (Kd) require at least one of the molecular species in solution and hence cannot be directly applied to the case of cell adhesion. We describe a novel method of measuring 2D binding characteristics of receptors and ligands that are attached to surfaces and whose bonds are subjected to forces. The method utilizes a common centrifugation assay to quantify adhesion. A model for the experiment has been formulated, solved exactly, and tested carefully. The model is stochastically based and couples the bond force to the binding affinity. The method was applied to examine tumor cell adherence to recombinant E-selectin. Satisfactory agreement was found between predictions and data. The estimated zero-force 2D Kd for E-selectin/carbohydrate ligand binding was approximately 5 x 10(3) microm(-2), and the bond interaction range was subangstrom. Our results also suggest that the number of bonds mediating adhesion was small (<5).

Cytokine-induced meningitis is dramatically attenuated in mice deficient in endothelial selectins

Leukocyte accumulation in cerebrospinal fluid and disruption of the blood-brain barrier are central components of meningitis and are associated with a poor prognosis. Genetically engineered deficiencies or functional inhibition of endothelial leukocyte adhesion receptors P-, or P- plus E-selectins, lead to deficits in leukocyte rolling and extravasation. However, their impact on meningeal inflammation has not been tested previously. An acute cytokine-induced meningitis model associated with significant cerebrospinal fluid leukocyte accumulation (averaging 14,000 leukocytes/microl as early as 4 h) and blood-brain barrier permeability was developed in adult mice. This model was applied to mice deficient in P-selectin and mice doubly deficient in P- and E-selectins. Partial inhibition of cerebrospinal fluid leukocyte influx and permeability was noted in P-selectin-deficient mice. Mice doubly deficient in P- and E-selectins displayed a near complete inhibition of these parameters. Our results suggest that P- and E-selectins cooperatively contribute to meningitis and that functional blocking of both endothelial selectins in conjunction with antibiotics may provide a therapeutic approach for treatment of bacterial meningitis.

Two waves of neutrophil emigration in response to corneal epithelial abrasion: distinct adhesion molecule requirements

PURPOSE

Corneal abrasion results in an inflammatory response characterized by leukocyte emigration into the corneal stroma. Adhesion molecules play a critical role in leukocyte emigration to wound sites, but differences are evident in different vascular beds. In this study, the contributions of two families of adhesion molecules to neutrophil emigration into the cornea were investigated.

METHODS

Re-epithelialization, patterns of neutrophil influx and CXC chemokine production were assessed in C57Bl/6 mice after removal of a 2-mm diameter area of central corneal epithelium. Comparisons were made between wild-type (WT) mice and mice with targeted deletions of genes for CD18 (CD18(-/-)) or P- and E-selectin (P/E-sel(-/-)) or in mice with antibody-induced neutropenia.

RESULTS

Wild-type mice exhibited neutrophil emigration in two waves, the first peaking at 18 hours and the second at 30 hours after wounding, 6 hours after epithelial wound closure and peak levels of corneal CXCL1. In CD18(-/-) animals, only a single wave of neutrophil influx was seen, and it was temporally and quantitatively equivalent to the second wave in WT. In P/E-sel(-/-) mice, neutrophil influx was markedly depressed throughout the 48-hour observation period. Re-epithelialization was significantly delayed in mice with adhesion molecule deletions and in neutropenic animals. Transfer of wild-type leukocytes into CD18(-/-) mice resulted in neutrophil emigration into the injured cornea within 18 hours of wounding and improved closure of the epithelium.

CONCLUSIONS

Neutrophil emigration into corneal stroma after epithelial abrasion occurs in two waves. The first is dependent on CD18 integrins and selectins, whereas the second is CD18-independent but requires selectins. Early leukocyte emigration appears to promote re-epithelialization.

Angiotensin II increases monocyte binding to endothelial cells

Angiotensin II (AII) is recognized as being an important factor in the pathogenesis of hypertension and atherosclerosis. Monocyte binding to affected endothelial cells is one of the earliest features of atherosclerosis. However, the effect of AII on monocyte binding has not been fully studied. Treatment of human aortic endothelial cells (HAEC) and rabbit aortic endothelial cells (RAEC) for 18 hours with AII induced the adhesion of monocytes but not neutrophils to these cells. This induction was reduced by inhibitors of AII receptors (Type I and Type II). Angiotensin II-induced monocyte binding was not associated with induction of E-selectin, vascular cell adhesion molecule-1 (VCAM-1), or intercellular adhesion molecule-1 (ICAM-1). These results suggest that AII can accelerate the rate of atherosclerosis by increasing monocyte binding to the endothelium.

Activation and homologous desensitization of human endothelial cells by CD40 ligand, tumor necrosis factor, and interleukin 1

We have reported previously that activation of human umbilical vein endothelial cells (HUVECs) through CD40, using a recombinant soluble form of trimerized CD40 ligand, leads to induction of E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1). Here, we compare the effects of CD40 ligand with those of tumor necrosis factor (TNF) and interleukin 1 (IL-1). All three ligands induce transient increases in E-selectin (peak 4 h) and VCAM-1 (peak 8-24 h), as well as sustained increases in ICAM-1 (plateau 24 h). Quantitatively, TNF is more potent than IL-1, which is much more potent than CD40 ligand. The same hierarchy is observed for transcriptional activation of an E-selectin promoter reporter gene construct in transiently transfected HUVECs. TNF and CD40 ligand each induced activation of the transcription factors NF-kappa B, IRF-1, and ATF-2/c-Jun, measured by electrophoretic mobility shift assays, but this response appeared quantitatively similar. All three agents transiently (peak 30 min) activated Jun NH2-terminal kinase (JNK), which has been implicated in transcription of E-selectin through its actions on ATF-2/c-Jun. Activation of JNK again showed a hierarchy of potency (TNF > IL-1 >> CD40 ligand), although the time course of induction was similar for all three agents. After 44 h of pretreatment, TNF, IL-1, and CD40 ligand each display homologous desensitization for reinduction of surface expression of E-selectin. A similar pattern of homologous desensitization for reactivation of JNK was observed. We conclude that TNF, IL-1, and CD40 ligand all activate similar responses in ECs, and that homologous desensitization of JNK may explain the inability of individual cytokines to reinduce E-selectin expression.

CD43 is a ligand for E-selectin on CLA+ human T cells

The recruitment of memory T cells from blood into tissues is a central element of immune surveillance and adaptive immune responses and a key feature of chronic cutaneous inflammatory diseases such as psoriasis and atopic dermatitis. Human memory T cells that infiltrate skin express the carbohydrate epitope cutaneous lymphocyte-associated antigen (CLA). Expression of the CLA epitope on T cells has been described on P-selectin glycoprotein ligand-1 (PSGL-1) and associated with the acquisition of both E-selectin and P-selectin ligand functions. In this report, we show that CD43, a sialomucin expressed constitutively on T cells, can also be decorated with the CLA epitope and serve as an E-selectin ligand. CLA expressed on CD43 was found exclusively on the high-molecular-weight (125 kDa) glycoform bearing core-2-branched O-linked glycans. CLA+ CD43 purified from human T cells supported tethering and rolling in shear flow via E-selectin but did not support binding of P-selectin. The identification and characterization of CD43 as a T-cell E-selectin ligand distinct from PSGL-1 expands the role of CD43 in the regulation of T-cell trafficking and provides new targets for the modulation of immune functions in skin.

Dynamic contact forces on leukocyte microvilli and their penetration of the endothelial glycocalyx

We develop a theoretical model to examine the combined effect of gravity and microvillus length heterogeneity on tip contact force (F(m)(z)) during free rolling in vitro, including the initiation of L-, P-, and E-selectin tethers and the threshold behavior at low shear. F (m)(z) grows nonlinearly with shear. At shear stress of 1 dyn/cm(2), F(m)(z) is one to two orders of magnitude greater than the 0.1 pN force for gravitational settling without flow. At shear stresses > 0.2 dyn/cm(2) only the longest microvilli contact the substrate; hence at the shear threshold (0.4 dyn/cm(2) for L-selectin), only 5% of microvilli can initiate tethering interaction. The characteristic time for tip contact is surprisingly short, typically 0.1-1 ms. This model is then applied in vivo to explore the free-rolling interaction of leukocyte microvilli with endothelial glycocalyx and the necessary conditions for glycocalyx penetration to initiate cell rolling. The model predicts that for arteriolar capillaries even the longest microvilli cannot initiate rolling, except in regions of low shear or flow reversal. In postcapillary venules, where shear stress is approximately 2 dyn/cm(2), tethering interactions are highly likely, provided that there are some relatively long microvilli. Once tethering is initiated, rolling tends to ensue because F(m)(z) and contact duration will both increase substantially to facilitate glycocalyx penetration by the shorter microvilli.

Angiotensin II-induced leukocyte adhesion on human coronary endothelial cells is mediated by E-selectin

Clinical data suggest a link between the activation of the renin-angiotensin system and cardiovascular ischemic events. Leukocyte accumulation in the vessel wall is a hallmark of early atherosclerosis and plaque progression. E-Selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) are adhesion molecules participating in mediating interactions between leukocytes and endothelial cells and have been found to be expressed in athero-sclerotic plaques. We investigated whether angiotensin II, the effector of the renin-angiotensin system, influences the endothelial expression of E-selectin, VCAM-1, and ICAM-1. In coronary endothelial cells derived from explanted human hearts, angiotensin II (10(-11) to 10(-5) mol/L) induced a concentration-dependent increase in E-selectin expression. The effect was measured by cell ELISA and duplex reverse-transcription polymerase chain reaction (RT-PCR) and reached its maximum at 10(-7) mol/L. Angiotensin II induced only a small increase in E-selectin expression in cardiac microvascular endothelial cells. VCAM-1 and ICAM-1 were not affected by angiotensin II stimulation. In addition, the effect of angiotensin II-induced E-selectin expression on leukocyte adhesion was quantified under flow conditions. Angiotensin II (10(-7) mol/L) increased leukocyte adhesion significantly to 67% of the maximal effect by tumor necrosis factor-alpha at a wall shear stress of 2 dyne/cm2. This adhesion was found to be E-selectin dependent, as demonstrated by blocking antibodies. The AT1-receptor antagonist DUP 753 significantly reduced E-selectin-dependent adhesion, whereas the AT2-receptor antagonist PD 123177 had no inhibitory effect. In addition, only AT1-receptor, but not AT2-receptor, mRNA could be detected by RT-PCR in coronary endothelial cells. Therefore, it is suggested that AT1 receptors mediate the effects of angiotensin II on E-selectin expression and leukocyte adhesion on coronary endothelial cells.

Sialyl Lewis(x)/E-selectin-mediated rolling in a cell-free system

Selections mediate transient adhesion of neutrophils to stimulated endothelial cells at sites of inflammation by binding counter-receptors that present carbohydrates such as sialyl Lewis(x). We have developed a cell-free adhesion assay using sialyl Lewis(x)-coated microspheres and E-selection-IgG chimera-coated substrates to investigate the premise that rolling primarily results from functional properties of selection-carbohydrate bonds, whereas cellular morphology and signaling act as secondary effects. Sialyl Lewis(x)-coated microspheres attach to and roll over E-selectin-IgG chimera-coated substrates between the physiological wall shear stresses of 0.7 and 2 dynes/cm2. Rolling velocities vary with time and depend on E-selectin-IgG chimera site density and wall shear stress. Our results show that sialyl Lewis(x) is a minimal functional recognition element required for rolling on E-selectin under flow.

E-selectin, thymus- and activation-regulated chemokine/CCL17, and intercellular adhesion molecule-1 are constitutively coexpressed in dermal microvessels: a foundation for a cutaneous immunosurveillance system

The success of the cutaneous immune system reflects its ability to rapidly and efficiently recruit leukocytes to areas of trauma and infection. Skin-homing memory T cells expressing cutaneous lymphocyte-associated Ag tether on the walls of postcapillary venules in inflamed skin via interaction with endothelial E-selectin and roll in response to the shear stress imparted by flowing blood. Rolling cells sample the vascular surface for chemoattractant compounds (e.g., thymus- and activation-regulated chemokine/CCL17 interacting with CCR4 on the leukocyte surface) and, if successfully stimulated, progress to firm arrest and transmigration mediated by LFA-1 and vascular ICAM-1. Although it is established that this sequence of events draws T cells into inflamed skin, the mechanisms directing trafficking of T cells to noninflamed skin are less well characterized. We hypothesized that basal expression and colocalization of E-selectin, chemokine (e.g., CCL17), and ICAM-1 in dermal vessels could serve to recruit T cells to noninflamed human skin. Immunohistochemical staining for E-selectin and CD31 demonstrated E-selectin expression in a restricted subset of dermal vessels in noninflamed human skin from three different sites. Confocal multicolor immunofluorescence imaging revealed a nonuniform distribution of E-selectin in dermal vessels as well as colocalization of E-selectin with CCL17 and ICAM-1. Coexpression of these molecules on blood vessels in noninflamed skin provides the basis for a model of cutaneous immunosurveillance system active in the absence of pathologic inflammation.

Quantifying rolling adhesion with a cell-free assay: E-selectin and its carbohydrate ligands

Rolling of neutrophils over stimulated endothelial cells is a prerequisite to firm attachment and subsequent transendothelial migration during the inflammatory response. The selectin family of adhesion molecules are thought to mediate rolling by binding counter-receptors that present carbohydrates, such as sialyl Lewis(x) (sLe[x]). Recently we described a cell-free system for rolling using sLe(x)-coated microspheres and E-selectin molecules on inert substrates. We showed that sLe(x)-coated microspheres rolled over E-selectin-IgG chimera substrates with dynamics that are similar to those of leukocytes rolling over stimulated endothelium. In this paper we provide a thorough quantitative description of the dynamics of adhesion for this system. We find that particle rolling velocity increases with increasing wall shear stress and decreases with increasing E-selectin or sLe(x) surface densities. Large changes in the average rolling velocity can occur with small changes in sLe(x) or E-selectin density; however, rolling velocity is more sensitive to E-selectin surface coverage than to the number of sLe(x) molecules on the microspheres. Aided by dimensional analysis, we show that decreasing the wall shear stress or increasing either receptor (E-selectin) or ligand (sLe[x]) surface coverage results in an equivalent decrease in particle rolling velocity. In addition, we find that different Lewis carbohydrates are more effective in mediating rolling on E-selectin, with effectiveness following the trend sialyl Lewis(a) > sialyl Lewis(x) >> sulfated Lewis(x) >> Lewis(x). Rolling velocity fluctuated with time for all carbohydrate-selectin pairs tested, and the magnitude of the velocity fluctuations was linearly proportional to the mean rolling velocity for all combinations of E-selectin site density, sLe(x) site density, wall shear stress, and carbohydrate chemistry tested.

Sulfation of a high endothelial venule-expressed ligand for L-selectin. Effects on tethering and rolling of lymphocytes

During lymphocyte homing, L-selectin mediates the tethering and rolling of lymphocytes on high endothelial venules (HEVs) in secondary lymphoid organs. The L-selectin ligands on HEV are a set of mucin-like glycoproteins, for which glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) is a candidate. Optimal binding in equilibrium measurements requires sulfation, sialylation, and fucosylation of ligands. Analysis of GlyCAM-1 has revealed two sulfation modifications (galactose [Gal]-6-sulfate and N-acetylglucosamine [GlcNAc]-6-sulfate) of sialyl Lewis x. Recently, three related sulfotransferases (keratan sulfate galactose-6-sulfotransferase [KSGal6ST], high endothelial cell N-acetylglucosamine-6-sulfotransferase [GlcNAc6ST], and human GlcNAc6ST) were cloned, which can generate Gal-6-sulfate and GlcNAc-6-sulfate in GlyCAM-1. Imparting these modifications to GlyCAM-1, together with appropriate fucosylation, yields enhanced rolling ligands for both peripheral blood lymphocytes and Jurkat cells in flow chamber assays as compared with those generated with exogenous fucosyltransferase. Either sulfation modification results in an increased number of tethered and rolling lymphocytes, a reduction in overall rolling velocity associated with more frequent pausing of the cells, and an enhanced resistance of rolling cells to detachment by shear. All of these effects are predicted to promote the overall efficiency of lymphocyte homing. In contrast, the rolling interactions of E-selectin transfectants with the same ligands are not affected by sulfation.

Endothelial signalling events during leukocyte transmigration

The notion that it takes two to tango is certainly true for leukocyte transendothelial migration. A growing pallet of leukocyte adhesion-induced signaling events in endothelial cells have been identified, mediating both short-term (i.e. permeability) as well as long-term (i.e. regulation of transcription) effects. Efficient paracellular migration (i.e. through endothelial cell-cell junctions) requires both intracellular calcium and the actin cytoskeleton, but also involves small GTPases, reactive oxygen species and protein kinases. The alternative route of transcellular migration appears to depend on components such as caveolae and intermediate filaments. This minireview discusses our current knowledge on the regulation of leukocyte transmigration through endothelial signalling.

Endothelial activation in monosodium urate monohydrate crystal-induced inflammation: in vitro and in vivo studies on the roles of tumor necrosis factor alpha and interleukin-1

OBJECTIVE

There is relatively little direct evidence for the roles of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) in activating endothelium in vivo. The aim of this study was to use in vitro and in vivo models to investigate the contribution of these cytokines to both E-selectin expression and the recruitment of polymorphonuclear cells (PMN) in monosodium urate monohydrate (MSU) crystal-induced inflammation.

METHODS

MSU crystals were incubated with freshly isolated mononuclear cells, after which the harvested supernatants were tested for their ability to induce E-selectin expression during coculture with human umbilical vein endothelial cells. Subsequent experiments were performed with the addition of neutralizing anticytokine antibodies/antisera. The role of TNF alpha was then studied in an MSU crystal-induced monarthritis model, in the presence or absence of anti-TNF alpha (5 mg/kg intravenously). 99mtechnetium (99mTc)-labeled PMN cells and (111)indium (111In)-labeled anti-E-selectin monoclonal antibody (MAb) 1.2B6 were intravenously administered 4 hours after intraarticular injection to quantify PMN recruitment and E-selectin expression in inflamed joints.

RESULTS

MSU crystals were a potent stimulus for IL-1 and TNF alpha production by monocytes in vitro, and these cytokines fully accounted for MSU crystal-stimulated, monocyte-mediated endothelial activation. In the MSU crystal-induced monarthritis model, TNF alpha blockade was very effective in suppressing both E-selectin expression and PMN emigration into the inflamed joints, as judged by gamma-camera image analysis and postmortem tissue counting following the intravenous injection of 99mTc-PMN and 111In-anti-E-selectin MAb.

CONCLUSION

IL-1 and TNF alpha appear to be the only factors released by monocytes following incubation with MSU crystals, which induce E-selectin expression in vitro. Anti-TNF alpha is effective in suppressing endothelial activation and PMN recruitment in vivo E-selectin imaging can be used to assess the endothelial response to therapy and may prove useful for clinical studies.

Neutrophils as inflammatory and immune effectors in photodynamic therapy-treated mouse SCCVII tumours

Neutrophils have become recognised as important contributors to the effectiveness of tumour eradication by photodynamic therapy (PDT). In this study, we have used the mouse SCCVII squamous cell carcinoma model to investigate the activity of neutrophils in tumours treated by PDT. Tumour levels of neutrophilic myeloperoxidase (MPO) demonstrated not only a massive and sustained sequestration of these cells in PDT-treated tumours but also revealed their activated state evidenced by the presence of released MPO. Among the adhesion molecules expressed on tumour vascular endothelium, ICAM-1 appears to be of primary importance in the invasion of neutrophils into PDT-treated tumours, because its functional blocking with monoclonal antibodies reduced the tumour cure rate. A marked upregulation of its ligands CD11b/CD18 and CD11c/CD18 found on neutrophils associated with PDT-treated tumours supports this assumption. To evaluate the role of inflammatory cytokines regulating neutrophil activity, neutralising antibodies were given to mice before PDT treatment. The results suggest that IL-1beta activity is critical for the therapeutic outcome, since its neutralisation diminished the cure rates of PDT-treated tumours. No significant effect was observed with anti-IL-6 and anti-TNF-alpha treatment. Further flow cytometry-based examination of neutrophils round in PDT-treated tumours revealed that these cells express MHC class II molecules, which suggests their engagement as antigen-presenting cells and involvement in the development of antitumour immune response.

Neutrophil adhesion in leukocyte adhesion deficiency syndrome type 2

We have previously reported a newly discovered congenital disorder of neutrophil adhesion, leukocyte adhesion deficiency syndrome type 2 (LAD II). The clinical manifestations of this syndrome are similar to those seen in the classic leukocyte adhesion deficiency syndrome, now designated type 1 (LAD I), but the two syndromes differ in the molecular basis of their adhesion defects. LAD I is caused by a deficiency in the CD18 integrin adhesion molecules while LAD II patients are deficient in expression of sialyl-Lewis X (SLeX), a carbohydrate ligand for selectins. In this report we demonstrate that neutrophils from a LAD II patient bind minimally or not at all to recombinant E-selectin, purified platelet P-selectin, or P-selectin expressed on histamine-activated human umbilical vein endothelial cells, but have normal levels of L-selectin and CD11b/CD18 integrin, and adhere to and migrate across endothelium when CD11b/CD18 is activated. We compare LAD I and LAD II patient neutrophil function in vitro, demonstrating that integrin and selectin adhesion molecules have distinct but interdependent roles in neutrophil adhesion during an inflammatory response.