Endothelial-leukocyte adhesion molecule 1 stimulates the adhesive activity of leukocyte integrin CR3 (CD11b/CD18, Mac-1, alpha m beta 2) on human neutrophils

Cholesterol binding to VCAM-1 promotes vascular inflammation

Hypercholesterolemia has long been implicated in endothelial cell (EC) dysfunction, but the mechanisms by which excess cholesterol causes vascular pathology are incompletely understood. Here we used a cholesterol-mimetic probe to map cholesterol-protein interactions in primary human ECs and discovered that cholesterol binds to and stabilizes the adhesion molecule VCAM-1. We show that accessible plasma membrane (PM) cholesterol in ECs is acutely responsive to inflammatory stimuli and that the nonvesicular cholesterol transporter Aster-A regulates VCAM-1 stability in activated ECs by controlling the size of this pool. Deletion of Aster-A in ECs increases VCAM-1 protein, promotes immune cell recruitment to vessels, and impairs pulmonary immune homeostasis. Conversely, depleting cholesterol from the endothelium in vivo dampens VCAM-1 induction in response to inflammatory stimuli. These findings identify cholesterol binding to VCAM-1 as a key step during EC activation and provide a biochemical explanation for the ability of excess membrane cholesterol to promote immune cell recruitment to the endothelium.

BTK inhibitor-induced defects in human neutrophil effector activity against Aspergillus fumigatus are restored by TNF-α

Inhibition of Bruton's tyrosine kinase (BTK) through covalent modifications of its active site (e.g., ibrutinib [IBT]) is a preferred treatment for multiple B cell malignancies. However, IBT-treated patients are more susceptible to invasive fungal infections, although the mechanism is poorly understood. Neutrophils are the primary line of defense against these infections; therefore, we examined the effect of IBT on primary human neutrophil effector activity against Aspergillus fumigatus. IBT significantly impaired the ability of neutrophils to kill A. fumigatus and potently inhibited reactive oxygen species (ROS) production, chemotaxis, and phagocytosis. Importantly, exogenous TNF-α fully compensated for defects imposed by IBT and newer-generation BTK inhibitors and restored the ability of neutrophils to contain A. fumigatus hyphal growth. Blocking TNF-α did not affect ROS production in healthy neutrophils but prevented exogenous TNF-α from rescuing the phenotype of IBT-treated neutrophils. The restorative capacity of TNF-α was independent of transcription. Moreover, the addition of TNF-α immediately rescued ROS production in IBT-treated neutrophils, indicating that TNF-α worked through a BTK-independent signaling pathway. Finally, TNF-α restored effector activity of primary neutrophils from patients on IBT therapy. Altogether, our data indicate that TNF-α rescued the antifungal immunity block imposed by inhibition of BTK in primary human neutrophils.

Neutrophils as drivers of vascular injury in sickle cell disease

While neutrophils are the main effectors of protective innate immune responses, they are also key players in inflammatory pathologies. Sickle cell disease (SCD) is a genetic blood disorder in which red blood cells (RBCs) are constantly destroyed in the circulation which generates a highly inflammatory environment that culminates in vascular occlusions. Vaso-occlusion is the hallmark of SCD and a predictor of disease severity. Neutrophils initiate and propagate SCD-related vaso-occlusion through adhesive interactions with the activated and dysfunctional endothelium, sickle RBCs, and platelets, leading to acute and chronic complications that progress to irreversible organ damage and ultimately death. The use of SCD humanized mouse models, in combination with in vivo imaging techniques, has emerged as a fundamental tool to understand the dynamics of neutrophils under complex inflammatory contexts and their contribution to vascular injury in SCD. In this review, we discuss the various mechanisms by which circulating neutrophils sense and respond to the wide range of stimuli present in the blood of SCD patients and mice. We argue that the central role of neutrophils in SCD can be rationalized to develop targets for the management of clinical complications in SCD patients.

First-in-Class Allosteric Inhibitors of DNMT3A Disrupt Protein-Protein Interactions and Induce Acute Myeloid Leukemia Cell Differentiation

We previously identified two structurally related pyrazolone (compound 1) and pyridazine (compound 2) allosteric inhibitors of DNMT3A through screening of a small chemical library. Here, we show that these compounds bind and disrupt protein-protein interactions (PPIs) at the DNMT3A tetramer interface. This disruption is observed with distinct partner proteins and occurs even when the complexes are acting on DNA, which better reflects the cellular context. Compound 2 induces differentiation of distinct myeloid leukemia cell lines including cells with mutated DNMT3A R882. To date, small molecules targeting DNMT3A are limited to competitive inhibitors of AdoMet or DNA and display extreme toxicity. Our work is the first to identify small molecules with a mechanism of inhibition involving the disruption of PPIs with DNMT3A. Ongoing optimization of compounds 1 and 2 provides a promising basis to induce myeloid differentiation and treatment of diseases that display aberrant PPIs with DNMT3A, such as acute myeloid leukemia.

Selectin-Mediated Signaling-Shedding Light on the Regulation of Integrin Activity in Neutrophils

As a consequence of tissue injury or infection, neutrophils are recruited in a stepwise recruitment process from the bloodstream into the surrounding tissue. Selectins are a family of adhesion molecules comprised of L-, E-, and P-selectin. Differences in expression patterns, protein structure, and ligand binding characteristics mediate distinct functions of each selectin. Interactions of selectins and their counter-receptors mediate the first contact of neutrophils with the endothelium, as well as subsequent neutrophil rolling along the endothelial surface. For efficient neutrophil recruitment, activation of β₂-integrins on the cell surface is essential. Integrin activation can be elicited via selectin- as well as chemokine-mediated inside-out signaling resulting in integrin conformational changes and clustering. Dysregulation of selectin-induced integrin activation on neutrophils is involved in the development of severe pathological disease conditions including leukocyte adhesion deficiency (LAD) syndromes in humans. Here, we review molecular mechanisms involved in selectin-mediated signaling pathways in neutrophils and their impact on integrin activation, neutrophil recruitment, and inflammatory diseases.

Leveling Up the Controversial Role of Neutrophils in Cancer: When the Complexity Becomes Entangled

Neutrophils are the most abundant immune cell in the circulation of human and act as gatekeepers to discard foreign elements that have entered the body. They are essential in initiating immune responses for eliminating invaders, such as microorganisms and alien particles, as well as to act as immune surveyors of cancer cells, especially during the initial stages of carcinogenesis and for eliminating single metastatic cells in the circulation and in the premetastatic organs. Since neutrophils can secrete a whole range of factors stored in their many granules as well as produce reactive oxygen and nitrogen species upon stimulation, neutrophils may directly or indirectly affect carcinogenesis in both the positive and negative directions. An intricate crosstalk between tumor cells, neutrophils, other immune cells and stromal cells in the microenvironment modulates neutrophil function resulting in both anti- and pro-tumor activities. Both the anti-tumor and pro-tumor activities require chemoattraction towards the tumor cells, neutrophil activation and ROS production. Divergence is seen in other neutrophil properties, including differential secretory repertoire and membrane receptor display. Many of the direct effects of neutrophils on tumor growth and metastases are dependent on tight neutrophil–tumor cell interactions. Among them, the neutrophil Mac-1 interaction with tumor ICAM-1 and the neutrophil L-selectin interaction with tumor-cell sialomucins were found to be involved in the neutrophil-mediated capturing of circulating tumor cells resulting in increased metastatic seeding. On the other hand, the anti-tumor function of neutrophils was found to rely on the interaction between tumor-surface-expressed receptor for advanced glycation end products (RAGE) and Cathepsin G expressed on the neutrophil surface. Intriguingly, these two molecules are also involved in the promotion of tumor growth and metastases. RAGE is upregulated during early inflammation-induced carcinogenesis and was found to be important for sustaining tumor growth and homing at metastatic sites. Cathepsin G was found to be essential for neutrophil-supported lung colonization of cancer cells. These data level up the complexity of the dual role of neutrophils in cancer.

Serum IL-23, E-selectin and sICAM levels in non-small cell lung cancer patients before and after radiotherapy

Objective

The functions of E-selectin, interleukin (IL)-23, and soluble intercellular adhesion molecule (sICAM) in patients with non-small cell lung cancer (NSCLC) patients before and after radiotherapy (RT) are poorly understood. The purpose of our study was to investigate serum IL-23, E-selectin and sICAM levels in NSCLC patients before and after RT.

Methods

Forty-four patients with pathologically confirmed NSCLC and 30 healthy individuals were included in the study. All patients received 66.6 Gy of concurrent RT.

Results

Significant differences were observed between serum IL-23, E-selectin and sICAM levels in controls and NSCLC patients both before and after radiotherapy. Inverse correlations were detected between serum IL-23 and E-selectin levels in NSCLC patients before and after RT. Positive correlations were detected between serum sICAM levels of NSCLC patients before and after RT and RT dose. No associations were observed between RT dose and IL-23 or E-selectin levels in patients before and after RT.

Conclusion

Serum IL-23, E-selectin and sICAM levels were elevated in NSCLC patients. While our results demonstrate the prognostic value of these parameters, further molecular studies of NSCLC patients are warranted.

"Stuck on sugars - how carbohydrates regulate cell adhesion, recognition, and signaling"

We have explored the fundamental biological processes by which complex carbohydrates expressed on cellular glycoproteins and glycolipids and in secretions of cells promote cell adhesion and signaling. We have also explored processes by which animal pathogens, such as viruses, bacteria, and parasites adhere to glycans of animal cells and initiate disease. Glycans important in cell signaling and adhesion, such as key O-glycans, are essential for proper animal development and cellular differentiation, but they are also involved in many pathogenic processes, including inflammation, tumorigenesis and metastasis, and microbial and parasitic pathogenesis. The overall hypothesis guiding these studies is that glycoconjugates are recognized and bound by a growing class of proteins called glycan-binding proteins (GBPs or lectins) expressed by all types of cells. There is an incredible variety and diversity of GBPs in animal cells involved in binding N- and O-glycans, glycosphingolipids, and proteoglycan/glycosaminoglycans. We have specifically studied such molecular determinants recognized by selectins, galectins, and many other C-type lectins, involved in leukocyte recruitment to sites of inflammation in human tissues, lymphocyte trafficking, adhesion of human viruses to human cells, structure and immunogenicity of glycoproteins on the surfaces of human parasites. We have also explored the molecular basis of glycoconjugate biosynthesis by exploring the enzymes and molecular chaperones required for correct protein glycosylation. From these studies opportunities for translational biology have arisen, involving production of function-blocking antibodies, anti-glycan specific antibodies, and synthetic glycoconjugates, e.g. glycosulfopeptides, that specifically are recognized by GBPs. This invited short review is based in part on my presentation for the IGO Award 2019 given by the International Glycoconjugate Organization in Milan.

The blood-brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by the pathological accumulation of amyloid beta (Aβ) peptides and neurofibrillary tangles containing hyperphosphorylated neuronal tau protein. AD pathology is also characterized by chronic brain inflammation, which promotes disease pathogenesis. In this context, the blood-brain barrier (BBB), a highly specialized endothelial cell membrane that lines cerebral microvessels, represents the interface between neural cells and circulating cells of the immune system. The BBB thus plays a key role in the generation and maintenance of chronic inflammation during AD. The BBB operates within the neurovascular unit (NVU), which includes clusters of glial cells, neurons and pericytes. The NVU becomes dysfunctional during AD, and each of its components may undergo functional changes that contribute to neuronal injury and cognitive deficit. In transgenic animals with AD-like pathology, recent studies have shown that circulating leukocytes migrate through the activated brain endothelium when certain adhesion molecules are expressed, penetrating into the brain parenchyma, interacting with the NVU components and potentially affecting their structural integrity and functionality. Therefore, migrating immune system cells in cerebral vessels act in concert with the modified BBB and may be integrated into the dysfunctional NVU. Notably, blocking the adhesion mechanisms controlling leukocyte-endothelial interactions inhibits both Aβ deposition and tau hyperphosphorylation, and reduces memory loss in AD models. The characterization of molecular mechanisms controlling vascular inflammation and leukocyte trafficking could therefore help to determine the basis of BBB dysfunction during AD and may lead to the development of new therapeutic approaches.

Differentiation of induced pluripotent stem cell-derived neutrophil granulocytes from common marmoset monkey (Callithrix jacchus)

BACKGROUND

Inherited and acquired marrow failure syndromes most commonly lead to defect in myeloid and/or neutrophil differentiation and/or function. Besides this, neutropenia induced by cancer-adjusted chemotherapy is a frequent clinical problem. In both cases, cell replacement therapy is a well-established, but due to necessity of donors limited and perilous procedure. Therefore, autologous cell replacement from patients' own marrow-derived cells lowers risk and bares new possibilities for therapy. Since the immune system of the marmoset monkey is known to show high similarity to humans, preclinical studies with these animals bare high hopes for immunologic research and cell replacement therapy.

STUDY DESIGN AND METHODS

Marmoset-induced pluripotent stem (iPS) cells (cj-iPSC) were first cultivated on mouse embryonic feeder cells in medium containing recombinant human vascular endothelial growth factor. After 13 days, CD34+/vascular endothelial growth factor receptor-2 (VEGFR2)- cells were sorted, treated with interleukin (IL-3), thrombopoietin, and stem cell factor for 20 days and further cultivated with granulocyte-colony-stimulating factor (G-CSF) and IL-3 for 10 days.

RESULTS

CD34+/VEGFR2- cells could be generated in high amounts (39.65 ± 6.01%; 2.31 × 10⁵ cells). Afterward, these hematopoietic progenitors could be successfully differentiated into mature cj-iPSC-derived neutrophils showing similar morphology, specific surface antigens, and neutrophil-specific gene products and in vitro phagocytic activity.

CONCLUSION

cj-iPSC-derived neutrophils bare high hopes in hematologic cell replacement therapy. They exhibit high morphologic similarity to native neutrophils and present neutrophil-specific surface antigens, antimicrobial proteins, and gene products yielding an auspicious approach for continuative experiments including tests in living animals.

The effect of soluble E-selectin on tumor progression and metastasis

Background

Distant metastasis resulting from vascular dissemination of cancer cells is the primary cause of mortality from breast cancer. We have previously reported that E-selectin expression on the endothelial cell surface mediates shear-resistant adhesion and migration of circulating cancer cells via interaction with CD44. As a result of shedding, soluble E-selectin (sE-selectin) from the activated endothelium is present in the serum. In this study, we aimed to understand the role of sE-selectin in tumor progression and metastasis.

Methods

We investigated the effect of sE-selectin on shear-resistant adhesion and migration of metastatic breast cancer cells and leukocytes in vitro and in vivo.

Results

We found that sE-selectin promoted migration and shear-resistant adhesion of CD44^+/high breast cancer cell lines (MDA-MB-231 and MDA-MB-468) to non-activated human microvessel endothelial cells (ES-HMVECs), but not of CD44^-/low breast cancer cell lines (MCF-7 and T-47D). This endothelial E-selectin independent, sE-selectin-mediated shear-resistant adhesion was also observed in a leukocyte cell line (HL-60) as well as human peripheral blood mononuclear cells (PBMCs). Additionally, the incubation of MDA-MB-231 cells with sE-selectin triggered FAK phosphorylation and shear-resistant adhesion of sE-selectin-treated cells resulted in increased endothelial permeabilization. However, CD44 knockdown in MDA-MB-231 and HL-60 cells resulted in a significant reduction of sE-selectin-mediated shear-resistant adhesion to non-activated HMVECs, suggesting the involvement of CD44/FAK. Moreover, functional blockade of ICAM-1 in non-activated HMVECs resulted in a marked reduction of sE-selectin-mediated shear-resistant adhesion. Finally, the pre-incubation of CD44⁺ 4 T1 murine breast cancer cells with sE-selectin augmented infiltration into the lung in E-selectin K/O mice and infusion of human PBMCs pre-incubated with sE-selectin stimulated MDA-MB-231 xenografted breast tumor growth in NSG mice.

Conclusions

Our data suggest that circulating sE-selectin stimulates a broad range of circulating cells via CD44 and mediates pleiotropic effects that promote migration and shear-resistant adhesion in an endothelial E-selectin independent fashion, in turn accelerating tissue infiltration of leukocytes and cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2366-2) contains supplementary material, which is available to authorized users.

Design strategies and applications of circulating cell-mediated drug delivery systems

Drug delivery systems, particularly nanomaterial-based drug delivery systems, possess a tremendous amount of potential to improve diagnostic and therapeutic effects of drugs. Controlled drug delivery targeted to a specific disease is designed to significantly improve the pharmaceutical effects of drugs and reduce their side effects. Unfortunately, only a few targeted drug delivery systems can achieve high targeting efficiency after intravenous injection, even with the development of numerous surface markers and targeting modalities. Thus, alternative drug and nanomedicine targeting approaches are desired. Circulating cells, such as erythrocytes, leukocytes, and stem cells, present innate disease sensing and homing properties. Hence, using living cells as drug delivery carriers has gained increasing interest in recent years. This review highlights the recent advances in the design of cell-mediated drug delivery systems and targeting mechanisms. The approaches of drug encapsulation/conjugation to cell-carriers, cell-mediated targeting mechanisms, and the methods of controlled drug release are elaborated here. Cell-based "live" targeting and delivery could be used to facilitate a more specific, robust, and smart payload distribution for the next-generation drug delivery systems.

New paradigms in inflammatory signaling in vascular endothelial cells

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

Retinoid agonist Am80-enhanced neutrophil bactericidal activity arising from granulopoiesis in vitro and in a neutropenic mouse model

Despite advances in the therapeutic use of recombinant granulocyte colony-stimulating factor (G-CSF) to promote granulopoiesis of human hematopoietic stem cells (HSCs), neutropenia remains one of the most serious complications of cancer chemotherapy. We discovered that retinoid agonist Am80 (tamibarotene) is more potent than G-CSF in coordinating neutrophil differentiation and immunity development. Am80-induced neutrophils (AINs) either in vitro or in neutropenic mouse model displayed strong bactericidal activities, similar to those of human peripheral blood neutrophils (PBNs) or mouse peripheral blood neutrophils (MPBNs) but markedly greater than did G-CSF–induced neutrophils (GINs). In contrast to GINs but similar to PBNs, the enhanced bacterial killing by AINs accompanied both better granule maturation and greater coexpression of CD66 antigen with the integrin β2 subunit CD18. Consistently, anti-CD18 antibody neutralized Am80-induced bactericidal activities of AINs. These studies demonstrate that Am80 is more effective than G-CSF in promoting neutrophil differentiation and bactericidal activities, probably through coordinating the functional interaction of CD66 with CD18 to enhance the development of neutrophil immunity during granulopoiesis. Our findings herein suggest a molecular rationale for developing new therapy against neutropenia using Am80 as a cost-effective treatment option.

Migration of leukocytes across the vascular intima molecules and mechanisms

The process of leukocyte emigration from the blood into a site of inflammation can be dissected into four distinct but continuous stages involving sequential interactions of different adhesion molecules on the leukocyte and endothelial surfaces. Although the molecules mediating adhesion to the luminal surface have been well studied, much less is known about the final stage of this process, transendothelial migration. This is the stage in which a leukocyte bound to the vascular wall passes between adjacent endothelial cells; it is a complex process in its own right, involving continuous structural, mechanical, and biochemical changes in both interacting cell types. Distinct cell adhesion molecule and signal transduction mechanisms that appear to be involved in this phase are discussed here.

A study of the Interaction Between Cetirizine and Plasma Membrane of Eosinophils, Neutrophils, Platelets and Lymphocytes using A fluorescence Technique

The effect of cetirizine on plasma membrane fluidity and heterogeneity of human eosinophils, neutrophils, platelets and lymphocytes was investigated using a fluorescence technique. Membrane fluidity and heterogeneity were studied by measuring the steady-state fluorescence anisotropy and fluorescence decay of 1-(4- trimethylammonium-phenyl)-6-phenyl-1, 3, 5-hexatriene (TMA-DPH) incorporated in the membrane. The results demonstrate that cetirizine (1 μg/ml) induced a significant increase in the Hpid order in the exterior part of the membrane and a decrease in membrane heterogeneity in eosinophils, neutrophils and platelets. Moreover, cetirizine blocked the PAF induced changes in membrane fluidity in these cells. Cetirizine did not influence significantly the plasma membrane of lymphocytes. These data may partially explain the effect ofcetirizine on inflammatory cell activities.

Serum Concentration and Chemotactic Activity of E-selectin (CD62E) in Inflammatory Bowel Disease

E-selectin (CD62E) is an endothelial specific glycoprotein belonging to the selectin family of adhesion molecules. Because a high expression of this molecule at intestinal mucosal surfaces in inflammatory bowel disease (IBD) has been described earlier, the aim was to assess serum levels of E-selectin (sE-selectin) and to correlate it to disease activity, and further to evaluate its chemotactic properties at physiological concentrations. Levels of sEselectin were measured by a sandwich ELISA technique in 31 IBD patients together with 15 healthy volunteers. In ulcerative colitis the median value was 0.46 nM (0.16–0.75), in Crohn’s disease 0.47 nM (0.22–1.24), and in healthy controls 0.34 nM (0.22–0.83). No statistically significant differences in sE-selectin were revealed between these groups (p > 0.05). The in vitro chemotactic capabilities of E-selectin (in the concentration range of 0.10–31.4 nM) were assessed using the leading front technique. A significantly increased migratory response was found at concentrations of 1.00 (p < 0.05) and 3.14 nM (p < 0.02). It is concluded that sE-selectin in contrast to sICAM-1 does not act as a sensitive indicator of local immune activation in IBD. However, E-selectin may be important for recruitment and accumulation of neutrophilic granulocytes and other phagocytes involved in the inflammatory process seen in IBD. Future investigations are encouraged in order to reveal its in vivo effects.

Regulation of mucosal addressin cell adhesion molecule 1 expression in human and mice by vascular adhesion protein 1 amine oxidase activity

Primary sclerosing cholangitis (PSC) and autoimmune hepatitis are hepatic complications associated with inflammatory bowel disease (IBD). The expression of mucosal addressin cell adhesion molecule 1 (MAdCAM-1) on mucosal endothelium is a prerequisite for the development of IBD, and it is also detected on the hepatic vessels of patients with liver diseases associated with IBD. This aberrant hepatic expression of MAdCAM-1 results in the recruitment of effector cells initially activated in the gut to the liver, in which they drive liver injury. However, the factors responsible for the aberrant hepatic expression of MAdCAM-1 are not known. In this study, we show that deamination of methylamine (MA) by vascular adhesion protein 1 (VAP-1) [a semicarbazide-sensitive amine oxidase (SSAO) expressed in the human liver] in the presence of tumor necrosis factor α induces the expression of functional MAdCAM-1 in hepatic endothelial cells and in intact human liver tissue ex vivo. This is associated with increased adhesion of lymphocytes from patients with PSC to hepatic vessels. Feeding mice MA, a constituent of food and cigarette smoke found in portal blood, led to VAP-1/SSAO-dependent MAdCAM-1 expression in mucosal vessels in vivo.

CONCLUSION

Activation of VAP-1/SSAO enzymatic activity by MA, a constituent of food and cigarette smoke, induces the expression of MAdCAM-1 in hepatic vessels and results in the enhanced recruitment of mucosal effector lymphocytes to the liver. This could be an important mechanism underlying the hepatic complications of IBD.

Heterotypic interactions enabled by polarized neutrophil microdomains mediate thromboinflammatory injury

Selectins and their ligands mediate leukocyte rolling, allowing interactions with chemokines that lead to integrin activation and arrest. Here we show that E-selectin is crucial for generating a secondary wave of activating signals, transduced specifically by E-selectin ligand-1, that induces polarized, activated alpha(M)beta(2) integrin clusters at the leading edge of crawling neutrophils, allowing capture of circulating erythrocytes or platelets. In a humanized mouse model of sickle cell disease, the capture of erythrocytes by alpha(M)beta(2) microdomains leads to acute lethal vascular occlusions. In a model of transfusion-related acute lung injury, polarized neutrophils capture circulating platelets, resulting in the generation of oxidative species that produce vascular damage and lung injury. Inactivation of E-selectin or alpha(M)beta(2) prevents tissue injury in both inflammatory models, suggesting broad implications of this paradigm in thromboinflammatory diseases. These results indicate that endothelial selectins can influence neutrophil behavior beyond its canonical rolling step through delayed, organ-damaging, polarized activation.

Integrin VLA-4 enhances sialyl-Lewisx/a-negative melanoma adhesion to and extravasation through the endothelium under low flow conditions

During their passage through the circulatory system, tumor cells undergo extensive interactions with various host cells including endothelial cells. The capacity of tumor cells to form metastasis is related to their ability to interact with and extravasate through endothelial cell layers, which involves multiple adhesive interactions between tumor cells and endothelium (EC). Thus it is essential to identify the adhesive receptors on the endothelial and melanoma surface that mediate those specific adhesive interactions. P-selectin and E-selectin have been reported as adhesion molecules that mediate the cell-cell interaction of endothelial cells and melanoma cells. However, not all melanoma cells express ligands for selectins. In this study, we elucidated the molecular constituents involved in the endothelial adhesion and extravasation of sialyl-Lewis(x/a)-negative melanoma cell lines under flow in the presence and absence of polymorphonuclear neutrophils (PMNs). Results show the interactions of alpha(4)beta(1) (VLA-4) on sialyl-Lewis(x/a)-negative melanoma cells and vascular adhesion molecule (VCAM-1) on inflamed EC supported melanoma adhesion to and subsequent extravasation through the EC in low shear flow. These findings provide clear evidence for a direct role of the VLA-4/VCAM-1 pathway in melanoma cell adhesion to and extravasation through the vascular endothelium in a shear flow. PMNs facilitated melanoma cell extravasation under both low and high shear conditions via the involvement of distinct molecular mechanisms. In the low shear regime, beta(2)-integrins were sufficient to enhance melanoma cell extravasation, whereas in the high shear regime, selectin ligands and beta(2)-integrins on PMNs were necessary for facilitating the melanoma extravasation process.

Targeting selectins and selectin ligands in inflammation and cancer

Inflammation and cancer metastasis are associated with extravasation of leukocytes or tumor cells from blood into tissue. Such movement is believed to follow a coordinated and sequential molecular cascade initiated, in part, by the three members of the selectin family of carbohydrate-binding proteins: E-selectin (CD62E), L-selectin (CD62L) and P-selectin (CD62P). E-selectin is particularly noteworthy in disease by virtue of its expression on activated endothelium and on bone-skin microvascular linings and for its role in cell rolling, cell signaling and chemotaxis. E-selectin, along with L- or P-selectin, mediates cell tethering and rolling interactions through the recognition of sialo-fucosylated Lewis carbohydrates expressed on structurally diverse protein-lipid ligands on circulating leukocytes or tumor cells. Major advances in understanding the role of E-selectin in inflammation and cancer have been advanced by experiments assaying E-selectin-mediated rolling of leukocytes and tumor cells under hydrodynamic shear flow, by clinical models of E-selectin-dependent inflammation, by mice deficient in E-selectin and by mice deficient in glycosyltransferases that regulate the binding activity of E-selectin ligands. Here, the authors elaborate on how E-selectin and its ligands may facilitate leukocyte or tumor cell recruitment in inflammatory and metastatic settings. Antagonists that target cellular interactions with E-selectin and other members of the selectin family, including neutralizing monoclonal antibodies, competitive ligand inhibitors or metabolic carbohydrate mimetics, exemplify a growing arsenal of potentially effective therapeutics in controlling inflammation and the metastatic behavior of cancer.

Getting to the site of inflammation: the leukocyte adhesion cascade updated

Neutrophil recruitment, lymphocyte recirculation and monocyte trafficking all require adhesion and transmigration through blood-vessel walls. The traditional three steps of rolling, activation and firm adhesion have recently been augmented and refined. Slow rolling, adhesion strengthening, intraluminal crawling and paracellular and transcellular migration are now recognized as separate, additional steps. In neutrophils, a second activation pathway has been discovered that does not require signalling through G-protein-coupled receptors and the signalling steps leading to integrin activation are beginning to emerge. This Review focuses on new aspects of one of the central paradigms of inflammation and immunity--the leukocyte adhesion cascade.

The oxidase activity of vascular adhesion protein-1 (VAP-1) induces endothelial E- and P-selectins and leukocyte binding

Leukocyte migration from the blood into tissues is pivotal in immune homeostasis and in inflammation. During the multistep extravasation cascade, endothelial selectins (P- and E-selectin) and vascular adhesion protein-1 (VAP-1), a cell-surface–expressed oxidase, are important in tethering and rolling. Here, we studied the signaling functions of the catalytic activity of VAP-1. Using human endothelial cells transfected with wild-type VAP-1 and an enzymatically inactive VAP-1 point mutant, we show that transcription and translation of E- and P-selectins are induced through the enzymatic activity of VAP-1. Moreover, use of VAP-1–deficient animals and VAP-1–deficient animals carrying the human VAP-1 as a transgene show a VAP-enzyme activity–dependent induction of P-selectin in vivo. Up-regulation of P-selectin was found both in high endothelial venules in lymphoid tissues and in flat-walled vessels in noninflamed tissues. VAP-1 activity in vivo led to increased P-selectin–dependent binding of lymphocytes to endothelial cells. These data show that the oxidase reaction catalyzed by VAP-1 alters the expression of other molecules involved in the leukocyte extravasation cascade. Our findings indicate cross-talk between adhesion molecules involved in the tethering and rolling of leukocytes and show that VAP-1–dependent signaling can prime the vessels for an enhanced inflammatory response.

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.

Complete identification of E-selectin ligands on neutrophils reveals distinct functions of PSGL-1, ESL-1, and CD44

The selectins and their ligands are required for leukocyte extravasation during inflammation. Several glycoproteins have been suggested to bind to E-selectin in vitro, but the complete identification of its physiological ligands has remained elusive. Here, we showed that E-selectin ligand-1 (ESL-1), P-selectin glycoprotein ligand-1 (PSGL-1), and CD44 encompassed all endothelial-selectin ligand activity on neutrophils by using gene- and RNA-targeted loss of function. PSGL-1 played a major role in the initial leukocyte capture, whereas ESL-1 was critical for converting initial tethers into steady slow rolling. CD44 controlled rolling velocity and mediated E-selectin-dependent redistribution of PSGL-1 and L-selectin to a major pole on slowly rolling leukocytes through p38 signaling. These results suggest distinct and dynamic contributions of these three glycoproteins in selectin-mediated neutrophil adhesion and signaling.

Spleen tyrosine kinase Syk is necessary for E-selectin-induced alpha(L)beta(2) integrin-mediated rolling on intercellular adhesion molecule-1

Engagement of neutrophils by E-selectin results in integrin activation. Here, we investigated primary mouse neutrophils in whole blood by using intravital microscopy and autoperfused flow chambers. Slow rolling on E-selectin coimmobilized with intercellular adhesion molecule-1 (ICAM-1) required P-selectin glycoprotein ligand (PSGL)-1, was dependent on alpha(L)beta(2) integrin (LFA-1), and required continuous E-selectin engagement. Slow rolling was abolished by pharmacological blockade of spleen tyrosine kinase (Syk) and was absent in Syk(-/-) bone-marrow chimeric mice. Treatment with tumor necrosis factor-alpha lowered rolling velocity further and induced CXC chemokine ligand-1 (CXCL1) and CXC chemokine receptor-2 (CXCR2)-dependent leukocyte arrest on E-selectin and ICAM-1. Arrest but not rolling was blocked by an allosteric inhibitor of LFA-1 activation. Neutrophil recruitment in a thioglycollate-induced peritonitis model was almost completely inhibited in Selplg(-/-) mice or Syk(-/-) bone-marrow chimeras treated with pertussis toxin. This identifies a second neutrophil-activation pathway that is as important as activation through G protein-coupled receptors (GPCRs).

Release of soluble E-selectin from activated endothelial cells upon apoptosis

Circulating soluble E-selectin is increased in diseases associated with endothelial apoptosis such as sepsis and acute respiratory distress syndrome. We investigated the mechanism by which endothelial cell (EC) apoptosis may promote soluble E-selectin release. We found that serum deprivation of EC caused apoptosis, yet it did not induce E-selectin EC surface expression. Tumor necrosis factor-alpha (TNFalpha) significantly increased EC E-selectin surface expression. Soluble E-selectin was noted, however, only in the medium of TNFalpha-activated, apoptotic EC. Preincubation of the EC with the caspase inhibitor z-VAD-fmk significantly attenuated soluble E-selectin levels in the culture medium of TNFalpha-activated, apoptotic EC, but it had no effect on E-selectin surface expression. These results indicate that TNFalpha activation, but not apoptosis, is necessary for E-selectin surface expression in EC. Furthermore, E-selectin release from EC requires caspase-3 activation. Thus, increased concentrations of circulating E-selectin in serum may serve as a marker for endothelial apoptosis in certain disease states.

The aetiology and pathogenesis of chronic allograft nephropathy

Renal transplantation is the ultimate form of renal replacement therapy, and is the treatment of choice for many patients with end-stage renal failure. The advent of calcineurin inhibitor based immunosuppression resulted in the 1-year renal allograft failure rate dropping from around 50% twenty years ago to less than 10% in more recent times. Despite a massive improvement in renal allograft survival in the first year following transplantation 10-year graft survival can be as low as 50%. Chronic allograft nephropathy (CAN) is recognised as the main cause of renal allograft failure following the first year after transplantation. The diagnosis of CAN can only be made histologically. Typically biopsy specimens in grafts with CAN demonstrate an overall fibrotic appearance effecting the vascular endothelium, renal tubules, interstitium, and glomerulus. The risk factors for CAN are divided into alloimmune and alloimmune independent. Alloimmune dependent factors include acute cellular rejection, severity of rejection, subclinical rejection and HLA mismatch. Alloimmune independent factors such as delayed graft function, donor age, Cytomegalovirus infection, donor/recipient co-morbidity and of course calcineurin inhibitor toxicity are important in the development of CAN. The pathogenesis of CAN is complex, multifactorial, and unfortunately incompletely understood. There are a number of pivotal steps in the initiation and propagation of the fibrosis seen in biopsy specimens from kidneys with CAN. Endothelial activation in response to one or more of the aforementioned risk factors stimulates leukocyte activation and recruitment. Recruited leukocytes subsequently infiltrate through the endothelium and induce key effector cells to secrete excessive and abnormal extracellular matrix (ECM). Enhanced deposition of ECM is a histological hallmark of CAN. This paper aims to present a concise yet accurate and up-to-date review of the literature concerning the aetiological factors and pathological processes which are present in the generation of CAN.

P-selectin activates integrin-mediated colon carcinoma cell adhesion to fibronectin

During hematogenous cancer metastasis, tumor cells separate from a primary mass, enter the bloodstream, disperse throughout the body, migrate across vessel walls, and generate distant colonies. The later steps of metastasis superficially resemble leukocyte extravasation, a process initiated by selectin-mediated cell tethering to the blood vessel wall followed by integrin-mediated arrest and transendothelial migration. Some cancer cells express P-selectin ligands and attach to immobilized P-selectin, suggesting that these cells can arrest in blood vessels using sequential selectin- and integrin-mediated adhesion, as do leukocytes. We hypothesize that selectin binding may regulate subsequent integrin-mediated steps in metastasis. Using a model system of cultured Colo 320 human colon adenocarcinoma cells incubated with soluble P-selectin-IgG chimeric protein, we have found that P-selectin can stimulate activation of the alpha(5)beta(1) integrin resulting in a specific increase of adhesion and spreading of these cells on fibronectin substrates. P-selectin binding also induced activation of p38 mitogen-activated protein kinase (p38 MAPK) and phosphatidylinositol 3-kinase (PI3-K). PI3-K inhibitors blocked P-selectin-mediated integrin activation, cell attachment, and cell spreading. Inhibition of p38 MAPK activation blocked cell spreading, but not cell attachment. P-selectin binding also resulted in formation of a signaling complex containing PI3-K and p38 MAPK. These results suggest that P-selectin binding to tumor cells can activate alpha(5)beta(1) integrin via PI3-K and p38 MAPK signaling pathways leading to increased cell adhesion. We propose that P-selectin ligands are important tumor cell signaling molecules that modulate integrin-mediated cell adhesion in the metastatic process.

Src-family kinases mediate an outside-in signal necessary for beta2 integrins to achieve full activation and sustain firm adhesion of polymorphonuclear leucocytes tethered on E-selectin

In cell suspensions subjected to high-shear rotatory motion, human PMN (polymorphonuclear cells) adhered to E-selectin-expressing CHO (Chinese-hamster ovary) cells (CHO-E), and formed homotypic aggregates when challenged by E-selectin-IgG fusion protein, by a mechanism that involved beta2 integrins. Both heterotypic and homotypic PMN adhesion was accompanied by tyrosine phosphorylation of a 110 kDa protein (P110). This event was prevented by blocking anti-(beta2 integrin) antibodies and by inhibitors of Src-family kinases, suggesting that it was part of an 'outside-in' signalling that was initiated by integrin engagement. Interestingly, Src-family kinase inhibitors prevented beta2-integrin-mediated (i) homotypic PMN adhesion triggered by E-selectin-IgG, (ii) heterotypic CHO-E/PMN adhesion in mixed-cell suspensions, and (iii) firm adhesion of PMN to CHO-E monolayers under physiological flow. Similarly to PMN treated with Src-family kinase inhibitors, PMN from hck-/-fgr-/- and hck-/-fgr-/-lyn-/- mice showed significant impairment of beta2-integrin-mediated adhesion to CHO-E. Moreover, the expression of beta2 integrin activation epitopes at the sites of cell-cell contact in CHO-E/PMN conjugates was abolished by Src-family kinase inhibitors. One component of P110 was identified as the FAK (focal adhesion kinase) Pyk2 (proline-rich tyrosine kinase 2), which was phosphorylated in a beta2 integrin- and Src-family-kinase-dependent manner. Thus, Src-family kinases, and perhaps Pyk2, mediate a signal necessary for beta2 integrin function in PMN tethered by E-selectin.

The merits of in vitro versus in vivo modeling in investigation of the immune system

Immunity is vital for determining self and for the recognition and swift eradication of foreign antigens without harming the host. Innate immunity developed in metazoan, multi-cellular organisms under overwhelming selection pressure of invasive microbes and, although imperfect, has performed admirably to enable the evolution of higher eukaryotes. Adaptive immunity developed within an existing innate immune system to more effectively eradicate foreign antigens, whether from pathogens, malignant cells, or microbial toxins, such that repeated stimulations with foreign antigens are more efficiently excluded. Investigation of the immune system requires both in vivo and in vitro experimentation, not only because of the inherent complexity of immunity and the required pertinence of using higher mammals to not falsely disrupt the immune system, but also to use isolates of the specific cellular and humoral components to determine function, signal transduction, and a possible role of these constituents without the complexity and redundancy of immunity in intact animals. The hypotheses of well-designed in vitro experiments must also be tested in intact in vivo models to determine relevance and to discard artifactual findings secondary to the in vitro environment. The following review outlines the basic constituents and functions of both adaptive and innate immunity to demonstrate the importance of both in vivo and in vitro investigation of immunity in our attempt to define host defense and to decrease morbidity and mortality in humans.

The involvement of selectins and their ligands in tumor-progression

About 70 years ago, Peyton Rous described the progression of cancer towards metastasis formation as "the process whereby tumors go from bad to worse". The interactions of tumor cells with endothelium are pivotal steps in this process. This review focuses on the role played by the selectins and their ligands in these interactions and especially in tumor cell extravasation. The working hypothesis of researchers studying tumor cell extravasation is that the tumor cells follow the extravasation strategy of leukocytes in their migration towards inflammatory sites. A significant portion of this review is, therefore, dedicated to the molecular mechanisms underlying leukocyte extravasation and to a comparison between the extravasation strategy employed by leukocytes and tumor cells. The review also summarizes some of the available data on signals generated by selectin-selectin ligand interactions.

Quantum proteolytic activation of chemokine CCL15 by neutrophil granulocytes modulates mononuclear cell adhesiveness

Monocyte infiltration into inflammatory sites is generally preceded by neutrophils. We show here that neutrophils may support this process by activation of CCL15, a human chemokine circulating in blood plasma. Neutrophils were found to release CCL15 proteolytic activity in the course of hemofiltration of blood from renal insufficiency patients. Processing of CCL15 immunoreactivity (IR) in the pericellular space is suggested by a lack of proteolytic activity in blood and blood filtrate, but a shift of the retention time (t(R)) of CCL15-IR, detected by chromatographic separation of CCL15-IR in blood and hemofiltrate. CCL15 molecules with N-terminal deletions of 23 (delta23) and 26 (delta26) aa were identified as main proteolytic products in hemofiltrate. Neutrophil cathepsin G was identified as the principal protease to produce delta23 and delta26 CCL15. Also, elastase displays CCL15 proteolytic activity and produces a delta21 isoform. Compared with full-length CCL15, delta23 and delta26 isoforms displayed a significantly increased potency to induce calcium fluxes and chemotactic activity on monocytes and to induce adhesiveness of mononuclear cells to fibronectin. Thus, our findings indicate that activation of monocytes by neutrophils is at least in part induced by quantum proteolytic processing of circulating or endothelium-bound CCL15 by neutrophil cathepsin G.

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.

Cryptococcal glucuronoxylomannan interferes with neutrophil rolling on the endothelium

The major capsular polysaccharide glucuronoxylomannan (GXM) of the pathogenic fungus Cryptococcus neoformans has been associated with depression of a variety of immunological host responses. For one, GXM has been shown to interfere with the migration of phagocytes to sites of inflammation by interference with both chemokinesis and leucocyte adhesion to the endothelium. We reported previously that GXM blocks the firm adhesion of neutrophils (PMNs) to endothelium in a static adhesion model, most probably by interfering with E-selectin binding pathways. Using a flow model, we now demonstrate that GXM also interferes with the initial rolling phase of PMN adhesion to endothelium (40% decrease) as well as to E-selectin-transfected CHO cells (43% inhibition). Furthermore, we show that CD14 and TLR4, which are known receptors for GXM, mediate this interference with PMN rolling. However, thus far, we are not able to identify the ligand of E-selectin on the surface of PMNs that is specifically affected by GXM. In conclusion, cryptococcal GXM interferes with both rolling and fixed binding of neutrophils on the endothelium, providing a novel means of contributing to the absence of neutrophil infiltration observed in cryptococcal infections.

Vascular endothelium and immune responses: implications for inflammation and angiogenesis

ECs are involved in several mechanisms during the immune response, particularly in inflammation. These cells are able to produce vasodilatory mediators and several factors lead to increased vascular permeability. ECs play a central role in leukocyte extravasation, a key feature of inflammation. Several adhesion molecules, termed integrins, selectins, immunoglobulins, and others, act in concert and regulate the sequence of distinct steps. Leukocyte-EC adhesion is regulated by the interactions of receptor-ligand CAM pairs, as well as by soluble mediators, such as proinflammatory cytokines. ECs are active participants in angiogenesis. The outcome of neovascularization is highly dependent on the balance or imbalance between angiogenic mediators and inhibitors. Angiogenic mediators form a complex interactive network that regulates the perpetuation of angiogenesis. Naturally-produced or administered angiostatic agents downregulate the effects of angiogenic factors. There have been several attempts to therapeutically interfere with the cellular and molecular mechanisms described above. Most studies were performed using animal models of various types of inflammation. A limited number of human clinical trials, such as the one using anti-ICAM-1 antibody in RA, had promising results. Specific targeting of pathologic endothelial function may be useful for the future management of various inflammatory diseases.

The galactose-binding lectin from Vatairea macrocarpa seeds induces in vivo neutrophil migration by indirect mechanism

To explore the pathways by which lectins induce an inflammatory response, the lectin from Vatairea macrocarpa (VML) seeds was used to induce neutrophil migration in rats. The lectin was shown to cause cell migration, with the effect partially blocked when galactose was added to inhibit lectin activity. Neutrophil migration was also reduced when peritoneal cavity of the animals was depleted of their resident cells beforehand, suggesting that neutrophil migration was mediated by an indirect mechanism. Pre-treatment of rats with thioglycollate increased recruitment of neutrophils while depletion of mast cells by the addition of compound 48/80 had little effect on neutrophil infiltration, suggesting the involvement of macrophages in the inflammatory process induced by the lectin. Inhibition of the cyclooxigenase, leukotriene and PAF activities by indomethacin, MK886 and BN50730, respectively, did not modify the pro-inflammatory effect previously observed. However, dexamethasone and thalidomide significantly reduced the population of neutrophils in the peritoneal cavity after lectin injection. The present study suggests that the effects produced by a galactose-binding lectin do not involve lipoxygenase, cyclooxygenase or PAF mediators that are well known to be involved in the inflammatory process. The blocking actions of dexamethasone and thalidimide suggest that as yet unidentified pro-inflammatory mediators are involved.

In vitro model for hematopoietic progenitor cell homing reveals endothelial heparan sulfate proteoglycans as direct adhesive ligands

Proteoglycans (PGs) play a dominant role within the bone marrow (BM), but their role in homing of transplanted hematopoietic progenitor cells (HPC) is unknown. In this study, the role of heparan sulfate (HS) PGs on BM endothelium as adhesive structures was investigated. HPC (primary CD34+ cells and cell line KG-1a) were able to bind fractionated heparin, which could be competed by highly sulfated heparin/HS-glycosaminoglycans (GAGs). Under flow conditions, HPC adhered to immobilized heparin after rolling over E-selectin. Rolling of KG-1a on BM endothelial cell (EC) line 4LHBMEC was completely E selectin-dependent. Addition of heparin/HS-GAGs, endothelial treatment with chlorate, or anti-HS all partially inhibited firm adhesion. Moreover, enzymatic removal of endothelial HS-GAGs reduced initial adhesion. Finally, HPC-bound PGs isolated from 4LHBMEC, which was largely inhibited by enzymatic HS-degradation. In summary, we identified sulfated structures on BM endothelium, most likely HSPGs, as a novel class of glycoconjugates involved in the multistep homing cascade of HPC.

Soluble E-selectin and soluble ICAM-1 levels as markers of the activity of atopic dermatitis in children

The expression of adhesion molecules is up-regulated in the skin of atopic dermatitis (AD) patients, and the levels of the soluble adhesion molecules sE-selectin and sICAM-1 have been reported to reflect the endothelial activation in the skin of AD patients. The objective of the study was to investigate the relationship between symptom score and levels of sE-selectin, sICAM-1 and sVCAM-1 before and after 2 weeks of treatment. Eighteen children with an exacerbation of AD were admitted and treated with corticosteroid dilutions under occlusive wet dressings (wet-wrap treatment). Symptom score (objective SCORAD) and levels of sE-selectin, sICAM-1, and sVCAM-1 were assessed before and after 2 weeks of treatment. A significant correlation between the objective SCORAD before treatment and the level of sE-selectin (p < 0.05), but not the level of sICAM-1 (p = 0.7) or sVCAM-1 (p = 0.5) was observed. The treatment resulted in a high degree of remission, which was reflected by a significant decrease in the level of sICAM-1 (p < 0.01), whereas there was only a trend in the level of sE-selectin to decrease (p = 0.08). The level of sE-selectin after 2 weeks of treatment still correlated significantly with the objective SCORAD before treatment (p < 0.005). Soluble E-selectin is a relative objective marker for the severity of AD. SCORAD is a treatment-sensitive symptom of AD, whereas E-selectin may be a more stable underlying systemic representation of AD.

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.

Beta1-integrin and IL-1alpha expression as bystander effect of medium from irradiated cells: the pilot study

Bystander effects have been proposed as a third action pathway of ionising radiation besides direct and indirect effects. The purpose of the study was to investigate whether expression of interleukin-1alpha (IL-1alpha) and beta1-integrin is elevated in bystander cells as a marker for bystander effects in comparison with classical markers such as the clonogenic assay, apoptosis and the presence of micronuclei. The hybrid cell line E.A. hy.926 obtained by fusion of HUVEC cells with the epithelial cell line A 459 was irradiated with 0-5 Gy. Bystander effects were established via medium transfer at 45 min and 4 h after irradiation from irradiated to nonirradiated cell populations. In order to exclude effects of the irradiated medium itself, irradiated medium only was also used for transfer to nonirradiated cells. Then, cells were fixed at 1, 2, 6, and 24 h after irradiation or medium transport and IL-1alpha and beta1-integrin were detected and evaluated. A higher number of beta1-integrin-positive cells was observed in both irradiated and bystander cell populations than in the control group at 1 and 24 h after irradiation with 1 Gy or medium transfer. Significantly higher numbers of IL-1alpha-positive cells were found at 1, 2, and 6 h after irradiation with 1 Gy or medium transfer as well as at 2 and 6 h after irradiation with 5 Gy or medium transfer. Clonogenic survival decreased dependently on the dose in irradiated cells but did not show any significant difference between the bystander cell populations and sham-irradiated cells. The irradiated medium itself did not have any effect. It is concluded that beta1-integrin and IL-1alpha expression may serve as more sensitive markers of post-irradiation responses in bystander cell populations than the classical radiobiological markers. Moreover, overexpression of beta1-integrin and IL-1alpha may induce increased susceptibility to inflammation of bystander cells.

Enhanced recruitment of Th2 and CLA-negative lymphocytes by the S128R polymorphism of E-selectin

E-selectin is a cytokine-inducible endothelial cell adhesion molecule that binds a restricted population of T lymphocytes consisting of Th1 memory cells bearing the cutaneous lymphocyte Ag (CLA). A serine to arginine (S128R) polymorphism in E-selectin has been reported at increased frequency in patients with systemic lupus erythematosus and atherosclerosis. Here we tested the hypothesis that the S128R substitution may contribute to increased vascular disease by altering the number and/or phenotype of lymphocytes interacting with E-selectin under shear flow. We observed that CHO cell monolayers transfected with S128R recruited significantly greater numbers of unfractionated lymphocytes than monolayers expressing an equivalent density of wild-type (WT) E-selectin. Depletion of the CLA(+) subpopulation or generation of CLA(-) lymphoblasts abolished rolling and arrest on WT E-selectin, but left a residual population that interacted with S128R. Generation of Th subsets revealed preferential interaction of Th0 and Th2, but not Th1, cells with S128R compared with WT. However, only T cells of a memory phenotype interacted with S128R, since neither monolayer supported rolling of CD45RA(+) cells. Our results demonstrate that the S128R polymorphism extends the range of lymphocytes recruited by E-selectin, which may provide a mechanistic link between this polymorphism and vascular inflammatory disease.

Cryptococcal glucuronoxylomannan inhibits adhesion of neutrophils to stimulated endothelium in vitro by affecting both neutrophils and endothelial cells

Cryptococcal infections are often characterized by a paucity of leukocytes in the infected tissues. Previous research has shown that the capsular polysaccharide glucuronoxylomannan (GXM) inhibits leukocyte migration. In this study we investigated whether the capsular polysaccharide GXM affects the migration of neutrophils (polymorphonuclear leukocytes [PMN]) through the endothelium by interfering with adhesion in a static adhesion model. Pretreatment of PMN with GXM inhibited PMN adhesion to tumor necrosis factor alpha (TNF-alpha)-stimulated endothelium up to 44%. Treatment of TNF-alpha-stimulated endothelium with GXM led to a 27% decrease in PMN adhesion. GXM treatment of both PMN and endothelium did not have an additive inhibitory effect. We demonstrated that GXM-induced L-selectin shedding does not play an important role in the detected inhibition of adhesion. L-selectin was still present on PMN in sufficient amounts after GXM treatment, since it could be further inhibited by blocking antibodies. Furthermore, blocking of GXM-related L-selectin shedding did not abolish the GXM-related inhibition of adhesion. GXM most likely exerts its effect on PMN by interfering with E-selectin-mediated binding. The use of blocking monoclonal antibodies against E-selectin, which was shown to decrease adhesion in the absence of GXM, did not cause additive inhibition of PMN adhesion after GXM pretreatment. The use of blocking antibodies also demonstrated that the inhibiting effect found after GXM treatment of endothelium probably involves interference with both intercellular adhesion molecule-1 and E-selectin binding.

Integration of inflammatory signals by rolling neutrophils

In inflammation, neutrophils roll along the endothelial wall of postcapillary venules and sample inflammatory signals. Neutrophil activation is required to generate beta(2) integrin bonds with the endothelium that are strong enough to withstand the flow forces and thus achieve arrest from the rolling state. Unlike naïve T cells, neutrophils are not only activated by ligation of G-protein coupled receptors with chemokines and other chemoattractants but also receive signals from engagement of adhesion molecules including the selectins and beta(2) integrins. Rolling neutrophils integrate the sum total of inputs received while scanning the inflamed endothelium. In this process, the velocity of rolling neutrophils systematically decreases as a function of their contact time with the inflamed endothelium. If an activation threshold is reached, beta(2) integrins switch to the high-affinity conformation, redistribute on the cell surface, and trigger arrest and adhesion. Rolling cells that do not reach the activation threshold detach from the endothelium and are released back into the circulation. The role of chemokines, adhesion molecules, and other activating inputs involved in this response as well as signaling pathways are the subjects of ongoing investigations. This review provides a conceptual framework for neutrophil recruitment from the flowing blood.