Adhesion molecule cascades direct lymphocyte recirculation and leukocyte migration during inflammation

Soluble intracellular adhesion molecule-1 is associated with cardiovascular disease risk and mortality in older adults

BACKGROUND

Intracellular adhesion molecule-1 (ICAM-1) regulates leukocyte-endothelial attachment, a process crucial to atherosclerosis. Circulating soluble ICAM-1 (sICAM-1) may serve as a marker of cardiovascular disease (CVD) progression.

OBJECTIVES

We examined the association of sICAM-1 with measures of subclinical CVD and risk of incident CVD events and death in older men and women (age > or = 65 years) from the Cardiovascular Health Study.

METHODS

Selected participants were free of clinical CVD at baseline. Non-exclusive incident case groups were angina (n = 534), myocardial infarction (n = 304), stroke (n = 327), and death (n = 842; CVD death = 310). A total 643 subjects were free of events during follow-up.

RESULTS

sICAM-1 was positively associated with C-reactive protein, interleukin-6 and fibrinogen and measures of subclinical CVD in these older men and women. In Cox regression models adjusted for age, gender, and race, increasing levels of sICAM-1 were associated with increased risk of all cause mortality in men and women. Hazard ratios (95% confidence intervals) for a one standard deviation increase in sICAM-1 (89.7 ng mL(-1)) were 1.3 (1.1-1.4) in men and 1.2 (1.1-1.3) in women. sICAM-1 was associated with increased risk of CVD death in women (1.2; 1.0-1.5), but not men (1.1; 0.9-1.3). There were no associations of sICAM-1 with non-fatal CVD events.

CONCLUSIONS

While sICAM-1 was associated with death in older men and women, there was a more marked association between sICAM-1 and CVD death in women.

The extracellular matrix protein mindin serves as an integrin ligand and is critical for inflammatory cell recruitment

Leukocyte recruitment to inflammation sites depends on interactions between integrins and extracellular matrix (ECM). In this report we show that mice lacking the ECM protein mindin exhibit severely impaired recruitment of neutrophils and macrophages in 4 different inflammation models. Furthermore, neutrophils directly bind to immobilized mindin, and mindin matrix mediates neutrophil migration in vitro. The adhesion of neutrophils to mindin is blocked by anti-integrin alpha4, anti-integrin alpha(M), and anti-integrin beta2 antibodies. We also show that HEK-293 cells transfected with cDNA encoding these integrins exhibit enhanced binding to immobilized mindin matrix and the increased binding can be blocked by anti-integrin antibodies. Our results suggest that mindin serves as a novel ligand for integrins and mindin-integrin interactions are critical for inflammatory cell recruitment in vivo.

The CXCR1 tail mediates beta1 integrin-dependent cell migration via MAP kinase signaling

In this study, we examined how IL-8 induces leukocyte migration on major beta1 integrin ligands derived from the extracellular matrix protein fibronectin. We assessed individual contributions of signaling by IL-8 receptors by transfection of CXCR1 and CXCR2 into rat basophilic leukemia (RBL) cells and human monocytic THP-1 cells. CXCR1 expressing cells migrated on the fibronectin ligands for alpha4beta1 and alpha5beta1 integrins in response to IL-8, whereas CXCR2 expressing cells did not. RBL cells expressing the chimeric CXCR1 receptor containing the cytoplasmic tail of CXCR2 had greatly blunted migration, while cells expressing the CXCR2 chimera with the tail of CXCR1 had augmented migration. Last, inhibitors of p38 and JNK MAP kinases blocked IL-8-induced migration in CXCR1+ cells. We conclude that IL-8 stimulated beta1 integrin-mediated leukocyte migration on fibronectin through CXCR1 is dependent on the C-terminal cytoplasmic domain of CXCR1 and subsequent p38 and JNK MAPK signaling.

Immunokinetics of autoreactive CD4 T cells in blood: a reporter for the “hit-and-run” autoimmune attack on pancreas and diabetes progression

Little is known about the fate of autoreactive CD4 T cells in blood. Using a mouse model for spontaneous autoimmune diabetes we demonstrated that the status of the autoimmune process in pancreas could be pictured through the frequency and phenotype of autoreactive CD4 T cells in the blood. Early during the prediabetic stage, the frequency of these cells in blood decreased as a consequence of their recruitment in the pancreas. This was followed by an imbalance between CD4(+)CD25(+) and CD4(+)CD69(+) T cells in the pancreas that was mirrored in the phenotype of autoreactive T cells in the blood. Waves of activated CD4(+)CD69(+) T cells in blood preceded the disease onset suggesting that the autoimmune attack on pancreas is a discontinuous "hit-and-run" rather than a continuous process. Tracking autoreactive CD4 T cells in blood may help in identifying prediabetic humans and monitoring the disease progression during therapeutic interventions.

Evaluation of the host transcriptional response to human cytomegalovirus infection

Gene expression data from human cytomegalovirus (HCMV)-infected cells were analyzed using DNA-Chip Analyzer (dChip) followed by singular value decomposition (SVD) and compared with a previous analysis of the same data that employed GeneChip software and a fold change filtering approach. dChip and SVD analysis revealed two clusters of coexpressed human genes responding differently to HCMV infection: one containing some genes identified previously, and another that was largely unique to this analysis. Annotating these genes, we identified several functional categories important to host cell responses to HCMV infection. These categories included genes involved in transcriptional regulation, oncogenesis, and cell cycle regulation, which were more prevalent in cluster 1, and genes involved in immune system regulation, signal transduction, and cell adhesion, which were more prevalent in cluster 2. Within these categories, we found genes involved in the host response to HCMV infection (mainly in cluster 1), as well as genes targeted by HCMV’s immune evasion strategies (mainly in cluster 2). As the second group of genes identified by the dChip and SVD approach was statistically and biologically significant, our results point out the advantages of using different methods to analyze gene expression data.

Human Thy-1 (CD90) on Activated Endothelial Cells Is a Counterreceptor for the Leukocyte Integrin Mac-1 (CD11b/CD18)

Leukocyte recruitment in response to inflammatory signals is in part governed by interactions between endothelial cell receptors belonging to the Ig superfamily and leukocyte integrins. In our previous work, the human Ig superfamily glycoprotein Thy-1 (CD90) was identified as an activation-associated cell adhesion molecule on human dermal microvascular endothelial cells. Furthermore, the interaction of Thy-1 with a corresponding ligand on monocytes and polymorphonuclear cells was shown to be involved in the adhesion of these leukocytes to activated Thy-1-expressing endothelial cells. In this study, we have identified the specific interaction between human Thy-1 and the leukocyte integrin Mac-1 (CD11b/CD18; alphaMbeta2) both in cellular systems and in purified form. Monocytes and polymorphonuclear cells were shown to adhere to transfectants expressing human Thy-1 as well as to primary Thy-1-expressing human dermal microvascular endothelial cells. Furthermore, leukocyte adhesion to activated endothelium as well as the subsequent transendothelial migration was mediated by the interaction between Thy-1 and Mac-1. This additional pathway in leukocyte-endothelium interaction may play an important role in the regulation of leukocyte recruitment to sites of inflammation.

P-selectin suppresses hepatic inflammation and fibrosis in mice by regulating interferon gamma and the IL-13 decoy receptor

The selectin family of cell adhesion molecules is widely thought to promote inflammatory reactions by facilitating leukocyte recruitment. However, it was unexpectedly found that mice with targeted deletion of the P-selectin gene (PsKO mice) developed unpolarized type 1/type 2 cytokine responses and severely aggravated liver pathology following infection with the type 2-promoting pathogen Schistosoma mansoni. In fact, liver fibrosis, which is dependent on interleukin 13 (IL-13), increased by a factor of more than 6, despite simultaneous induction of the antifibrotic cytokine interferon gamma (IFN-gamma). Inflammation, as measured by granuloma size, also increased significantly in the absence of P-selectin. When infected PsKO mice were treated with neutralizing anti-IFN-gamma monoclonal antibodies, however, granuloma size was restored to wild-type levels; this finding revealed the potent proinflammatory role of IFN-gamma when expressed concomitantly with IL-13. Untreated PsKO mice also exhibited a significant (sixfold) reduction in decoy IL-13 receptor (IL-13 receptor alpha-2) expression when compared with infected wild-type animals. It is noteworthy, however, that when decoy receptor activity was restored in PsKO mice by treatment with soluble IL-13 receptor alpha-2-Fc, the exacerbated fibrotic response was completely inhibited. Thus, reduced expression of the decoy IL-13 receptor mediated by the elevated type 1 cytokine response probably accounts for the enhanced activity of IL-13 in PsKO mice and for the resultant increase in collagen deposition. In conclusion, the current study has revealed the critical role of P-selectin in the progression of chronic liver disease caused by schistosome parasites. By suppressing IFN-gamma and up-regulating the decoy IL-13 receptor, P-selectin dramatically inhibits the pathologic tissue remodeling that results from chronic type 2 cytokine-mediated inflammation.

The state diagram for cell adhesion mediated by two receptors

Leukocyte recruitment from the bloodstream to surrounding tissues is an essential component of the immune response. Capture of blood-borne leukocytes onto vascular endothelium proceeds via a two-step mechanism, with each step mediated by a distinct receptor-ligand pair. Cells first transiently adhere, or "roll" (via interactions between selectins and sialyl-Lewis-x), and then firmly adhere to the vascular wall (via interactions between integrins and ICAM-1). We have reported that a computational method called adhesive dynamics (AD) accurately reproduces the fine-scale dynamics of selectin-mediated rolling. This paper extends the use of AD simulations to model the dynamics of cell adhesion when two classes of receptors are simultaneously active: one class (selectins or selectin ligands) with weakly adhesive properties, and the other (integrins) with strongly adhesive properties. AD simulations predict synergistic functions of the two receptors in mediating adhesion. At a fixed density of surface ICAM-1, increasing selectin densities lead to greater pause times and an increased tendency toward firm adhesion; thus, selectins mechanistically facilitate firm adhesion mediated by integrins. Conversely, at a fixed density of surface selectin, increasing ICAM-1 densities lead to greater pause times and an increased tendency to firm adhesion. We present this relationship in a two-receptor state diagram, a map that relates the densities and properties of adhesion molecules to various adhesive behaviors that they code, such as rolling or firm adhesion. We also present a state diagram for neutrophil activation, which relates beta(2)-integrin density and integrin-ICAM-1 kinetic on rate to neutrophil adhesive behavior. The predictions of two-receptor adhesive dynamics are validated by the ability of the model to reproduce in vivo neutrophil rolling velocities from the literature.

Processing and presentation of the islet autoantigen GAD by vascular endothelial cells promotes transmigration of autoreactive T-cells

Type 1 diabetes is characterized by T-cell infiltration of the islets of Langerhans and abundant HLA class II molecule expression on islet endothelial cells (ECs). The specificity of infiltrating T-cells for islet autoantigens has been amply demonstrated in animal models, and is implicit in human diabetes, but the processes regulating endothelial transmigration of islet autoantigen-specific T-cells into islets are not known. We examined the ability of ECs expressing HLA class II molecules to process and present the islet autoantigen GAD65 and examined the effects of presentation on transmigration of GAD65-specific T-cells. Primary cultures of human vascular ECs expressing the DRB1*0401 (VEC1) and DRB1*0301 (VEC2) genotypes were established and de novo expression of HLA class II molecules induced with interferon-gamma. Under these conditions, VEC1 efficiently processed and presented whole GAD65 to the HLA-DR4-restricted murine T-cell hybridoma T33.1 that recognizes the 274-286 epitope of GAD65. Using a transwell system, we examined the effect of GAD65 presentation on migration of GAD65-specific T-cells across EC monolayers. Migration of T33.1 hybridoma cells and of the human T-cell clone, PM1#11 (recognizes GAD65 epitope 339-352 presented by HLA-DR3) across VEC1 and VEC2, respectively, were greatly enhanced in the presence of GAD65, commencing more rapidly and achieving a higher peak migration at 3 h. Migrated PM1#11 cells retained full proliferative capacity. These results support the hypothesis that presentation of autoantigens by islet endothelium in vivo could promote transmigration of circulating islet autoantigen-specific T-cells primed in regional lymph nodes against islet autoantigens.

Piperlactam S suppresses macrophage migration by impeding F-actin polymerization and filopodia extension

This study was designed to evaluate the anti-inflammatory effect of piperlactam S on chemoattractant-induced migration, functions underlying leukocyte recruitment in vitro. Results showed that RAW264.7 macrophages migrate toward complement 5a, a powerful chemoattractant for macrophages. This phenomenon could be suppressed concentration dependently by piperlactam S (0.3-30 microM). Fluorescence staining demonstrated that piperlactam S and cytochalasin B both effectively reversed complement 5a-induced cell polarization, filopodia extension, as well as the increase in the cell content of F-actin. Functional inhibition by antibodies suggested that Mac-1 (CD11b) integrin plays a central role in complement 5a-induced migration. However, piperlactam S failed to modify Mac-1 expression. Furthermore, complement 5a triggered the activation of Cdc42, a Rho-family protein involved in the regulation of filopodia extension, with a time course that paralleled that of filopodia extension and which was inhibited by piperlactam S. In summary, piperlactam S exerts anti-inflammatory effects possibly by interfering with cell migration, impeding F-actin polymerization, filopodia formation, and/or Cdc42 activation. However, the detailed mechanism by which piperlactam S regulates the above processes needs further study.

In vitro cellular handling and in vivo targeting of E-selectin-directed immunoconjugates and immunoliposomes used for drug delivery to inflamed endothelium

PURPOSE

Drug targeting to activated endothelial cells is now being explored as a new approach to interfere with chronic inflammation. This study compares a dexamethasone-anti-E-selectin immunoconjugate (dexa-AbEsel) with anti-E-selectin immunoliposomes (AbEsel-immunoliposomes) that contain dexamethasone, regarding in vitro binding and internalization as well as in vivo accumulation in activated endothelial cells.

METHODS

In vitro binding and internalization of dexa-AbEsel and the AbEsel-immunoliposomes into TNFalpha-activated HUVECs was studied using confocal laser scanning microscopy and radiolabeled compounds. Tissue accumulation of both compounds was studied in a murine delayed-type hypersensitivity model using immunohistochemistry.

RESULTS AND CONCLUSIONS

Both preparations were selectively internalized by activated endothelial cells. Dexa-AbEsel was internalized by activated HUVECs to a larger extent than the AbEsel-immunoliposomes, although in theory the high drug-loading capacity of the liposomes may enable a larger amount of dexamethasone to be delivered intracellularly. Both dexa-AbEsel and AbEsel-immunoliposomes accumulated in activated endothelial cells in murine inflamed skin. AbEsel-immunoliposomes, but not dexa-AbEsel, were additionally detected in control skin, though to a lesser extent, and in macrophages of the liver and the spleen. Studies on therapeutic effects and side effects in models of chronic inflammation are now necessary to establish pharmacodynamics of dexa-AbEsel and/or AbEsel-immunoliposomes in the treatment of chronic inflammation.

Effect of nicotine replacement and quitting smoking on circulating adhesion molecule profiles (sICAM-1, sCD44v5, sCD44v6)

BACKGROUND

Soluble ICAM-1 (sICAM-1; sCD54), sCD44v5 and sCD44v6 are circulating adhesion molecules, with immunomodulatory potential, that have been frequently attributed diagnostic, prognostic and aetiological significance in a number of inflammatory and malignant diseases. We have previously shown that systemic concentrations of these molecules are increased significantly in tobacco smokers, but reduce to within normal levels at 12 months following successful quitting.

MATERIALS AND METHODS

We have been able to extend these observations by measuring levels before and 4, 8, 22 and 52 weeks after smoking cessation in subjects receiving high-dose nicotine replacement therapy (25 mg of nicotine; n = 34) or placebo patches (n = 34) for 26 weeks. Smoking cessation was confirmed by regular measurement of expired-air CO levels and by plasma cotinine analysis.

RESULTS

Plasma sICAM-1, sCD44v5 and sCD44v6 concentrations all declined rapidly within 4 weeks of smoking cessation (P < 0.001 for all declines). Additionally, no differences were observed between those using nicotine replacement and those who were not for sICAM-1, sCD44v5, or sCD44v6.

CONCLUSIONS

The recovery in smoking-associated adhesion molecule profiles represents an almost immediate beneficial effect of smoking cessation. Nicotine replacement therapy is an effective aid to quitting and does not affect these recoveries. The elevated levels of these important risk factors in smokers (sICAM-1, sCD44v5 and sCD44v6) are linked to noxious element(s) in tobacco smoke other than nicotine or nicotine metabolites.

Cellular handling of a dexamethasone-anti-E-selectin immunoconjugate by activated endothelial cells: comparison with free dexamethasone

PURPOSE

For selective inhibition of endothelial cell activation in chronic inflammation, we have developed a dexamethasone-anti-E-selectin immunoconjugate. The present study was performed to evaluate the cellular handling of this immunoconjugate by activated primary endothelial cells and to compare its drug delivery capacity with free dexamethasone.

METHODS

The binding, uptake, and degradation of 125I-radiolabeled dexamethasone-anti-E-selectin immunoconjugate by TNFalpha-activated endothelial cells were studied for different time periods and at different concentrations, as well as in the presence of inhibitors for E-selectin binding and lysosomal degradation. Its drug delivery capacity was compared with the uptake of unconjugated 3H-labeled dexamethasone.

RESULTS

The immunoconjugate was internalized by E-selectin expressing activated endothelial cells and degraded in the lysosomal compartment. The receptor-mediated binding and uptake was saturable, implying a maximal attainable intracellular concentration of the drug. In contrast, free dexamethasone entered both resting and activated endothelial cells by passive diffusion.

CONCLUSIONS

The dexamethasone-anti-E-selectin immunoconjugate is capable of selective delivering the coupled drug into activated endothelial cells. This targeting concept enables disease-induced drug delivery in which intracellular concentrations can be reached comparable with those obtained after incubation with 3 FM dexamethasone.

A functional role for circulating mouse L-selectin in regulating leukocyte/endothelial cell interactions in vivo

L-selectin mediates the initial capture and subsequent rolling of leukocytes along inflamed vascular endothelium and mediates lymphocyte migration to peripheral lymphoid tissues. Leukocyte activation induces rapid endoproteolytic cleavage of L-selectin from the cell surface, generating soluble L-selectin (sL-selectin). Because human sL-selectin retains ligand-binding activity in vitro, mouse sL-selectin and its in vivo relevance were characterized. Comparable with humans, sL-selectin was present in adult C57BL/6 mouse sera at approximately 1.7 micro g/ml. Similar levels of sL-selectin were present in sera from multiple mouse strains, despite their pronounced differences in cell surface L-selectin expression levels. Adhesion molecule-deficient mice prone to spontaneous chronic inflammation and mice suffering from leukemia/lymphoma had 2.5- and 20-fold increased serum sL-selectin levels, respectively. By contrast, serum sL-selectin levels were reduced by 70% in Rag-deficient mice lacking mature lymphocytes. The majority of serum sL-selectin had a molecular mass of 65-75 kDa, consistent with its lymphocyte origin. Slow turnover may explain the relatively high levels of sL-selectin in vivo. The t(1/2) of sL-selectin, assessed by transferring sera from wild-type mice into L-selectin-deficient mice and monitoring serum sL-selectin levels by ELISA, was >20 h, and it remained detectable for longer than 1 wk. Short-term in vivo lymphocyte migration assays demonstrated that near physiologic levels ( approximately 0.9 micro g/ml) of sL-selectin decreased lymphocyte migration to peripheral lymph nodes by >30%, with dose-dependent inhibition occurring with increasing sL-selectin concentrations. These results suggest that sL-selectin influences lymphocyte migration in vivo and that the increased sL-selectin levels present in certain pathologic conditions may adversely affect leukocyte migration.

Bromelain treatment alters leukocyte expression of cell surface molecules involved in cellular adhesion and activation

Bromelain is a natural proteinase preparation derived from pineapple stem that is marketed for oral use as a digestive aid and as an antiinflammatory agent. Bromelain treatment in vitro has been previously shown to selectively remove certain cell surface molecules that may affect lymphocyte migration and activation. This study reports the effects of bromelain on a broad range of cell surface molecules and on lymphocytes, monocytes, and granulocytes under physiologically relevant conditions. In vitro bromelain treatment of leukocytes in whole blood proteolytically altered 14 of 59 leukocyte markers studied. Constitutively expressed bromelain-sensitive molecules included CD7, CD8alpha, CD14, CD16, CD21, CD41, CD42a, CD44, CD45RA, CD48, CD57, CD62L, CD128a, and CD128b. The proteolytic effect of bromelain increased as the concentration of plasma decreased, with EC50 ranging from >1000 microg/ml for 100% plasma to approximately 1 microg/ml in the absence of plasma, indicating the presence of an inhibitor of bromelain in plasma. alpha2-macroglobulin purified from plasma mimicked the inhibitory effect of whole plasma on bromelain activity. If proteolysis is required for the antiinflammatory actions of oral bromelain, these data suggest that the required concentrations are more likely to be achieved locally in the gastrointestinal tract or in other tissue sites where the plasma concentration is low, rather than in the bloodstream. The cell surface molecules altered by bromelain are involved in leukocyte homing and cellular adhesion and activation. Thus bromelain could potentially exert an antiinflammatory effect by multiple mechanisms, including alterations in leukocyte migration and activation.

Inhibition of airway inflammation and hyperreactivity by an antioxidant mimetic

A catalytic antioxidant, AEOL 10113, was used in a murine model of asthma to test the hypothesis that oxidants contribute to the pathogenesis of asthma. Balb/c mice were immunized and challenged with ovalbumin. AEOL 10113 was administered to the mice by intratracheal instillation during ovalbumin challenges. Enhanced pause as an indicator of airway reactivity and differential cell count of lavage cells as an indicator of airway inflammation were assessed. Lung expressions of the adhesion molecules VCAM-1 and ICAM-1 were measured. We found that treatment of ovalbumin-challenged mice with AEOL 10113 drastically reduced the severity of airway inflammation as evidenced by the reduced numbers of eosinophils, neutrophils, and lymphocytes found in bronchoalveolar lavage fluid. Inhibition of ovalbumin-induced airway inflammation is associated with inhibited expression of VCAM-1, which is a key adhesion molecule responsible for the recruitment of inflammatory cells into the lungs of ovalbumin-challenged mice. In addition, treatment with AEOL 10113 reduced the magnitude of ovalbumin-induced airway hyperreactivity to methacholine. These results suggest that oxidative stress is an important factor in the pathogenesis of asthma and that a synthetic catalytic antioxidant could be effective in the treatment of asthma.

Synthesis and applications of end-labeled neoglycopolymers

[reaction: see text] Neoglycopolymers that vary in length and contain a single fluorescent reporter group were synthesized using ring-opening metathesis polymerization (ROMP). The utility of these materials is demonstrated by the development of a cellular binding assay for L-selectin, a cell surface protein that plays a role in inflammation. The data reveal that these multivalent ligands interact with multiple copies of L-selectin.

Transendothelial migratory pathways of V delta 1+TCR gamma delta+ and V delta 2+TCR gamma delta+ T lymphocytes from healthy donors and multiple sclerosis patients: involvement of phosphatidylinositol 3 kinase and calcium calmodulin-dependent kinase II

We have previously reported that the Vdelta2(+)TCRgammadelta(+) T lymphocyte subset, expressing the NK receptor protein 1a (NKRP1a; CD161), is expanded in patients with relapsing-remitting multiple sclerosis and uses this molecule to migrate through endothelium. In this work, we show that Vdelta1(+) and Vdelta2(+) gammadelta T lymphocytes use distinct signal transduction pathways to accomplish this function. Indeed, we have found that Vdelta1(+) cells lack NKRP1a and selectively express the platelet endothelial cell adhesion molecule 1 (PECAM1; CD31), which drives transendothelial migration of this cell subset, at variance with Vdelta2(+) T cells, which are PECAM1 negative and use NKRP1a for transmigration. Interestingly, when Vdelta2(+) T cells were pretreated with two specific inhibitors of the calcium calmodulin-dependent kinase II KN62 and KN93, but not with the inactive compound KN92, the number of migrating cells and the rate of transmigration were significantly decreased. In turn, the phosphatidylinositol 3 kinase blockers wortmannin and LY294002 exerted a dose-dependent inhibition of Vdelta1(+) cell migration. Finally, NKRP1a and PECAM1 engagement led to activation of different signal transduction pathways: indeed, oligomerization of NKRP1a on Vdelta2(+) T cells activates calcium calmodulin-dependent kinase II, while occupancy of PECAM1 on Vdelta1(+) cells triggers the phosphatidylinositol 3 kinase-dependent Akt/protein kinase Balpha activation. These findings suggest that subsets of gammadelta T lymphocytes may migrate to the site of lesion in multiple sclerosis using two different signaling pathways to extravasate.

Mechanisms of L-selectin-induced activation of the nuclear factor of activated T lymphocytes (NFAT)

Selectins are mediating transient contacts of leukocytes with endothelium during inflammatory processes and in the development of the immune system. L-selectin expressed on almost all leukocytes also functions as a signaling receptor. Recently, we have identified different signaling pathways in T lymphocytes by L-selectin. One signaling cascade leads via the tyrosine kinase p56lck to the small G-proteins Ras and Rac and to MAP-kinases. A second independent pathway results in ceramide release. In this study, an L-selectin-induced translocation of the transcription factor NFAT to the nucleus was identified. Using genetically modified JCaM1.6 cells, pharmacological inhibitors, and antisense molecules, it was shown that L-selectin-induced NFAT activation depends on src-tyrosine kinases, calcineurin and small G-proteins. MAP-kinases and actin filaments were identified as Ras effectors involved in NFAT translocation. We conclude that L-selectin cross-linking results in activation of NFAT by different signaling pathways. The activation of NFAT might modulate the immune response of leukocytes interacting with endothelial cells.

Origin of endothelial progenitors in human postnatal bone marrow

This study demonstrates that a CD34(-), vascular endothelial cadherin(-) (VE-cadherin(-)), AC133(+), and fetal liver kinase(+) (Flk1(+)) multipotent adult progenitor cell (MAPC) that copurifies with mesenchymal stem cells from postnatal human bone marrow (BM) is a progenitor for angioblasts. In vitro, MAPCs cultured with VEGF differentiate into CD34(+), VE-cadherin(+), Flk1(+) cells - a phenotype that would be expected for angioblasts. They subsequently differentiate into cells that express endothelial markers, function in vitro as mature endothelial cells, and contribute to neoangiogenesis in vivo during tumor angiogenesis and wound healing. This in vitro model of preangioblast-to-endothelium differentiation should prove very useful in studying commitment to the angioblast and beyond. In vivo, MAPCs can differentiate in response to local cues into endothelial cells that contribute to neoangiogenesis in tumors. Because MAPCs can be expanded in culture without obvious senescence for more than 80 population doublings, they may be an important source of endothelial cells for cellular pro- or anti-angiogenic therapies.

Selective intracellular delivery of dexamethasone into activated endothelial cells using an E-selectin-directed immunoconjugate

In chronic inflammatory diseases, the endothelium is an attractive target for pharmacological intervention because it plays an important role in leukocyte recruitment. Hence, inhibition of endothelial cell activation and consequent leukocyte infiltration may improve therapeutic outcome in these diseases. We report on a drug targeting strategy for the selective delivery of the anti-inflammatory drug dexamethasone to activated endothelial cells, using an E-selectin-directed drug-Ab conjugate. Dexamethasone was covalently attached to an anti-E-selectin Ab, resulting in the so-called dexamethasone-anti-E-selectin conjugate. Binding of the conjugate to E-selectin was studied using surface plasmon resonance and immunohistochemistry. Furthermore, internalization of the conjugate was studied using confocal laser scanning microscopy and immuno-transmission electron microscopy. It was demonstrated that the dexamethasone-anti-E-selectin conjugate, like the unmodified anti-E-selectin Ab, selectively bound to TNF-alpha-stimulated endothelial cells and not to resting endothelial cells. After binding, the conjugate was internalized and routed to multivesicular bodies, which is a lysosome-related cellular compartment. After intracellular degradation, pharmacologically active dexamethasone was released, as shown in endothelial cells that were transfected with a glucocorticoid-responsive reporter gene. Furthermore, intracellularly delivered dexamethasone was able to down-regulate the proinflammatory gene IL-8. In conclusion, this study demonstrates the possibility to selectively deliver the anti-inflammatory drug dexamethasone into activated endothelial cells, using an anti-E-selectin Ab as a carrier molecule.

The influence of tobacco smoking on adhesion molecule profiles

Sequential interactions between several adhesion molecules and their ligands regulate lymphocyte circulation and leukocyte recruitment to inflammatory foci. Adhesion molecules are, therefore, central and critical components of the immune and inflammatory system. We review the evidence that tobacco smoking dysregulates specific components of the adhesion cascade, which may be a common factor in several smoking-induced diseases. Smoking causes inappropriate leukocyte activation, leukocyte-endothelial adhesion, and neutrophil entrapment in the microvasculature, which may help initiate local tissue destruction. Appropriate inflammatory reactions may thus be compromised. In addition to smoke-induced alterations to membrane bound endothelial and leukocyte adhesion molecule expression, which may help explain the above phenomena, smoking has a profound influence on circulating adhesion molecule profiles, most notably sICAM-1 and specific sCD44 variants. Elevated concentrations of soluble adhesion molecules may simply reflect ongoing inflammatory processes. However, increasing evidence suggests that specific soluble adhesion molecules are immunomodulatory, and that alterations to soluble adhesion molecule profiles may represent a significant risk factor for several diverse diseases. This evidence is discussed herein.