Erythroid adhesion molecules in sickle cell disease: Effect of hydroxyurea

In sickle cell disease, the complex scenario of vaso-occlusive crisis (VOC) typical of this disease is clearly multifactorial and not fully understood. Cell-cell and cell-cell matrix interactions mediated by adhesive molecules present on blood cells and endothelial cells (ECs) are thought to play an important role. Early studies have shown that sickle red blood cells (RBCs) are abnormally adherent to ECs and some of the molecules involved in these interactions have been identified, such as the alpha4beta1 integrin and CD36, exclusively present on stress reticulocytes, and CD47 on mature RBCs. More recently, attention focused on Lu/BCAM, the unique RBC receptor for laminin, and on ICAM-4, a red cell-specific adhesion receptor, which is a ligand for a large repertoire of integrins (alphaLbeta2, alphaMbeta2, alphaxbeta2, alphaVbeta3). The counter-receptors on ECs and the role of plasma proteins forming bridges between blood cells and ECs have been clarified in part. It has also been shown that reticulocytes from SCD patients express higher levels of alpha4beta1 integrin and CD36, and that under hydroxyurea (HU) therapy, both cell adhesion to ECs or extracellular matrix proteins and the levels of these adhesion molecules are reduced. These findings are consistent with the view that enhanced adhesion of blood cells to ECs is largely determined by the membrane expression level of adhesion molecules and could be a crucial factor for triggering or aggravating vaso-occlusion. In SCD patients, membrane expression of Lu/BCAM (and perhaps ICAM-4) is enhanced on RBCs whose adherence to laminin or ECs is also increased. Interestingly, Lu/BCAM- and ICAM-4-mediated adhesion are enhanced by the stress mediator epinephrine through a PKA-dependent pathway initiated by a rise in intracellular cAMP and leading to receptor activation by phosphorylation according to the same signaling pathway. More recently, studies based on quantitative expression analysis of adhesion molecules on RBCs and during erythroid differentiation in patients undergoing HU therapy, surprisingly revealed that Lu/BCAM level was enhanced, although alpha4beta1, CD36 and ICAM-4 (to a lower extent) levels were indeed reduced. CD47 and CD147 expression were also enhanced in HU-treated patients. Based on these findings we suggest that the signalization cascade leading to receptor activation rather than the expression level only of adhesion molecules may be the critical factor regulating cell adhesion, although both mechanisms are not mutually exclusive.     

Short exposure of intestinal epithelial cells to TNF-alpha and histamine induces Mac-1-mediated neutrophil adhesion independent of protein synthesis.

Neutrophils play an important role in intestinal inflammation by interacting with intestinal epithelial cells. In this study, we evaluated neutrophil adhesion to intestinal epithelial cells using intestinal epithelial cell line HT29 stimulated with tumor necrosis factor alpha (TNF-alpha) and histamine for a short time (30 min). The TNF-alpha and histamine stimulation markedly increased neutrophil adhesion. The increased adhesion was inhibited by anti-CD11b and anti-CD18 monoclonal antibodies (mAbs), but not by anti-CD11a and anti-CD54 (ICAM-1) mAbs. It is interesting that flow cytometric analysis revealed that ICAM-1 expression on HT29 cells was not changed by TNF-alpha and histamine stimulation. Moreover, the increased adhesion was inhibited by proteinase K treatment but not cycloheximide treatment of HT29 cells. Together these observations suggest that short exposure of HT29 cells to TNF-alpha and histamine induces CD11b/CD18 (Mac-1)-dependent but CD11a/CD18 (LFA-1)-independent neutrophil adhesion to intestinal epithelial cells, and ICAM-1 is not likely to be involved in the interactions. Furthermore, epithelial cell ligand(s) for neutrophils is likely protein molecule(s) that is expressed on the cell by stimulation independent protein synthesis. However, it is also possible that neutrophil activating factor(s), which stimulates neutrophils to bind with epithelial ligands via Mac-1, is expressed by epithelial cells during stimulation.     

Inefficiency of C3H/HeN Mice to Control Chlamydial Lung Infection Correlates with Downregulation of Neutrophil Activation during the Late Stage of Infection

We previously reported that massive infiltration of neutrophils in C3H/HeN （C3H） mice could not efficiently control Chlamydia muridarum （Cm） infection and might contribute to the high susceptibility of these mice to lung infection. To further define the nature of neutrophil responses in C3H mice during chlamydial infection, we examine the expression of adhesion molecules and CDllb related to neutrophils infiltration and activation, respectively, following intranasal Cm infection. The results showed that the expression of selectins （E-selectin, P-selectin and L-selectin）, and intercellular cell adhesion molecule-1 （ICAM-1） in the lung of C3H mice increased more significantly than in C57BL/6 （B6） mice, the more resistant strain. These results correlated well with the massive neutrophils infiltration in C3H mice. In contrast, CDllb expression on peripheral blood and lung neutrophils in C3H mice exhibited a significant reduction compared with B6 mice during the late phage of infection （day 14）. These findings suggest that the high-level expression of adhesion molecules in C3H mice may enhance neutrophils recruitment to the lung, but the decline of CDllb expression on neutrophils may attenuate neutrophil function. Therefore, CDllb down-regulation on neutrophils may contribute to the failure of C3H mice to control chlamydial lung infection.     

Biological function of CD40 on human endothelial cells: costimulation with CD40 ligand and interleukin-4 selectively induces expression of vascular cell adhesion molecule-1 and P-selectin resulting in preferential adhesion of lymphocytes

The expression of adhesion molecules on vascular endothelial cells determines the pattern of migration and extravasation of leucocytes in inflammation and immunity. Here we show that costimulation with CD40 ligand (CD40L) and interleukin (IL)-4 (or IL-13) gives rise to a unique pattern of adhesion molecule expression by human umbilical vein endothelial cells (HUVEC). CD40 ligation alone enhanced expression of vascular cell adhesion molecule-1 (VCAM-1), intracellular adhesion molecule-1 (ICAM-1) and E-selectin whereas IL-4 and IL-13 increased expression of VCAM-1 and P-selectin but not ICAM-1 or E-selectin. When IL-4 and CD40L were combined there was an additional increase of both VCAM-1 and P-selectin, but ICAM-1 and E-selectin were both inhibited. The combined effects of IL-4 and CD40L signalling were not the result of altered response kinetics, enhanced sensitivity of the endothelium, or increased expression of CD40 or the IL-4 receptor. The rise in VCAM-1 expression induced by combined IL-4 and CD40L stimulation was slower and more sustained than with tumour necrosis factor-alpha (TNF-alpha) and occurred only on a subset (75-80%) of the endothelial cell population compared to 100% with TNF-alpha. Costimulation with IL-4 and CD40L increased adhesion of T cells and B cells above levels obtained with either signal alone, but decreased adhesion of neutrophils. Furthermore, CD40 and IL-4 synergistically increased IL-6 but decreased IL-8 production by HUVEC. These results show that interactions between IL-4 and CD40 on endothelial cells give rise to specific patterns of adhesion molecule expression and cytokine production that may have important implications for lymphocyte and neutrophil migration and function at sites of inflammation.     

CD8(+)CD28(-) T lymphocytes from HIV-1-infected patients secrete factors that induce endothelial cell proliferation and acquisition of Kaposi's sarcoma cell features.

Kaposi's sarcoma (KS) develops more frequently in human immunodeficiency virus type 1 (HIV-1)-infected patients. In this study, we report that molecules released by CD8(+)CD28(-) T lymphocytes from HIV-1-infected patients promote endothelial-cell (EC) growth and induce ECs to acquire spindle cell morphology and upregulation of intercellular adhesion molecule-1 (ICAM-1), E-selectin, and vascular endothelial cell growth factor receptor-3 (VEGFR-3) (a typical feature of the KS cell phenotype). The effects observed on ECs cocultured with in vivo activated CD28(-) cells were partly reproduced when ECs were grown in medium containing interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). At concentrations similar to those found in the supernatant of in vivo activated CD28(-) cells, the two proinflammatory cytokines sustained EC growth and survival only when combined. We, therefore, conclude that CD28(-) T lymphocytes from HIV-1-infected patients exert their effect on ECs through a mechanism involving both IFN-gamma and TNF-alpha. This finding may have wide implications for our basic understanding of the immunopathology of KS.     

The junctional adhesion molecule JAM-C regulates polarized transendothelial migration of neutrophils in vivo

The migration of neutrophils into inflamed tissues is a fundamental component of innate immunity. A decisive step in this process is the polarized migration of blood neutrophils through endothelial cells (ECs) lining the venular lumen (transendothelial migration (TEM)) in a luminal-to-abluminal direction. By real-time confocal imaging, we found that neutrophils had disrupted polarized TEM ('hesitant' and 'reverse') in vivo. We noted these events in inflammation after ischemia-reperfusion injury, characterized by lower expression of junctional adhesion molecule C (JAM-C) at EC junctions, and they were enhanced by blockade or genetic deletion of JAM-C in ECs. Our results identify JAM-C as a key regulator of polarized neutrophil TEM in vivo and suggest that reverse TEM of neutrophils can contribute to the dissemination of systemic inflammation.     

Cyclic-strain-induced endothelial cell expression of adhesion molecules and their roles in monocyte-endothelial interaction.

Vascular endothelial cells (ECs) are constantly subjected to hemodynamic forces that may regulate monocyte-endothelial interaction in vivo. To examine the effects of cyclic strain on endothelial expression of monocyte adhesion molecules, E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) ECs were exposed to physiologically relevant levels of cyclic strain. When ECs were under 25% maximal strain at 30 cycles/min for 24 h, the expression of E-selectin significantly (p<0.05) increased, by 83%, compared to control ECs under static conditions. Similarly, monocyte adhesion to ECs under strain (maximum of 15 or 25% at 30 and 60 cycles/min for 24 h) also significantly (p<0.05) increased, by >82%. This cyclic-strain-induced monocyte adhesion was substantially inhibited (83.5%) by anti-E-selectin antibody. ICAM-1 expression also significantly increased, by 62%, when ECs were under 25% maximal strain at 30 cycles/min for 3 h whereas VCAM-1 expression by ECs under strain (for 0.5, 3, and 24 h) did not change compared to static ECs. When ECs were treated with anti-ICAM-1 antibody and monocytes with anti-VLA-4 antibody, an increase in monocyte adhesion to ECs under cyclic strain was reduced significantly. These results demonstrate that cyclic strain can induce EC expression of monocyte adhesion molecules E-selectin, ICAM-1, and VCAM-1 in a time-dependent manner and thus can mediate monocyte adhesion.     

Role of leukocyte adhesion molecules in lung and dermal vascular injury after thermal trauma of skin.

Acute second degree thermal injury of rat skin involving 25 to 30% total body surface of anesthetized rats results at 4 hours in evidence of vascular injury both locally (in skin) and remotely (involving lung). The neutrophil dependency for both types of injury has now been established. Monoclonal antibodies to various adhesion molecules have been used to define the requirements for these molecules in the development of vascular injury. In dermal vascular injury, a requirement for Mac-1 (CD11b/CD18) but not for leukocyte function-associated antigen-1 (LFA-1, CD11a/CD18) has been established. In this model requirements have also been demonstrated for intercellular adhesion molecule-1 (ICAM-1) and E- and L-selectin but not for very late arising antigen-4 (VLA-4) or P-selectin. With respect to lung vascular injury, dual requirements for both leukocyte function-associated antigen-1 and Mac-1 were found as well as for ICAM-1 and E- and L-selectin but not for VLA-4 and P-selectin. In the lung, there was a close correlation between neutrophil content of the tissue (as assessed by myeloperoxidase) and the effects of protective interventions (directed against blocking of adhesion molecules). These data emphasize the roles of beta 2 integrins, selectins (L and E), and ICAM-1 in events that lead to neutrophil-mediated vascular injury of dermis and lung after thermal trauma to skin.     

Regulation of ICAM-3 (CD50) membrane expression on human neutrophils through a proteolytic shedding mechanism

The regulation of the cell surface expression of ICAM-3 (CD50) was investigated in human neutrophils. Immunofluorescence flow cytometry analysis revealed a remarkable and very rapid down-regulation of the ICAM-3 cell surface expression upon neutrophil activation with stimulating agents such as phorbol myristate acetate (PMA) or calcium ionophore. A similar low expression of ICAM-3 was observed on neutrophils from patients undergoing hemodialysis with cell-activating cellulosic membranes. Internalization assays with ¹²⁵I-labeled anti-ICAM-3 monoclonal antibody (mAb) suggested that ICAM-3-down-regulation was due to antigen release from the cell surface towards the outer milieu, rather than to antigen internalization. Immunoprecipitation studies confirmed this down-regulatory effect, and revealed the presence of ICAM-3 in cell-free supernatants from activated neutrophils. Furthermore, the presence of a soluble form of ICAM-3 with a range of concentrations of 0–296 ng/ml in the plasma from healthy human volunteers was detected by using a two-site mAb radioimmunoassay. A proteolytic mechanism likely accounts for this process since protease inhibitors virtually abrogated the PMA-induced down-regulation of ICAM-3. Functional studies showed that anti-ICAM-3 mAb were able to trigger homotypic neutrophil aggregation both before and after ICAM-3 down-regulation, indicating that the fraction of ICAM-3 molecules remaining on the neutrophil surface upon activation are still capable of sustaining cell adhesion. In contrast, the loss of L-selectin (CD62L) on activated neutrophils was almost complete, thus leading to an impairment of L-selectin-mediated neutrophil-endothelial cell adhesion. These results indicate that ICAM-3 is released to the medium upon neutrophil stimulation and that both ICAM-3 and L-selectin have a role in the neutrophil adhesive phenomena.     

Modulation of intercellular adhesion molecule 1 (ICAM-1) expression on the human mast-cell line (HMC)-1 by inflammatory mediators

The effect of inflammatory mediators on the expression of several surface adhesion molecules on the human mast-cell line (HMC)-1 was studied. By flow cytometry, it could be shown that among several surface adhesion molecules (ICAM-UCDS4, VLA-4/CD49d, Mac-UCD11b, LFA-1/CD11a, LFA-2/CD2, LFA-3/CDS8, VCAM-1), only the constitutively expressed immunoglobulin family member intercellular adhesion molecule-1 (ICAM-1) is modulated by proinflammatory cytokines on HMC-1 mast cells. Stimulation with tumor necrosis factor-a (TNF-α) and interferon-γ (IFN-γ) resulted, in addition to interleukin-(lL-)4, in selective upregulation of ICAM-1 expression. Costimulation of either IL-4 or IFN-γ with TNF-α further increased the ICAM-1 expression as compared to the stimuli alone. In contrast, stem-cell factor (SCF), granulocyte/macrophage colonystimulating factor (GM-CSF), IL-10, IL-8, monocyte chemotactic and activating factor (MCAF), and the complement split product C5a failed to modulate the expression of any adhesion molecule examined. The levels of cytoplasmic free calcium in HMC-1 mast cells were not altered by cross-linking surface ICAM-1, suggesting linkage of other intracellular signaling pathways. This cytokine-induced upregulation of ICAM-1 expression might reveal a putative regulatory mechanism of mast-cell interaction with effector cells bearing the counterparts of ICAM-1 (CD54), the molecules Mac-1 (CD11b/CD18) and leukosialin (CD43), and the principal ligand LFA-1 (CD11a/CD18).     

Increased adhesion of human monocytes to IL-4-stimulated human venous endothelial cells via CD11/CD18, and very late antigen-4 (VLA-4)/vascular cell adhesion molecule-1 (VCAM-1)-dependent mechanisms.

Expression of adhesion molecules on endothelial cells (EC) can be up-regulated or induced by cytokines. The aim of the present study was to investigate the effect of IL-4 on both the expression of adhesion molecules on EC and monocyte adhesion to EC. Flow cytometric analysis showed that VCAM-1 expression on EC was up-regulated after stimulation with IL-4 for 24 h, whereas the expression of E-selectin (formerly called endothelial leucocyte adhesion molecule-1 (ELAM-1)) was not enhanced, and that of intercellular adhesion molecule-1 (ICAM-1) only slightly. The adhesion of monocytes to EC increased to maximum values upon stimulation of EC with IL-4 for 24 h. Coating of monocytes with MoAb against the integrin beta 2-subunit (CD18) significantly inhibited their adhesion to IL-4-stimulated EC; maximal inhibition was found when monocytes were coated with anti-CD18 MoAb in combination with MoAb against CD49d (the alpha-chain of VLA-4), whereas no inhibition was found when monocytes were coated only with MoAb against CD49d. Monocyte adhesion was not significantly inhibited when IL-4-stimulated EC were coated with MoAbs against ICAM-1 or VCAM-1 alone or in combination. Adhesion of monocytes was inhibited to a greater extent when in addition to coating of monocytes with MoAb against CD18 the EC were coated with MoAb against VCAM-1. From these results we conclude that monocytes bind to IL-4-stimulated EC via interaction of CD11/CD18 molecules on the monocytes with an as yet unknown endothelial ligand, and interaction of VLA-4 on monocytes with VCAM-1 on EC.     

Escherichia coli induces transuroepithelial neutrophil migration by an intercellular adhesion molecule-1-dependent mechanism.

During bacterial infections at mucosal sites, neutrophils migrate to the mucosa and cross the epithelial barrier. We have examined neutrophil migration across Escherichia coli-stimulated uroepithelial cell layers in an attempt to more fully understand this process. Stimulation of uroepithelial cells with E. coli or interleukin-1 alpha (IL-1 alpha) induced transepithelial neutrophil migration in a time- and stimulant dose-dependent manner. Uroepithelial cell lines and nontransformed uroepithelial cells expressed intercellular adhesion molecule-1 (ICAM-1) but not ICAM-2, E-selectin, or P-selectin. Epithelial ICAM-1 expression was enhanced after stimulation with E. coli or IL-1 alpha. Anti-ICAM-1 antibody reduced transepithelial neutrophil migration by 61 to 85%, indicating that neutrophils bound ICAM-1 on the epithelial surface. Antibodies to CD18 and CD11b reduced migration by 70 to 79%, suggesting that CD11b/CD18 (Mac-1) was acting as the neutrophil receptor for ICAM-1 in this process. Anti-CD11a antibodies had no effect on neutrophil migration. In conclusion, E. coli induced ICAM-1- and Mac-1-dependent transepithelial neutrophil migration. Previous studies have shown that urinary tract epithelial cells secrete IL-8 when exposed to E. coli or IL-1 alpha. These observations suggest that epithelial cells play an active role in neutrophil migration during urinary tract infections.     

Effect of maternal anti-HPA-1a antibodies and polyclonal IVIG on the activation status of vascular endothelial cells

Maternal anti-HPA-1a antibodies can cause severe fetal and neonatal alloimmune thrombocytopenia (FNAIT), complicated by intracranial haemorrhage (ICH). Antenatal treatment with maternal intravenous immunoglobulin (IVIG) seems to protect against ICH even when thrombocytopenia persists. The aim of this study was to investigate if anti-HPA-1a antibodies and IVIG potentially affect vascular endothelial cells (ECs) in order to identify susceptibility for ICH. Human umbilical cord endothelial cells (HUVEC) were incubated with anti-HPA-1a antibodies with or without polyclonal IVIG and evaluated for EC activation. Maternal sera with anti-HPA-1a antibodies affected neither the EC expression of intracellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1) and tissue factor (TF) nor the release of van Willebrand factor (vWF) or interleukin (IL)-8 nor the integrity of ECs. Maternal sera obtained after IVIG treatment and polyclonal IVIG decrease constitutive and cytokine-induced ICAM-1 and VCAM-1 expression on ECs. The results show that maternal anti-HPA-1a antibodies cause no activation or damage of ECs in this model. The clinical relevance of the de-activating properties of IVIG on EC activation with respect to ICH deserves further investigation.     

Interleukin-3, -5, and granulocyte macrophage colony-stimulating factor-induced adhesion molecule expression on eosinophils by p38 mitogen-activated protein kinase and nuclear factor-[kappa] B

We investigated the intracellular signaling mechanisms for cytokine interleukin (IL)-3, IL-5, or granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced expression of adhesion molecules including very late antigen 4 (CD49 d), macrophage antigen-1 (CD11b), leukocyte function-associated antigen-1 (CD11a/CD18), intercellular adhesion molecule (ICAM)-1, and ICAM-3 on eosinophils. The expression of adhesion molecules and nuclear factor (NF)-kappaB pathway was measured by flow cytometry and cDNA expression array, respectively. The phosphorylation of inhibitor kappaB-alpha and p38 mitogen-activated protein kinase (MAPK) was detected by Western blot, whereas NF-kappaB activity was measured by electrophoretic mobility shift assay. IL-3, IL-5, and GM-CSF could enhance p38 MAPK and NF-kappaB activity and induce ICAM-1, CD11b, and CD18 expressions on eosinophils. They could suppress ICAM-3 expression, but had no effect on CD49 d expression. Either SB 203580 or MG-132 was able to offset the cytokine-induced expression of ICAM-1. Only SB 203580 could reverse the effect on CD11b, CD18, and ICAM-3 expressions. Therefore, the expression of ICAM-1 might involve both p38 MAPK and NF-kappaB activities, whereas the regulation of CD11b, CD18, and ICAM-3 expressions might be mediated through p38 MAPK but not NF-kappaB. These cytokines therefore play a crucial role, via the p38 MAPK and NF-kappaB pathways, in the expression of important adhesion molecules on eosinophils in allergic inflammation.     

Diminished adhesion of Anaplasma phagocytophilum-infected neutrophils to endothelial cells is associated with reduced expression of leukocyte surface selectin

Anaplasma phagocytophilum propagates within neutrophils and causes a disease marked by inflammatory tissue injury or complicated by opportunistic infections. We hypothesized that infection with A. phagocytophilum modifies the binding of neutrophils to endothelial cells and the expression of neutrophil adhesion molecules and studied these changes in vitro. Infected dimethyl sulfoxide-differentiated HL-60 cells and neutrophils showed reduced binding to cultured brain and systemic endothelial cells and lost expression of P-selectin glycoprotein ligand 1 (PSGL-1, CD162) and L-selectin (CD62L) (to 33 and 5% of control values, respectively), at a time when the levels of beta(2) integrin and immunoglobulin superfamily adhesion molecules and activation markers Mac-1 and intercellular adhesion molecule 1 increased (5 to 10 times that of the control). The loss of CD162 and CD62L expression was inhibited by EDTA, which suggests that neutrophil activation and sheddase cleavage occurred. The loss of selectin expression and the retained viability of the neutrophils persisted for at least 18 h with A. phagocytophilum infection, whereas Escherichia coli and Staphylococcus aureus rapidly killed neutrophils. The adhesion defect might increase the numbers of infected cells and their persistence in the blood prior to tick bites. However, decreased CD162 expression and poor endothelial cell binding may partly explain impaired host defenses, while simultaneous neutrophil activation may aggravate inflammation. These observations may help us to understand the modified biological responses, host inflammation, and immune response that occur with A. phagocytophilum infections.     

Molecular basis of endothelial cell morphogenesis in three-dimensional extracellular matrices

Although many studies have focused on blood vessel development and new blood vessel formation associated with disease processes, the question of how endothelial cells (ECs) assemble into tubes in three dimensions (i.e., EC morphogenesis) remains unanswered. EC morphogenesis is particularly dependent on a signaling axis involving the extracellular matrix (ECM), integrins, and the cytoskeleton, which regulates EC shape changes and signals the pathways necessary for tube formation. Recent studies reveal that genes regulating this matrix-integrin-cytoskeletal (MIC) signaling axis are differentially expressed during EC morphogenesis. The Rho GTPases represent an important class of molecules involved in these events. Cdc42 and Rac1 are required for the process of EC intracellular vacuole formation and coalescence that regulates EC lumen formation in three-dimensional (3D) extracellular matrices, while RhoA appears to stabilize capillary tube networks. Once EC tube networks are established, supporting cells, such as pericytes, are recruited to further stabilize these networks, perhaps by regulating EC basement membrane matrix assembly. Furthermore, we consider recent work showing that EC morphogenesis is balanced by a tendency for newly formed tubes to regress. This morphogenesis-regression balance is controlled by differential gene expression of such molecules as VEGF, angiopoietin-2, and PAI-1, as well as a plasmin- and matrix metalloproteinase-dependent mechanism that induces tube regression through degradation of ECM scaffolds that support EC-lined tubes. It is our hope that this review will stimulate increased interest and effort focused on the basic mechanisms regulating capillary tube formation and regression in 3D extracellular matrices.     

Evaluation of the effects of defensins on neutrophil functions

Defensins are known to be the microbicidal components of neutrophil granules, which contribute to oxygen-independent antimicrobial mechanisms. In this study, we have examined the effect of defensins on neutrophil functions, such as adhesion, superoxide anion generation, phagocytosis and chemotaxis. Guinea-pig defensins increased the expression of CD11b, CD11c and CD54 (intercellular adhesion molecule ICAM-1) on human neutrophils, and induced adhesion of guinea-pig and human neutrophils. When the effect of guinea-pig defensins on superoxide anion generation was examined, defensins inhibited superoxide anion generation during phagocytosis of complement-opsonized particles. Furthermore, defensins inhibited complement-dependent phagocytosis. However, they did not inhibit the binding of complement-opsonized particles to neutrophils, suggesting that defensins possibly inhibit complement-dependent phagocytosis by affecting the ingestion step but not the binding step. Defensins exhibited neither chemotactic nor chemokine activity. Interestingly, 10–20% of total defensins were released extracellularly from phagocytosing neutrophils. Together these observations indicate that, in addition to their antimicrobial activity, defensins may have the ability to modulate the functions of neutrophils at sites of infection or inflammation.accepted by M. J. Parnham     

Modulation of neutrophil influx with cell adhesion molecule specific antibodies during nonspecific and immune mediated inflammatory reactions

Neutrophils are essential for the host defence against infection. However, neutrophils may also mediate damage namely during immune mediated pathologies. We therefore tested whether targeting of different cell adhesion molecules with specific monoclonal antibodies might reduce immune mediated neutrophil recruitment but spare the nonspecific accumulation of neutrophils that is essential for the resistance against acute infections. Neutrophil recruitment was induced by either intraperitoneal injection of casein as a nonspecific phlogistic agent or by i.p. injection of antigen in Mycobacterium bovis Bacille Calmette-Guérin (BCG) immune mice. Similar degrees of inhibition of neutrophil accumulation were observed in both models of inflammation with antibodies directed at CD11a, ICAM-1 and CD11b with the latter showing the most marked effects. Individual targeting of selectins was without effect in immune mediated responses whereas targeting of L or E selectin inhibited nonspecific recruitment of neutrophils. This was apparently not owing to a dosage effect nor to a kinetic difference. The inhibitory effect of anti-CD11b antibodies was most likely as a result of activation of circulating neutrophils rather than the blocking of receptor-ligand interactions. We were therefore unable to selectively abrogate immune mediated neutrophil recruitment with the use of the antibodies selected in this study.     

Hug tightly and say goodbye: role of endothelial ICAM-1 in leukocyte transmigration

Stable adhesion of leukocytes to endothelium is crucial for transendothelial migration (TEM) of leukocytes evoked during inflammatory responses, immune surveillance, and homing and mobilization of hematopoietic progenitor cells. The basis of stable adhesion involves expression of intercellular adhesion molecule-1 (ICAM-1), an inducible endothelial adhesive protein that serves as a counter-receptor for beta(2)-integrins on leukocytes. Interaction of ICAM-1 with beta(2)-integrins enables leukocytes to adhere firmly to the vascular endothelium and subsequently, to migrate across the endothelial barrier. The emerging paradigm is that ICAM-1, in addition to firmly capturing leukocytes, triggers intracellular signaling events that may contribute to active participation of the endothelium in facilitating the TEM of adherent leukocytes. The nature, duration, and intensity of ICAM-1-dependent signaling events may contribute to the determination of the route (paracellular vs. transcellular) of leukocyte passage; these aspects of ICAM-1 signaling may in turn be influenced by density and distribution of ICAM-1 on the endothelial cell surface, the source of endothelial cells it is present on, and the type of leukocytes with which it is engaged. This review summarizes our current understanding of the "ICAM-1 paradigm" of TEM with an emphasis on the signaling events mediating ICAM-1 expression and activated by ICAM-1 engagement in endothelial cells.