Transient adhesion of neutrophils to endothelium

The differential role of CR3 (CD11b/CD18) and CR4 (CD11c/CD18) in the adherence, migration and podosome formation of human macrophages and dendritic cells under inflammatory conditions

CR3 and CR4, the leukocyte specific β2-integrins, involved in cellular adherence, migration and phagocytosis, are often assumed to have similar functions. Previously however, we proved that under physiological conditions CR4 is dominant in the adhesion to fibrinogen of human monocyte-derived macrophages (MDMs) and dendritic cells (MDDCs). Here, using inflammatory conditions, we provide further evidence that the expression and function of CR3 and CR4 are not identical in these cell types. We found that LPS treatment changes their expression differently on MDMs and MDDCs, suggesting a cell type specific regulation. Using mAb24, specific for the high affinity conformation of CD18, we proved that the activation and recycling of β2-integrins is significantly enhanced upon LPS treatment. Adherence to fibrinogen was assessed by two fundamentally different approaches: a classical adhesion assay and a computer-controlled micropipette, capable of measuring adhesion strength. While both receptors participated in adhesion, we demonstrated that CR4 exerts a dominant role in the strong attachment of MDDCs. Studying the formation of podosomes we found that MDMs retain podosome formation after LPS activation, whereas MDDCs lose this ability, resulting in a significantly reduced adhesion force and an altered cellular distribution of CR3 and CR4. Our results suggest that inflammatory conditions reshape differentially the expression and role of CR3 and CR4 in macrophages and dendritic cells.

Effects of Dialysis Membrane Nature on Intradialytic Phagocytizing Activity

Blood-membrane contact in the extracorporeal circuit affects the activation of many biological systems. Among these, phagocytizing activity has been reported to be influenced by the nature of the hemodialysis membrane used, whether cellulosic or synthetic.

This work reports on an ex-vivo, comparative test between cellulosics and synthetics concerning the effects of blood-membrane contact on the polymorphonucleate and monocyte phagocytizing function, both during and after the hemodialysis session.

By means of flow cytometry, we evaluated the capacity for phagosoma formation and oxidative burst both in polymorphonucleates and monocytes. Ten hemodialysis patients were included in the study. Six separate dialysis procedures for each patient were considered, one per dialyzer (3 cellulosic and 3 synthetic membranes). Tests were performed at 15', 60', 210’ and 4 hours after the session end. Comparative evaluation was made according to Student's t test.

Polymorphonucleate phagocytosis and oxidative burst activation were globally more marked for synthetic than cellulosic membranes, tending to level out in the post-dialysis. This result could be affected by their functional exhaustion following pulmonary sequestration. Monocyte intradialytic phagocytosis and oxidative burst proved more activated by cellulosic membrane. All differences tended to vanish in the post-dialysis.

d(-) Lactic Acid-Induced Adhesion of Bovine Neutrophils onto Endothelial Cells Is Dependent on Neutrophils Extracellular Traps Formation and CD11b Expression

Bovine ruminal acidosis is of economic importance as it contributes to reduced milk and meat production. This phenomenon is mainly attributed to an overload of highly fermentable carbohydrate, resulting in increased d(−) lactic acid levels in serum and plasma. Ruminal acidosis correlates with elevated acute phase proteins in blood, along with neutrophil activation and infiltration into various tissues leading to laminitis and aseptic polysynovitis. Previous studies in bovine neutrophils indicated that d(−) lactic acid decreased expression of L-selectin and increased expression of CD11b to concentrations higher than 6 mM, suggesting a potential role in neutrophil adhesion onto endothelia. The two aims of this study were to evaluate whether d(−) lactic acid influenced neutrophil and endothelial adhesion and to trigger neutrophil extracellular trap (NET) production (NETosis) in exposed neutrophils. Exposure of bovine neutrophils to 5 mM d(−) lactic acid elevated NET release compared to unstimulated neutrophil negative controls. Moreover, this NET contains CD11b and histone H₄ citrullinated, the latter was dependent on PAD4 activation, a critical enzyme in DNA decondensation and NETosis. Furthermore, NET formation was dependent on d(−) lactic acid plasma membrane transport through monocarboxylate transporter 1 (MCT1). d(−) lactic acid enhanced neutrophil adhesion onto endothelial sheets as demonstrated by in vitro neutrophil adhesion assays under continuous physiological flow conditions, indicating that cell adhesion was a NET- and a CD11b/ICAM-1-dependent process. Finally, d(−) lactic acid was demonstrated for the first time to trigger NETosis in a PAD4- and MCT1-dependent manner. Thus, d(−) lactic acid-mediated neutrophil activation may contribute to neutrophil-derived pro-inflammatory processes, such as aseptic laminitis and/or polysynovitis in animals suffering acute ruminal acidosis.

Effect of everolimus on the immunomodulation of the human neutrophil inflammatory response and activation

The primary cause of mortality at 5 years following a cardiac transplantation is the development of atherosclerosis, termed coronary allograft vasculopathy (CAV). This pathology is characterized by diffused intimal hyperplasia and emanates from coronary arterial injuries caused by immune inflammatory cells. Neutrophils play an important role in this inflammatory process; however, their potential participation in the pathogenesis of CAV is poorly understood. Despite their essential contribution to the prevention of graft rejection, immunosuppressive drugs could have detrimental effects owing to their pro-inflammatory activities. Thus, we investigated the impact of different immunosuppressive drugs on the inflammatory response of neutrophils isolated from the blood of healthy volunteers. Under basal conditions, mammalian target of rapamycin (mTOR) inhibitors (sirolimus and everolimus) had the most potent anti-inflammatory effect, decreasing both IL-8 release (≈−80%) and vascular endothelial growth factor (VEGF) release (≈−65%) and preserving the release of the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1RA). In TNF-α-treated neutrophils, pre-incubation with everolimus provided the most potent effect, simultaneously reducing the release of both VEGF and IL-8 while doubling the release of IL-1RA. This latter effect of everolimus was maintained even when administered in combination with other immunosuppressive drugs. Sirolimus and everolimus decreased the tumor necrosis factor (TNF)-α-induced adhesion of neutrophils to human endothelial cells and human extracellular matrix. This effect was largely dependent on the ability of these compounds to alter β₂-integrin/CD18 activation. Our results suggest a potential mechanism for the beneficial effect of everolimus in the prevention of CAV in heart transplant recipients.

Effect of PAF on polyrnorphonuclear leucocyte plasma membrane polarity: a fluorescence study

The effect of PAF on the plasma membrane polarity of polymorphonuclear leukocytes (PMNs) was investigated by measuring the steady-state fluorescence emission spectra of 2-dimethylamino(6-1auroyl) naphthalene (Laurdan), which is known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer, displaying spectral sensitivity to the polarity of its surrounding. Laurdan shows a marked steady-state emission blue-shift in non-polar solvents, with respect to polar solvents. Our results demonstrate that PAF (10(-7) M) induces a blue shift of the fluorescence emission spectra of Laurdan. These changes are blocked in the presence of the PAF antagonist, L-659,989. Our data indicate that the interaction between PAF and PMNs is accompanied by a decrease in polarity in the hydrophobic-hydrophilic interface of the plasma membrane.

NPC 15669 blocks neutrophil CD18 increase and lung injury during cardiopulmonary bypass in pigs

During cardiopulmonary bypass (CPB), neutrophils become activated due to contact with extracorporeal surfaces and binding of complement fragments C3a and C5a, leading to extravasation and subsequent tissue damage. In this study, the effects of the leumedin NPC 15669 (N [9H - (2,7 dimethylfluorenyl - 9 - methoxy) car bonyl]-L-leucine), a leukocyte recruitment inhibitor, were evaluated in a pig model of CPB. NPC 15669 caused significant inhibition of CPB associated increase in CD18 upregulation, lung tissue myeloperoxidase content, and percentage wet weight compared to controls. Lung histology revealed clear airways and minimal neutrophil infiltration in treated animals vs. significant oedema and cellular infiltration in controls. It is concluded that CPB causes a dramatic increase in neutrophil CD18, and that leumedins are effective in inhibiting neutrophil activation and subsequent tissue injury when administered during CPB.

Hormonal control of inflammatory responses

Almost any stage of inflammatory and immunological responses is affected by hormone actions. This provides the basis for the suggestion that hormones act as modulators of the host reaction against trauma and infection. Specific hormone receptors are detected in the reactive structures in inflamed areas and binding of hormone molecules to such receptors results in the generation of signals that influence cell functions relevant for the development of inflammatory responses. Diversity of hormonal functions accounts for recognized pro- and anti-inflammatory effects exerted by these substances. Most hormone systems are capable of influencing inflammatory events. Insulin and glucocorticoids, however, exert direct regulatory effects at concentrations usually found in plasma. Insulin is endowed with facilitatory actions on vascular reactivity to inflammatory mediators and inflammatory cell functions. Increased concentrations of circulating glucocorticoids at the early stages of inflammation results in downregulation of inflammatory responses. Oestrogens markedly reduce the response to injury in a variety of experimental models. Glucagon and thyroid hormones exert indirect anti-inflammatory effects mediated by the activity of the adrenal cortex. Accordingly, inflammation is not only merely a local response, but a hormone-controlled process.

Role of transcription factors in small intestinal ischemia-reperfusion injury and tolerance induced by ischemic preconditioning

BACKGROUND

Small intestinal ischemia-reperfusion (I/R) injury, a clinically important condition, induces severe organ damage. Ischemic preconditioning (IPC) produces tolerance to long-term I/R by inducing a short-term I/R. Herein, we have examined the reduction in the extent of injury by IPC.

METHODS

Small intestinal I/R injury was induced in rats by clamping the superior mesenteric artery (SMA) for 30 minutes followed by reperfusion for various 30 minutes. The IPC + I/R group underwent a short-term I/R (IPC) prior to long-term I/R. Nuclear factor-κB (NF-κB) activity was analyzed by an electrophoretic mobility shift assay and cytokine mRNA levels, by reverse transcription-polymerase chain reaction. Apoptosis-related genes were analyzed by Western blotting and immunohistochemistry, and apoptotic cells, by TUNEL staining.

RESULTS

The animals were subjected to 30 minutes of ischemia followed by 30 minutes of reperfusion. NF-κB activity increased in the I/R group and decreased in the IPC + I/R group. The IPC + I/R group showed decreased cytokine in mRNA levels. Expression of the proapoptotic gene caspase-3 was increased in the I/R and decreased in the IPC + I/R group. Expression of the antiapoptotic gene Bcl-xL was increased in the IPC + I/R group. The number of apoptotic cells was increased in the I/R and decreased in the IPC + I/R group.

CONCLUSION

Small intestinal I/R injury was reduced by IPC produced by clamping the SMA; thus, IPC may have potential clinical applications in the future.

Hydrodynamic shear rate regulates melanoma-leukocyte aggregation, melanoma adhesion to the endothelium, and subsequent extravasation

Adhesion to and subsequent extravasation through the endothelial lining of blood vessels is critical for tumor cells to establish metastases. Recent studies have indicated that polymorphonuclear neutrophils (PMNs) may enhance melanoma adhesion to the endothelium (EC) and subsequent extravasation under dynamic flow conditions. However, little is known about hydrodynamics involved in the tumor microenvironment within the microcirculation. In this study, effects of hydrodynamic flow on regulating melanoma cell adhesion to the EC have been investigated. Results indicate that under flow conditions, interactions between melanoma cells and the EC are distinctly different from PMN-EC interactions. Without expressions of surface integrins or sialylated molecules, most melanoma cells that express a high-level of intercellular adhesion molecule (ICAM-1) are not able to effectively adhere to the inflamed EC by themselves. Binding of melanoma cells and PMNs through ICAM-1 on melanoma cells and beta(2) integrins on PMNs has been shown to enhance melanoma cell arrest on the EC. Although PMN tethering on the EC is regulated by both the shear rate and shear stress, melanoma cell adhesion to the EC and subsequent extravasation via tethering PMN on the EC is predominantly regulated by shear rate, which partly is due to the shear-rate-dependent PMN-melanoma aggregation in shear flow. These findings provide a rationale and mechanistic basis for understanding of leukocyte-tumor cell interactions under flow conditions during tumor cell extravasation and metastasis.

Two-dimensional kinetics of beta 2-integrin and ICAM-1 bindings between neutrophils and melanoma cells in a shear flow

Cell adhesion, mediated by specific receptor-ligand interactions, plays an important role in biological processes such as tumor metastasis and inflammatory cascade. For example, interactions between beta 2-integrin (lymphocyte function-associated antigen-1 and/or Mac-1) on polymorphonuclear neutrophils (PMNs) and ICAM-1 on melanoma cells initiate the bindings of melanoma cells to PMNs within the tumor microenvironment in blood flow, which in turn activate PMN-melanoma cell aggregation in a near-wall region of the vascular endothelium, therefore enhancing subsequent extravasation of melanoma cells in the microcirculations. Kinetics of integrin-ligand bindings in a shear flow is the determinant of such a process, which has not been well understood. In the present study, interactions of PMNs with WM9 melanoma cells were investigated to quantify the kinetics of beta 2-integrin and ICAM-1 bindings using a cone-plate viscometer that generates a linear shear flow combined with a two-color flow cytometry technique. Aggregation fractions exhibited a transition phase where it first increased before 60 s and then decreased with shear durations. Melanoma-PMN aggregation was also found to be inversely correlated with the shear rate. A previously developed probabilistic model was modified to predict the time dependence of aggregation fractions at different shear rates and medium viscosities. Kinetic parameters of beta 2-integrin and ICAM-1 bindings were obtained by individual or global fittings, which were comparable to respectively published values. These findings provide new quantitative understanding of the biophysical basis of leukocyte-tumor cell interactions mediated by specific receptor-ligand interactions under shear flow conditions.

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.

Drusen complement components C3a and C5a promote choroidal neovascularization

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in industrialized nations, affecting 30-50 million people worldwide. The earliest clinical hallmark of AMD is the presence of drusen, extracellular deposits that accumulate beneath the retinal pigmented epithelium. Although drusen nearly always precede and increase the risk of choroidal neovascularization (CNV), the late vision-threatening stage of AMD, it is unknown whether drusen contribute to the development of CNV. Both in patients with AMD and in a recently described mouse model of AMD, early subretinal pigmented epithelium deposition of complement components C3 and C5 occurs, suggesting a contributing role for these inflammatory proteins in the development of AMD. Here we provide evidence that bioactive fragments of these complement components (C3a and C5a) are present in drusen of patients with AMD, and that C3a and C5a induce VEGF expression in vitro and in vivo. Further, we demonstrate that C3a and C5a are generated early in the course of laser-induced CNV, an accelerated model of neovascular AMD driven by VEGF and recruitment of leukocytes into the choroid. We also show that genetic ablation of receptors for C3a or C5a reduces VEGF expression, leukocyte recruitment, and CNV formation after laser injury, and that antibody-mediated neutralization of C3a or C5a or pharmacological blockade of their receptors also reduces CNV. Collectively, these findings establish a mechanistic basis for the clinical observation that drusen predispose to CNV, revealing a role for immunological phenomena in angiogenesis and providing therapeutic targets for AMD.

Atopic ocular surface disease: implications on tear function and ocular surface mucins

PURPOSE

To describe tear function, mucin alterations, and ocular surface disorder in patients with atopic diseases.

METHODS

Subjects underwent corneal sensitivity measurements, Schirmer test, tear film break-up time (BUT) assay, and fluorescein and rose Bengal staining of the ocular surface. Conjunctival impression cytology and brush cytology were also conducted. Impression cytology samples underwent PAS and immunohistochemical staining for MUC5AC. Brush cytology specimens underwent evaluation for inflammatory cell expression and RT-PCR for MUC5AC mRNA expression. Differences related to tear function and ocular surface examination parameters among patients with and without corneal ulceration and healthy control subjects were studied.

RESULTS

Mean corneal sensitivity and BUT values were significantly lower in atopic patients with corneal ulcers compared with patients without ulcers and controls (P<0.001). Brush cytology specimens from patients with corneal ulcers revealed significantly higher expression of inflammatory cells compared with patients without ulcers and controls (P<0.001). Impression cytology samples from eyes with corneal ulcers showed significant squamous metaplasia and reduction of goblet cell density compared with eyes without ulcers and control subjects. Specimens from eyes with corneal ulcers showed PAS (+) mucin pick up and did not stain positive for MUC5AC. MUC5AC mRNA expression was significantly lower in eyes with corneal ulcers compared with in eyes without ulcers and control subjects.

CONCLUSIONS

Ocular surface inflammation, tear film instability, and decreased conjunctival MUC5AC mRNA expression are important in the pathogenesis of noninfectious corneal shield ulcers in atopic ocular surface disease.

Dual function for a unique site within the beta2I domain of integrin alphaMbeta2

Integrin activation has been postulated to occur in part via conformational changes in the I domain of the beta subunit (the betaI domain), especially near the F-alpha(7) loop, in response to "inside-out" signaling. However, direct evidence for a role of the F-alpha(7) loop in ligand binding and activity modulation is still lacking. Here, we report our finding that the F-alpha(7) loop (residues 344-358) within the beta(2)I domain has dual functions in ligand binding by alpha(M)beta(2). On the one hand, it supports intercellular adhesion molecule 1 (ICAM-1) binding to alpha(M)beta(2) directly as part of a recognition interface formed by five noncontiguous segments (Pro(192)-Glu(197), Asn(213)-Glu(220), Leu(225)-Leu(230), Ser(324)-Thr(329), and Glu(344)-Asp(348)) on the apex of the beta(2)I domain. On the other hand, it controls the open and closed conformation of the alpha(M)beta(2) receptor, thereby indirectly affecting alpha(M)beta(2) binding to other ligands. Switching the five constituent sequences of the ICAM-1-binding site within the beta(2)I domain to their beta(1) counterparts destroyed ICAM-1 binding but had no effect on the gross conformations of the receptor. Of the five ICAM-1 binding-defective mutants, four had normal or even stronger interaction with Fg and C3bi, as reported in our previous study. Synthetic peptides derived from the identified site inhibited alpha(M)beta(2)-ICAM-1 interaction and supported direct binding to ICAM-1. Most importantly, perturbation of the F-alpha(7) loop caused conformational changes within the beta(2)I domain, which was further propagated to other regions of alpha(M)beta(2). Altogether, our data demonstrate that inside-out signaling could modulate ligand binding directly by changing the ligand-binding pocket per se and/or indirectly by inducing multiple conformational changes within the receptor.

Immunobiologic consequences of assist devices

The aberrant state of monocyte and T-cell activation resulting from these host-device interaction is accompanied by two parallel processes: (1) selective loss of Th1 cytokine-producing CD4 T cells through activation-induced cell death, and (2) unopposed activation of Th2 cytokine-producing CD4 T cells resulting in B-cell hyperreactivity and dysregulated immunoglobulin synthesis via Th2 cytokines and heightened CD40 ligand-CD40 interactions. The net result of these events is that on one hand the VAD recipient develops progressive defects in cellular immunity and is at increased risk of serious infection, and on the other hand the VAD recipient is more likely to develop allosensitization, posing a significant risk to successful transplant outcome.

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.

Regulation of adhesion of AML14.3D10 cells by surface clustering of beta2-integrin caused by ERK-independent activation of cPLA2

We examined the role of cell surface clustering of beta2-integrin caused by protein kinase C (PKC)-activated-cPLA2 in adhesion of eosinophilic AML14.3D10 (AML) cells. Phorbol 12-myristate 13-acetate (PMA) caused time- and concentration-dependent adhesion of AML cells to plated bovine serum albumin (BSA), which was blocked by anti-CD11b or anti-CD18 monoclonal antibodies (mAb) directed against beta2-integrin. Inhibition of PKC with Ro-31-8220 or rottlerin blocked PMA-induced cell adhesion in a concentration-dependent fashion. Inhibition of cytosolic phospholipase A2 (cPLA2) with trifluoromethyl ketone or methyl arachidonyl fluorophosphonate also blocked PMA-induced cell adhesion. PMA caused time-dependent p42/44 mitogen-activated protein kinase (MAPK) (ERK) phosphorylation in these cells. U0126, a MAPK/extracellular signal-regulated protein kinase kinase (MEK) inhibitor, at the concentrations that blocked PMA-induced ERK phosphorylation, had no effect on PMA stimulated AML cell adhesion. Neither p38 MAPK nor c-Jun N-terminal kinase (JNK) was phosphorylated by PMA. PMA also caused increased cPLA2 activity, which was inhibited by Ro-31-8220, but not U0126. Confocal immunofluorescence microscopy showed that PMA caused clustering of CD11b on the cell surface, which was blocked by either PKC or cPLA2 inhibition. PMA stimulation also caused up-regulation of CD11b on the AML cell surface. However, this up-regulation was not affected by cPLA2- or PKC-inhibition. Using the mAb, CBRM1/5, we also demonstrated that PMA does not induce the active conformation of CD11b/CD18. Our data indicate that PMA causes AML cell adhesion through beta2-integrin by PKC activation of cPLA2. This pathway is independent of MEK/ERK and does not require change of CD11b/CD18 to its active conformation. We find that avidity caused by integrin surface clustering - rather than conformational change or up-regulation of CD11b/CD18 - causes PMA stimulated adhesion of AML cells.

Fosfomycin inhibits neutrophil function via a protein kinase C-dependent signaling pathway

We investigated effects of fosfomycin (FOM) on neutrophil function, specifically the oxidative burst and adhesion molecule expression (CD11b/CD18, or MAC-1) using flow cytometry assay. Preincubation of polymorphonuclear leukocytes (PMNL) with FOM from 1 to 100 microg/ml prior to stimulation by phorbol 12-myristate 13-acetate (PMA, 2 ng/ml) significantly suppressed the oxidative burst in a concentration-dependent manner. However, FOM did not affect the oxidative burst of PMNL stimulated by a chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP). Stimulation with PMA (2 ng/ml) caused a rapid up-regulation of CD11b surface expression on PMNL, followed by time-dependent loss of this receptor. FOM also suppressed loss of CD11b in PMNL stimulated by PMA. FOM then inhibits the PMA-induced oxidative burst and CD11b epitope loss in PMNL. The suppressive effect appears to be mediated by the protein kinase C-dependent signaling pathway.

Hemodialysis Membranes: Interleukins, Biocompatibility, and Middle Molecules

ABSTRACT. Maintenance hemodialysis patients display evidence of elevated interleukin-1 (IL-1) and tumor necrosis factor alpha release after stimulation either by contaminated dialysate, bioincompatible membrane material, or both. This release is followed by the stimulated secretion of a large number of other interleukins, particularly IL-6, the cytokine principally responsible for acute-phase protein synthesis. It has been shown that high levels of the circulating proinflammatory cytokines IL-1, tumor necrosis factor alpha, IL-6, and IL-13 are associated with mortality in hemodialysis patients. Essential functions of polymorphonuclear leukocytes—that is, phagocytosis, oxygen species production, upregulation of specific cell surface receptor proteins, or apoptosis—are disturbed in patients with end-stage renal disease. These are further altered as a result of complement activation by the hemodialysis procedure, particularly if bioincompatible dialyzers are used. Polymorphonuclear leukocyte degranulation occurring during extracorporeal circulation does not depend on complement activation but rather on intracellular calcium and the presence or absence of the degranulation inhibitory proteins angiogenin and complement factor D. Clinical signs and symptoms of end-stage renal disease patients are at least in part related to the accumulation of middle molecules such as β2-microglobulin, parathyroid hormone, advanced glycation end products, advanced lipoxidation end products, advanced oxidation protein products (formed as a result of oxidative stress, carbonyl stress, or both), granulocyte inhibitory proteins, or leptin. Currently available membrane materials do not provide long-lasting, effective reduction of middle molecules in patients who require maintenance hemodialysis.

M(+) group a streptococci are phagocytized and killed in whole blood by C5a-activated polymorphonuclear leukocytes

Historically, resistance to phagocytosis has been determined by incubating group A streptococci in human blood and comparing the numbers of CFU before and after incubation. Utilizing a flow cytometry-based technique, we have investigated the phagocytosis of M(+) group A streptococci by polymorphonuclear leukocytes (PMNs) in heparinized human peripheral whole blood. Intracellular labeling of streptococci with a nontoxic fluorescent dye allowed us to quantify the association and phagocytosis of M(+) streptococci by PMNs in whole blood in the presence or absence of C5a, a physiologically important chemotactic activator of PMNs. We found that wild-type strains of group A streptococci that are resistant to phagocytosis (determined by the classical Lancefield method) readily associate with C5a-activated whole-blood PMNs. In the absence of opsonizing M-type-specific antibodies, the M(+) streptococci associated with PMNs are phagocytized and killed. In addition, blockade of the beta(2) integrin, CD11b/CD18, with anti-human CD11b monoclonal antibody inhibited association between M(+) streptococci and C5a-activated PMNs. These findings establish a new relationship between M(+) streptococci and PMNs, in which C5a-activated PMNs have the capacity to kill M(+) streptococci in whole blood through a receptor-mediated phagocytic mechanism.

Role of intracellular chloride in the reversible activation of neutrophil beta 2 integrins: a lesson from TNF stimulation

The process of beta(2) integrin activation, which enhances the interaction of these heterodimers with ligands, plays a crucial role in the adherence-dependent neutrophilic polymorphonuclear leukocytes' (PMN) responses to TNF. Our previous observation, showing that a marked decrease of the high basal Cl(-) content (Cl(-)(i)) is an essential step in the TNF-induced activation of PMN, stimulated this study, which investigates the role of alterations of Cl(-)(i) in the activation of beta(2) integrins triggered by TNF. Here we show that TNF enhances the expression of activation-specific neoepitopes of beta(2) integrins, namely, epitope 24, a unique epitope present on all three leukocyte integrin alpha subunits, and epitope CBRM1/5, localized to the I domain on the alpha-chain of Mac-1 (CD11bCD18). Moreover, we demonstrate that the conformational changes underlying the expression of the neoepitopes are dependent on a drop in Cl(-)(i) because 1) inhibition of Cl(-)(i) decrease is invariably accompanied by inhibition of beta(2) integrin activation, 2) Cl(-)(i) decrease induced by means other than agonist stimulation, i.e., by placing PMN in Cl(-)-free buffers, activates beta(2) integrins, and 3) restoration of the original Cl(-)(i) levels is accompanied by deactivation of beta(2) integrins. We also show that Cl(-)(i) decrease is required for TNF-induced cytoplasmic alkalinization, but such a rise in pH(i) does not seem to be relevant for beta(2) integrin activation. The results of our study emphasize the role of Cl(-) as a new PMN "second messenger."

Immunobiology of left ventricular assist devices

The increasing use of implanted biomaterial devices has made it evident that no material is biologically inert. As a result of direct contact with elements of the blood circulation, such as during hemodialysis or after left ventricular assist device (LVAD) implantation, significant changes in systemic immunologic and thrombostatic functions occur. The clinical success of LVAD implantation has, nevertheless, been accompanied by complications arising from an aberrant state of monocyte and T-cell activation, leading to heightened susceptibility of circulating CD4 T cells to undergo activation-induced cell death; this results in progressive defects in cellular immunity and an increased risk of serious infection. Because of the increased state of T-cell activation and the selective loss of Th1 cytokine producing CD4 T cells, LVAD recipients also develop B-cell hyperreactivity and dysregulated immunoglobulin syntheses by unopposed production of Th2 cytokines and increased CD40 Ligand-CD40 interactions. LVADs are currently being evaluated as a permanent therapy for end-stage heart failure. Because these immune dysfunctions appear to be related to the effects of excessive biomaterial associated T-cell activation, future efforts will need to be directed at either altering the physical properties of the materials interacting with the host circulation or pharmacological intervention aimed at inhibiting T-cell activation.

Soluble E-selectin acts in synergy with platelet-activating factor to activate neutrophil beta 2-integrins. Role of tyrosine kinases and Ca2+ mobilization

Selectins play a critical role in neutrophil recruitment to sites of inflammation, in tethering and rolling of neutrophils on vascular endothelium, as well as triggering beta(2)-integrin-mediated adhesion. We have previously demonstrated potential pro-inflammatory effects of soluble E-selectin upon neutrophil effector functions, using a soluble recombinant molecule (E-zz), which increased beta(2)-integrin-mediated adhesion, decreased beta(2)-integrin-dependent migration, and triggered reactive oxygen species generation and release. In this study, we have examined the intracellular signals following neutrophil activation by soluble E-selectin. We show that exposure of neutrophils to E-selectin and platelet-activating factor (PAF) in combination induced a synergistic effect upon beta(2)-integrin-mediated adhesion. Although soluble E-selectin did not induce Ca(2+) mobilization in neutrophils by itself, elevation of intracellular Ca(2+) was specifically prolonged in response to PAF but not leukotriene B(4) or N-formyl-Met-Leu-Phe. The prolonged Ca(2+) mobilization observed in the presence of E-selectin was dependent on Ca(2+) influx from intracellular stores rather than influx of extracellular Ca(2+) through SKF 96365-sensitive channels. The specific alteration of Ca(2+) mobilization reported here appears not to have a role in the synergistic effects of E-selectin and PAF upon neutrophil O(2) release but may be involved in augmentation of beta(2)-integrin-mediated adhesion.

Bound and soluble adhesion molecule and cytokine levels in patients with severe burns

We measured endotoxins, inflammatory cytokines and soluble adhesion molecules in the blood of 17 severe burn patients to determine the involvement of these factors in the pathophysiology of severe burns. All seventeen patients had burns with a total burn surface area of 20% or more and a burn index of 15% or more. Endotoxin was measured by an endotoxin-specific assay and tumor necrosis factor-alpha, interleukin 6 and interleukin 8 and soluble adhesion molecules were measured by enzyme-linked immunosorbent assay. CD11a, CD11b and CD18, measured by flow cytometry, were elevated in the non-surviving group, the septic shock group and the multiple organ dysfunction syndrome group, suggesting a close connection between these adhesion molecules and burns complicated by infection. Soluble adhesion molecules were found to indirectly reflect the level of endothelial cell adhesion molecules, suggesting that inflammatory cytokines may also be involved in their production.

Inhibition of CD11-CD18 complex prevents acute lung injury and reduces mortality after peritonitis in rabbits

Acute lung injury is frequent after severe peritonitis. The aim of this study was to investigate whether inhibition of the adhesion molecule CD11-CD18 on polymorphonuclear leukocytes (PMNs) would have any beneficial effects on pulmonary function and mortality in an animal model reproducing these clinical conditions. Acute peritonitis was induced in 36 rabbits by intraperitoneal injection of zymosan (0.6 g/kg) suspended in mineral oil; 20 were pretreated with a murine-specific IgG2a anti-CD18 monoclonal antibody, 16 (controls) with nonspecific purified murine IgG (1 mg/kg). The animals were followed for 10 d, then killed for histologic examination of the lungs. Blood samples were taken on Days 0, 1, 3, 7, and 10 for red blood cell (RBC), white blood cell (WBC), and platelet counts, pH, PO(2), PCO(2), carbon dioxide content (HCO(3)(-)) measurements, and renal and liver tests. Treatment with the anti-CD18 monoclonal antibody reduced mortality by approximately 40% (p < 0.05). PO(2) was higher in these treated animals than in the control animals throughout the study (p < 0.05 on Day 1, 3, and 10). On Day 1 control animals had significant leukopenia, whereas anti-CD18-treated animals had a moderate increase of the number of circulating WBC compared with baseline values (p < 0.05 between groups). The lungs of the anti-CD18-treated animals showed minor signs of inflammation and PMN infiltration whereas controls had interstitial and intra-alveolar edema and a large number of granulocytes. Quantification of PMNs by morphometry showed that there were constantly less granulocytes in the lungs of the animals treated with the anti-CD18 antibody (p < 0.001). PMN infiltration correlated with the levels of PO(2) (p < 0.001). Lung tissue of anti-CD18-treated rabbits contained less malonyldialdehyde, a by-product of membrane lipid peroxidation by PMN oxygen radicals (950 +/- 120 versus 1,710 +/- 450 pM/mg of protein) and, conversely, more of the antioxidant alpha-tocopherol (136 +/- 22 versus 40 +/- 9 ng/mg of protein), than the control rabbits (p < 0.01). In this particular model of ARDS the monoclonal antibody against the CD11-CD18 complex had a beneficial effect, reducing PMN infiltration and oxygen radical release in the lungs, preventing alveolocapillary membrane damage, improving gas exchange and, finally, significantly reducing mortality.

Nitric oxide-releasing compounds inhibit neutrophil adhesion to endothelial cells

In the present work, we demonstrated that chemically different nitric oxide (NO)-releasing compounds inhibit tumor necrosis factor alpha (TNF-alpha)-induced polymorphonuclear leukocyte adhesion to endothelial cells in vitro. Two mesoionic oxatriazole derivatives GEA 3162 (1,2,3,4-oxatriazolium,5-amino-3(3, 4-dichlorophenyl)-chloride) and GEA 3175 (1,2,3,4-oxatriazolium, -3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulfonyl]amino]-, hydroxide inner salt) were compared to the earlier-known NO donor SIN-1 (3-morpholino-sydnonimine). GEA 3162 (3-10 microM) and GEA 3175 (10-30 microM) inhibited human polymorphonuclear leukocyte adhesion to B(4) endothelial cells in a dose-dependent manner being more potent than SIN-1. In the present model, leukocytes rather than endothelial cells seemed to be the target of the effect of NO. Flow cytometric analysis showed that NO-releasing compounds did not alter TNF-alpha induced CD11/CD18 surface expression in polymorphonuclear leukocytes. The inhibitory action of NO-releasing compounds on adhesion paralleled with the increased synthesis of cGMP in polymorphonuclear leukocytes. Analogues of cGMP inhibited polymorphonuclear leukocyte adhesion indicating a role for cGMP in the action of NO donors. The results suggest that exogenous NO in the form of NO-releasing compounds inhibits polymorphonuclear leukocyte adhesion to endothelial cells, which may be implicated in the regulation of leukocyte migration and leukocyte-mediated tissue injury.

Natural responses to unnatural materials: A molecular mechanism for foreign body reactions

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Inhibition by dipyridamole of neutrophil adhesion to vascular endothelium during coronary bypass surgery

BACKGROUND

Release of reactive oxygen radicals by activated neutrophils and neutrophil adhesion to endothelial cells have been observed after cardiopulmonary bypass. The aim of the present study was to evaluate the effects of preoperative dipyridamole treatment on neutrophil superoxide anion generation and endothelial cell-neutrophil interactions.

METHODS

Two groups of patients scheduled for elective coronary artery bypass grafting were randomized to receive oral dipyridamole or a placebo. Nitro blue tetrazolium scores of circulating neutrophils, neutrophil CD11b/CD18 expression, and their adhesion to human umbilical vein endothelial cells were assayed before anesthesia, 30 minutes after the beginning of cardiopulmonary bypass, at the end of bypass, and 60 minutes postoperatively.

RESULTS

In both groups, cardiopulmonary bypass resulted in a significant increase in nitro blue tetrazolium scores in circulating neutrophils as well as a significant increase in both neutrophil CD11b/CD18 expression and neutrophil adhesion to endothelial cells. The extent of neutrophil superoxide anion generation was higher in the control group; a significant (p < 0.01) reduction in neutrophil adhesion to endothelial cells was observed 1 hour postoperatively in the dipyridamole group. In 5 patients treated with dipyridamole, the incubation of activated polymorphonuclear leukocytes with adenosine deaminase significantly increased their adhesion to endothelial cells (p < 0.05).

CONCLUSIONS

Our study demonstrated that preoperative treatment with oral dipyridamole significantly reduces both neutrophil superoxide anion generation and extent of neutrophil adhesion to endothelial cells after coronary bypass grafting procedures with cardiopulmonary bypass. The mechanism is probably mediated by endogenous adenosine.

Specific activation of leukocyte beta2 integrins lymphocyte function-associated antigen-1 and Mac-1 by chemokines mediated by distinct pathways via the alpha subunit cytoplasmic domains

We show that CC chemokines induced a sustained increase in monocyte adhesion to intercellular adhesion molecule-1 that was mediated by Mac-1 (alphaMbeta2) but not lymphocyte function-associated antigen-1 (LFA-1; alphaLbeta2). In contrast, staining for an activation epitope revealed a rapid and transient up-regulation of LFA-1 activity by monocyte chemotactic protein-1 (MCP-1) in monocytes and Jurkat CCR2 chemokine receptor transfectants or by stromal-derived factor-1alpha in Jurkat cells. Differential kinetics for activation of Mac-1 (sustained) and LFA-1 (transient) avidity in response to stromal-derived factor-1alpha were confirmed by expression of alphaM or alphaL in alphaL-deficient Jurkat cells. Moreover, expression of chimeras containing alphaL and alphaM cytoplasmic domain exchanges indicated that alpha cytoplasmic tails conferred the specific mode of regulation. Coexpressing alphaM or chimeras in mutant Jurkat cells with a "gain of function" phenotype that results in constitutively active LFA-1 demonstrated that Mac-1 was not constitutively active, whereas constitutive activity was mediated via the alphaL cytoplasmic tail, implying the presence of distinct signaling pathways for LFA-1 and Mac-1. Transendothelial chemotaxis of monocytes in response to MCP-1 was dependent on LFA-1; however, Mac-1 was involved at MCP-1 concentrations stimulating its avidity, showing differential contributions of beta2 integrins. Our data suggest that a specific regulation of beta2 integrin avidity by chemokines may be important in leukocyte extravasation and may be triggered by distinct activation pathways transduced via the alpha subunit cytoplasmic domains.

Effects of oxidized low density lipoprotein, lipid mediators and statins on vascular cell interactions

The integrin heterodimer CDllb/CD18 (alphaMbeta2, Mac-1, CR3) expressed on monocytes or polymorphonuclear leukocytes (PMN) is a receptor for iC3b, fibrinogen, heparin, and for intercellular adhesion molecule (ICAM)-1 on endothelium, crucially contributing to vascular cell interactions in inflammation and atherosclerosis. In this report, we summarize our findings on the effects of lipid mediators and lipid-lowering drugs. Exposure of endothelial cells to oxidized low density lipoprotein (oxLDL) induces upregulation of ICAM-1 and increases adhesion of monocytic cells expressing Mac-1. Inhibition experiments show that monocytes use distinct ligands, i.e. ICAM-1 and heparan sulfate proteoglycans for adhesion to oxLDL-treated endothelium. An albumin-transferable oxLDL activity is inhibited by the antioxidant pyrrolidine dithiocarbamate (PDTC), while 8-epi-prostaglandin F2alpha (8-epi-PGF2alpha) or lysophosphatidylcholine had no effect, implicating yet unidentified radicals. Sequential adhesive and signaling events lead to the firm adhesion of rolling PMN on activated and adherent platelets, which may occupy areas of endothelial denudation. Shear-resistant arrest of PMN on thrombin-stimulated platelets in flow conditions requires distinct regions of Mac-1, involving its interactions with fibrinogen bound to platelet alphallbbeta3, and with other platelet ligands. Both arrest and adhesion strengthening under flow are stimulated by platelet-activating factor and leukotriene B4, but not by the chemokine receptor CXCR2. We tested whether Mac-1-dependent monocyte adhesiveness is affected by inhibitors of hydroxy-methylglutaryl-Coenzyme A reductase (statins) which improve morbidity and survival of patients with coronary heart disease. As compared to controls, adhesion of isolated monocytes to endothelium ex vivo was increased in patients with hypercholesterolemia. Treatment with statins decreased total and low density lipoprotein (LDL) cholesterol plasma levels, surface expression of Mac-1, and resulted in a dramatic reduction of Mac-1-mediated monocyte adhesion to endothelium. The inhibition of monocyte adhesion was reversed by mevalonate but not LDL in vitro, indicating that isoprenoid precursors are crucial for adhesiveness of Mac-1. Such effects may crucially contribute to the clinical benefit of statins, independent of cholesterol-lowering, and may represent a paradigm for novel, anti-inflammatory mechanisms of action by this class of drugs.

Rapid secretion of prestored interleukin 8 from Weibel-Palade bodies of microvascular endothelial cells

Interleukin (IL)-8, a C-X-C chemokine, activates integrin-mediated adhesion of neutrophils. Presentation of IL-8 on the endothelial cell surface may promote leukocyte extravasation. We found that cultured human microvascular endothelial cells from the intestine (HIMEC) and from nasal polyps (PMEC), but not human umbilical vein endothelial cells (HUVEC), contained IL-8 in intracellular granules that coexpressed von Willebrand factor (vWf ). This observation was corroborated by the immunohistochemical observation of double-positive granules (IL-8(+)vWf+) in vessels of small and large intestine, nasal mucosa, and skin, whereas umbilical cords revealed no endothelial IL-8. After treatment of HIMEC or PMEC with histamine or thrombin, a dramatic increase in supernatant IL-8 concentration was observed within 3 min, whereas no increase in IL-8 was detected in supernatants of identically treated HUVEC cultures. Histamine or thrombin treatment also caused IL-8-containing granules to rapidly disappear from HIMEC. In HUVEC, IL-8-containing granules were inducible by treatment with recombinant human IL-1beta for 24 h; additional histamine treatment doubled IL-8 secretion from HUVEC in the same rapid manner observed for mucosal EC. These data suggested that IL-8 prestored in microvascular endothelial cells may provide a rapid pathway for specific activation of neutrophil adhesion at sites of acute inflammation.

Effect of pyridoxal 5'-phosphate on human neutrophil respiratory burst and adhesion on serum coated microplates

The effect of pyridoxal 5'-phosphate (PP) on human polymorphonuclear leukocytes respiratory burst and on cellular adhesion on serum coated microplates was investigated. No dose-response effect was observed after 10 min pre-treatment at 37 degrees C of human neutrophils with increasing doses of PP, ranging from 0.05 mM/L to 0.5 mM/L. The production of superoxide anion (O2-), after challenging cells with 0.5 pM/L formyl-methyonyl-leucyl-phenylalanine, 50 ng/mL phorbol myristate acetate or 50 pg/mL concanavalin A was comparable to that observed by pre-treating cells with phosphate buffered saline only (control, no PP), therefore indicating that PP did not affect neutrophil respiratory burst in our assay conditions. Evaluation of the effect on cellular adhesion onto fetal bovine serum pre-coated microplates produced the same results. As previous results showed that PP in the range of 0.01 mM/L to 0.6 mM/L proved to be an efficient inhibitor of neutrophil aggregation, the evidence reported here might contribute to establish PP as a good in vitro leukocyte anti-aggregant which does not affect other functional parameters.

Neutrophil-endothelial cells modulation in diabetic patients undergoing coronary artery bypass grafting

OBJECTIVE

Diabetes mellitus is a well-known risk factor in patients undergoing coronary artery bypass grafting. Myocardial and pulmonary injury often occurs after cardiopulmonary bypass (CPB), mediated in part by neutrophil activation and adhesion to endothelial cells. The objectives of the present study are to compare the degree of neutrophil activation and neutrophil-endothelial cells adhesive interactions in diabetic patients after CPB.

METHODS

Nitro-blu tetrazolium scores, CD 11b expression and neutrophil-endothelial cells adhesion were assessed in blood samples from 15 diabetic and 15 control patients who had undergone elective coronary bypass grafting. Blood samples were obtained at baseline, 30 min after beginning CPB, at the end of CPB and 60 min postoperatively. At the same sampling points as above, blood glucose levels were also checked in all patients.

RESULTS

Diabetes was associated with a significant basal increase in neutrophil CD1 lb expression and adhesion to endothelial cells as well as with an increased superoxide anion production. The increased adhesion of diabetic neutrophils persisted by the end of the CPB to 60 min postoperatively independently of the blood glucose levels. Antibodies directed against CD1 lb and CD18 significantly reduced the degree of neutrophil adhesion observed 60 min postoperatively.

CONCLUSIONS

These results indicate that diabetes mellitus is associated with an increased neutrophil-endothelial cell adhesion probably mediated by the CD1 1b/CD18 molecule; this, in turn, might be responsible for the increased risk of postoperative complications observed in diabetic patients undergoing coronary artery bypass grafting.

Serum-mediated recognition of liposomes by phagocytic cells of the reticuloendothelial system - The concept of tissue specificity

The mechanisms responsible for the clearance and recognition of intravenously injected liposomes by phagocytic cells of the reticuloendothelial system are presently not well understood. Here, we address a multiplicity of physicochemical and physiopathological factors which influence the clearance kinetics and tissue distribution of liposomes administered into the circulation. Emphasis is particularly drawn towards the concept of liposome-blood protein interaction and its role in liposome recognition by various phagocytes of the reticuloendothelial system.

Current therapeutic apheresis technologies for inflammatory bowel disease

A large number of physicians have indicated that patients with inflammatory bowel diseases (IBD) such as ulcerative colitis (UC) and Crohn's disease (CD) respond to current apheresis technology treatment. However, the mechanism of the apheresis procedure is undefined for patients with IBD. IBD appears to be caused by a complex of interactions from the genes, environment, and the immune system; therefore, the immune system plays a crucial role in the inflammatory responses. In this process, lots of interactions occur simultaneously, and they cross relate with each other. This review paper briefly discusses the etiology and pathogenesis of IBD and attempts to elucidate the mechanism that occurs after apheresis treatment.

Two signaling mechanisms for activation of alphaM beta2 avidity in polymorphonuclear neutrophils

Circulating polymorphonuclear neutrophils (PMN) are quiescent, nonadherent cells that rapidly activate at sites of inflammation, where they develop the capacity to perform a repertoire of functions that are essential for host defense. Induction of integrin-mediated adhesion, which requires an increase in integrin avidity, is critical for the development of these effector functions. Although a variety of stimuli can activate integrins in PMN, the signaling cascades involved are unclear. Phosphatidylinositol (PI) 3-kinase has been implicated in integrin activation in a variety of cells, including PMN. In this work, we have examined activation of the PMN integrin alphaM beta2, assessing both adhesion and generation of the epitope recognized by the activation-specific antibody CBRM1/5. We have found that PI 3-kinase has a role in activation of alphaM beta2 by immune complexes, but we have found no role for it in alphaM beta2 activation by ligands for trimeric G protein-coupled receptors, including formylmethionylleucylphenylalanine (fMLP), interleukin-8, and C5a. Cytochalasin D inhibition suggests a role for the actin cytoskeleton in immune complex activation of alphaM beta2, but cytochalasin has no effect on fMLP-induced activation. Similarly, immune complex activation of the Rac/Cdc42-dependent serine/threonine kinase Pak1 is blocked by PI 3-kinase inhibitors, but fMLP-induced activation is not. These results demonstrate that two signaling pathways exist in PMN for activation of alphaM beta2. One, induced by FcgammaR ligation, is PI 3-kinase-dependent and requires the actin cytoskeleton. The second, initiated by G protein-linked receptors, is PI 3-kinase-independent and cytochalasin-insensitive. Pak1 may be in a final common pathway leading to activation of alphaM beta2.

Nitric oxide modulation of neutrophil-endothelium interaction: difference between arterial and venous coronary bypass grafts

OBJECTIVES

This study sought to evaluate the relation between the pattern of neutrophil-endothelial adhesion in saphenous vein (SV) and internal mammary artery (IMA) grafts and the endothelial production of nitric oxide (NO).

BACKGROUND

Autologous IMA and SV grafts (SVGs) are increasingly used as conduits for coronary bypass grafting. Previous studies have demonstrated a greater production of endothelial-derived relaxing factor (NO) from IMA than from SVGs. Because of the well known role of NO in modulating the adhesion of polymorphonuclear leukocytes to the endothelium, we studied the pattern of neutrophil adhesion to the endothelium of IMA and SVs under basal conditions and after inhibition of NO synthesis.

METHODS

Segments of IMA and SVs were obtained from 20 patients undergoing coronary artery bypass graft surgery. We evaluated the adhesion of both unstimulated and activated neutrophils to the endothelial surface of IMA and SVs in both basal conditions and after inhibition of NO synthesis with Nomega-nitro-L-arginine methyl ester.

RESULTS

Under basal conditions, no difference in unstimulated neutrophil adhesion to endothelium was observed between the two vessel conduits. After neutrophil activation, a significantly (p < 0.05) greater adhesion of neutrophils was observed in the SV than in the IMA. After inhibition of NO release, the adhesion of activated neutrophils increased in both vessels, and no significant difference between them was observed. The increased adhesion was attenuated by both L-arginine and sodium nitroprusside.

CONCLUSIONS

The lesser neutrophil adhesion to the endothelium of the IMA is a consequence of enhanced release of NO at this level; this effect could be responsible for the better early and long-term patency of this conduit over the SVG in coronary bypass grafting.