Neutrophil integrin assay for clinical studies

Regulation of neutrophil function by selective targeting of glycan epitopes expressed on the integrin CD11b/CD18

Polymorphonuclear neutrophils (PMNs) play a critical role in the innate immune response to invading pathogens. However, dysregulated mucosal trafficking of PMNs and associated epithelial tissue damage is a pathological hallmark of numerous inflammatory conditions including inflammatory bowel disease. The glycoprotein CD11b/CD18 plays a well-described role in regulating PMN transepithelial migration and PMN inflammatory functions. Previous studies have demonstrated that targeting of the N-linked glycan Lewis X on CD11b blocks PMN transepithelial migration (TEpM). Given evidence of glycosylation-dependent regulation of CD11b/CD18 function, we performed MALDI TOF Mass Spectrometry (MS) analyses on CD11b/CD18 purified from human PMNs. Unusual glycan epitopes identified on CD11b/CD18 included high Mannose oligosaccharides recognized by the Galanthus Nivalis lectin and biantennary galactosylated N-glycans recognized by the Phaseolus Vulgaris erythroagglutinin lectin. Importantly, we show that selective targeting of glycans on CD11b with such lectins results in altered intracellular signaling events that inhibit TEpM and differentially affect key PMN inflammatory functions including phagocytosis, superoxide release and apoptosis. Taken together, these data demonstrate that discrete glycan motifs expressed on CD11b/CD18 such as biantennary galactose could represent novel targets for selective manipulation of CD11b function and reduction of PMN-associated tissue damage in chronic inflammatory diseases.

Determining beta2-integrin and intercellular adhesion molecule 1 binding kinetics in tumor cell adhesion to leukocytes and endothelial cells by a gas-driven micropipette assay

Interactions between polymorphonuclear neutrophils (PMNs) and tumor cells have been reported to facilitate the adhesion and subsequent extravasation of tumor cells through the endothelium under blood flow, both of which are mediated by binding β(2)-integrin to intercellular adhesion molecule 1 (ICAM-1). Here the adhesions between human WM9 metastatic melanoma cells, PMNs, and human pulmonary microvascular endothelial cells (HPMECs) were quantified by a gas-driven micropipette aspiration technique (GDMAT). Our data indicated that the cellular binding affinity of PMN-WM9 pair was 3.9-fold higher than that of the PMN-HPMEC pair. However, the effective binding affinities per molecular pair were comparable between the two cell pairs no matter whether WM9 cells or HPMECs were quiescent or cytokine-activated, indicating that the stronger adhesion between PMN-WM9 pair is mainly attributed to the high expression of ICAM-1 on WM9 cells. These results proposed an alternative mechanism, where WM9 melanoma cells adhere first with PMNs near vessel-wall regions and then bind to endothelial cells via PMNs under blood flow. In contrast, the adhesions between human MDA-MB-231 metastatic breast carcinoma cells and PMNs showed a comparable cellular binding affinity to PMN-HPMEC pair because the ICAM-1 expressions on MDA-MB-231 cells and HPMECs are similar. Furthermore, differences were observed in the intrinsic forward and reverse rates of the β(2)-integrin-ICAM-1 bond between PMN-TC and PMN-EC pairs. This GDMAT assay enables us to quantify the binding kinetics of cell adhesion molecules physiologically expressed on nucleated cells. The findings also further the understanding of leukocyte-facilitated tumor cell adhesion from the viewpoint of molecular binding kinetics.

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 systemic inflammatory response induced by trauma is reflected by multiple phenotypes of blood neutrophils

Secondary morbidity and mortality after trauma are mainly due to a dysfunctional immune system. Severe injury can trigger a systemic inflammatory response, which is characterised by pre-activation or priming of neutrophils in peripheral blood. Signals initiated as result of local tissue damage can further activate these neutrophils leading to post-injury inflammatory complications. Additional trauma caused by surgical intervention can worsen the inflammatory response, thereby increasing the risk of these inflammatory complications. Limiting surgical procedures through damage control principles can reduce the risk of secondary morbidity. Inflammatory complications after injury cannot adequately be predicted using the current anatomical and physiological-based scoring systems. In this review we propose a methodology focussing on the activation state of the systemic inflammatory response with focus on neutrophils to aid in the risk assessment of secondary morbidity after trauma. Neutrophils are essential effector cells during the post-injury systemic inflammatory response. Neutrophils differentially express an array of surface receptors by which the cells can respond and adapt to changing environmental signals. The determination of specific expression profiles of neutrophil receptors can aid in phenotyping and quantifying the systemic inflammatory response. This article reviews the application of these specific signatures of neutrophil receptors as a consequence of severe injury.

In vitro and in vivo effects of salbutamol on neutrophil function in acute lung injury

BACKGROUND

Intravenous salbutamol (albuterol) reduces lung water in patients with the acute respiratory distress syndrome (ARDS). Experimental data show that it also reduces pulmonary neutrophil accumulation or activation and inflammation in ARDS.

AIM

To investigate the effects of salbutamol on neutrophil function.

METHODS

The in vitro effects of salbutamol on neutrophil function were determined. Blood and bronchoalveolar lavage (BAL) fluid were collected from 35 patients with acute lung injury (ALI)/ARDS, 14 patients at risk from ARDS and 7 ventilated controls at baseline and after 4 days' treatment with placebo or salbutamol (ALI/ARDS group). Alveolar-capillary permeability was measured in vivo by thermodilution (PiCCO). Neutrophil activation, adhesion molecule expression and inflammatory cytokines were measured.

RESULTS

In vitro, physiological concentrations of salbutamol had no effect on neutrophil chemotaxis, viability or apoptosis. Patients with ALI/ARDS showed increased neutrophil activation and adhesion molecule expression compared with at risk-patients and ventilated controls. There were associations between alveolar-capillary permeability and BAL myeloperoxidase (r = 0.4, p = 0.038) and BAL interleukin 8 (r = 0.38, p = 0.033). In patients with ALI/ARDS, salbutamol increased numbers of circulating neutrophils but had no effect on alveolar neutrophils.

CONCLUSION

At the onset of ALI/ARDS, there is increased neutrophil recruitment and activation. Physiological concentrations of salbutamol did not alter neutrophil chemotaxis, viability or apoptosis in vitro. In vivo, salbutamol increased circulating neutrophils, but had no effect on alveolar neutrophils or on neutrophil activation. These data suggest that the beneficial effects of salbutamol in reducing lung water are unrelated to modulation of neutrophil-dependent inflammatory pathways.

Differential Expression of the C5a Receptor and Complement Receptors 1 and 3 after LPS Stimulation of Neutrophils and Monocytes

Animal experiments recently suggested that administration of anti-C5a, anti-C5a receptor or soluble complement receptor type-1 may be of value in the treatment of septic shock. Because results regarding C5a receptor expression (C5a-R, CD-88) have been found to differ between septic animals and patients, the aim of this study was to investigate the neutrophil and monocyte receptor expression of CD-88 and complement receptor-1 (CR-1, CD-35) after stimulation with lipopolysaccharide (LPS) ex vivo. Whole blood or isolated neutrophils and monocytes from healthy people were incubated with LPS in a dose range of 0.1-1000 ng/ml. The expressions of CD-88 and CD-35 were analysed by means of flow cytometry. For comparison, the expressions of complement receptor-3 (CR-3, CD-11b/CD-18), Fc-gamma receptor type-I (CD-64) and CEACAM-8 (CD-66b) were also investigated. In whole blood, CD-88 expression on neutrophils was reduced (P < 0.05). The expressions of CD-35 and CD-11b were increased both on neutrophils (P < 0.001; P < 0.05) and on monocytes (P < 0.001; P < 0.001). No effect was observed on isolated cells. In agreement with the findings in septic patients, LPS reduced the neutrophil C5a-R expression, whereas the expressions of CR-1 and CR-3 were increased. The effects of LPS were indirect and were mediated via factors in the blood. The clinical significance of this is not known, but may be associated with decreased chemotaxis.

Use of serial analysis of gene expression (SAGE) technology reveals new granulocytic markers

Because of its short life span in blood, its low RNA content and its highly condensed nucleus, the granulocyte was initially considered as a terminally differentiated cell unable to express novel genes. However, mature granulocytes still contain a variety of mRNAs and may respond to external stimuli by rapid and complex changes in gene expression. The present work was undertaken to provide a wider view of the gene expression profile in unstimulated circulating PMNs. We used serial analysis of gene expression (SAGE) adapted to downsized extracts (SADE) to cope with their small mRNA content. As cell samples of the highest degree of purity were crucial for this project, we adapted a magnetic cell sorting method to reach the required high levels of purity (99.55 +/- 0.19%) together with low activation rates (1.37 +/- 0.28). We analyzed 20,787 tags identifying 8547 different transcripts, of which 47.8% were unknown, 34.6% were transcripts of known genes, and 13.8% matched with expressed sequence tags (EST). Highly expressed genes were those involved in cell mobility, diapedesis, cell signaling and destruction of micro-organisms. In addition, this method led to the identification of genes which had not previously been reported in granulocytes. These results could provide new molecular markers and a reliable reference for the investigation of pathologies involving alteration of the granulocyte gene expression profile.

Rheological properties of the blood influencing selectin-mediated adhesion of flowing leukocytes

We studied how the rheological properties of blood influenced capture and rolling adhesion of leukocytes as well as their margination in the bloodstream. When citrated, fluorescently labeled blood was perfused through glass capillaries coated with P-selectin, leukocytes formed numerous rolling attachments. The number of attached leukocytes increased as the hematocrit was increased between 10% and 30% and was essentially constant from 30% to 50%. In EDTA-treated blood, adhesion was absent, and the flux of marginated cells varied little with increasing hematocrit. However, the velocity of marginated leukocytes increased monotonically, whereas the volumetric flow rate was constant, implying that the flow velocity profile became blunted and wall shear rate increased. Thus increasing hematocrit promoted attachment for a given total flow rate, without increasing margination, even though wall shear rate and blood viscosity increased. Blood was diluted to 20% hematocrit with plasma, 40-kDa dextran (to reduce red blood cell aggregation), or 500-kDa dextran (to enhance aggregation). Increasing aggregation correlated with increasing leukocyte adhesion and with more slow-flowing leukocytes near the wall. Thus flowing erythrocytes promote leukocyte adhesion, either by causing margination of leukocytes or by initiating and stabilizing attachments that follow.

Propofol depressed neutrophil hydrogen peroxide production more than midazolam, whereas adhesion molecule expression was minimally affected by both anesthetics in rats with abdominal sepsis

The treatment of sepsis may require mechanical ventilation of the lungs and sedation. Because neutrophils are the most important effector cells for protecting against sepsis, and propofol and midazolam are the most widely used anesthetics for sedation, we studied the effects of these two anesthetics on the neutrophil function during sepsis. Sepsis was induced in rats by cecal ligation and puncture. At either 4 h or 24 h after cecal ligation and puncture, blood and peritoneal neutrophils were obtained, incubated with the test anesthetics, and the hydrogen peroxide (H(2)O(2)) production and CD11b/c expression were determined by flow cytometry. In both early (at 4 h) and late (at 24 h) sepsis, propofol and midazolam depressed H(2)O(2) production by blood and peritoneal neutrophils at clinical concentrations. Propofol caused more depression than midazolam (P < 0.005). In both early and late sepsis, the effect of the anesthetics on the up-regulation of the stimulation-induced CD11b/c expression on blood neutrophils was minimal at clinical concentrations. If these results ultimately become clinically relevant, midazolam may be preferable to propofol for sedation during sepsis.

Characteristics of leucocyte adhesion directly observed in flowing whole blood in vitro

Use of whole blood in adhesion assays allows analysis of the rheological and haematological factors that may influence adhesion, and avoids the need for isolation procedures that may modify the properties of leucocytes. We have adapted an in vitro flow model to allow videomicroscopy of leucocytes fluorescently labelled with rhodamine 6G (20 microg/ml) in anticoagulated whole blood. Blood was perfused at a range of wall shear rates (35-280/s) through a vertical glass capillary with a rectangular cross-section (microslide) that had been coated with P-selectin (10 microg/ml). Nearly all adherent cells were rolling in blood that had been anticoagulated with buffered citrate, but 40-50% became immobilized when heparin or thrombin inhibitor (PPACK) were used. The efficiency of leucocyte adhesion decreased steadily during 1-4 h of blood storage. Smaller fluorescent cells (lymphocytes) adhered less efficiently than larger cells (granulocytes) and rolled faster. Adhesion decreased monotonically with increasing wall shear rate or stress, but the velocity of rolling varied little. Among healthy volunteer donors, adhesion correlated with blood leucocyte count, but did not vary significantly with natural variation in haematocrit, blood viscosity or red cell aggregation. In conclusion, we have characterized adhesion of leucocytes in flowing whole blood, identified key experimental variables and demonstrated that physical environmental factors can markedly influence adhesive behaviour.

Bactericidal/permeability-increasing protein preserves leukocyte functions after major liver resection

OBJECTIVE

To analyze postoperative leukocyte functions in patients undergoing hemihepatectomy, and to assess the effect of treatment with the endotoxin-neutralizing agent bactericidal/permeability-increasing protein (rBPI21).

SUMMARY BACKGROUND DATA

Extensive liver resection is associated with a high incidence of infectious complications. Because elimination of pathogenic microorganisms occurs mainly by leukocytes, this increased rate of infections is most likely due to an impaired function of these cells. Endotoxin, translocated from the gut into the systemic circulation as a result of increased gut permeability and reduced hepatic clearance function after major liver resection, may play an important role in the impairment of posthepatectomy leukocyte function.

METHODS

To investigate whether hemihepatectomy results in impaired leukocyte functions and to determine the role of endotoxin in this process, leukocyte oxidative burst and leukocyte antigen expression were studied in three groups of patients: patients undergoing a hemihepatectomy and receiving rBPI21 treatment, patients undergoing hemihepatectomy and receiving placebo, and as an extra control group patients undergoing other major abdominal surgeries. Blood samples were collected before surgery, 2 hours after surgery, and at days 1, 2, 5, and 7. Phorbol myristate acetate-stimulated oxidative burst was measured using dihydrorhodamine, and leukocyte surface expression of the antigens CD11b, CD16, and CD14 was investigated by indirect immunofluorescence. Both oxidative burst and membrane surface expression were quantified by flow cytometry. An indication of the antiendotoxin effect of rBPI21 treatment was provided by assessment of plasma lipopolysaccharide binding protein (LBP) levels by enzyme-linked immunosorbent assay.

RESULTS

The oxidative burst in the hemihepatectomized patients receiving placebo and the controls increased 2 hours after surgery, whereas it decreased in the rBPI21-treated patients, resulting in significant differences between the groups. On day 1, neutrophil CD11b expression and monocyte CD14 expression in the rBPI21-treated patients and controls were significantly lower than in the placebo group. At 2 hours, CD16 expression in the placebo-treated patients was significantly higher than in the rBPI21-treated patients and controls. On day 5 and day 7, plasma LBP levels were significantly higher in the placebo-treated patients compared with the rBPI21-treated patients.

CONCLUSIONS

The results of this study show that patients undergoing major liver resection have an increased activation of leukocytes compared with those undergoing other major abdominal surgery. This enhanced activation may contribute to the increased risk of infection in these patients. Administration of the endotoxin-neutralizing agent rBPI21 to hemihepatectomy patients was shown to reduce plasma LBP levels, to preserve leukocyte functions partially, and to reduce leukocyte activation to the level of other, nonhepatic abdominal surgery.

Differential ability of exogenous chemotactic agents to disrupt transendothelial migration of flowing neutrophils

Neutrophils migrate through endothelium using an ordered sequence of adhesive interactions and activating signals. To investigate the consequences of disruption of this sequence, we characterized adhesion and migration of neutrophils perfused over HUVEC that had been treated with TNF-alpha for 4 h and evaluated changes caused by exogenously added chemotactic agents. When HUVEC were treated with 2 U/ml TNF, flowing neutrophils adhered, with the majority rolling and relatively few migrating through the monolayer. If fMLP, IL-8, zymosan-activated plasma (a source of activated complement factor C5a), epithelial cell-derived neutrophil-activating peptide (ENA-78), or growth-regulating oncogene, GRO-alpha, was perfused over these neutrophils, they stopped rolling and rapidly migrated over the monolayer, but did not penetrate it. When HUVEC were treated with 100 U/ml TNF, the majority of adherent neutrophils transmigrated. If neutrophils were treated with fMLP, IL-8, C5a, ENA-78, or GRO-alpha just before perfusion over this HUVEC, transmigration, but not adhesion, was abolished. However, when platelet-activating factor was used to activate neutrophils, migration through HUVEC treated with 100 U/ml TNF was not impaired, and migration through HUVEC treated with 2 U/ml TNF was actually increased. Transmigration required ligation of CXC chemokine receptor-2 on neutrophils, and differential desensitization of this receptor (e.g., by fMLP but not platelet-activating factor) may explain the pattern of disruption of migration. Thus, transmigration may require presentation of the correct activators in the correct sequence, and inappropriate activation (e.g., by systemic activators) could cause pathological accumulation of neutrophils in the vessel lumen.

The use of flow cytometry to measure neutrophil function

Neutrophils are important professional phagocytic cells that provide the host with a first line of defense against acute bacterial and fungal diseases and recurrent, severe or unusual infections are associated with inherited defects of neutrophil function. Furthermore, abundant evidence links inappropriate neutrophil-mediated tissue damage to the pathogenesis of conditions such as acute respiratory distress syndrome, septicemia with multiorgan failure, ischemia-reperfusion injury and rheumatoid arthritis. Flow cytometry has been increasingly used to evaluate the functional capabilities of neutrophils. In this review, we discuss the use of flow cytometry to assess neutrophil functional responses including calcium mobilization, F-actin assembly, adhesion, aggregation, degranulation, phagocytosis and reactive oxygen species (ROS) production. The use of flow cytometry to identify neutrophil priming is also discussed. The advantage of flow cytometry is that the majority of neutrophil functions can be measured using a small volume of whole blood that reduces artifactual changes in function caused by purification procedures. The advent of numerous new fluorochromes and multiparametric analysis allows the simultaneous measurement of several neutrophil functions in the same population of cells. Flow cytometric analysis provides a rapid screen for abnormalities of neutrophil function and reflects more accurately their behavior in vivo.

Granulocyte colony-stimulating factor induces neutrophil sequestration in rabbit lungs

The effects of intravenous injection of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on circulating neutrophil numbers, pulmonary vascular permeability, and morphologic changes in the lung were examined in rabbits. Intravenous injection of rhG-CSF caused a rapid, profound neutropenia due to neutrophil sequestration primarily within capillaries but also in larger microvessels of the lungs. Examination of neutrophil deformability using microfilters revealed that granulocyte colony-stimulating factor (G-CSF) treatment caused a rapid stiffening of neutrophils through the polymerization of F-actin but not microtubule assembly. The expression of CD11b, CD11c, and CD18 on human neutrophils after G-CSF treatment increased, but CD11a did not. Intravenous injection of rhG-CSF did not induce neutrophil emigration or albumin leakage into alveolar space, wet/dry lung weight ratios were unchanged, and no pathologic changes in lung histology were observed. These studies indicate that injection of rhG-CSF caused a rapid neutropenia and neutrophil sequestration in the lungs that is likely to be mediated through a G-CSF-induced decrease in neutrophil deformability, although neutrophil-endothelial cell adhesion may also play a role. However, this G-CSF-induced neutrophil sequestration did not induce a massive lung injury.

Treatment of neutrophils with cytochalasins converts rolling to stationary adhesion on P-selectin

We investigated how disruption of the actin cytoskeleton with cytochalasins modified adhesion of neutrophils rolling on a platelet monolayer in vitro at 37 degrees C. When perfused at a wall shear stress of 0.1 Pa over rolling cells, cytochalasin B, cytochalasin D and dihydro-cytochalasin B each induced dose-dependent (approximately 1-10 microg/ml) conversion to stationary attachment over minutes. Stopping was associated with cell elongation to a teardrop shape. Increased deformability of cytochalasin-treated cells was independently evidenced by more rapid entry into a micropipette. Spherical shape and rolling were reestablished concurrently on washout of the cytochalasins, while increasing the shear stress in the range 0.2 to 1.0 Pa induced tear-drop-shaped cells to restart rolling even in the continued presence of cytochalasin. When cells were pretreated with cytochalasin B, they attached efficiently at 0.1 Pa, rolled initially and only stopped after approximately 30 seconds when elongation had been established. Adhesion was selectin-mediated in the presence or absence of cytochalasin B, as judged by inhibition of attachment by antibody against P-selectin and failure of antibody against beta2-integrin CD18 to influence adhesion. Cessation of rolling is unlikely to have arisen from an increase in adhesive contact area induced by deformation because stopped cells were found to be attached only at their pointed end. Failure of adhesive bonds to peel may have arisen because selectin ligands freed of cytoskeletal restraint were dragged into this tethered region and clustered there, and because force applied to bonds was influenced by the change in cell shape. These results suggest that cytoskeletal structure is an important modulator of dynamic adhesive responses of leukocytes, via effects on adhesion receptors and cellular mechanics.

Reactivity of workshop monoclonal antibodies on paraformaldehyde-fixed porcine blood mononuclear cells

One hundred sixty-four monoclonal antibodies (mAbs) of the second international swine CD workshop were tested for their reactivity with porcine blood mononuclear cells before and after fixing the cells with varying concentrations of paraformaldehyde (PFA) (1, 5 and 10 g l-1). A total of 38 (out of 134) positive reacting mAbs were significantly affected in their binding behavior on fixed cells. Modulation was seen as reduction in binding (staining intensity and/or % positive cells, n = 18) or in elevated values (n = 20). Modified mAb binding occurred after fixing cells with 5 to 10 g l-1 PFA.

Actin polymerisation regulates integrin-mediated adhesion as well as rigidity of neutrophils

Activation of adherent neutrophils causes them to convert from selectin-mediated rolling to integrin-mediated immobilisation and migration. Migration is known to depend on formation and redistribution of filamentous (F) actin, but although immobilisation in seconds parallels early cortical actin polymerisation, no link has been proven. We tested the effect of the actin-polymerising agent jasplakinolide (10 microM) on adhesive and mechanical properties of neutrophils. Pretreated cells were able to adhere and roll on immobilised platelets in a flow-based adhesion assay, but whereas untreated rolling cells became immobilised in seconds when chemotactic formyl peptide (fMLP, 0.1 microM) was superfused over them, the cells treated with jasplakinolide continued rolling. Pretreatment with jasplakinolide also blocked de novo expression of integrin CD11b and shape change which otherwise occurred in minutes after treatment with fMLP. Jasplakinolide directly caused actin polymerisation within neutrophils, evidenced by a marked increase in rigidity (resistance to aspiration into a 5 microm micropipette) and increase in association of actin with the Triton-insoluble cytoskeleton. These results indicate that rearrangement of the actin cytoskeleton regulates integrin-mediated adhesion of activated neutrophils, as well as their migration and mechanical properties.

The function of neutrophils isolated by a magnetic antibody cell separation technique is not altered in comparison to a density gradient centrifugation method

Most comparative studies on neutrophil (PMN) isolation techniques have shown either activation or functional impairment of the cells due to the different separation processes. We have established a preparation method for PMN from human whole blood employing iron tagged, magnetizable antibodies against the cell surface antigen CD15. The aim of our study was to test whether this magnetic separation (MACS) alters cellular functions of PMN in comparison to a conventional density gradient technique (Percoll). The purity, cell yield, and pre-activation of the cells were evaluated. The latter was assessed by quantifying the expression of the integrin CD11b using flow cytometry. Furthermore, as functional tests, cell morphology and the oxidative burst reaction were investigated. We have shown that the use of 'magnetic' antibodies leads to highly purified PMN (> 99% of isolated leukocytes), while there is still contamination by eosinophils (about 6%) after Percoll separation. Platelet contamination was about the same in both procedures (approx. one platelet per two PMN). The basal expression of CD11b and, hence, neutrophil activation, was significantly lower and the upregulation of CD11b in response to FMLP was more pronounced after magnetic separation, as compared to density gradient centrifugation. The MACS technique did not lead to polarisation of PMN, nor did it affect the oxidative burst. This study suggests that magnetic separation is a simple, time-saving technique, yielding highly purified and functionally intact PMN.

Time course of beta 2-integrin CD11b/CD18 (Mac-1, alpha M beta 2) upregulation on neutrophils and monocytes after coronary artery bypass grafting. CD11b upregulation after CABG surgery

Although upregulation of CD11b/CD18 receptor, i.e. activation of neutrophils and monocytes, during cardiopulmonary bypass is well documented, the duration of the active state after uncomplicated operation is less understood. We therefore investigated CD11b expression of phagocytes in blood samples collected 2-4, 24, 48 and 72 h after coronary artery bypass grafting. CD11b expression on neutrophils was significantly elevated at 2-4 and 24 hours after operation as compared with baseline. On monocytes, expression peaked at 24 h and returned to baseline by 72 h. Because CD11b is a sensitive marker, effects of different sampling techniques on its expression were also studied. CD11b expression was similar in samples collected with a syringe from arterial or central venous catheter or with open technique from cubital vein. On neutrophils from healthy subjects, sampling with syringe caused small (10%) but statistically significant increase of expression. We conclude that activated neutrophils disappear from circulation within hours after CABG surgery while activated monocytes may continue circulating for 2-3 days, and that CD11b sampling can be done with a syringe.

Effect of activation on adhesion of flowing neutrophils to cultured endothelium: time course and inhibition by a calcium channel blocker (nitrendipine)

1. Adhesion of neutrophils to vascular endothelium plays an important role in inflammation and thrombosis. Modulation of adhesion may be therapeutic in these conditions. 2. A flow model was used to quantify adhesion of neutrophils to human cultured umbilical vein endothelial cells. The time course of the neutrophil response to activation by N-formyl-methionyl-leucylphenylalanine (fMLP, 10(-7) M) was studied and the inhibitory effects of the calcium-channel blockers, nitrendipine and nifedipine, were investigated. 3. Neutrophils adhered firmly to the endothelial cells without rolling, but initial attachment was highly dependent on shear stress; doubling the stress from 0.05 to 0.1Pa decreased the number of neutrophils adhering by over 80%. 4. Adhesion rapidly increased after activation of neutrophils by fMLP, peaking at 1-3 min post-treatment, and then decreased over the next 10-12 min. A monoclonal antibody to the beta 2-integrin component CD18 inhibited adhesion by over 80% for activated or unactivated cells. 5. The Ca-channel blocker, nitrendipine, but not nifedipine, significantly inhibited the fMLP-induced increase of adhesion in a dose-dependent manner (10(-8) to 10(-6) M). Dihydropyridines may be useful agents for modifying neutrophil function.