Human polymorphonuclear leucocytes stimulated by tumour necrosis factor-alpha show increased adherence to extracellular matrix proteins which is mediated via the CD11b/18 complex

Endoplasmic Reticulum Protein 72 Regulates Integrin Mac-1 Activity to Influence Neutrophil Recruitment

BACKGROUND

Integrins mediate the adhesion, crawling, and migration of neutrophils during vascular inflammation. Thiol exchange is important in the regulation of integrin functions. ERp72 (endoplasmic reticulum-resident protein 72) is a member of the thiol isomerase family responsible for the catalysis of disulfide rearrangement. However, the role of ERp72 in the regulation of Mac-1 (integrin αMβ2) on neutrophils remains elusive.

METHODS

Intravital microscopy of the cremaster microcirculation was performed to determine in vivo neutrophil movement. Static adhesion, flow chamber, and flow cytometry were used to evaluate in vitro integrin functions. Confocal fluorescent microscopy and coimmunoprecipitation were utilized to characterize the interactions between ERp72 and Mac-1 on neutrophil surface. Cell-impermeable probes and mass spectrometry were used to label reactive thiols and identify target disulfide bonds during redox exchange. Biomembrane force probe was performed to quantitatively measure the binding affinity of Mac-1. A murine model of acute lung injury induced by lipopolysaccharide was utilized to evaluate neutrophil-associated vasculopathy.

RESULTS

ERp72-deficient neutrophils exhibited increased rolling but decreased adhesion/crawling on inflamed venules in vivo and defective static adhesion in vitro. The defect was due to defective activation of integrin Mac-1 but not LFA-1 (lymphocyte function-associated antigen-1) using blocking or epitope-specific antibodies. ERp72 interacted with Mac-1 in lipid rafts on neutrophil surface leading to the reduction of the C654-C711 disulfide bond in the αM subunit that is critical for Mac-1 activation. Recombinant ERp72, via its catalytic motifs, increased the binding affinity of Mac-1 with ICAM-1 (intercellular adhesion molecule-1) and rescued the defective adhesion of ERp72-deficient neutrophils both in vitro and in vivo. Deletion of ERp72 in the bone marrow inhibited neutrophil infiltration, ameliorated tissue damage, and increased survival during murine acute lung injury.

CONCLUSIONS

Extracellular ERp72 regulates integrin Mac-1 activity by catalyzing disulfide rearrangement on the αM subunit and may be a novel target for the treatment of neutrophil-associated vasculopathy.

The Promiscuous Profile of Complement Receptor 3 in Ligand Binding, Immune Modulation, and Pathophysiology

The β2-integrin receptor family has a broad spectrum of physiological functions ranging from leukocyte adhesion, cell migration, activation, and communication to the phagocytic uptake of cells and particles. Among the members of this family, complement receptor 3 (CR3; CD11b/CD18, Mac-1, αMβ2) is particularly promiscuous in its functional profile and ligand selectivity. There are close to 100 reported structurally unrelated ligands for CR3, and while many ligands appear to cluster at the αMI domain, molecular details about binding modes remain largely elusive. The versatility of CR3 is reflected in its functional portfolio, which includes prominent roles in the removal of invaders and cell debris, induction of tolerance and synaptic pruning, and involvement in the pathogenesis of numerous autoimmune and chronic inflammatory pathologies. While CR3 is an interesting therapeutic target for immune modulation due to these known pathophysiological associations, drug development efforts are limited by concerns of potential interference with host defense functions and, most importantly, an insufficient molecular understanding of the interplay between ligand binding and functional impact. Here, we provide a systematic summary of the various interaction partners of CR3 with a focus on binding mechanisms and functional implications. We also discuss the roles of CR3 as an immune receptor in health and disease, as an activation marker in research and diagnostics, and as a therapeutic target.

VEGFR2 promotes central endothelial activation and the spread of pain in inflammatory arthritis

Chronic pain can develop in response to conditions such as inflammatory arthritis. The central mechanisms underlying the development and maintenance of chronic pain in humans are not well elucidated although there is evidence for a role of microglia and astrocytes. However in pre-clinical models of pain, including models of inflammatory arthritis, there is a wealth of evidence indicating roles for pathological glial reactivity within the CNS. In the spinal dorsal horn of rats with painful inflammatory arthritis we found both a significant increase in CD11b⁺ microglia-like cells and GFAP⁺ astrocytes associated with blood vessels, and the number of activated blood vessels expressing the adhesion molecule ICAM-1, indicating potential glio-vascular activation. Using pharmacological interventions targeting VEGFR2 in arthritic rats, to inhibit endothelial cell activation, the number of dorsal horn ICAM-1⁺ blood vessels, CD11b⁺ microglia and the development of secondary mechanical allodynia, an indicator of central sensitization, were all prevented. Targeting endothelial VEGFR2 by inducible Tie2-specific VEGFR2 knock-out also prevented secondary allodynia in mice and glio-vascular activation in the dorsal horn in response to inflammatory arthritis. Inhibition of VEGFR2 in vitro significantly blocked ICAM-1-dependent monocyte adhesion to brain microvascular endothelial cells, when stimulated with inflammatory mediators TNF-α and VEGF-A₁₆₅a. Taken together our findings suggest that a novel VEGFR2-mediated spinal cord glio-vascular mechanism may promote peripheral CD11b⁺ circulating cell transmigration into the CNS parenchyma and contribute to the development of chronic pain in inflammatory arthritis. We hypothesise that preventing this glio-vascular activation and circulating cell translocation into the spinal cord could be a new therapeutic strategy for pain caused by rheumatoid arthritis.

Topical delivery of l-theanine ameliorates TPA-induced acute skin inflammation via downregulating endothelial PECAM-1 and neutrophil infiltration and activation

l-theanine, the most abundant free amino acid in tea, has been documented to possess many different bioactive properties through oral or intragastrical delivery. However, little is known about the effect of topical delivery of l-theanine on acute inflammation. In the present study, by using 12-O-tetradecanoylphorbol-13-acetate (TPA, 2.5 μg/ear)-induced ear edema model in mice, we first found that single-dose local pretreatment of l-theanine 30 min before TPA time- and dose-dependently suppressed the increases in both skin thickness and weight. Subsequently l-theanine ameliorated TPA-induced erythema, vascular permeability increase, epidermal and dermal hyperplasia, neutrophil infiltration and activation via downregulating the expression of PECAM-1 (a platelet endothelial adhesion molecule-1) in blood vessels and the production of pro-inflammatory cytokines IL-1β, TNF-α, and mediator cyclooxygenase-2 (COX-2), which is mainly expressed in neutrophils. It highlighted the potential of l-theanine as a locally administrable therapeutic agent for acute cutaneous inflammation.

Pathobiology of neutrophil-epithelial interactions

Polymorphonuclear neutrophils (PMNs) are innate immune system cells that play an essential role in eradicating invading pathogens. PMN migration to sites of infection/inflammation requires exiting the microcirculation and subsequent crossing of epithelial barriers in mucosa-lined organs such as the lungs and intestines. Although these processes usually occur without significant damage to surrounding host tissues, dysregulated/excessive PMN transmigration and resultant bystander-tissue damage are characteristic of numerous mucosal inflammatory disorders. Mechanisms controlling PMN extravasation have been well characterized, but the molecular details regarding regulation of PMN migration across mucosal epithelia are poorly understood. Given that PMN migration across mucosal epithelia is strongly correlated with disease symptoms in many inflammatory mucosal disorders, enhanced understanding of the mechanisms regulating PMN transepithelial migration should provide insights into clinically relevant tissue-targeted therapies aimed at ameliorating PMN-mediated bystander-tissue damage. This review will highlight current understanding of the molecular interactions between PMNs and mucosal epithelia and the associated functional consequences.

UPF1 regulates myeloid cell functions and S100A9 expression by the hnRNP E2/miRNA-328 balance

UPF1 is a key player in nonsense mediated mRNA decay (NMD) but also involved in posttranscriptional gene regulation. In this study we found that UPF1 regulates the expression of genes with functions in inflammation and myeloid cell differentiation via hnRNP E2. The majority of the UPF1-regulated genes identified in monocytic cells contain a binding site for hnRNP E2 within 5′ UTR located introns with hnRNP E2 acting here as splicing regulator. We found that miRNA-328 which is significantly induced during monocytic cell differentiation acts independently from its gene silencing function as RNA decoy for hnRNP E2. One representative gene controlled by the hnRNP E2/miRNA-328 balance is S100A9 which plays an important role in cell differentiation and oxidative stress response of monocytes. Induction of miRNA-328 expression during cell differentiation antagonizes the blockade by hnRNP E2 which results in the upregulation of CD11b expression and ROS production in monocytic cells. Taken together, our data indicate that upregulation of miR-328 is responsible for the induction of hnRNP E2 target genes during myeloid cell differentiation.

Mas receptor deficiency exacerbates lipopolysaccharide-induced cerebral and systemic inflammation in mice

Beyond the classical actions of the renin-angiotensin system on the regulation of cardiovascular homeostasis, several studies have shown its involvement in acute and chronic inflammation. The G protein-coupled receptor Mas is a functional binding site for the angiotensin-(1-7); however, its role in the immune system has not been fully elucidated. In this study, we evaluated the effect of genetic deletion of Mas receptor in lipopolysaccharide (LPS)-induced systemic and cerebral inflammation in mice. Inflammatory response was triggered in Mas deficient (Mas(-/-)) and C57BL/6 wild-type (WT) mice (8-12 weeks-old) by intraperitoneal injection of LPS (5 mg/kg). Mas(-/-) mice presented more intense hypothermia compared to WT mice 24 h after LPS injection. Systemically, the bone marrow of Mas(-/-) mice contained a lower number of neutrophils and monocytes 3 h and 24 h after LPS injection, respectively. The plasma levels of inflammatory mediators KC, MCP-1 and IL-10 were higher in Mas(-/-) mice 24 h after LPS injection in comparison to WT. In the brain, Mas(-/-) animals had a significant increase in the number of adherent leukocytes to the brain microvasculature compared to WT mice, as well as, increased number of monocytes and neutrophils recruited to the pia-mater. The elevated number of adherent leukocytes on brain microvasculature in Mas(-/-) mice was associated with increased expression of CD11b - the alpha-subunit of the Mac-1 integrin - in bone marrow neutrophils 3h after LPS injection, and with increased brain levels of chemoattractants KC, MIP-2 and MCP-1, 24 h later. In conclusion, we demonstrated that Mas receptor deficiency results in exacerbated inflammation in LPS-challenged mice, which suggest a potential role for the Mas receptor as a regulator of systemic and brain inflammatory response induced by LPS.

The leucocyte β2 (CD18) integrins: the structure, functional regulation and signalling properties

Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted β2 integrins comprise four members, namely αLβ2, αMβ2, αXβ2 and αDβ2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.

Random phage-epitope library based identification of a peptide antagonist of Mac-1 β2 integrin ligand binding

The leukocyte β2 integrin Mac-1 (CD11b/CD18) plays a pivotal role in inflammation and host defense. To develop peptide antagonists selectively inhibiting the function of Mac-1, we used a random constrained 6-mer (cys-6aa-cys) peptide library to map the structural features of CD11b, by determining the epitope of neutralizing monoclonal antibody mAb 44a (anti-CD11b). We have used a stringent phage display strategy, which resulted in the identification of one disulfide C-RLKEKH-C constrained peptide by direct biopanning of library on decreasing amounts of purified mAb 44a. The selected peptide mimics a discontinuous epitope, a peculiar shape on the CD11b-I-domain surface. Competitive ELISA experiments with different Mac-1 ligands showed that C-RLKEKH-C is able to bind to fibrinogen, iC3b, and C1q. Furthermore, the monomeric circular peptide C-RLKEKH-C, was effective in blocking the interaction between (125)I-fibrinogen and Mac-1 (IC(50)=3.35±0.1×10(-6)M), and inhibited the adhesion of human neutrophils to fibrinogen and iC3b. These data provide information about the relative location of amino acids on the I-domain surface using mAb 44a imprint of the CD11b protein. The derived mimotope may help in the design of future anti-inflammatory therapeutic agents that can act as specific therapeutic agents targeting PMNs mediated inflammation.

Effects of endothelial basement membrane on neutrophil adhesion and migration

The influence of the sub-endothelial basement membrane (BM) on the adhesion and migration of leukocytes is not well-defined. We therefore investigated the behaviour of human neutrophils on purified BM proteins and on BM deposited by short- or long-term cultures of endothelial cells (EC). The adhesion, but not migration velocities, of neutrophils activated with interleukin-8 was dependent on the coating concentrations of purified collagen, laminin or fibronectin. In contrast, adhesion was similar on matrices deposited by 3-day or 20-day cultures of EC, but neutrophils migrated more slowly on the distinct BM that formed over 20 days. In addition, while adhesion on all surfaces was greatly reduced when neutrophils were treated with antibody against beta(2)-integrins, antibody against beta(1)-integrins only inhibited adhesion to the 20-day BM. Thus, the native BM has distinct effects on integrin usage and migration by neutrophils, which are not reproduced by purified proteins or matrix deposited early during endothelial culture.

CD11b-mediated migratory property of peripheral blood B cells

BACKGROUND

CD11b belongs to the integrin family and is expressed on neutrophils, monocytes, natural killer cells, and a subset of lymphocytes. Although CD11b expressed on neutrophils and monocytes has been extensively investigated and has been reported to play an important role in the migration of these subsets of leukocytes, the function of CD11b expressed on a subset of B cells has not yet been clarified.

OBJECTIVE

To elucidate the functional activity of CD11b expressed on B cells, we characterized the CD11b-expressing cells among the B-cell population and investigated their migratory ability.

METHODS

Isolated peripheral blood CD19 + B cells were analyzed by flow cytometry. The migratory ability of B cells was evaluated by the transwell assay, and the contribution of CD11b to this ability was investigated by using an anti-CD11b blocking mAb.

RESULTS

The majority of CD27 - IgD + naive B cells were CD11b - , whereas most CD27 + memory cells were CD11b +. Among the CD27 + memory cells, expression of CD11b was stronger on the IgD - cells than on the IgD + cells. In the transwell assay, the migrating cells were predominantly CD27 + IgD - cells, most of which expressed CD11b. The addition of an anti-CD11b blocking mAb resulted in the significant reduction of the number of migrating B cells.

CONCLUSION

Memory B cells express CD11b and, in contrast with naive B cells, have high migratory ability. CD11b plays an essential role in the homing process of memory cells.

Association of BAP31 with CD11b/CD18

The beta2 integrin CD11b/CD18 is an integral membrane protein that is present in the plasma membrane and secondary granules of neutrophils and functions as a major adhesion molecule. Upon cellular activation, there is translocation of intracellular pools of CD11b/CD18 to the plasma membrane in concert with enhanced cellular adhesion. Although much is known about the function of CD11b/CD18, how this protein is transported within the cell is less well defined. Here we report that CD11b/CD18 specifically binds to BAP31, a member of a novel class of sorting proteins regulating cellular anterograde transport. Through experiments aimed at identifying CD11b/CD18-binding proteins, we produced a monoclonal antibody termed E1B2 that recognizes a 28-kDa membrane protein that co-precipitates with CD11b/CD18. Microsequence analysis of the E1B2 antigen revealed that it is BAP31. Co-association of CD11b/CD18 and BAP31 was confirmed in co-immunoprecipitation and protein binding assays. Additional experiments revealed that the binding of BAP31 to CD11b/CD18 was not dependent on divalent cations nor mediated by the I-domain of CD11b. Using glutathione S-transferase fusion chimeras, we determined that binding of CD11b/CD18 to BAP31 is mediated through interactions with the cytoplasmic tail of BAP31. Immunolocalization studies revealed colocalization of BAP31 and CD11b/CD18 within neutrophil secondary granules. Subcellular fractionation studies in polymorphonuclear leukocytes (PMN) revealed similar patterns of redistribution of BAP31 and CD11b/CD18 from fractions enriched in secondary granules to the plasma membrane following stimulation with formylmethionylleucylphenylalanine (fMLP). Given the known sorting properties of BAP31, these findings suggest that BAP31 may play a role in regulating intracellular trafficking of CD11b/CD18 in neutrophils.

Immunological evaluation of the new stable ultrasound contrast agent LK565: a phase one clinical trial

Background

Ultrasound contrast agents (UCAs) allow the enhancement of vascular definition, thereby providing more diagnostic information. LK565 is a new second-generation UCA based on synthetic polymers of aspartic acid which is eliminated from the blood stream via phagocytosis. LK565 forms very stable air-filled microspheres and is capable of repeated passage through the pulmonary capillary bed after peripheral intravenous injection. This characteristic allows examination of the cardiac function or extracardiac vessel abnormalities up to 15 minutes.

Methods

A phase one clinical study was conducted on 15 healthy volunteers to identify the development of an undesirable immune response. Phagocytosis capacity, TNF-α secretion, and MHC class II upregulation of monocytes was monitored, as well as microsphere specific antibody development (IgM, IgG). Furthermore, the kinetics of the activation surface markers CD69, CD25, CD71, and CD11b on leukocytes were analyzed.

Results

Due to LK565-metabolism the administration of the UCA led to saturation of phagocytes which was reversible after 24 hrs. Compared to positive controls neither significant TNF-α elevation, neither MHC class II and activation surface markers upregulation, nor specific antibody development was detectable.

Conclusion

The administration of LK565 provides a comfortable duration of signal enhancement, esp. in echocardiography, without causing a major activation cascade or triggering an adaptive immune response. To minimize the risk of undesirable adverse events such as anaphylactoid reactions, immunological studies should be included in clinical trials for new UCAs. The use of LK565 as another new ultrasound contrast agent should be encouraged as a safe means to provide additional diagnostic information.

Modification of human polymorphonuclear neutrophilic cell (PMN)-adhesion on biomaterial surfaces by protein preadsorption under static and flow conditions

Biomaterials induce a specific reaction after implantation in the human body. This reaction depends on the chemical and physico-chemical properties of the material as well as on the site and type of implantation. We have used a dynamic model, the parallel-plate flow-chamber, to examine the interactions of different biomaterials with polymorphonuclear neutrophilic cell (PMN) and how these interactions are influenced by protein preadsorption. Our results clearly show that for hydrophobic materials, glass and PE, which induce a prominent adhesion of PMN, the mixture of albumin and fibrinogen induces the best inhibitory effect. On hydrophilic biomaterial surfaces, untreated TCPS and PC-coated TCPS, reveal only a minor influence of adsorbed proteins on PMN adhesion because of a primary low adhesive surface for PMN and proteins as well. Human citrated plasma leads only to a slight inhibition of PMN adhesion. On the hydrophobic materials, glass and PE, bovine serum albumin (BSA) had the best anti-adhesive potential with respect to PMN. The coating using phosphorylcholine is an excellent surface modification to prevent PMN-adhesion and protein adsorption. The results of our experiments suggest that investigations under static and flow conditions are also needed to determine the influence of protein adsorption on other relevant blood cell populations, for example, platelets and monocytes.

The interplay between integrins alphaMbeta2 and alpha5beta1 during cell migration to fibronectin

A directed migration of leukocytes through the extracellular matrix requires the regulated engagement of integrin cell adhesion receptors. The integrin alpha(M)beta(2) (CD11b/CD18, Mac-1) is progressively upregulated to high levels on migrating phagocytic leukocytes in response to inflammatory stimuli and is able to bind numerous ligands in the interstitial matrix. The role of alpha(M)beta(2) in migration of leukocytes through the extracellular matrix and its cooperation with other leukocyte integrins during migration are not understood. Using a model system consisting of cells that express different levels of alpha(M)beta(2) and an invariable level of endogenous integrin alpha(5)beta(1), we have explored a situation relevant to migrating neutrophils when alpha(M)beta(2) and alpha(5)beta(1) engage the same ligand, fibronectin. We show that fibronectin is a ligand for alpha(M)beta(2) and that both alpha(M)beta(2) and alpha(5)beta(1) on the alpha(M)beta(2)-expressing cells contribute to adhesion to fibronectin. However, migration of these cells to fibronectin is mediated by alpha(5)beta(1), whereas alpha(M)beta(2) retards migration. The decrease in migration correlates directly with the increased alpha(M)beta(2) density. Ligation of alpha(M)beta(2) with function-blocking antibodies can reverse this effect. The restorative effects of antibodies are caused by the removal of restraint imposed by the excess of alpha(M)beta(2)-fibronectin adhesive bonds. These findings indicate that alpha(M)beta(2) can increase general cell adhesiveness which results in braking of cell migration mediated by integrin alpha(5)beta(1). Because alpha(M)beta(2) binds numerous proteins in the extracellular matrix with a specificity overlapping that of the beta(1) integrins, the results suggest that alpha(M)beta(2) can affect the beta(1) integrin-mediated cell migration.

Ex-vivo regulation of endotoxin-induced tissue factor in whole blood by eicosanoids

The influence of several eicosanoids of the lipoxygenase pathway was examined in an ex vivo system of human whole blood subjected to stimulation by lipopolysaccharide (LPS). Exogenously added leukotriene B4 [5(S),12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid (LTB4)] or 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) significantly (P<0.05) enhanced LPS-evoked expression of monocyte tissue factor (TF) activity in a concentration-dependent manner. 15(S)-HETE, on the other hand, exerted such activity only when added at certain concentrations, whereas 5(S)-HETE was devoid of any apparent activity. LPS-induced TF activity was inhibited by the lipoxygenase inhibitors nordihydroguaiaretic acid, CGS 23885 and ZM 230487, by 59, 32 and 88%, respectively. Furthermore, the production of LTB4 in LPS-stimulated whole blood was investigated, in the absence or presence of either tumor necrosis factor alpha (TNFalpha) or phorbol-12-myristate-13-acetate (PMA). LPS alone induced a moderate time-dependent and concentration-dependent release of LTB4, reaching the maximum concentration (1260 +/- 202 pg/ml) within 90 min at 5 ng/ml LPS. The prior and concurrent presence of PMA (5 ng/ml) or TNFalpha (10 ng/ml) further enhanced the LTB4 production approximately twofold (P < 0.05). TNFalpha added alone evoked approximately twice the LTB4 production seen when LPS (2200 +/- 243 versus 1260 +/- 203 pg/ml) was added alone. Considering these results, LPS and TNFalpha emerge as important agonists of LTB4 production in whole blood. LTB4 in turn appears to be of importance for the expression of TF in monocytes, potentially amplifying the thrombogenic potential of these cells.

A molecular basis for integrin alphaMbeta 2 ligand binding promiscuity

The leukocyte integrin alpha(M)beta(2) is a highly promiscuous leukocyte receptor capable of binding a multitude of unrelated ligands. To understand the molecular basis for the broad ligand recognition of alpha(M)beta(2), the inter-integrin chimera was created. In the chimeric integrin, the betad-alpha5 loop-alpha5 helix segment comprised of residues Lys(245)-Arg(261) from the alpha(M)I domain of alpha(M)beta(2) was inserted into the framework of alpha(L)beta(2). The construct was expressed in HEK 293 cells, and the ability of generated cells to adhere to fibrinogen and its derivatives was characterized first. Grafting the alpha(M)(Lys(245)-Arg(261)) sequence converted alpha(L)beta(2) into a fibrinogen-binding protein capable of mediating efficient and specific adhesion similar to that of wild-type alpha(M)beta(2). Verifying a switch in the binding specificity of alpha(L)beta(2), the chimeric receptor became competent to support cell migration to fibrinogen. Mutations at positions Phe(246), Asp(254), and Pro(257) within Lys(245)-Arg(261) of alpha(M)beta(2) produced significant decreases in cell adhesion, illustrating the critical role of these residues in ligand binding. The insertion of alpha(M)(Lys(245)-Arg(261)) imparted to the chimeric integrin the ability to recognize many typical alpha(M)beta(2) protein ligands. Furthermore, cells expressing the chimeric receptor, but not alpha(L)beta(2), were able to stick to uncoated plastic, which represents the hallmark of wild-type alpha(M)beta(2). These results suggest that alpha(M)(Lys(245)-Arg(261)) serves as a consensus binding site for interaction with a variety of distinct molecules and, thus, may define the degenerate recognition properties inherent to alpha(M)beta(2).

Degranulation of primary and secondary granules in adherent human neutrophils

The aim of this study was to investigate whether neutrophil adhesion to extracellular matrix proteins like fibronectin, fibrinogen, and albumin influence the release proteins from primary and secondary granules of neutrophils stimulated by phorbol-myristate-acetate (PMA) and formyl-methionyl-leucyl-phenylalanine (f-MLP). Isolated granulocytes plated on wells coated with fibronectin, fibrinogen, and albumin were stimulated with f-MLP (10-7 mol/l), PMA (10-9 mol/l), Mn2+ (5 mmol/l), or combinations of these stimuli, and the degree of adhesion to protein-coated surfaces and the amount of granule proteins released was quantified during 90 min of incubation. PMA, in combination with Mn2+, induced a maximum release of approximately 80% of the intracellular content of lactoferrin and human neutrophil lipocalin (HNL) and 15-20% of the myeloperoxidase (MPO) content regardless of the protein used. PMA or f-MLP alone induced 30-40% release of lactoferrin and HNL depending on the protein that the cells were plated on. Adhesion and release of lactoferrin and HNL were quantitatively related when induced by PMA and PMA plus Mn2+, but not by f-MLP. The mean release of lactoferrin and HNL showed a significant negative relationship to the viability of the cells. In conclusion, adhesion modulates neutrophil degranulation, but it is not always quantitatively related or related in time.

CXCR2 regulation of tumor necrosis factor-alpha adherence-dependent peroxide production is significantly diminished after severe injury in human neutrophils

BACKGROUND

Primed neutrophils are thought to play a key role in inflammatory pathology. We have shown though in vitro studies that interleukin (IL)-8 and growth-related oncogene-alpha (GROalpha) (CXCR2-specific chemokines) regulate the respiratory burst via the CXCR2 receptor. We have also shown in vivo, CXCR2 receptors are down-regulated in severely injured patients. Our hypothesis is that regulation of the respiratory burst by CXCR2 is lost after severe injury.

METHODS

Patient neutrophils were studied within 24 hours of admission to the hospital; excluded were severe head injury and patients with Injury Severity Score < 16. Patient and normal neutrophils were isolated by Ficoll-Hypaque centrifugation after dextran sedimentation. Neutrophils were plated with buffer, 50 nmol/L IL-8 or GROalpha on fibronectin-coated plates for 15 minutes, then stimulated with 10 ng/mL of TNFalpha. CXCR2 expression was measured by flow cytometry. Receptor function was assessed by calcium mobilization.

RESULTS

One female and 10 male patients with an average age of 37 +/- 3 and Injury Severity Score of 24 +/- 5 suffered blunt injury. CXCR2 showed a 32% +/- 7% loss, whereas CXCR1 showed 15% +/- 6% reduction. GROalpha stimulation of patient neutrophils showed 60% +/- 16% decrease in calcium mobilization, whereas IL-8 showed no decline. At 40 minutes, IL-8 and GROalpha significantly inhibited TNFalpha adherence-dependent peroxide production in normal neutrophils (35% +/- 4% and 45% +/- 3%, respectively; p < 0.05). Both IL-8 and GROalpha lost the ability to suppress the respiratory burst in severely injured patients, but GROalpha had a significantly greater loss of this suppression (p = 0.004).

CONCLUSION

IL-8 and GROalpha lose the ability to regulate the TNFalpha-induced respiratory burst. This may contribute to neutrophil dysregulation after injury and result in organ injury.

Agonist-induced adherence of equine neutrophils to fibronectin- and serum-coated plastic is CD18 dependent

Adherence to vascular endothelium and extracellular matrix proteins is a pre-requisite for neutrophil accumulation at sites of inflammation. In this study, equine neutrophil adherence to fibronectin and autologous serum-coated plastic in response to PAF, hrIL-8, hrC5a and PMA has been measured. In addition, the mechanisms involved have been investigated using monoclonal antibodies (MoAbs) against the beta2 integrin CD18. PAF and hrC5a caused similar, concentration dependent, increases in adherence to fibronectin- and serum-coated plastic (maximum responses 19 +/- 4% and 19 +/- 3% for PAF and 15 +/- 4% and 16 +/- 2% for hrC5a on fibronectin- and serum-coated plastic, respectively). Adherence in response to PMA, although not reaching a maximum over the time course studied, was of a similar magnitude on the two surfaces (41 +/- 1% and 38 +/- 2% with 10(-7) M PMA on fibronectin- and serum-coated plastic, respectively). In contrast, the maximum adherence caused by hrIL-8 was significantly lower on fibronectin- than on serum-coated plastic (9 +/- 3% vs. 17 +/- 2%; 10(8) x M hrIL-8). Pre-incubation with MoAbs against CD18 (H20A and 6.5E) caused concentration related inhibition of stimulus-induced adherence to both fibronectin- and serum-coated plastic. Equine neutrophil adherence in response to PAF, hrIL-8, hrC5a and PMA therefore appears to be mediated by a CD18 dependent mechanism.

Simultaneous analysis of eosinophil and neutrophil adhesion to plasma and tissue fibronectin, fibrinogen, and albumin

A simple and convenient assay for the simultaneous measurement of eosinophil and neutrophil adhesion is described. Incubations were performed in microtitre plates coated with different proteins. Adhesion of eosinophils and neutrophils was determined by the use of specific radioimmunoassays for eosinophil cationic protein (ECP) and myeloperoxidase (MPO). Using this assay, Mn2+ induced a significant increase of the adhesion of eosinophils to plasma fibronectin and fibrinogen in a time-dependent fashion, while a small increase of the adhesion of neutrophils to these two proteins was observed. In contrast, a time-dependent potent increment of the adhesion of both eosinophils and neutrophils to tissue fibronectin and albumin was found. Tissue fibronectin preferentially supported eosinophil adhesion compared with that of neutrophils in the presence of Mn2+. PMA (10(-9) mol/l) induced a significant increase in the adhesion of eosinophils and neutrophils of the same pattern to all four proteins. However, when granulocytes were stimulated by Mn2+ in combination with PMA, eosinophils and neutrophils showed different patterns of response to plasma fibronectin and fibrinogen, respectively, but the same pattern of response to tissue fibronectin. f-MLP stimulated an early increase of the adhesion of neutrophils to fibrinogen, while a weak stimulation of the adhesion of eosinophils to plasma fibronectin and fibrinogen and of neutrophils to plasma fibronectin was observed. Co-stimulation with f-MLP and Mn2+ did not induce any additive effects on granulocyte adhesion. In conclusion, the assay allows rapid quantification of eosinophil and neutrophil adhesion and can be used to directly compare the response of neutrophils and eosinophils. The assay is thus suitable for studies aimed at identifying agents with a selective effect on either of the cells.

Actin polymerization induces shedding of FcgammaRIIIb (CD16) from human neutrophils

FcgammaRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcgammaRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcgammaRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcgammaRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcgammaRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcgammaRIIIb. This effect was not restricted to FcgammaRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.

Triggering of Chloride Ion Efflux from Human Neutrophils as a Novel Function of Leukocyte β2 Integrins: Relationship with Spreading and Activation of the Respiratory Burst

PMN residing on immobilized fibronectin have been shown to respond to TNF with an intense and long lasting Cl− efflux that leads to a marked decrease of the unusually high basal Cl− content of these phagocytes. The finding that this Cl− efflux depends, at least in part, on β2 integrin engagement stimulated the present investigation, which addresses the question as to whether β2 integrins per se, in the absence of PMN agonists, are able to generate signals triggering Cl− efflux. We induced β2 integrin cross-linking by plating PMN onto surface-bound mAbs directed against either the common β-chain (CD18) or the individual α-chains (CD11a, CD11b, CD11c) of LFA-1, CR3, and gp150/95. Anti-CD18 mAbs triggered a marked release of Cl− ions, which was accompanied by spreading and activation of the respiratory burst. Cross-linking of gp150/95 and LFA-1 generated the most powerful signals for the activation of Cl− efflux. The results of three independent experimental approaches, i.e., kinetic studies, use of Cl− transport inhibitors, and modulation of Cl− efflux with different amounts of anti-β2 integrin mAbs, indicated that Cl− efflux regulates both spreading and respiratory burst triggered by β2 integrin cross-linking. Cl− efflux appears to be independent on either alterations of [Ca2+]i or changes in the plasma membrane potential and shows sensitivity to a raise in pHi. This study uncovers a new signaling ability of β2 integrins and contributes to highlight the role of Cl− efflux in the outside-in signal transduction pathway regulating adherence-dependent PMN responses.

Human Polymorphonuclear Leukocytes Adhere to Complement Factor H Through an Interaction That Involves αMβ2 (CD11b/CD18)

The work presented here demonstrates that human complement factor H is an adhesion ligand for human neutrophils but not for eosinophils. The adherence of polymorphonuclear leukocytes (PMNs) to plastic wells coated with factor H depended on divalent metal ions and was augmented by C5a and TNF-α. PMN adhesion to factor H in the presence or absence of C5a was blocked specifically by mAbs against CD11b or CD18. Affinity purification using factor H Sepharose followed by immunoprecipitation using mAbs to various integrin chains identified Mac-1 (CD11b/CD18) as a factor H binding receptor. The presence of surface bound factor H enhanced neutrophil activation resulting in a two- to fivefold increase in the generation of hydrogen peroxide by PMNs stimulated by C5a or TNF-α. When factor H was mixed with PMNs, 1.4 to 3.8-fold more cells adhered to immobilized heparin or chondroitin A. In addition, augmented adhesion of PMNs was measured when factor H, but not HSA or C9, was absorbed to wells that were first coated with heparin or chondroitin A. The adhesion of PMNs to glycosaminoglycan-factor H was blocked by mAbs to CD11b and CD18. These studies demonstrate that factor H is an adhesion molecule for human neutrophils and suggest that the interaction of factor H with glycosaminoglycans may facilitate the tethering of this protein in tissues allowing factor H to serve as a neutrophil adhesion ligand in vivo.

Neutrophil expression of CD11b/CD18 and IL-8 secretion during normothermic cardiopulmonary bypass

OBJECTIVE

To assess blood polymorphonuclear neutrophil (PMN) activation status during normothermic cardiopulmonary bypass (CPB), the expression of the PMN adhesion molecule CD11b/CD18 was measured. Basal state as well as ex vivo capacity of PMN to be stimulated by a bacterial peptide (FMLP) were investigated. Because interleukin-8 (IL-8) is known to induce CD11b/CD18 expression in vitro in PMN, IL-8 plasma levels were concomitantly measured.

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Thirteen patients scheduled for cardiac surgery.

INTERVENTIONS

Systemic arterial and pulmonary arterial blood samples were withdrawn at the same moment during the first 4 hours after the onset of CPB.

MEASUREMENTS AND MAIN RESULTS

Twenty minutes after the onset of CPB, basal expression of PMN CD11b/CD18 was upregulated, whereas IL-8 plasma levels remained unchanged. The increase in PMN CD11b expression was maintained until the fourth hour after the onset of CPB. At this time, elevation of IL-8 plasma levels was maximal. No differences were found between pulmonary and systemic arterial IL-8 plasma levels, even after aortic unclamping. The capacity of PMN to be stimulated ex vivo by FMLP remained normal.

CONCLUSIONS

Normothermic CPB induced a fast increase in CD11b expression, which appeared to be similar to that observed during hypothermia. IL-8 was probably not related to the very early CD11b upregulation, but could be involved in pulmonary PMN sequestration during pulmonary reperfusion and contribute to the maintained expression of PMN CD11b. Although partially activated, PMNs maintain a normal capacity to respond to a further FMLP stimulation and thus to bacterial infection.

Endogenous fibronectin of blood polymorphonuclear leukocytes: stimulus-induced secretion and proteolysis by cell surface-bound elastase

In an accompanying study, we described the presence of intact fibronectin, a large adhesive molecule, in the specific granules of blood PMNs. Secretion of fibronectin by blood PMNs is poorly understood, and the fate of this fibronectin is practically unknown. In the present study we demonstrate that nanomolar concentrations of phorbol ester or the chemoattractants fMLP, PAF, and LTB4 induce fibronectin secretion from blood PMNs. Phorbol ester induced secretion of approximately 85% of the total fibronectin content, as well as expression of small amounts on the cell surface of the activated PMNs. Secreted fibronectin was proteolytically cleaved and, after 20 min, four major fragments of 150, 120, 90, and 80 kDa containing a midchain epitope were identified by Western blot analysis. Kinetic studies indicated that fibronectin was rapidly secreted as an intact molecule and that proteolysis started within minutes and proceeded for at least 1 h. If cells were removed after 5 min TPA treatment, no further proteolysis of the secreted fibronectin was observed, indicating participation of cell-bound proteinases. From a cocktail of proteinase inhibitors, PMSF was the most active in suppressing fibronectin proteolysis. Studies with specific peptidyl inhibitors of human leukocyte elastase and cathepsin G, major serine proteinases of PMNs, demonstrated some inhibition with the cathepsin G inhibitor, while the human leukocyte elastase inhibitor almost completely abolished fibronectin proteolysis. A monoclonal antibody to the elastase had a similar effect. The results indicate that intact fibronectin is a secretory product of blood PMNs and that this endogenous adhesive molecule is within minutes extracellularly processed by cell surface-bound elastase.

Endogenous fibronectin of blood polymorphonuclear leukocytes: immunochemical characterization and subcellular localization

Fibronectin, a large dimeric glycoprotein synthesized and secreted by several cell types, mediates cell adherence to surfaces. In infections and inflammatory responses, blood polymorphonuclear leukocytes (PMNs) adhere to cells and matrix proteins during extravasation and accumulation at inflammatory sites. The presence of fibronectin in blood PMNs has been poorly studied, and the characteristics and subcellular localization of this endogenous adhesive molecule are practically unknown. By immunofluorescence flow cytometry, purified rabbit antibodies and a monoclonal antibody to plasma fibronectin reacted with isolated blood PMNs, only after permeabilization of the cells. By Western blot analysis, the antibodies recognized, under reducing conditions, a protein with an apparent molecular mass of 230 kDa in the cell lysate. Eleven monoclonal antibodies to common frame fibronectin epitopes, including the RGD-containing cell-binding domain, also reacted with PMN fibronectin by Western blotting. In contrast, two antibodies to ED-A, the alternatively spliced region characteristic of "cellular" fibronectin, were unreactive, but recognized platelet fibronectin. On average, 1 million PMNs contained 6.8 ng +/- 1.4 (SD) of fibronectin, as measured by sandwich ELISA. Immunogold labeling and electron microscopy studies indicated localization of most fibronectin in PMN granules. Moreover, double-immunofluorescence and digital image analysis demonstrated colocalization of fibronectin with lactoferrin, a marker of specific (secondary) granules. The results indicate that blood PMNs contain approximately 8000 molecules per cell of intact ED-A-negative fibronectin localized mainly in their specific granules.

Chloride ion efflux regulates adherence, spreading, and respiratory burst of neutrophils stimulated by tumor necrosis factor-alpha (TNF) on biologic surfaces

Chloride ion efflux is an early event occurring after exposure of neutrophilic polymorphonuclear leukocytes (PMN) in suspension to several agonists, including cytokines such as tumor necrosis factor-alpha (TNF) and granulocyte/macrophage-colony stimulating factor (Shimizu, Y., R.H. Daniels, M.A. Elmore, M.J. Finnen, M.E. Hill, and J.M. Lackie. 1993. Biochem. Pharmacol. 9:1743-1751). We have studied TNF-induced Cl- movements in PMN residing on fibronectin (FN) (FN-PMN) and their relationships to adherence, spreading, and activation of the respiratory burst. Occupancy of the TNF-R55 and engagement of beta 2 integrins cosignaled for an early, marked, and prolonged Cl- efflux that was accompanied by a fall in intracellular chloride levels (Cl-i). A possible causal relationship between Cl- efflux, adherence, and respiratory burst was first suggested by kinetic studies, showing that TNF-induced Cl- efflux preceded both the adhesive and metabolic response, and was then confirmed by inhibition of all three responses by pretreating PMN with inhibitors of Cl- efflux, such as ethacrynic acid. Moreover, Cl- efflux induced by means other than TNF treatment, i.e., by using Cl(-)-free media, was followed by increased adherence, spreading, and metabolic activation, thus mimicking TNF effects. These studies provide the first evidence that a drastic decrease of Cl-i in FN-PMN may represent an essential step in the cascade of events leading to activation of proadhesive molecules, reorganization of the cytoskeleton network, and assembly of the O2(-)-forming NADPH oxidase.

Fibrin regulates neutrophil migration in response to interleukin 8, leukotriene B4, tumor necrosis factor, and formyl-methionyl-leucyl-phenylalanine

We have examined the capacity of four different chemoattractants/cytokines to promote directed migration of polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of extracellular matrix proteins. About 20% of PMN migrated through fibrin gels and plasma clots in response to a gradient of interleukin 8 (IL-8) or leukotriene B4 (LTB4). In contrast, < 0.3% of PMN migrated through fibrin gels in response to a gradient of tumor necrosis factor alpha (TNF) or formyl-methionyl-leucyl-phenylalanine (FMLP). All four chemoattractants stimulated PMN to migrate through gels composed of collagen IV or of basement membrane proteins (Matrigel), or through filters to which fibronectin or fibrinogen had been adsorbed. PMN stimulated with TNF or FMLP adhered and formed zones of close apposition to fibrin, as measured by the exclusion of a 10-kD rhodamine-polyethylene glycol probe from the contact zones between PMN and the underlying fibrin gel. By this measure, IL-8- or LTB4-treated PMN adhered loosely to fibrin, since 10 kD rhodamine-polyethylene glycol permeated into the contact zones between these cells and the underlying fibrin gel. PMN stimulated with FMLP and IL-8, or FMLP and LTB4, exhibited very little migration through fibrin gels, and three times as many of these cells excluded 10 kD rhodamine-polyethylene glycol from their zones of contact with fibrin as PMN stimulated with IL-8 or LTB4 alone. These results show that PMN chemotaxis is regulated by both the nature of the chemoattractant and the composition of the extracellular matrix; they suggest that certain combinations of chemoattractants and matrix proteins may limit leukocyte movements and promote their localization in specific tissues in vivo.

Involvement of LFA-1 and ICAM-1 in the herpetic disease resulting from HSV-1 corneal infection

Herpes simplex virus type 1 (HSV-1) corneal infection in immunologically normal mice results in a transient epithelial lesion followed in about 2 weeks by a potentially blinding inflammatory response in the corneal stroma, and a mild blepharitis. Similarly infected T cell-deficient mice do not develop corneal stromal inflammation, but exhibit severe periocular skin disease and succumb to viral encephalitis. The role of certain adhesion molecules in both T cell activation, and in the extravasation of inflammatory cells from the blood into inflammatory sites is now being established. These studies investigated the involvement of the adhesion pair LFA-1/ICAM-1 in the disease that results from HSV-1 corneal infection in mice. Treatment of mice with mAb to LFA-1 beginning 1 day before HSV-1 corneal infection resulted in a delay in the onset of stromal inflammation, but ultimately stromal inflammation developed to a normal extent. This treatment also caused a significant exacerbation of periocular skin disease, but did not render mice susceptible to encephalitis. Treatment with mAb to ICAM-1 beginning 1 day before HSV-1 corneal infection caused an acceleration of both stromal inflammation and periocular skin disease, and rendered mice uniformly susceptible to lethal encephalitis. Treatment with either mAb beginning 6 days after HSV-1 corneal infection did not significantly affect the clinical course of herpetic disease. Our findings suggest that LFA-1 may play a role in the early phase of corneal stromal inflammation following HSV-1 corneal infection. Both LFA-1 and ICAM-1 appear to be important for protection of the skin from HSV-1 infection.(ABSTRACT TRUNCATED AT 250 WORDS)