Intracellular localization of a leukocyte adhesion glycoprotein family in the tertiary granules of human neutrophils

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

Neutrophils drive endoplasmic reticulum stress-mediated apoptosis in cancer cells through arginase-1 release

Human neutrophils constitutively express high amounts of arginase-1, which depletes arginine from the surrounding medium and downregulates T-cell activation. Here, we have found that neutrophil arginase-1, released from activated human neutrophils or dead cells, induced apoptosis in cancer cells through an endoplasmic reticulum (ER) stress pathway. Silencing of PERK in cancer cells prevented the induction of ER stress and apoptosis. Arginase inhibitor Nω-hydroxy-nor-arginine inhibited apoptosis and ER stress response induced by conditioned medium from activated neutrophils. A number of tumor cell lines, derived from different tissues, were sensitive to neutrophil arginase-1, with pancreatic, breast, ovarian and lung cancer cells showing the highest sensitivity. Neutrophil-released arginase-1 and arginine deprivation potentiated the antitumor action against pancreatic cancer cells of the ER-targeted antitumor alkylphospholipid analog edelfosine. Our study demonstrates the involvement of neutrophil arginase-1 in cancer cell killing and highlights the importance and complex role of neutrophils in tumor surveillance and biology.

L-selectin expression is regulated by CXCL8-induced reactive oxygen species produced during human neutrophil rolling

Neutrophils destroy invading microorganisms by phagocytosis by bringing them into contact with bactericidal substances, among which ROS are the most important. However, ROS also function as important physiological regulators of cellular signaling pathways. Here, we addressed the involvement of oxygen derivatives in the regulation of human neutrophil rolling, an essential component of the inflammatory response. Flow experiments using dihydroethidium-preloaded human neutrophils showed that these cells initiate an early production of intracellular ROS during the rolling phase of the adhesion cascade, a phenomenon that required cell rolling, and the interaction of the chemokine receptor CXCR2 with their ligand CXCL8. Flow cytometry experiments demonstrated that L-selectin shedding in neutrophils is triggered by ROS through an autocrine-paracrine mechanism. Preincubation of neutrophils with the NADPH oxidase complex inhibitor diphenyleniodonium chloride significantly increased the number of rolling neutrophils on endothelial cells. Interestingly, the same effect was observed when CXCL8 signaling was interfered using either a blocking monoclonal antibody or an inhibitor of its receptor. These findings indicate that, in response to CXCL8, neutrophils initiate ROS production during the rolling phase of the inflammatory response. This very early ROS production might participate in the modulation of the inflammatory response by inducing L-selectin shedding in neutrophils.

Non-invasive near-infrared fluorescence imaging of the neutrophil response in a mouse model of transient cerebral ischaemia

Near-infrared fluorescence (NIRF) imaging enables non-invasive monitoring of molecular and cellular processes in live animals. Here we demonstrate the suitability of NIRF imaging to investigate the neutrophil response in the brain after transient middle cerebral artery occlusion (tMCAO). We established procedures for ex vivo fluorescent labelling of neutrophils without affecting their activation status. Adoptive transfer of labelled neutrophils in C57BL/6 mice before surgery resulted in higher fluorescence intensities over the ischaemic hemisphere in tMCAO mice with NIRF imaging when compared with controls, corroborated by ex vivo detection of labelled neutrophils using fluorescence microscopy. NIRF imaging showed that neutrophils started to accumulate immediately after tMCAO, peaking at 18 h, and were still visible until 48 h after reperfusion. Our data revealed accumulation of neutrophils also in extracranial tissue, indicating damage in the external carotid artery territory in the tMCAO model. Antibody-mediated inhibition of α4-integrins did reduce fluorescence signals at 18 and 24, but not at 48 h after reperfusion, compared with control treatment animals. Antibody treatment reduced cerebral lesion volumes by 19%. In conclusion, the non-invasive nature of NIRF imaging allows studying the dynamics of neutrophil recruitment and its modulation by targeted interventions in the mouse brain after transient experimental cerebral ischaemia.

Human polymorphonuclear neutrophils express RANK and are activated by its ligand, RANKL

The receptor activator of NF-κB (RANK) is especially well studied in the context of bone remodeling, and RANK and its ligand, RANKL, are key molecules in the induction of bone resorbing osteoclasts. We now report that polymorphonuclear neutrophils (PMNs) contain preformed RANK, stored in secretory vesicles and in specific granules. Upon stimulation of PMNs in vitro, RANK was translocated to the cell membrane. In patients with persistent bacterial infections, RANK surface expression was enhanced compared with that of healthy individuals. The functional activity of RANK was assessed by determining migration of PMNs toward RANKL. A time- and dose-dependent migration was seen, leading to the conclusion that RANK on PMNs is functional. We presume that regulated RANK expression contributes to the fine tuning of PMN migration, for example, on and through inflamed endothelium that is known to express RANKL.

Selective fusion of azurophilic granules with Leishmania-containing phagosomes in human neutrophils

Leishmania parasites use polymorphonuclear neutrophils as intermediate hosts before their ultimate delivery to macrophages following engulfment of parasite-infected neutrophils. This leads to a silent and unrecognized entry of Leishmania into the macrophage host cell. Neutrophil function depends on its cytoplasmic granules, but their mobilization and role in how Leishmania parasites evade intracellular killing in neutrophils remain undetermined. Here, we have found by ultrastructural approaches that neutrophils ingested Leishmania major promastigotes, and azurophilic granules fused in a preferential way with parasite-containing phagosomes, without promoting parasite killing. Azurophilic granules, identified by the granule marker myeloperoxidase, also fused with Leishmania donovani-engulfed vacuoles in human neutrophils. In addition, the azurophilic membrane marker CD63 was also detected in the vacuole surrounding the parasite, and in the fusion of azurophilic granules with the parasite-engulfed phagosome. Tertiary and specific granules, involved in vacuole acidification and superoxide anion generation, hardly fused with Leishmania-containing phagosomes. L. major interaction with neutrophils did not elicit production of reactive oxygen species or mobilization of tertiary and specific granules. By using immunogold electron microscopy approaches in the engulfment of L. major and L. donovani by human neutrophils, we did not find a significant contribution of endoplasmic reticulum to the formation of Leishmania-containing vacuoles. Live Leishmania parasites were required to be optimally internalized by neutrophils. Our data suggest that Leishmania promastigotes modulate their uptake by neutrophils, and regulate granule fusion processes in a rather selective way to favor parasite survival in human neutrophils.

Rab27a regulates exocytosis of tertiary and specific granules in human neutrophils

The correct mobilization of cytoplasmic granules is essential for the proper functioning of human neutrophils in host defense and inflammation. In this study, we have found that human peripheral blood neutrophils expressed high levels of Rab27a, whereas Rab27b expression was much lower. This indicates that Rab27a is the predominant Rab27 isoform present in human neutrophils. Rab27a was up-regulated during neutrophil differentiation of HL-60 cells. Subcellular fractionation and immunoelectron microscopy studies of resting human neutrophils showed that Rab27a was mainly located in the membranes of specific and gelatinase-enriched tertiary granules, with a minor localization in azurophil granules. Rab27a was largely absent from CD35-enriched secretory vesicles. Tertiary and specific granule-located Rab27a population was translocated to the cell surface upon neutrophil activation with PMA that induced exocytosis of both tertiary and specific granules. Specific Abs against Rab27a inhibited Ca(2+) and GTP-gamma-S activation and PMA-induced exocytosis of CD66b-enriched tertiary and specific granules in electropermeabilized neutrophils, whereas secretion of CD63-enriched azurophil granules was scarcely affected. Human neutrophils lacked or expressed low levels of most Slp/Slac2 proteins, putative Rab27 effectors, suggesting that additional proteins should act as Rab27a effectors in human neutrophils. Our data indicate that Rab27a is a major component of the exocytic machinery of human neutrophils, modulating the secretion of tertiary and specific granules that are readily mobilized upon neutrophil activation.

Role of vesicle-associated membrane protein-2, through Q-soluble N-ethylmaleimide-sensitive factor attachment protein receptor/R-soluble N-ethylmaleimide-sensitive factor attachment protein receptor interaction, in the exocytosis of specific and tertiary granules of human neutrophils

We have examined the role of the R-soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) synaptobrevin-2/vesicle-associated membrane protein (VAMP)-2 in neutrophil exocytosis. VAMP-2, localized in the membranes of specific and gelatinase-containing tertiary granules in resting human neutrophils, resulted translocated to the cell surface following neutrophil activation under experimental conditions that induced exocytosis of specific and tertiary granules. VAMP-2 was also found on the external membrane region of granules docking to the plasma membrane in activated neutrophils. Specific Abs against VAMP-2 inhibited Ca(2+) and GTP-gamma-S-induced exocytosis of CD66b-enriched specific and tertiary granules, but did not affect exocytosis of CD63-enriched azurophilic granules, in electropermeabilized neutrophils. Tetanus toxin disrupted VAMP-2 and inhibited exocytosis of tertiary and specific granules. Activation of neutrophils led to the interaction of VAMP-2 with the plasma membrane Q-SNARE syntaxin 4, and anti-syntaxin 4 Abs inhibited exocytosis of specific and tertiary granules in electropermeabilized neutrophils. Immunoelectron microscopy showed syntaxin 4 on the plasma membrane contacting with docked granules in activated neutrophils. These data indicate that VAMP-2 mediates exocytosis of specific and tertiary granules, and that Q-SNARE/R-SNARE complexes containing VAMP-2 and syntaxin 4 are involved in neutrophil exocytosis.

Downregulation of mac-1 expression in monocytes by surface-bound IgG

Physical and functional association between the beta2-integrin Mac-1 (CD11b/CD18) and receptors of immunoglobulin G (IgG) (FcgammaRs) has been previously reported. In this study, we examined the modulation of Mac-1 expression by IgG in different leucocyte populations. Our data show that human monocytes, but not neutrophils, macrophages, dendritic or natural killer cells, downregulate the expression of Mac-1 after overnight exposure to surface-bound IgG. This effect, which requires at least 6 h of incubation, is not associated with a general downmodulation of membrane antigens, and is selectively induced by immobilized IgG (iIgG), as the stimulation of monocytes with N-formyl-methionyl-leucyl-phenylalanine, lipopolysaccharide, tumour necrosis factor-alpha (TNF-alpha) or soluble IgG did not modify the Mac-1 expression after 18 h in culture. The loss of Mac-1 was completely prevented by blocking antibodies (Abs) directed to FcgammaRII (CD32) or CD18. On the other hand, the serine protease inhibitor, phenyl methyl sulphonyl fluoride, but not inhibitors of cysteine proteases or neutral endopeptidases, partially prevented the downregulation of Mac-1 by iIgG. Monocytes cultured overnight on iIgG exhibited a dramatic decrease in their capacity to ingest zymosan particles that could be attributed to the reduced expression of Mac-1. However, there was no inhibition of TNF-alpha production induced by zymosan, suggesting that Mac-1-dependent responses require different levels of its expression to be fully activated.

Involvement of SNAP-23 and syntaxin 6 in human neutrophil exocytosis

To understand the molecular basis of exocytosis in human neutrophils, the role of syntaxin 6 and SNAP-23 in neutrophil degranulation was examined. Human syntaxin 6 was cloned and identified as a 255-amino acid protein with a carboxy-terminal transmembrane region and two coiled-coil domains. Syntaxin 6 was localized mainly in the plasma membrane of human resting neutrophils, whereas SNAP-23 was located primarily in the mobilizable tertiary and specific granules. SNAP-23 was translocated to the cell surface, colocalizing with syntaxin 6, on neutrophil activation. In vitro binding studies established that SNAP-23 binds to syntaxin 6. Coimmunoprecipitation assays indicated that SNAP-23 interacts with syntaxin 6 in vivo, and this interaction was dramatically increased on neutrophil activation. Antibodies against SNAP-23 inhibited Ca++ and GTP-γ-S–induced exocytosis of CD67-enriched specific granules, but they hardly affected exocytosis of the CD63-enriched azurophilic granules, when introduced into electropermeabilized neutrophils. Anti–syntaxin 6 antibodies prevented exocytosis of both CD67- and CD63-enriched granules in electropermeabilized neutrophils. These data show that syntaxin 6 and SNAP-23 are involved in human neutrophil exocytosis, demonstrating that vesicle SNAP receptor-target SNAP receptor (v-SNARE– t-SNARE) interactions modulate neutrophil secretion. Syntaxin 6 acts as a target for secretion of specific and azurophilic granules, whereas SNAP-23 mediates specific granule secretion.

Involvement of SNAP-23 and syntaxin 6 in human neutrophil exocytosis

To understand the molecular basis of exocytosis in human neutrophils, the role of syntaxin 6 and SNAP-23 in neutrophil degranulation was examined. Human syntaxin 6 was cloned and identified as a 255-amino acid protein with a carboxy-terminal transmembrane region and two coiled-coil domains. Syntaxin 6 was localized mainly in the plasma membrane of human resting neutrophils, whereas SNAP-23 was located primarily in the mobilizable tertiary and specific granules. SNAP-23 was translocated to the cell surface, colocalizing with syntaxin 6, on neutrophil activation. In vitro binding studies established that SNAP-23 binds to syntaxin 6. Coimmunoprecipitation assays indicated that SNAP-23 interacts with syntaxin 6 in vivo, and this interaction was dramatically increased on neutrophil activation. Antibodies against SNAP-23 inhibited Ca++ and GTP-γ-S–induced exocytosis of CD67-enriched specific granules, but they hardly affected exocytosis of the CD63-enriched azurophilic granules, when introduced into electropermeabilized neutrophils. Anti–syntaxin 6 antibodies prevented exocytosis of both CD67- and CD63-enriched granules in electropermeabilized neutrophils. These data show that syntaxin 6 and SNAP-23 are involved in human neutrophil exocytosis, demonstrating that vesicle SNAP receptor-target SNAP receptor (v-SNARE– t-SNARE) interactions modulate neutrophil secretion. Syntaxin 6 acts as a target for secretion of specific and azurophilic granules, whereas SNAP-23 mediates specific granule secretion.

Corticotropin-Releasing Factor Receptor 1 in Mouse Spleen: Expression After Immune Stimulation and Identification of Receptor-Bearing Cells

A specific polyclonal Ab against the N-terminal domain of corticotropin-releasing factor (CRF) receptor, type 1 (CRF-R1), was employed to an immunohistochemical analysis of the spleen from naive mice and mice exposed to an immune challenge. Cell types stained with anti-CRF-R1 Ab were identified by their nuclear shapes and colocalization with the cell type-specific markers ER-MP58, ER-MP20, Moma-1, Moma 2, anti-CD3e mAbs, and anti-Ig Ab. Only a few clusters of CRF-R1+ cells were found in spleen sections of naive mice at sites typical for granulopoietic islands. However, a 17-fold increase in the mean number of CRF-R1+ cells was noted within hours following a challenge of acute systemic inflammation induced by i.p. administration of LPS. The majority of these cells were identified as mature neutrophils. CRF-R1 was shown to mediate suppression of the IL-1β secretion by these cells. However, at later time points a large number of granulocyte-macrophage precursors was strongly labeled with anti-CRF-R1 Ab. Western blot analysis of splenic membranes from animals treated with LPS revealed a m.w. of approximately 70,000 for CRF-R1. Subcellular staining patterns were suggestive for the predominant localization of CRF-R1 on granule membranes. CRF-R1 mRNA was detected in spleen but not in bone marrow and peripheral blood leukocytes from naive mice. Thus, it was indicated that CRF-R1 was not produced constitutively by mature or immature neutrophils. Its production was rather triggered by inflammatory stimuli.

Major co-localization of the extracellular-matrix degradative enzymes heparanase and gelatinase in tertiary granules of human neutrophils

The expression of cell-surface adhesion proteins and the release of extracellular-matrix degradative enzymes constitute crucial processes for the attachment of neutrophils to the endothelium and for the subsequent extravasation of these cells through the endothelial layer. We have analysed in resting human neutrophils the subcellular localization of heparanase, a heparan-sulphate-degrading endoglycosidase that can degrade basement-membrane components, thereby facilitating neutrophil passage into the tissue during an inflammatory reaction. By subcellular fractionation of postnuclear supernatants from resting human neutrophils on continuous sucrose gradients, we have found that heparanase activity was mainly located in gelatinase-containing tertiary granules. Using a specific antibody, the 96-kDa heparanase protein was further located in the gelatinase-rich subcellular fractions. Following immunoblotting and immunoprecipitation analysis in the distinct subcellular fractions, we also found co-localization of heparanase and Mo1 (CD11b/CD18), a leucocyte integrin involved in the attachment of neutrophils to the endothelium, in the fractions enriched in gelatinase-containing tertiary granules. Treatment of human neutrophils with tumour necrosis factor or granulocyte/macrophage colony-stimulating factor induced an increase in the CD11b/CD18 cell-surface expression, as well as the release of both gelatinase (matrix metalloproteinase-9) and heparanase, but not of other granule markers, indicating a major co-localization of gelatinase, heparanase and CD11b/CD18 in the same organelle. Furthermore, confocal laser scanning microscopy using specific antibodies against gelatinase and heparanase revealed a major co-localization of both enzymes in intracellular cytoplasmic granules. The major localization of heparanase and CD11b/CD18 in the gelatinase-containing tertiary granule supports the notion that mobilization of this organelle can regulate extravasation of human neutrophils.

Intracellular location of SNAP-25 in human neutrophils

Exocytosis plays an essential role in the physiological functions of human neutrophils. Although SNAP-25 is considered to play a key role in vesicle-membrane fusion, it has been detected almost exclusively in the neuronal system. Using different specific antibodies to SNAP-25, we have identified in the membrane fraction of resting human neutrophils an immunoreactive band with the same molecular mass observed in brain homogenates. Immunoblot analysis of subcellular fractions of neutrophils revealed that SNAP-25 protein was found in the granule membrane fraction, but not in the cytosolic and plasma membrane fractions. Granule localization for neutrophil SNAP-25 was further demonstrated by confocal and immunoelectron microscopy. Furthermore, SNAP-25 was mainly located in the morphologically defined neutrophil peroxidase-negative granules, which are mobilizable upon cell activation. In addition, the protein was specifically cleaved by botulinal neurotoxin A, as observed in brain homogenate. These findings reveal the presence of SNAP-25 in the granule membranes of human neutrophils.

Localization of rap1 and rap2 proteins in the gelatinase-containing granules of human neutrophils

The subcellular localization of rap proteins in resting human neutrophils was investigated by immunoblot analysis with specific anti-rap2 and anti-rap1 antibodies of the membrane proteins obtained from distinct subcellular fractions. Rap2 protein was mainly located in gelatinase-containing granules, whereas rap1 protein was detected both in gelatinase-containing granules and in fractions enriched in plasma membrane. Neither rap1 nor rap2 proteins were found in the cytosol or in azurophilic granules. Rap2B, not rap2A, appeared to be the major rap2 protein in human neutrophils. The identification and subcellular localization of rap1 and rap2 proteins at the membranes of gelatinase-rich granules suggest that these proteins could play a role in the regulation of the rapid and selective mobilization of gelatinase-containing granules in human neutrophils.

The damaging potential of leukocyte activation in the microcirculation

Traditionally leukocytes have been regarded as beneficial cells, owing to their immunologic and antimicrobial activity. Recent evidence suggests, however, an additional role of granulocytes and monocytes as mediators of cardiovascular complications, such as ischemia, reperfusion, diabetes, physiologic shock, venous ulceration, and other conditions. Granulocytes and monocytes have a large volume, and stiff cytoplasm; they have the ability to adhere to endothelium and to other substrates; and they exert several forms of cytotoxicity. Granulocytes and monocytes may be trapped in the microcirculation, may obstruct capillaries and thereby induce a no-reflow phenomenon, and may initiate organ dysfunction via oxygen free radical production and proteolytic cleavage. Few organs seem to be spared from the potential destructive actions of these cells, and novel approaches are required to interfere with leukocyte accumulation in local regions of the peripheral circulation.

Molecular basis for a severe case of leukocyte adhesion deficiency

The leukocyte integrins LFA-1, Mac-1 and p150,95 (CD11a/CD18, CD11b/CD18, CD11c/CD18) mediate crucial leukocyte adhesive functions in immune and inflammatory reactions. Leukocyte adhesion deficiency (LAD) disease is caused by the defective expression of these adhesion molecules on leukocytes, and is characterized by recurrent infections and impaired pus formation due to the blockade of leukocyte migration into inflamed tissues. LAD is originated by heterogeneous mutations affecting the CD18 gene and, based on the severity of the deficiency, two phenotypes (severe and moderate) have been defined. Biochemical and genetic studies have allowed the classification of five different types of LAD. We have identified a type V LAD patient (severe phenotype, and normal size and levels of both CD18 precursor and CD18 mRNA), and determined its molecular basis. Reverse transcription-polymerase chain reaction and cloning and sequencing of CD18 cDNA derived from this patient revealed three silent mutations and a missense mutation that leads to the substitution of glycine at position 169 for an arginine. Analysis of patient-derived cDNA clones revealed the concomitant presence of aberrant splicing within the 5' region of the CD18 gene. The description of an identical mutation at residue 169 in an unrelated severe LAD patient raises the possibility that severe LAD type V is caused by a unique genetic defect.

Thrombospondin receptor expression in human neutrophils coincides with the release of a subpopulation of specific granules

The extracellular matrix (ECM) protein thrombospondin (TSP) binds specifically to polymorphonuclear leucocyte (PMN) surface receptors and promotes cell adhesion and motility. TSP receptor expression increases 30-fold after activation with the synthetic chemotactic peptide, N-formylmethionyl-leucylphenylalanine (FMLP) or the Ca2+ ionophore A23187, in combination with cytochalasin B. The expression of TSP receptors was correlated with the exocytosis of both specific and azurophil granules. Newly expressed TSP receptors are not derived from easily mobilized specific granules since agents that trigger some specific granule release [phorbol myristate acetate (PMA), FMLP or ionophore A23187 alone] do not increase TSP receptor expression. In this study we used the anion-channel blocker, 4,4'-di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS) to investigate the source of these newly expressed receptors. When PMNs were exposed to cytochalasin B and FMLP or to cytochalasin B and ionophore A23187 in the presence of 30-100 microM-DIDS, TSP receptor expression increased coincidently with vitamin B12-binding protein release from specific granules. Under these same conditions, the release of the azurophil granule component, myeloperoxidase, was significantly inhibited. Using agonists that cause release of specific granules, or both specific granules and azurophil granules, we determined that DIDS blocked the release of PMA-mobilized specific granules and cytochalasin B plus FMLP- or cytochalasin B plus ionophore A23187-mobilized myeloperoxidase-containing azurophil granules but not specific granules mobilized by cytochalasin B plus FMLP or cytochalasin B plus ionophore A23187. These results suggested that PMNs contain at least two subpopulations of specific granules: one that is easily mobilized, lacks TSP receptors and is inhibitable by DIDS, and one that is difficult to mobilize, contains a large pool of TSP receptors and the release of which is enhanced in the presence of DIDS.

Biochemical and functional characterization of the leucocyte tyrosine phosphatase CD45 (CD45RO, 180 kD) from human neutrophils. In vivo upregulation of CD45RO plasma membrane expression on patients undergoing haemodialysis

The biochemical and functional characterization, and the regulation of plasma membrane expression of the leucocyte tyrosine phosphatase CD45, have been investigated in neutrophils from healthy donors and patients undergoing haemodialysis. CD45 proteins of 180 kD and 130-150 kD were precipitated from neutrophils from both healthy subjects and haemodialysed patients. Prolonged storing, as well as trypsin treatment of samples containing the 180-kD CD45 protein, generated the 130-150-kD polypeptides. The 130-150-kD CD45 polypeptides carried extracellular CD45 epitopes, including the sialic acid-related UCHL1 epitope (CD45RO). Furthermore, these trypsin-generated CD45 polypeptides did not possess phosphatase activity, which could be detected on the 180-kD protein. A remarkable quantitative increase of cell surface expression of the neutrophil CD45 components was detected both after in vitro neutrophil activation and after dialysis treatment with neutropenic membranes. The CD45 biochemical pattern did not qualitatively change upon either in vitro or in vivo dialysis-induced neutrophil activation. The upregulated expression of CD45 on neutrophils from dialysed patients correlated with the neutropenic effect induced by the different dialyser membranes. Maximal upregulation of CD45 expression was observed after 15 min of dialysis with neutropenic membranes, and normal expression levels were restored after 1 h. By contrast, increase of CD45 plasma membrane expression induced in vitro by treatment of normal neutrophils with the degranulatory agents fMLP or Ca2+ ionophore was maintained. These results demonstrate that neutrophil cell surface expression of the 180-kD CD45 protein is upregulated during the in vivo haemodialysis process, and suggest that a proteolytic activity could regulate the enzymatic activity of CD45 by degranulation of its cytoplasmic phosphatase domains.

Down-regulation by tumor necrosis factor-alpha of neutrophil cell surface expression of the sialophorin CD43 and the hyaluronate receptor CD44 through a proteolytic mechanism

Adhesion of human neutrophils to endothelial cells is a crucial step during migration to the extravascular sites of inflammation. A large number of molecules, including the CD44 and LAM-1 antigens, have been described to participate in this process. We have investigated the regulation by human recombinant tumor necrosis factor-alpha (TNF-alpha) of human neutrophil plasma membrane expression of both CD44 and LAM-1 adhesion molecules, as well as that of CD43 sialophorin, which has been involved in adhesion and activation of leukocytes. The expression of these three antigens was down-regulated in neutrophils upon TNF-alpha treatment, as determined by immunofluorescence and immunoprecipitation experiments. However, the expression of other cell surface molecules, such as CD45 or CD11b, was up-regulated. Similar regulatory effects were also observed upon neutrophil treatment with other activating agents such as the chemoattractant peptide formyl-Met-Leu-Phe, the calcium ionophore A23187, or the phorbol ester phorbol 12-myristate 13-acetate. Protease inhibitors virtually abrogated the TNF-alpha-induced down-regulation of CD43 and CD44 expression, but not that of LAM-1, suggesting the involvement of a protease activity in this process. These results underline the role of TNF-alpha on the differential regulation of cell surface expression of neutrophil adhesion molecules, thus implying modifications in the neutrophil adhesive properties.

Differentially regulated cell surface expression of leukocyte adhesion receptors on neutrophils

To elucidate the molecular mechanisms accounting for hemodialysis-induced neutropenia, the regulation of plasma membrane expression of leukocyte adhesion glycoproteins was investigated by both flow cytometry and immunoprecipitation techniques. The members of the LFA family of integrins, Mac-1/Mo1 (CD11/CD18) and gp150/95 (CD11c/CD18), involved in adhesion of myeloid cells to endothelia and other substrates, were found to be overexpressed on the plasma membrane of neutrophils from patients undergoing hemodialysis with a Cuprophane dialyzer, whereas no change was observed in the expression of LFA-1 (CD11a/CD18). By contrast, dialysis with Cuprophane membranes, as well as in vitro treatment with different activating agents, induced a downregulation on the expression of both the Leu-8/LAM-1 antigen, the human neutrophil peripheral lymph node homing receptor, and the CD43 major sialoglycoprotein involved in leukocyte homotypic adhesion. Kinetics studies showed that these up- and downregulatory processes of antigen expression occur very rapidly, correlating with maximal neutropenia. Recovery of initial levels of expression of CD11b/CD18 and Leu-8/LAM-1 adhesion molecules was observed after one hour of hemodialysis. However, the basal expression of CD43 was not restored by that time. The coordinated upregulation of CD11b and CD11c and downregulation of LAM-1 and CD43 adhesion receptors provide molecular mechanisms for understanding leukoaggregation, adherence to endothelia, and extravasation of neutrophils ultimately leading to the hemodialysis-induced neutropenia.

Mobilization of gelatinase-rich granules as a regulatory mechanism of early functional responses in human neutrophils

Components involved in superoxide anion production (cytochrome b) and in cell adhesion processes (CD11b, CD11c, CD18), two early functional responses of neutrophils during acute inflammation, are intracellularly located in resting human neutrophils. We have found a correlation between secretion of gelatinase and overexpression in the plasma membrane of CD11b, CD11c, CD18 and cytochrome b upon cell activation. Gelatinase and lactoferrin were parallely released after cell activation with different stimuli, but a better correlation between antigen up-regulation and gelatinase release was obtained. Total translocation of the intracellular pool of these mobilizable molecules to plasma membrane was achieved under conditions that induced total degranulation of the gelatinase-rich granule population, whereas 50% and 90% of the lactoferrin-containing secondary granules and peroxidase-containing primary granules, respectively, remained unfused. These results suggest a mechanism by which neutrophil function can be regulated through mobilization of gelatinase-rich granules, which can be considered as a subpopulation of secondary granules.

An enzyme-assessed microplate-assay for neutrophil adherence. I. IgA-induced adherence of human PMNs

The binding of PMNs to extracellular matrix and cells is crucial to PMN host defense. Adherence mechanisms and the many families of molecules involved are major areas of study. We present here details of an enzyme-assessed microtiter plate assay for neutrophil adherence. This assay uses low numbers of cells (50,000/well) and permits analysis of several hundred wells in a short period of time, by using an ELISA reader. With this assay we observed 5- to 10-fold increases in the number of adherent human PMNs in response to nanogram amounts of LPS or as little as 5.0 micrograms/ml of aggregated IgA. Although fluoride blocked the LPS-induced adherence response, IgA-induced cell binding was largely unaffected.

Preparation and characterization of plasma membrane vesicles from human polymorphonuclear leukocytes

It would be advantageous to prepare models of the neutrophil plasma membrane in order to examine the role of the plasma membrane in transmembrane signal transduction in the human neutrophil and to dissect ligand-receptor interactions and structural changes in the cell surface upon stimulation. A number of investigators have prepared neutrophil membrane vesicles by homogenization, sonication, or centrifugation--techniques that can result in the loss of substantial amounts of surface membrane material, disruption of lysosomes causing proteolysis of membrane proteins, and contamination of the plasma membrane fraction by internal membranes. These limitations have been overcome in the present studies by employing a modification of the method previously developed in this laboratory. Human neutrophils were suspended in a buffer simulating cytoplasmic ionic and osmotic conditions and disrupted by nitrogen cavitation. The resultant cavitate was freed of undisrupted cells and nuclei and then centrifuged through discontinuous isotonic/isoosmotic Percoll gradients, which resolved four fractions: alpha (intact azurophilic granules), beta (intact specific granules), gamma (membrane vesicles), and delta (cytosol). The gamma fraction was highly enriched in alkaline phosphatase, a marker of the plasma membrane. In addition, this fraction contained less than 5% of the amounts of lysosomes (indicated by lysozyme activity) and nuclei (indicated by DNA content) found in intact cells or in unfractionated cavitate. Furthermore, the gamma fraction contained less than 10% of the levels of endoplasmic reticulum, Golgi, mitochondrial, and lysosomal membranes in cells or cavitates, as determined by assays for glucose 6-phosphatase, galactosyl transferase, monoamine oxidase, and Mo1 (CD11b/CD18; Mac-1), respectively. Finally, 75% of the membrane vesicles were sealed, as indicated by assay of ouabain-sensitive (Na+,K+) ATPase activity, and 55% were oriented right-side-out, as determined by exposure of concanavalin A (ConA) receptors and sialic acid residues on the surfaces of the vesicles. These heterogeneous preparations could be enriched for right-side-out vesicles by their selective adherence to ConA-coated plates and subsequent detachment by rinsing the surfaces of the plates with alpha-methylmannoside. This enrichment protocol did not affect the integrity of the vesicles and resulted in populations in which greater than 85% of the vesicles were oriented right-side-out. This procedure thus permits the preparation of sealed, right-side-out membrane vesicles that may be used as valid experimental models of the neutrophil plasma membrane in a variety of functional studies.

Biochemical and antigenic characterization of CD45 polypeptides expressed on plasma membrane and internal granules of human neutrophils

The expression of CD45 polypeptides, a phosphotyrosine phosphatase complex specific of leukocytes, has been investigated in both resting and activated neutrophils by using anti-CD45 monoclonal antibodies (MAb) which specifically recognize different polypeptide components of the CD45 molecular complex. Polypeptides of 180 and 130-150 kDa were equally precipitated by either a conventional CD45 MAb recognizing an antigenic determinant shared by the four CD45 glycoproteins (220, 205, 190 and 180 kDa) or by the anti-180 kDa UCHL1 MAb. These polypeptides were overexpressed on neutrophil plasma membranes after degranulatory stimulation. Conversely, neither the anti-220 kDa CD45R nor anti-220/205/190 kDa MAb reacted with CD45 molecules from resting or activated neutrophils. Furthermore, permeabilization analysis and comparative immunoprecipitation studies with different anti-CD45 MAb from fractions enriched in various neutrophil granules revealed that CD45 polypeptides (180 and 130-150 kDa) from internal granules are antigenic and biochemically identical to those expressed on plasma membrane.