Mechanisms in neutrophil priming: characterization of the oxidative response induced by formylmethionyl-leucyl-phenylalanine in human exudated cells

TREM-1 is required for enhanced OpZ-induced superoxide generation following priming

Inflammatory agents, microbial products, or stromal factors pre-activate or prime neutrophils to respond to activating stimuli in a rapid and aggressive manner. Primed neutrophils exhibit enhanced chemotaxis, phagocytosis, and respiratory burst when stimulated by secondary activating stimuli. We previously reported that Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) mediates neutrophil effector functions such as increased superoxide generation, transepithelial migration, and chemotaxis. However, it is unclear whether TREM-1 is required for the process of priming itself or for primed responses to subsequent stimulation. To investigate this, we utilized in vitro and in vivo differentiated neutrophils that were primed with TNF-α and then stimulated with the particulate agonist, opsonized zymosan (OpZ). Bone marrow progenitors isolated from WT and Trem-1-/- mice were transduced with estrogen regulated Homeobox8 (ER-Hoxb8) fusion transcription factor and differentiated in vitro into neutrophils following estrogen depletion. The resulting neutrophils expressed high levels of TREM-1 and resembled mature in vivo differentiated neutrophils. The effects of priming on phagocytosis and oxidative burst were determined. Phagocytosis did not require TREM-1 and was not altered by priming. In contrast, priming significantly enhanced OpZ-induced oxygen consumption and superoxide production in WT but not Trem-1-/- neutrophils indicating that TREM-1 is required for primed oxidative burst. TREM-1-dependent effects were not mediated during the process of priming itself as priming enhanced degranulation, ICAM-1 shedding, and IL-1ß release to the same extent in WT and Trem-1-/- neutrophils. Thus, TREM-1 plays a critical role in primed phagocytic respiratory burst and mediates its effects following priming.

Cellular Response of Neutrophils to Bismuth Subnitrate and Micronized Keratin Products In Vitro

The aim of this study was to assess the effect of bismuth subnitrate and micronized keratin on bovine neutrophils in vitro. We hypothesized that recruitment and activation of neutrophils into the teat canal and sinus are the mechanisms of action of bismuth subnitrate and keratin-based teat sealant formulations. To test this, a chemotaxis assay (Experiment 1) and a myeloperoxidase (MPO) assay (Experiment 2) were conducted in vitro. Blood was sampled from 12 mid-lactation dairy cows of variable ages. Neutrophils were extracted and diluted to obtain cell suspensions of approximately 10⁶ cells/mL. In Experiment 1, test substances were placed in a 96-well plate, separated from the cell suspension by a 3 µm pore membrane and incubated for 3 h to allow neutrophils to migrate through the membrane. In Experiment 2, neutrophils were exposed to the test products and the amount of MPO released was measured by optical density. Results showed that neutrophils were not activated by bismuth or keratin products (p < 0.05) in all of the tests performed. These results suggest that the mechanisms of action of bismuth subnitrate and keratin-based teat sealants do not rely on neutrophil recruitment and activation in the teat canal and sinus after treatment.

Galectin-3 type-C self-association on neutrophil surfaces; The carbohydrate recognition domain regulates cell function

Galectin-3 is an endogenous β-galactoside-binding lectin comprising a carbohydrate recognition domain (CRD) linked to a collagen-like N-domain. Both domains are required for galectin-3 to induce cellular effects; a C-terminal fragment of galectin-3, galectin-3C, containing the CRD but lacking the N-domain, binds cell surface glycoconjugates but does not induce cellular effects since cross-linking promoted by the N-domain is thought to be required. Instead, galectin-3C is proposed to antagonize the effects of galectin-3 by competing for binding sites. The aim of this study was to investigate the effects of galectin-3C on galectin-3 interactions with human neutrophils. Recombinant galectin-3C inhibited galectin-3-induced production of reactive oxygen species in primed neutrophils. Surprisingly, this inhibition was not due to competitive inhibition of galectin-3 binding to the cells. In contrast, galectin-3C potentiated galectin-3 binding, in line with emerging evidence that galectin-3 can aggregate not only through the N-domain but also through the CRD. The cell surface interaction between galectin-3C and galectin-3 was corroborated by colocalization of fluorescently labeled galectin-3 and galectin-3C. Galectin-3C can be generated in vivo through cleavage of galectin-3 by proteases. Indeed, in circulation, galectin-3 and galectin-3C were both attached to the cell surface of neutrophils, which displayed great capacity to bind additional galectin-3 and galectin-3C. In conclusion, galectin-3C enhances galectin-3 binding to neutrophils by nonactivating type-C self-association, in parallel to inhibiting neutrophil activation by galectin-3 (induced by type-N self-association). This implicates type-C self-association as a termination system for galectin-3-induced cell activation, with the purpose of avoiding oxidant-dependent tissue damage.

Collection of in vivo transmigrated neutrophils from human skin

A wealth of knowledge on the life and death of human neutrophils has been obtained by the in vitro study of isolated cells derived from peripheral blood. However, neutrophils are of main importance, physiologically as well as pathologically, after they have left circulation and transmigrated to extravascular tissues. The journey from blood to tissue is complex and eventful, and tissue neutrophils are in many aspects distinct from the cells left in circulation. Here we describe how to obtain human tissue neutrophils in a controlled experimental setting from aseptic skin lesions created by the application of negative pressure. One protocol enables the direct analysis of the blister content, infiltrating leukocytes as well as exudate fluid, and is a simple method to follow multiple parameters of aseptic inflammation in vivo. Also described is the skin chamber technique, a method based on denuded skin blisters which are subsequently covered by collection chambers filled with autologous serum. Although slightly more artificial as compared to analysis of the blister content directly, the cellular yield of this skin chamber method is sufficient to perform a large number of functional analyses of in vivo transmigrated cells.

Cord blood neutrophils display a galectin-3 responsive phenotype accentuated by vaginal delivery

BACKGROUND

Term neonates are at increased risk of infections due to undeveloped immune mechanisms, and proper neutrophil function is important for perinatal immune defence. Galectin-3, an endogenous β-galactoside-binding lectin, is emerging as an inflammatory mediator and we have previously shown that primed/activated, but not resting, adult neutrophils respond to this lectin by production of reactive oxygen species (ROS). We investigated if galectin-3 is of importance in perinatal immune defence, focusing on plasma levels and neutrophil responsiveness.

METHODS

Neutrophils were isolated from peripheral blood of healthy adults and cord blood (CB) after elective Caesarean section (CSCB) and vaginal delivery (VDCB). ROS production was measured by chemiluminescence, L-selectin expression by flow cytometry, and interleukin-8 (IL-8) and galectin-3 concentrations by ELISA. Statistical evaluations were performed using the Mann-Whitney test.

RESULTS

In response to galectin-3, CSCB neutrophils showed a small but clear ROS production not evident in adult cells, signifying that neonatal neutrophils exist in a primed state. IL-8 production was elevated in CSCB cells while L-selectin exposure was equal to adult cells. Comparing CSCB to VDCB neutrophils, the latter showed an extensive galectin-3 responsiveness, indicating that the degree of priming is dependent on mode of delivery. VDCB neutrophils were increasingly prone to shed L-selectin, while the amount of IL-8 was similar to CSCB cells. The endogenous galectin-3 levels were higher in neonatal as compared to adult plasma, unaffected by mode of delivery.

CONCLUSIONS

Neutrophils enter a pre-primed state already in the fetus. Upon exposure to the inflammatory stimuli that are associated with labor, the neutrophils develop a reactive phenotype with extensive priming features.

Oxidative stress and therapeutic opportunities: focus on the Ewing's sarcoma family of tumors

Reactive oxygen species (ROS) are highly reactive by-products of energy production that can have detrimental as well as beneficial effects. Unchecked, high levels of ROS result in an imbalance of cellular redox state and oxidative stress. High levels of ROS have been detected in most cancers, where they promote tumor development and progression. Many anticancer agents work by further increasing cellular levels of ROS, to overcome the antioxidant detoxification capacity of the cancer cell and induce cell death. However, adaptation of the level of cellular antioxidants can lead to drug resistance. The challenge for the design of effective cancer therapeutics exploiting oxidative stress is to tip the cellular redox balance to induce ROS-dependent cell death but without increasing the antioxidant activity of the cancer cell or inducing toxicity in normal cells.

In vivo-transmigrated human neutrophils are resistant to antiapoptotic stimulation

Neutrophils respond to microbial invasion or injury by transmigration from blood to tissue. Transmigration involves cellular activation and degranulation, resulting in altered levels of surface receptors and changed responsiveness to certain stimuli. Thus, fundamental functional changes are associated with neutrophil transmigration from blood to tissue. Neutrophils isolated from peripheral blood spontaneously enter apoptosis, a process that can be accelerated or delayed by different pro- or antiapoptotic factors. How tissue neutrophils that have transmigrated in vivo regulate cell death is poorly understood. In this study, in vivo-transmigrated neutrophils (tissue neutrophils) were collected using a skin chamber technique and compared with blood neutrophils from the same donors with respect to regulation of cell death. Skin chamber fluid contained a variety of cytokines known to activate neutrophils and regulate their lifespan. Freshly prepared tissue neutrophils had elevated activity of caspase 3/7 but were fully viable; spontaneous cell death after in vitro culture was also similar between blood and tissue neutrophils. Whereas apoptosis of cultured blood neutrophils was delayed by soluble antiapoptotic factors (e.g., TLR ligands), tissue neutrophils were completely resistant to antiapoptotic stimulation, even though receptors were present and functional. In vitro transmigration of blood neutrophils into skin chamber fluid did not fully confer resistance to antiapoptotic stimulation, indicating that a block of antiapoptotic signaling occurs specifically during in vivo transmigration. We describe a novel, functional alteration that takes place during in vivo transmigration and highlights the fact that life and death of neutrophils may be regulated differently in blood and tissue.

Tumour necrosis factor (TNF)-alpha primes murine neutrophils when triggered via formyl peptide receptor-related sequence 2, the murine orthologue of human formyl peptide receptor-like 1, through a process involving the type I TNF receptor and subcellular granule mobilization

Neutrophil granulocytes play an important role in innate host defence against microbial invasions and they are also the key effector cells in mediating host tissue damage. These functions often rely on the production of reactive oxygen species (ROS) from the membrane-bound NADPH-oxidase system. The magnitude of ROS production varies depending on the state of the cells, i.e. resting or primed. Many priming agents as well as potent NADPH-oxidase activators have been identified and characterized for human neutrophils. The cytokine tumour necrosis factor (TNF)-alpha is one prominent example of a priming agent and the synthetic hexapeptide WKYMVm is an agonist that triggers an activation of the NADPH-oxidase of human neutrophils through two members of the formyl peptide family of receptors, formyl peptide receptor (FPR) and FPR-like 1 (FPRL1). This peptide also activates murine neutrophils but the precise receptor involved has not been previously characterized. We show in this study that WKYMVm activates stably transfected HL60 cells expressing murine formyl peptide receptor-related sequence 2 (Fpr-rs2) and that activation of murine neutrophils with WKYMVm is blocked by an FPRL1-specific antagonist. WKYMVm is thus an agonist for Fpr-rs2 and we suggest that this receptor is in fact the mouse orthologue of FPRL1. In addition, we show that the WKYMVm response in murine neutrophils can be primed by TNF-alpha and this priming process involves mobilization of subcellular granules. The results obtained using neutrophils derived from TNF receptor type I (TNFRI)-deficient animals suggest that TNF-alpha exerts its priming effect via the TNFRI.

A skin chamber technique as a human model for studies of aseptic inflammatory reactions

Using a combination of induced skin blistering and collection chambers permits dynamic studies of the aseptic inflammatory reaction in humans. Blisters filled with interstitial fluid can be generated by applying negative pressure to normal skin for up to 2 h. The blisters are subsequently denuded to form superficial "skin windows" that are well defined with regard to area and depth. The denuded areas are covered with a separate collection chamber filled with a suitable medium and left for 18-24 h. During this period, neutrophils and inflammatory agents accumulate in the chamber medium, and sequential events in the inflammatory process can be studied by repeated sampling. Inactive medium or isolated peripheral blood cells from the same individual can be used as controls for both cellular functions and the pro-/anti-inflammatory mediators that are generated or released.

Changes in activation states of murine polymorphonuclear leukocytes (PMN) during inflammation: a comparison of bone marrow and peritoneal exudate PMN

To study different activation states in polymorphonuclear leukocytes (PMN) in mice, we compared the function of murine PMN obtained from the bone marrow (BMPMN) with those of PMN obtained by intraperitoneal induction with thioglycolate (TGPMN) or uric acid (UAPMN). When stimulated with chemotactic peptides, e.g., formyl-methionyl-leucyl-phenylalanine (fMLF), WKYMVM, or WKYMVm, the TGPMN and UAPMN showed greatly enhanced generation of reactive oxygen species (ROS) compared with BMPMN, which suggests that exudation to the peritoneum per se induces a primed state in the cells. The WKYMVm peptide was the most potent stimulant of ROS generation, and it desensitized for subsequent stimulation with fMLF or WKYMVM. This desensitization was broken by the addition of cytochalasin B. The TGPMN and UAPMN appeared to be fully primed, since no increase in response was induced by pretreatment with tumor necrosis factor alpha (TNF-alpha). In contrast, the BMPMN response was increased 2.5- to 3-fold. The differences in oxidative responses were supported by degranulation studies. Preincubation with TNF-alpha promoted CR3 expression on BMPMN, and this level of expression was also enhanced by WKYMVm. In contrast, CR3 expression on untreated TGPMN and UAPMN was already similar to that on TNF-alpha-primed BMPMN and could be only slightly enhanced by TNF-alpha treatment. Taken together, these results indicate that BMPMN are in a resting state and have the capacity to become primed, while peritoneal exudate PMN are already fully primed upon isolation. These results have major implications for murine neutrophil research and show the importance of defining which PMN subsets to use when investigating murine models.

Newcastle disease virus neuraminidase primes neutrophils for stimulation by galectin-3 and formyl-Met-Leu-Phe

Human neutrophils are activated by the beta-galactoside-binding lectin galectin-3, provided that the cells are primed by in vivo extravasation or by in vitro preactivation with, for example, LPS. Removal of terminal sialic acid can change neutrophil functionality and responsiveness due to exposure of underlying glycoconjugate receptors or change in surface charge. Here, we investigated whether such alteration of the cell surface carbohydrate composition can alter the responsiveness of the cells to galectin-3. Neutrophils were treated with neuraminidases (NA) of different origins: Clostridium perfringens (CP), Salmonella typhimurium, Vibrio cholerae, and Newcastle disease virus (NDV). In the presence of NDV-NA, but no other NA, the otherwise non-responding neutrophils responded readily to galectin-3 by activation of the NADPH-oxidase. The galectin-3 priming effect was inhibited by the sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetyl-neuraminic acid. Earlier studies have shown that priming of the neutrophil response to galectin-3 with, for example, LPS is paralleled by degranulation of intracellular vesicles and granules and upregulation of potential galectin-3 receptors. Also, NDV-NA (but not CP-NA) treatment induced degranulation, shown as an upregulation of complement receptor 3. Since not only the galectin response but also the response to the chemoattractant fMLF was primed, NDV-NA appears to induce a general priming phenomenon, possibly due to receptor upregulation by degranulation.

NADPH-oxidase activation in murine neutrophils via formyl peptide receptors

Neutrophils play a key role at inflammatory sites where, in addition to destroying infecting microorganisms, they may also have deleterious effects on host tissues. Both activities involve activation of the NADPH-oxidase that produces bactericidal and tissue-destructive reactive oxygen species (ROS). We activated the murine NADPH-oxidase using different types of neutrophil activators and characterized the oxidative responses with respect to magnitude, localization, and kinetics. We show that agonist-induced activation of murine neutrophils results exclusively in extracellular release of ROS and no intracellular production could be detected. We also show that the formylated peptide, formyl-Met-Leu-Phe (fMLF), is a much less potent activator of the murine NADPH-oxidase than of the human analogue. Nevertheless, fMLF responses can be primed by pretreating the murine neutrophils with either cytochalasin B or bacterial lipopolysaccharide. Finally, we show that a synthetic hexapeptide, WKYMVM, is a more potent stimulus than fMLF for murine neutrophils and that these two agonists probably act via nonidentical high-affinity receptors.

Lipopolysaccharide-induced granule mobilization and priming of the neutrophil response to Helicobacter pylori peptide Hp(2-20), which activates formyl peptide receptor-like 1

The cecropin-like bactericidal peptide Hp(2-20) from Helicobacter pylori induces activation of the NADPH oxidase in human neutrophils via formyl peptide receptor-like 1 (FPRL1) (J. Bylund, T. Christophe, F. Boulay, T. Nyström, A. Karlsson, and C. Dahlgren, Antimicrob. Agents Chemother. 45:1700-1704, 2001). Here we investigated the ability of bacterial lipopolysaccharide (LPS) to prime this response. Neutrophils treated with LPS for 30 min at 37 degrees C produced substantially more superoxide anion than control cells upon stimulation with Hp(2-20). Hence, LPS primed the cells for subsequent stimulation through FPRL1. To study the molecular background of this priming phenomenon, we measured the degrees of granule mobilization and concomitant receptor upregulation to the cell surface in LPS-treated cells. Exposure of complement receptors 1 and 3 as well as the formyl peptide receptor (FPR) was markedly increased after LPS treatment. Since approximately 60% of the gelatinase granules were mobilized while the specific granules were retained, we hypothesized that the gelatinase granules were potential stores of FPRL1. The presence of FPRL1 mainly in the gelatinase granules was confirmed by Western blotting of subcellular fractions of resting neutrophils. These results suggest that the mechanism behind the LPS-induced priming of FPRL1-mediated responses lies at the level of granule (receptor) mobilization.

Lipopolysaccharide-induced gelatinase granule mobilization primes neutrophils for activation by galectin-3 and formylmethionyl-Leu-Phe

We have earlier shown that galectin-3, a lactose-binding mammalian lectin that is secreted from activated macrophages, basophils, and mast cells, induces activation of the NADPH oxidase in exudated but not in peripheral blood neutrophils (A. Karlsson, P. Follin, H. Leffler, and C. Dahlgren, Blood 91:3430-3438, 1998). The alteration in responsiveness occurring during extravasation correlated with mobilization of the gelatinase and/or specific granules to the cell surface, indicating a role for mobilizable galectin-3 receptors. In this study we have investigated galectin-3-induced NADPH oxidase activation, measured as superoxide production, in lipopolysaccharide (LPS)-primed neutrophils. Upon galectin-3 challenge, the LPS-primed cells produced superoxide, both extracellularly and intracellularly. A primed extracellular response to formylmethionyl-Leu-Phe (fMLF) was also achieved. The exposure of complement receptors 1 and 3 as well as the formyl peptide receptor on the cell surface was markedly increased after LPS treatment, indicating that granule fusion with the plasma membrane had occurred. Further assessment of specific markers for neutrophil granules showed that the LPS treatment had mobilized the gelatinase granules but only a minor fraction of the specific granules. We thus suggest that the mechanism behind LPS priming lies at the level of granule (receptor) mobilization for galectin-3 as well as for fMLF.

The synthetic chemoattractant Trp-Lys-Tyr-Met-Val-DMet activates neutrophils preferentially through the lipoxin A4 receptor

A D-methionine–containing peptide, Trp-Lys-Tyr-Met-Val-D-Met-NH2 (WKYMVm), featuring a unique receptor specificity was investigated with respect to its ability to activate neutrophil effector functions. The peptide was found to be more potent than the N-formylated peptide N-formyl-Met-Leu-Phe (fMLF) at inducing neutrophil chemotaxis, mobilization of neutrophil complement receptor 3 (CR3), and activation of the neutrophil NADPH-oxidase. The fact that binding of fML[3H]F was inhibited by both fMLF and WKYMVm suggests that N-formyl peptide receptor (FPR) is shared by these peptides. However, the neutrophil response induced by the WKYMVm peptide was insensitive to the fMLF antagonists, cyclosporin H, and Boc-FLFLF that specifically block the function of the FPR. These results suggest that even though WKYMVm may bind FPR the cells are activated preferentially through a receptor distinct from the FPR. Using transfected HL-60 cells expressing either the FPR or its neutrophil homologue FPRL1, also referred to as LXA4R because it has been shown to bind lipoxin A4, we show that WKYMVm is about 300-fold more active at mobilizing intracellular calcium through FPRL1 than through FPR. The WKYMVm activates FPRL1-expressing cells in a cyclosporin H-independent manner with an EC50 of around 75 pmol/L, whereas it activates FPR-expressing cells with an EC50 of around 25 nmol/L. The observation that exudated cells are primed in their response to WKYMVm suggests that FPRL1/LXA4R like FPR is stored in mobilizable organelles.

Respiratory burst in human neutrophils

During phagocytosis of microbial intruders, professional phagocytes of our innate immune system increase their oxygen consumption through the activity of an NADPH-oxidase that generates superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)). These oxygen metabolites give rise to yet other reactive oxygen species that are strongly anti-microbial but which may also cause damage by destructing surrounding tissue and inducing apoptosis in other immune reactive cells. The development of methodology to measure the generation/release of phagocyte respiratory burst products is thus of great importance, and a number of different techniques are currently in use for this purpose. Three of the techniques that we have used, (luminol/isoluminol amplified chemiluminescence, cytochrome C reduction, and PHPA oxidation technique) are described in more detail in this review. We hope to convince the readers that these techniques are valuable tools in basic as well as more clinically oriented research dealing with phagocyte function. The basic principles for luminol/isoluminol-amplified chemiluminescence is used as the starting point for discussing methodological problems related to measurements of oxygen metabolites generated by professional phagocytes.

Skin chamber technique for study of in vivo exudated human neutrophils

The development of new techniques for isolation of neutrophils extravasated in vivo have been essential for studying the dynamics of the inflammatory response in humans. Methods for generating inflammatory skin reactions were first presented in the mid 1950s, and later a skin blistering technique based on suction was introduced. With this procedure, small areas of denuded dermis, called "skin windows", are created and covered with special chambers containing a medium that attracts exudated neutrophils. By comparing the neutrophils collected in such chambers with those isolated from peripheral blood, it is possible to investigate the functional modifications that neutrophils undergo when attracted to an inflammatory process. The skin-blister chamber technique represents an aseptic, non-traumatic and reproducible model of inflammation that can be used to study in vivo activated human neutrophils. The background, methodological aspects and options of this technique are described, together with the functional characteristics of exudated neutrophils.

Galectin-3 Activates the NADPH-Oxidase in Exudated but not Peripheral Blood Neutrophils

Galectin-3, a lactose-binding mammalian lectin that is secreted from activated macrophages, basophils, and mast cells, was investigated with respect to its ability to activate the human neutrophil NADPH-oxidase. The galectin-3–induced activity was determined with in vivo exudated cells (obtained from a skin chamber) and compared with that of peripheral blood neutrophils. Galectin-3 was found to be a potent activator of the NADPH-oxidase only in exudated neutrophils and the binding of galectin-3 to the surface of these cells was increased compared with peripheral blood cells. Different in vitro priming protocols resulting in degranulation were used to mimic the exudation process in terms of increasing the receptor exposure on the cell surface. Galectin-3 could induce an oxidative response similar to that in exudated cells only after a significant amount of the intracellular organelles had been mobilized. This increase in oxidative response was paralleled by an increased binding of galectin-3 to the surface of the cells. The major conclusion of the study is that galectin-3 is a potent stimulus of the neutrophil respiratory burst, provided that the cells have first experienced an extravasation process. The results also imply that the neutrophil response to galectin-3 could be mediated through receptors mobilized from intracellular granules, and we report the presence of galectin-3–binding proteins in such organelles.

Galectin-3 Activates the NADPH-Oxidase in Exudated but not Peripheral Blood Neutrophils

Galectin-3, a lactose-binding mammalian lectin that is secreted from activated macrophages, basophils, and mast cells, was investigated with respect to its ability to activate the human neutrophil NADPH-oxidase. The galectin-3–induced activity was determined with in vivo exudated cells (obtained from a skin chamber) and compared with that of peripheral blood neutrophils. Galectin-3 was found to be a potent activator of the NADPH-oxidase only in exudated neutrophils and the binding of galectin-3 to the surface of these cells was increased compared with peripheral blood cells. Different in vitro priming protocols resulting in degranulation were used to mimic the exudation process in terms of increasing the receptor exposure on the cell surface. Galectin-3 could induce an oxidative response similar to that in exudated cells only after a significant amount of the intracellular organelles had been mobilized. This increase in oxidative response was paralleled by an increased binding of galectin-3 to the surface of the cells. The major conclusion of the study is that galectin-3 is a potent stimulus of the neutrophil respiratory burst, provided that the cells have first experienced an extravasation process. The results also imply that the neutrophil response to galectin-3 could be mediated through receptors mobilized from intracellular granules, and we report the presence of galectin-3–binding proteins in such organelles.

Desensitization of Formyl Peptide Receptors Is Abolished in Calcium Ionophore-Primed Neutrophils: An Association of the Ligand-Receptor Complex to the Cytoskeleton Is Not Required for a Rapid Termination of the NADPH-Oxidase Response

Binding of ligands to N-formyl peptide chemoattractant receptors exposed on human neutrophils generates signals in the cells that induce an activation of the superoxide anion producing NADPH-oxidase. Ligand binding is followed by a rapid association of the ligand-receptor complex with the cytoskeleton, a process leading to desensitization of the cells with respect to NADPH-oxidase activation. We show that neutrophils that have experienced an intracellular calcium rise obtained through interaction with the calcium-specific ionophore ionomycin are “primed” with respect to the FMLP-induced production of superoxide anions. Mobilization of FMLP receptors from intracellular pools is one well-known mechanism behind the primed response. Based on our finding that ionomycin-treated neutrophils could not be desensitized, we suggest that the lack of association between the ligand-receptor complex and the cytoskeleton is an additional priming mechanism. Since in vivo-exudated neutrophils, which also had mobilized intracellular organelles, could be desensitized, we suggest that the abolished desensitization in ionomycin-treated neutrophils is not due to an inability of newly recruited receptors to couple to the cytoskeleton. We show that a rapid termination of FMLP-induced superoxide anion production is obtained in both desensitizable and nondesensitizable neutrophils, suggesting that the desensitization phenomenon is of limited importance in the oxidase termination process.

Escherichia coli-induced activation of neutrophil NADPH-oxidase: lipopolysaccharide and formylated peptides act synergistically to induce release of reactive oxygen metabolites

The prevailing view of neutrophil NADPH-oxidase activation during interaction with bacteria is that the production of toxic oxygen metabolites should be directed into the phagosome containing the engulfed prey. However, in this report we show that a common Escherichia coli strain, HB101, may induce a release of neutrophil oxygen metabolites to the extracellular milieu. This phenomenon is dependent on three factors: (i) the mobilization (upregulation) of neutrophil secretory vesicles prior to interaction with the bacteria, (ii) soluble bacterial factors binding to the formylmethionyl-leucyl-phenylalanine receptor and tentatively identified as formylated peptides, and (iii) a bacterium-associated priming factor identified as lipopolysaccharide.

Neutrophil Migration Activity (NMA) - A new migration test for the monitoring of wound healing in traumatology?

A new PMN migration test was introduced in traumatology to measure the acute, inflammatory response after surgery in a patient with uncomplicated wound healing and in a case of acute, early postoperative infection. Polymorphonuclear neutrophil granulocyte (PMN) - behaviour was studied by quantifying the neutrophil migration activity (NMA), which combines PMN-stimulation and PMN-distribution in a migration filter device simulating "in vivo"-conditions. While in uncomplicated wound healing the NMA was within the normal range, in an acute, early infection migratory stimulation reached a maximum on the 5th postsurgical day followed by a decrease during the following days. This decrease is probably an expression of an increased PMN-turnover and excessive phagocytosis. PMN-behaviour changing from migration to phagocytosis is regarded as an indicator of wound healing complications before clinical symptoms occur.

Effect of cytochalasin B on intracellular free calcium concentration in human polymorphonuclear leukocytes after repeated stimulation with n-formyl-methionyl-leucyl-phenylalanine

Cytochalasin B can influence various functions of human polymorphonuclear leukocytes, including chemotaxis, lysosomal enzyme release, and reactive oxygen species generation. In this study we investigated the effect of cytochalasin B on the increase in intracellular free calcium concentration after three consecutive additions of 10(-7) M N-formyl-methionyl-leucyl-phenylalanine. The interval between stimulations was 5 min. Intracellular free calcium concentration was monitored using the fluorescent calcium indicator FURA-2AM. Cytochalasin B (3.3 micrograms/ml) added 60 s before the cell stimulation enhanced all three polymorphonuclear leukocyte calcium responses by increasing the N-formyl-methionyl-leucyl-phenylalanine-induced calcium influx from the extracellular space. Cytochalasin B increased the peak intracellular free calcium concentration and elevated the plateau phase level, but had no influence on its shape. In addition, pretreatment with cytochalasin B of polymorphonuclear leukocytes suspended in low calcium medium restored their capacity to respond to a third stimulation with N-formyl-methionyl-leucyl-phenylalanine. Finally, in resting cells cytochalasin B caused a moderate increase in intracellular free calcium concentration which was independent of extracellular calcium.

Polymorphonuclear leucocyte migration response in uneventful wound healing following trauma surgery. A contribution to the search for objectifiable criteria in wound healing monitoring

In a study of the clinical importance of polymorphonuclear granulocytes (PMN) for the monitoring of wound healing we investigated the postsurgical course of nine patients all of whom had undergone trauma surgery and had no wound complications. The "stimulated random PMN locomotion" was evaluated by a new migration filter device which preserves the cells in their genuine priming state, simulating in vivo conditions. The percentage of all activated PMN, expressed by the total migration index (TMI) reflected the highest median immediately after surgery (Zmax = 30.1%) and dropped to the lowest value on day 13 (Zmin = 13.9%). The mean invasion depth (T/2) of the cells along the migration distance into the filter showed only slight variations over time. The neutrophil migration activity (NMA), described by T/2 and TMI, behaved in a similar way to TMI. In studying physiological healing, preliminary results indicate that TMI, which expresses PMN activation, is an efficient tool in the postoperative monitoring of patients, and might in the future serve as a basis for an early warning system for wound healing complications.

Factor-specific changes in oxidative burst response of human neutrophils in skin-window exudates

Human neutrophils were isolated from blood and aseptic inflammatory exudates. The respiratory burst response was measured as superoxide (O2-) production by a microplate assay system and polarographically as oxygen consumption. Exudate cells exhibited a respiratory burst in response to n-formyl-methionyl-leucyl-phenyl-alanine (FMLP) that was two- to threefold higher than the burst exhibited by peripheral blood cells. The O2- production induced by substance P was also found to be fivefold higher in exudate cells, while the metabolic response to other stimulants such as concanavalin A (con A), phorbol-myristate acetate (PMA), NaF, and immunocomplexes was not primed. Serum-treated zymosan (STZ)-stimulated activity was primed by only 11%. In contrast, superoxide production in response to tumor necrosis factor-alpha (TNF) was decreased in exudate versus blood cells by about 50%. Therefore, the skin-window cells, compared to blood cells, appear to be at the same time primed, unmodified, and desensitized, according to the different stimulants employed.

Phagocytosis following translocation of the neutrophil b-cytochrome from the specific granule to the plasma membrane is associated with an increased leakage of reactive oxygen species

The effect of neutrophil b-cytochrome translocation on the respiratory burst activation generated during phagocytosis of yeast particles was investigated. Secretion of neutrophil specific granules was induced by the calcium ionophore ionomycin prior to phagocytosis. The secretory process is associated with a translocation from the specific granules to the plasma membrane of the respiratory burst b-cytochrome. Respiratory burst activity was measured as release of hydrogen peroxide in the absence of azide (extracellular leakage) and in the presence of azide (total production). The subcellular localization of the b-cytochrome was found to affect the extracellular release of hydrogen peroxide in that a plasma membrane localization was associated with a significantly increased release during phagocytosis. It should be pointed out, however, that most of the hydrogen peroxide, both in control and in ionomycin-treated cells, is produced intracellularly, probably in the phagosomes.