Video-rate dynamics of exocytotic events associated with phagocytosis in neutrophils

Protrudin-mediated ER-endosome contact sites promote phagocytosis

During phagocytosis, endosomes both contribute with membrane to forming phagosomes and promote phagosome maturation. However, how these vesicles are delivered to the phagocytic cup and the phagosome has been unknown. Here, we show that Protrudin-mediated endoplasmic reticulum (ER)-endosome contact sites facilitate anterograde translocation of FYCO1 and VAMP7-positive late endosomes and lysosomes (LELys) to forming phagocytic cups in a retinal pigment epithelial-derived cell line (RPE1). Protrudin-dependent phagocytic cup formation required SYT7, which promotes fusion of LELys with the plasma membrane. RPE1 cells perform phagocytosis of dead cells (efferocytosis) that expose phosphatidylserine (PS) on their surface. Exogenous addition of apoptotic bodies increased the formation of phagocytic cups, which further increased when Protrudin was overexpressed. Overexpression of Protrudin also led to elevated uptake of silica beads coated with PS. Conversely, Protrudin depletion or abrogation of ER-endosome contact sites inhibited phagocytic cup formation resulting in reduced uptake of PS-coated beads. Thus, the Protrudin pathway delivers endosomes to facilitate formation of the phagocytic cup important for PS-dependent phagocytosis.

Modulation of Immune Responses by Particle Size and Shape

The immune system has to cope with a wide range of irregularly shaped pathogens that can actively move (e.g., by flagella) and also dynamically remodel their shape (e.g., transition from yeast-shaped to hyphal fungi). The goal of this review is to draw general conclusions of how the size and geometry of a pathogen affect its uptake and processing by phagocytes of the immune system. We compared both theoretical and experimental studies with different cells, model particles, and pathogenic microbes (particularly fungi) showing that particle size, shape, rigidity, and surface roughness are important parameters for cellular uptake and subsequent immune responses, particularly inflammasome activation and T cell activation. Understanding how the physical properties of particles affect immune responses can aid the design of better vaccines.

Physical Constraints and Forces Involved in Phagocytosis

Phagocytosis is a specialized process that enables cellular ingestion and clearance of microbes, dead cells and tissue debris that are too large for other endocytic routes. As such, it is an essential component of tissue homeostasis and the innate immune response, and also provides a link to the adaptive immune response. However, ingestion of large particulate materials represents a monumental task for phagocytic cells. It requires profound reorganization of the cell morphology around the target in a controlled manner, which is limited by biophysical constraints. Experimental and theoretical studies have identified critical aspects associated with the interconnected biophysical properties of the receptors, the membrane, and the actin cytoskeleton that can determine the success of large particle internalization. In this review, we will discuss the major physical constraints involved in the formation of a phagosome. Focusing on two of the most-studied types of phagocytic receptors, the Fcγ receptors and the complement receptor 3 (αMβ2 integrin), we will describe the complex molecular mechanisms employed by phagocytes to overcome these physical constraints.

Feeding synthetic zeolite to transition dairy cows alters neutrophil gene expression

Synthetic zeolites are used to control the availability of dietary minerals (e.g., Ca, Mg, and P) in dairy cows. Due to calcium demand increasing with lactation onset, most cows become hypocalcemic immediately postpartum, which likely contributes to poorer immune function because calcium is important for immune cell signaling. To overcome postpartum hypocalcemia, we fed transition cows synthetic zeolite A (sodium aluminosilicate) precalving and hypothesized that it would alter calcium and thus neutrophil function during the transition period. Multiparous Holstein-Friesian cows in late gestation were randomly allocated to an untreated control group (n = 10) or a treatment group in which each cow received 500 g of zeolite A daily (n = 10) for 14 d prior to the expected calving date (actual duration = 17 ± 3 d prepartum). The cows grazed pasture, and each was supplemented with 2 kg/d of maize silage (dry matter basis), with or without zeolite, until calving. Blood samples for neutrophil isolation and analysis of plasma indicators of mineral status, energy status, liver function, and inflammation were collected pretreatment (covariate; d -19); on d -14 and -7 precalving; on the day of calving (d 0); and on d 1, 4, 7, and 28 postcalving. Neutrophils were isolated and gene expression was analyzed using microfluidic gene expression arrays. Neutrophil respiratory burst was assessed using stimulation with phorbol 12-myristate 13-acetate and flow cytometry. Plasma calcium and phosphorus revealed a treatment by time interaction; cows offered zeolite had greater plasma calcium concentrations at d 0, 1, and 4 postcalving and plasma phosphorus concentrations were lower in zeolite-treated cows during the precalving period until d 1 postcalving compared with control animals. Zeolite treatment downregulated neutrophil gene expression of CXCR4 and S100A8 and tended to lower gene expression for other immune mediators (CXCR1, IFNG, S100A12, and S100A9) compared with the control. Zeolite treatment did not affect neutrophil respiratory burst or expression of the other genes investigated. Plasma concentrations of cytokine IL-6 were reduced with zeolite treatment, which was most evident immediately postcalving (d 0, 1, and 7). Overall, feeding zeolite precalving had few effects on neutrophil gene expression and function; however, the lower gene expression of neutrophil inflammatory mediators may be due to altered availability of dietary minerals prepartum and indicates that zeolite A may control inflammation during the transition period.

Ultraspecific live imaging of the dynamics of zebrafish neutrophil granules by a histopermeable fluorogenic benzochalcone probe

Neutrophil granules (NGs) are key components of the innate immune response and mark the development of neutrophilic granulocytes in mammals. However, there has been no specific fluorescent vital stain up to now to monitor their dynamics within a whole live organism. We rationally designed a benzochalcone fluorescent probe (HAB) featuring high tissue permeability and optimal photophysics such as elevated quantum yield, pronounced solvatochromism and target-induced fluorogenesis. Phenotypic screening identified HAB as the first cell- and organelle-specific small-molecule fluorescent tracer of NGs in live zebrafish larvae, with no labeling of other cell types or organelles. HAB staining was independent of the state of neutrophil activation, labeling NGs of both resting and phagocytically active neutrophils with equal specificity. By high-resolution live imaging, we documented the dynamics of HAB-stained NGs during phagocytosis. Upon zymosan injection, labeled NGs were rapidly recruited to the forming phagosomes. Despite being a reversible ligand, HAB could not be displaced by high concentrations of pharmacologically relevant competing chalcones, indicating that this specific labeling was the result of the HAB's precise physicochemical signature rather than a general feature of chalcones. However, one of the competitors was discovered as a promising interstitial fluorescent tracer illuminating zebrafish histology, similarly to BODIPY-ceramide. As a yellow-emitting histopermeable vital stain, HAB functionally and spectrally complements most genetically incorporated fluorescent tags commonly used in live zebrafish biology, holding promise for the study of neutrophil-dependent responses relevant to human physiopathology such as developmental defects, inflammation and infection. Furthermore, HAB intensely labeled isolated live human neutrophils at the level of granulated subcellular structures consistent with human NGs, suggesting that the labeling of NGs by HAB is not restricted to the zebrafish model but also relevant to mammalian systems.

Armed for destruction: formation, function and trafficking of neutrophil granules

Neutrophils respond nearly instantly to infection, rapidly deploying a potent enzymatic and chemical arsenal immediately upon entering an infected site. This capacity for rapid and potent responses is endowed by stores of antimicrobial proteins contained in readily mobilizable granules. These granules contain the proteins necessary to mediate the recruitment, chemotaxis, antimicrobial function and NET formation of neutrophils. Four granule types exist, and are sequentially deployed as neutrophils enter infected sites. Secretory vesicles are released first, enabling recruitment of neutrophils out of the blood. Next, specific and gelatinase granules are released to enable neutrophil migration and begin the formation of an antimicrobial environment. Finally, azurophilic granules release potent antimicrobial proteins at the site of infection and into phagosomes. The step-wise mobilization of these granules is regulated by calcium signaling, while specific trafficking regulators and membrane fusion complexes ensure the delivery of granules to the correct subcellular site. In this review, we describe neutrophil granules from their formation through to their deployment at the site of infection, focusing on recent developments in our understanding of the signaling pathways and vesicular trafficking mechanisms which mediate neutrophil degranulation.

Bordetella parapertussis Circumvents Neutrophil Extracellular Bactericidal Mechanisms

B. parapertussis is a whooping cough etiological agent with the ability to evade the immune response induced by pertussis vaccines. We previously demonstrated that in the absence of opsonic antibodies B. parapertussis hampers phagocytosis by neutrophils and macrophages and, when phagocytosed, blocks intracellular killing by interfering with phagolysosomal fusion. But neutrophils can kill and/or immobilize extracellular bacteria through non-phagocytic mechanisms such as degranulation and neutrophil extracellular traps (NETs). In this study we demonstrated that B. parapertussis also has the ability to circumvent these two neutrophil extracellular bactericidal activities. The lack of neutrophil degranulation was found dependent on the O antigen that targets the bacteria to cell lipid rafts, eventually avoiding the fusion of nascent phagosomes with specific and azurophilic granules. IgG opsonization overcame this inhibition of neutrophil degranulation. We further observed that B. parapertussis did not induce NETs release in resting neutrophils and inhibited NETs formation in response to phorbol myristate acetate (PMA) stimulation by a mechanism dependent on adenylate cyclase toxin (CyaA)-mediated inhibition of reactive oxygen species (ROS) generation. Thus, B. parapertussis modulates neutrophil bactericidal activity through two different mechanisms, one related to the lack of proper NETs-inducer stimuli and the other one related to an active inhibitory mechanism. Together with previous results these data suggest that B. parapertussis has the ability to subvert the main neutrophil bactericidal functions, inhibiting efficient clearance in non-immune hosts.

ROS production in phagocytes: why, when, and where?

In the phagocytosis field, ROS production by the phagocyte NOX has been associated with pathogen killing for the last 50 years. Since the discovery of nonphagocyte NOX, numerous other roles for ROS production have been identified. Oxidative stress and ROS-mediated signaling have received much attention in recent years. Much lower concentrations of ROS may be required for signaling compared with microbial killing. Based on the discoveries in nonphagocytic cells, it became logical to look for ROS functions distinct from pathogen killing, even in phagocytes. ROS are now linked to various forms of cell death, to chemotaxis, and to numerous modifications of cellular processes, including the NOX itself. ROS functions are clearly concentration-dependent over a wide range of concentrations. How much is required for which function? Which species are required for how much time? Is ROS signaling only a side effect of bactericidal ROS production? One major obstacle to answer these questions is the difficulty of reliable quantitative ROS detection. Signal transduction often takes place on a subcellular scale over periods of seconds or minutes, so the detection methods need to provide appropriate time and space resolution. We present examples of local ROS production, decreased degradation, signaling events, and potentially ROS-sensitive functions. We attempt to illustrate the current limitations for quantitative spatiotemporal ROS detection and point out directions for ongoing development. Probes for localized ROS detection and for combined detection of ROS, together with protein localization or other cellular parameters, are constantly improved.

The role of calcium signaling in phagocytosis

Immune cells kill microbes by engulfing them in a membrane-enclosed compartment, the phagosome. Phagocytosis is initiated when foreign particles bind to receptors on the membrane of phagocytes. The best-studied phagocytic receptors, those for Igs (FcgammaR) and for complement proteins (CR), activate PLC and PLD, resulting in the intracellular production of the Ca(2+)-mobilizing second messengers InsP3 and S1P, respectively. The ensuing release of Ca(2+) from the ER activates SOCE channels in the plasma and/or phagosomal membrane, leading to sustained or oscillatory elevations in cytosolic Ca(2+) concentration. Cytosolic Ca(2+) elevations are required for efficient ingestion of foreign particles by some, but not all, phagocytic receptors and stringently control the subsequent steps involved in the maturation of phagosomes. Ca(2+) is required for the solubilization of the actin meshwork that surrounds nascent phagosomes, for the fusion of phagosomes with granules containing lytic enzymes, and for the assembly and activation of the superoxide-generating NADPH oxidase complex. Furthermore, Ca(2+) entry only occurs at physiological voltages and therefore, requires the activity of proton channels that counteract the depolarizing action of the phagocytic oxidase. The molecules that mediate Ca(2+) ion flux across the phagosomal membrane are still unknown but likely include the ubiquitous SOCE channels and possibly other types of Ca(2+) channels such as LGCC and VGCC. Understanding the molecular basis of the Ca(2+) signals that control phagocytosis might provide new, therapeutic tools against pathogens that subvert phagocytic killing.

Reactive oxygen species in phagocytic leukocytes

Phagocytic leukocytes consume oxygen and generate reactive oxygen species in response to appropriate stimuli. The phagocyte NADPH oxidase, a multiprotein complex, existing in the dissociated state in resting cells becomes assembled into the functional oxidase complex upon stimulation and then generates superoxide anions. Biochemical aspects of the NADPH oxidase are briefly discussed in this review; however, the major focus relates to the contributions of various modes of microscopy to our understanding of the NADPH oxidase and the cell biology of phagocytic leukocytes.

Videovisualization of dynamic cell responses and its molecular analysis for nanomedicine

This report proposes and reviews a new approach that provides a more straightforward methodology for visualizing and determining molecular mechanisms as they occur within cells. A direct observation of the dynamic behavior of cells using a video microscope shows unexpected but very rational behavior that challenges us to elucidate its molecular mechanism. Since mass spectrometry is a rapid and sensitive tool for molecular analysis, single-cell matrix-assisted laser desorption-ionization time of flight mass spectrometry is useful and a morphological and molecular analysis combined method called video-mass-scope is also proposed. For analysis of the function of new molecules, single molecular imaging should be straightforward and the dynamic image of molecular movement or transport, called nanokinetics, is also necessary for the application to nanomedicine. Various research examples, based mainly on biological self-defense or secretion processes, are reviewed. The combination of these analytical techniques will enable us to understand the dynamic molecular mechanisms of cells and this knowledge could be applied to nanomedicine in the future.

Nanokinetics of drug molecule transport into a single cell

Aims: To analyze drug transport at a single cell level, a mast cell line, RBL-2H3, was treated with cell-permeable fluorescent compounds, such as quinacrine, and was monitored by a fluorescence video microscope. Methods: Small areas in the video that corresponded to granules and part of the cytosol in a cell were chosen and the signal intensity in these areas was monitored sequentially. Results: The initial rate of quinacrine uptake through the cell membrane calculated from the fluorescent signal was correlated with quinacrine concentration, and it decreased at a lower temperature, showing that the transport was an energy-requiring process, such as active transport. The kinetics of the transport through the microgranular membrane did not depend on the temperature but the pH in the cytosol, therefore this process should be passive transport by pH gradient. Conclusion: These data indicate that the observation of video microscope-mediated drug transport using fluorescent dye is useful in kinetic analysis at the nanometer scale.

Mechanics of neutrophil phagocytosis: behavior of the cortical tension

The mechanical implementation of phagocytosis requires a well-coordinated deployment of cytoplasm and membrane during the creation of a phagosome. We follow the time course of this process in initially round passive neutrophils presented with antibody-coated beads of radii 1.1 to 5.5 microm. In particular, we monitor the cortical tension as the apparent cellular surface area increases due to cell-driven deformations induced by phagocytosis. The behavior of the tension is then compared with conditions of similar area expansion caused by externally imposed deformations during cell aspiration into a micropipette. Whereas the resting tension remains low for an area expansion of up to only 30% during aspiration, it remains low even after an area expansion of up to 80% in phagocytosis. This is probably the result of membrane insertion from inner stores by exocytosis. We further find that the onset of viscous tension, proportional to the rate of area expansion and caused by the unfurling of plasma membrane wrinkles, is significantly delayed in phagocytosis compared with aspiration. We propose that this is the result of phagocytosis-triggered enzymatic activity that releases spare plasma membrane normally sequestered by velcro-like bonds in a reservoir of surface folds and villi.

Imaging of Zn2+ release from pancreatic beta-cells at the level of single exocytotic events

Regulated secretion of Zn2+ from isolated pancreatic beta-cells was imaged using laser-scanning confocal microscopy. In the method, beta-cells were incubated in a solution containing the novel fluorescent Zn2+ indicator FluoZin-3. Zn2+ released from the cells reacted with the dye to form a fluorescent product, which was detected by the confocal microscope. The new dye is much brighter than Zinquin, previously used for this application, allowing detection limits of 10-40 nM and temporal resolution of 16 ms/image. The high temporal resolution allowed imaging of isolated fluorescent transients that occurred at the edge of the cells following stimulation with 20 mM glucose or 40 mM K+. Fluorescent transients took 16-50 ms to reach a peak from the initial rise and returned to baseline after 170 +/- 50 ms (n = 78 transients from 15 cells). It was concluded that the transients correspond to detection of exocytotic release of Zn2+. Analysis of the temporal and spatial dispersion of the transients indicates that the release of Zn2+ is not diffusion limited but is instead kinetically controlled in agreement with previous observations of insulin release detected by amperometry.

Phagosomal oxidative activity during beta2 integrin (CR3)-mediated phagocytosis by neutrophils is triggered by a non-restricted Ca2+ signal: Ca2+ controls time not space

The temporal and spatial relationship between particle binding to the neutrophil by beta2 integrin (CR3), the Ca2+ elevation and subsequent oxidase activation has been unclear. This is because of the difficulty in studying the time course of individual phagocytic events in individual neutrophils. Here, we have used a micromanipulation technique to present C3bi-opsonised zymosan particles to the neutrophil under observation. In this way, the moment of particle contact, pseudopod formation and internalisation has been established and cytosolic free Ca2+ and oxidation of dichlorodihydrofluorescein (DCDHF)-labelled particles determined simultaneously. Using this approach, we have found that the Ca2+ signal, which is triggered by CR3-mediated phagocytosis, can be resolved into two temporally separated components. The first Ca2+ signal occurs during beta2 integrin engagement as the phagocytic cup forms but does not trigger oxidation of the particle. The second global Ca2+ signal, which is triggered about the time of phagosomal closure, causes an abrupt activation of the oxidase. This second Ca2+ signal was not restricted to the region of the phagosome yet only triggered the oxidase activation locally in the phagosome, with no evidence of activation at other sites in the neutrophil. This points to a dual control of oxidase activation, with Ca2+ controlling the timing of oxidase activation but slower and more localised molecular events, perhaps involving oxidase assembly and phosphatidylinositol 3-phosphate generation, determining the site of oxidase activation.

Age-related changes in the calcium homeostasis of adherent neutrophils

The elderly are susceptible to infections and show a decline in neutrophil (PMN) functions that are regulated by cytosolic calcium [Ca2+]i. This study measures [Ca2+]i in suspended and adherent PMN of young and elderly individuals by using flow cytometry, confocal microscopy, the bacterial peptide fMLP, and the fluorescent Ca2+ indicator fluor-3/acettoxymethyl ester. PMN from both age groups show a steep and transient fMLP-induced Ca2+ increase. This increase is independent of external divalent cations and is desensitized by a subsequent exposure to the same agonist. Adherent PMN of the elderly express elevated [Ca2+]i before (basal) and after fMLP activation but show reduced ability to mobilize Ca2+ into and from the cytosol. PMN of the elderly take longer (13.7 +/- 3 s) to attain the maximal response compared to those of young adults (5.7 +/- 0.8 s). PMN from both age groups show heterogeneity in the time and magnitude of this response. However, PMN of the elderly show a decrease in the proportion of cells with prompt and effective reaction and an increase in the representation of a cell subpopulation manifesting delayed response. We conclude that age-related delayed and reduced PMN response to a bacterial peptide could hamper functional activities that are essential in host protection against infections.

Quantal release of free radicals during exocytosis of phagosomes

Secretion of lysosomes and related organelles is important for immune system function. High-resolution membrane capacitance techniques were used to track changes in membrane area in single phagocytes during opsonized polystyrene bead uptake and release. Secretagogue stimulation of cells preloaded with beads resulted in immediate vesicle discharge, visualized as step increases in capacitance. The size of the increases were consistent with phagosome size. This hypothesis was confirmed by direct observation of dye release from bead-containing phagosomes after secretagogue stimulation. Capacitance recordings of exocytosis were correlated with quantal free radical release, as determined by amperometry. Thus, phagosomes undergo regulated secretion in macrophages, one function of which may be to deliver sequestered free radicals to the extracellular space.

Lack of fusion of azurophil granules with phagosomes during phagocytosis of Mycobacterium smegmatis by human neutrophils is not actively controlled by the bacterium

Biogenesis of phagolysosomes is a very rapid event in neutrophils which takes place with nascent unclosed phagosomes, leading to the release of lysosomal enzymes such as beta-glucuronidase in the extracellular medium. We have previously shown that, under nonopsonic conditions, both pathogenic and nonpathogenic mycobacteria uncouple phagocytosis from fusion of azurophil granules (specialized secretory lysosomes) with phagosomes. In the present study we questioned whether they actively act on neutrophils to block this process or use phagocytic receptors that negatively control the biogenesis of phagolysosomes. As for live unicellular Mycobacterium smegmatis, we observed that nonopsonic phagocytosis of heat-killed mycobacteria did not induce the release of beta-glucuronidase, indicating that M. smegmatis does not actively act on the fusion process in neutrophils. In contrast, phagocytosis of unicellular M. smegmatis opsonized in immune serum or that of small nonopsonized mycobacterial aggregates restored the biogenesis of phagolysosomes. Aggregates were internalized in a CR3- and cholesterol-dependent manner as unicellular mycobacteria. However, aggregates but not unicellular bacteria triggered F-actin and Hck recruitment at the phagosomes, events that have been associated with lysosome fusion. Thus, we propose that M. smegmatis does not actively control the fusion of azurophil granules at early time points postinfection and that mycobacterial aggregates recruit large clusters of receptors at the neutrophil surface which could trap proteins implicated in the biogenesis of phagolysosomes.

Membrane dynamics in phagocytosis

Engulfment of particles by phagocytes involves remodeling of the plasma membrane. We review recent work that suggests that focal exocytosis of endomembranes plays an important role in pseudopod extension during phagocytosis.

Requirement for N-ethylmaleimide-sensitive factor activity at different stages of bacterial invasion and phagocytosis

Bacterial invasion, like the process of phagocytosis, involves extensive and localized protrusion of the host cell plasma membrane. To examine the molecular mechanisms of the membrane remodeling that accompanies bacterial invasion, soluble NSF attachment protein receptor (SNARE)-mediated membrane traffic was studied in cultured cells during infection by Salmonella typhimurium. A green fluorescent protein-tagged chimera of VAMP3, a SNARE characteristic of recycling endosomes, was found to accumulate at sites of Salmonella invasion. To analyze the possible role of SNARE-mediated membrane traffic in bacterial infection, invasion was measured in cells expressing a dominant-negative form of N-ethylmaleimide-sensitive factor (NSF), an essential regulator of membrane fusion. Inhibition of NSF activity did not affect cellular invasion by S. typhimurium nor the associated membrane remodeling. By contrast, Fcgamma receptor-mediated phagocytosis was greatly reduced in the presence of the mutant NSF. Most important, dominant-negative NSF significantly impaired the fusion of Salmonella-containing vacuoles with endomembranes. These observations indicate that the membrane protrusions elicited by Salmonella invasion, unlike those involved in phagocytosis, occur via an NSF-independent mechanism, whereas maturation of Salmonella-containing vacuoles is NSF-dependent.

Induction of necrosis in human neutrophils by Shigella flexneri requires type III secretion, IpaB and IpaC invasins, and actin polymerization

Infection by Shigella flexneri is characterized by infiltration of neutrophils in the intestinal mucosa and by a strong inflammatory reaction. Although neutrophils are constitutively programmed to die by apoptosis, we show that isolated human neutrophils undergo necrosis 2 h after infection with virulent S. flexneri strain M90T but not with the virulence plasmid-cured strain BS176. This was demonstrated by the release of azurophil granule proteins concomitant with the release of lactate dehydrogenase (LDH), disruption of the plasma membrane, and absence of DNA fragmentation. Mutants with the mxiD1 gene, coding for an essential component of the secretion type III machinery, or the genes coding for IpaB or IpaC invasins deleted were not cytotoxic. Neutrophil necrosis occurred independently of the bacterial ability to leave phagosomes, and it involved actin polymerization, as the addition of cytochalasin D after phagocytosis of Shigella inhibited the release of LDH. In conclusion, Shigella kills neutrophils by necrosis, a process characterized by the release of tissue-injurious granular proteins. This probably contributes to disruption of the epithelial barrier, leading to the dysentery observed in shigellosis and allowing Shigella to enter its host cells.

The use of flow cytometry to measure neutrophil function

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

Singlet oxygen ((1)Delta(g)O(2)) as the principal oxidant in myeloperoxidase-mediated bacterial killing in neutrophil phagosome

Intraphagosomal viability of wild type E. coli and lycopene (a powerful (1)O(2) quencher)-producing transformant E. coli was investigated using human polymorphonuclear leukocytes as the cells for phagocytosis of opsonized viable bacteria. While the viability of both wild type and the transformant E. coli decreased very rapidly in the phagosome, but the viability of the lycopene-transformant in phagosomes was about 1.7 times higher than that of wild type E. coli after 5 min of incubation. The results were very similar to the results obtained when E. coli strains were exposed to (1)O(2) generated in myeloperoxidase-H(2)O(2)-Br(-) system (a pure (1)O(2) generating system) at pH 4.5. The reason for HOCl, which may be generated in the myeloperoxidase-H(2)O(2)-Cl(-) system under physiological conditions but does not become involved in bactericidal action, could be explained by the near neutral pH in phagosomes at which bacterial killing by chlorination is extensively attenuated. This is the first report which proved (1)O(2)-mediated bacterial killing in neutrophil-bacterial phagosomal system.

Fusion of Azurophil Granules with Phagosomes and Activation of the Tyrosine Kinase Hck Are Specifically Inhibited During Phagocytosis of Mycobacteria by Human Neutrophils

Pathogenic mycobacteria parasitize macrophages and reside within phagosomes, which do not fuse with lysosomal granules. Mycobacteria are also internalized by neutrophils, which possess at least two types of granules, specific and azurophil granules, the latter being specialized lysosomes. Here, we investigated the ability of mycobacteria to inhibit the fusion of these granules with their phagosomes in human neutrophils. It was found that when pathogenic (Mycobacterium kansasii and Mycobacterium avium) or nonpathogenic (Mycobacterium smegmatis and Mycobacterium phlei) mycobacteria were internalized by neutrophils, they induced the inhibition of azurophil granule fusion with phagosomes even when they were serum opsonized. In contrast, secretion of specific granule content and production of O2−, both of which contribute to the neutrophil bactericidal response, were triggered. Hck is a Src family tyrosine kinase associated with azurophil granules. During internalization of zymosan, azurophil granules fused with phagosomes and Hck was activated and translocated to the phagosomal membrane, whereas in neutrophils engulfing mycobacteria, Hck did not translocate and remained unactivated. The activation of the tyrosine kinase Fgr was not affected. These results indicate that 1) pathogenic and nonpathogenic mycobacteria trigger similar bactericidal responses in neutrophils, 2) phagocytosis and fusion of azurophil granules can be uncoupled by mycobacteria, and 3) Hck could be one of the key elements of the azurophil secretory pathway that are altered during phagocytosis of mycobacteria.

Pepsinogen secretion: coupling of exocytosis visualized by video microscopy and [Ca2+]i in single cells

Conventional in vitro studies of pepsinogen secretion have measured secretion into the bulk medium and have demonstrated the critical role of Ca2+ in the process. The present study was undertaken to obtain further details of the process of secretion and its relation to Ca2+ changes over very short time periods. The relation between Ca2+ mobilization and exocytosis in an isolated individual peptic cell of the bullfrog was investigated by a method to measure both intracellular Ca2+ ([Ca2+]i), using a fluorescent Ca2+ indicator, fura 2, and exocytosis from single cells using a video microscope analyzing system. Bombesin (3.2 x 10(-7) M) and bethanechol (3.2 x 10(-4) M) caused a rapid increase in [Ca2+]i (initial peak) and a corresponding high frequency of initial exocytosis. After the initial peak, [Ca2+]i was maintained at a somewhat elevated level over the baseline (sustained phase), with a corresponding low frequency of exocytosis. Both the sustained phase of elevated [Ca2+]i and the related exocytosis were eliminated by the depletion of extracellular Ca2+. Low concentrations of bombesin (3.2 x 10(-10) M) and bethanechol (3.2 x 10(-7) M) caused sustained low-amplitude Ca2+ oscillations with correspondingly low frequencies but also caused sustained exocytosis. These data show that 1) cellular response differs between high and low concentrations of stimulus, 2) there is a close relation between [Ca2+]i and exocytosis, 3) exocytosis follows elevation of [Ca2+]i by 14-45 s (n = 6), and 4) there is a significant positive correlation between the peak [Ca2+]i and the number of exocytoses.