Name: measuring phagosome ph by ratiometric fluorescence microscopy
Uploaded: 2015-12-07T14:00:00
Description: Watch this Scientific Journal Video about Measuring Phagosome pH by Ratiometric Fluorescence Microscopy at JoVE.com

The authors are financially supported by the Swiss National Science Foundation through an operating grant N&#176; 31003A-149566 (to N.D.), and The Sir Jules Thorn Charitable Overseas Trust through a Young Investigator Subsidy (to P.N.).

Déclaration éthique: Toutes les manipulations d&#39;animaux ont été effectuées en stricte conformité avec les directives du Comité de recherche animale de l&#39;Université de Genève. 1. Préparation des cibles phagocytaires <ol><li> Ajouter 20 mg de zymosan séché à 10 ml de solution saline stérile de phosphate tamponnée (PBS). Vortex et à la chaleur dans un bain d&#39;eau bouillante pendant 10 min. Refroidir et centrifuger à 2000 g pendant 5 min. </li><li> Retirer...

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K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagocytosis+and+phagosome+acidification+are+required+for+pathogen+processing+and+MyD88-dependent+responses+to+Staphylococcus+aureus.">Phagocytosis and phagosome acidification are required for pathogen processing and MyD88-dependent responses to Staphylococcus aureus.</a> J Immunol. 184 (12), 7071-7081 (2010).</li><li>Clarke, M., Maddera, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagocyte+meets+prey:+uptake,+internalization,+and+killing+of+bacteria+by+Dictyostelium+amoebae.">Phagocyte meets prey: uptake, internalization, and killing of bacteria by Dictyostelium amoebae.</a> Eur J Cell Biol. 85 (9-10), 1001-1010 (2006).</li><li>Jankowski, A., Scott, C. 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W., Geisow, M., Garcia, R., Harper, A., Miller, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+respiratory+burst+of+phagocytic+cells+is+associated+with+a+rise+in+vacuolar+pH.">The respiratory burst of phagocytic cells is associated with a rise in vacuolar pH.</a> Nature. 290 (5805), 406-409 (1981).</li><li>Savina, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NOX2+controls+phagosomal+pH+to+regulate+antigen+processing+during+crosspresentation+by+dendritic+cells.">NOX2 controls phagosomal pH to regulate antigen processing during crosspresentation by dendritic cells.</a> Cell. 126 (1), 205-218 (2006).</li><li>Rybicka, J. M., Balce, D. R., Chaudhuri, S., Allan, E. R., Yates, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagosomal+proteolysis+in+dendritic+cells+is+modulated+by+NADPH+oxidase+in+a+pH-independent+manner.">Phagosomal proteolysis in dendritic cells is modulated by NADPH oxidase in a pH-independent manner.</a> EMBO J. 31 (4), 932-944 (2012).</li><li>Mantegazza, A. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NADPH+oxidase+controls+phagosomal+pH+and+antigen+cross-presentation+in+human+dendritic+cells.">NADPH oxidase controls phagosomal pH and antigen cross-presentation in human dendritic cells.</a> Blood. 112 (12), 4712-4722 (2008).</li><li>Balce, D. R., Allan, E. R., McKenna, N., Yates, R. 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P., Duchen, M. R., Segal, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+HVCN1+channel+conducts+protons+into+the+phagocytic+vacuole+of+neutrophils+to+produce+a+physiologically+alkaline+pH.">The HVCN1 channel conducts protons into the phagocytic vacuole of neutrophils to produce a physiologically alkaline pH.</a> bioRxiv. , (2014).</li><li>Al-Fageeh, M. B., Smales, C. 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Bien que plus de temps que d&#39;autres méthodes, telles que la spectroscopie et FACS, qui emploient une stratégie similaire en utilisant un colorant sensible au pH couplé à des objectifs, mais mesurer le pH moyen d&#39;une population de phagosomes, microscopie offre plusieurs avantages. La première est que interne et externe lié, mais pas intériorisé, les particules peuvent être aisément distingué sans avoir à ajouter d&#39;autres produits chimiques, comme le bleu trypan ou des anticorps, pour étancher ou ...

Phagocytosis, the process through which innate immune cells engulf large particles, evolved from the eating mechanism of single-celled organisms, and involves binding to a target, enveloping it with a membrane and pinching the membrane off to form a vacuole within the cytosol called a phagosome. While the phagosomal membrane is derived from the plasma membrane, active protein and lipid sorting, as well as fusion with endomembranes during phagosome formation, transform the phagosome into a distinct organelle within the cell with degradative properties that allow the killing, neutralization and breakdown of the ingested material1-3. This process, called phagosomal maturation, relies on the delivery of a host of proteolytic and microbicidal enzymes, including the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase which transfers electrons into phagosomes producing the strong oxidant O2- and its derivative reactive oxygen species (ROS) 2,4. 
The luminal pH of phagosomes has a profound influence on several events required for phagosome function. First, pH influences trafficking of endomembranes in general, as pH-dependent conformational changes of transmembrane trafficking regulators alters the recruitment of trafficking determinants such as Arfs, Rabs and vesicular coat-proteins, which in turn define which vesicles may fuse with phagosomes 5-8. Second, the ionic composition of the phagosomal lumen is also transformed as phagosomes mature, and some ion transporters, such as the Na+/H+ exchanger or ClC family Cl-/H+ antiporters, which promote phagocytic function, rely on H+ translocation 9,10. Similarly, ROS production is intimately linked with phagosomal pH. ROS and its toxic oxidant byproducts have long been recognized as crucial for phagosomal killing in neutrophils 4,11,12, and have been shown to play critical roles in other phagocytes including macrophages, dendritic cells (DCs) and amoeba 13-16. The NADPH oxidase is an electrogenic enzyme that releases H+ in the cytosol as NADPH is consumed, and that requires the simultaneous transfer of H+ through companion HVCN1 channels alongside the transported electrons into the phagosomal lumen, in order to alleviate the massive depolarization that would otherwise lead to self-inhibition of the enzyme 17-21. Finally, several proteolytic enzymes have optimal activity at different pH, so time-dependent phagosomal pH changes can influence which enzymes are active and when. The importance of phagosomal pH is highlighted by organisms such as Mycobacterium tuberculosis, Franciscella tularensis and Salmonella typherium that subvert phagocytic killing at least in part by altering phagosomal pH 22-24.
In mammals the main phagocytes are neutrophils, macrophages and dendritic cells, and depending on cell type, time-dependent phagosomal pH changes can vary widely, and appear to play different roles. In macrophages a strong and rapid acidification mediated by the ATP-dependent proton pump vacuolar ATPase (V-ATPase) is one of the key factors mediating killing 25-27, resembling the mechanisms present in amoeba that use phagocytosis as an eating mechanism 28. In these cells activation of acidic proteases is thought to play a key role. In contrast, neutrophil killing relies more on ROS as well as HOCl produced by myeloperoxidase (MPO)11, and the pH remains neutral or alkaline during the first 30 min acidifying only later 29,30. Neutral pH has been suggested to favor the activity of oxidative proteases such as certain cathepsins. In DCs phagosomal pH is controversial, with some reporting acidification and others neutral or alkaline pH 31,32, but ROS and pH may profoundly influence the ability of these cells to present antigens to T cells, one of their main functions 33. 
Importantly, hormones, chemokines and cytokines may produce signaling events that induce maturation and changes in phagocyte behavior, and in turn influence phagosomal pH 34,35. Similarly, drugs, for example the antimalarial chloroquine, which is also considered for anti-cancer therapies 36, may affect phagosomal pH and therefore immune outcomes. Thus, a variety of cell biologists, immunologists, microbiologists and drug developers may be interested in measuring phagosomal pH when seeking to understand the mechanisms underlying the effects of a particular genetic disruption, bioactive compound or microorganism on innate and adaptive immune responses. 
Here we describe a method for measuring phagosomal pH in neutrophils that allowed us to show the importance of the HVCN1 channel in regulating neutrophil phagosomal pH 19. The method is based on the ratiometric property of fluorescein isothiocyanate (FITC) whose fluorescence emission at 535 nm is pH sensitive when excited at 490 nm but not 440 nm 37. When this dye is chemically coupled to a target, in this case zymosan, it can be followed using wide-field fluorescence microscopy, where cells are imaged as they phagocytose, and phagosomal pH changes are measured in real time as the phagosome matures. The actual pH is then gleaned by performing a calibration experiment where cells that have phagocytosed are exposed to solutions of different pH that contain the ionophores nigericin and monensin, that allow the rapid equilibration of the pH within phagosomes with the external solution. Ratio values are then compared to the known pH of solutions, a calibration curve is constructed by nonlinear regression and the resulting equation used to calculate pH from the ratio value.

<table>
	<tbody>
		<tr>
			<td>Zymosan A powder</td>
			<td>Sigma-Aldrich</td>
			<td>Z4250</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Fluorescein isothiocyanate</td>
			<td>Sigma-Aldrich</td>
			<td>F7250</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Anti-zymosan antibody (Zymosan A Bioparticles opsonizing reagent)</td>
			<td>Life Technologies</td>
			<td>Z2850</td>
			<td>Sigma-Aldrich O6637 is an equivalent product. Alternatively 25% serum can be used as an opsonizing reagent.</td>
		</tr>
		<tr>
			<td>4-Aminobenzoic hydrazide (4-ABH)</td>
			<td>Santa Cruz</td>
			<td>sc-204107</td>
			<td>Toxic, use gloves, various providers exist</td>
		</tr>
		<tr>
			<td>Diphenyleneiodonium chloride (DPI)</td>
			<td>Sigma-Aldrich</td>
			<td>D2926</td>
			<td>Toxic, use gloves, various providers exist</td>
		</tr>
		<tr>
			<td>Concanamycin A (ConcA)</td>
			<td>Sigma-Aldrich</td>
			<td>27689</td>
			<td>Toxic, use gloves, various providers exist</td>
		</tr>
		<tr>
			<td>Nigericin</td>
			<td>Sigma-Aldrich</td>
			<td>N7143</td>
			<td>Toxic, use gloves, various providers exist</td>
		</tr>
		<tr>
			<td>Monensin</td>
			<td>Enzo</td>
			<td>ALX-380-026-G001</td>
			<td>Toxic, use gloves, various providers exist</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (PBS)</td>
			<td>Life Technologies</td>
			<td>14200-075</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Hank&#39;s balance salt solution</td>
			<td>Life Technologies</td>
			<td>14025092</td>
			<td>Ringer&#39;s balanced salt solution or other clear physiological buffers may be substituted.</td>
		</tr>
		<tr>
			<td>Sodium carbonate (Na2CO3)</td>
			<td>Sigma-Aldrich</td>
			<td>S7795</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>2-(N-Morpholino)ethanesulfonic acid (MES)</td>
			<td>Sigma-Aldrich</td>
			<td>M3671&#160;</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES)</td>
			<td>Sigma-Aldrich</td>
			<td>H3375</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>N-Methyl-D-glucamine (NMDG)</td>
			<td>Sigma-Aldrich</td>
			<td>M2004&#160;</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Ethylene glycol-bis(2-aminoethylether)-N,N,N&#8242;,N&#8242;-tetraacetic acid (EGTA)</td>
			<td>Sigma-Aldrich</td>
			<td>3777</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>&#160;Tris(hydroxymethyl)aminomethane (Tris)</td>
			<td>Sigma-Aldrich</td>
			<td>T1503&#160;</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Potassium chloride (KCl)</td>
			<td>Sigma-Aldrich</td>
			<td>P9333</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Sigma-Aldrich</td>
			<td>S7653</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Magnesium chloride (MgCl2)</td>
			<td>Sigma-Aldrich</td>
			<td>M8266</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Absolute Ethanol (EtOH)</td>
			<td>Sigma-Aldrich</td>
			<td>2860</td>
			<td>Various providers exist</td>
		</tr>
		<tr>
			<td>Glass-bottom 35 mm petri dishes (Fluorodish)</td>
			<td>World Precision Instruments</td>
			<td>FD35-100</td>
			<td>Ibidi &#181;-clear dishes or coverslips with appropriate imaging chambers may be sustituted</td>
		</tr>
		<tr>
			<td>Sonicating water bath</td>
			<td>O. Kleiner AG</td>
			<td></td>
			<td>A sonicator may be used instead, various instrument providers exist</td>
		</tr>
		<tr>
			<td>Heamocytometer</td>
			<td>Marienfeld GmbH</td>
			<td></td>
			<td>Various instrument providers exist</td>
		</tr>
		<tr>
			<td>Widefield live imaging microscope</td>
			<td>Carl Zeiss AG</td>
			<td></td>
			<td>Various instrument providers exist, but the microscope must be able to image 440/535 and 490/535 excitation/emission respective. Spinning disk confocal set-ups with brightfield capabilities may substituted, but zymosan tend to go out of focus more often.&#160;&#160;</td>
		</tr>
		<tr>
			<td>Peristaltic pump (Dynamax RP-1)</td>
			<td>Rainin</td>
			<td></td>
			<td>Various instrument providers exist</td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Schott Gerate GmbH</td>
			<td></td>
			<td>Various instrument providers exist</td>
		</tr>
		<tr>
			<td>Manual Counter</td>
			<td>Milian SA</td>
			<td></td>
			<td>Various instrument providers exist</td>
		</tr>
	</tbody>
</table>

measuring phagosome ph by ratiometric fluorescence microscopy

La phagocytose est un processus fondamental par lequel les cellules immunitaires innées engloutissent les bactéries, les cellules apoptotiques ou d&#39;autres particules étrangères dans le but de tuer ou neutraliser la matière ingérée, ou de le présenter comme antigènes et d&#39;initier des réponses immunitaires adaptatives. Le pH de phagosomes est un paramètre critique régulation de fission ou fusion avec endomembranes et l&#39;activation des enzymes protéolytiques, des événements qui permettent à la vacuole phagocytaire à mûrir dans une organelle dégradable. En outre, la translocation des ions H + est requis pour la production de niveaux élevés d&#39;espèces oxygénées réactives (ROS), qui sont essentiels pour la destruction efficace et signalisation à d&#39;autres tissus de l&#39;hôte. De nombreux agents pathogènes intracellulaires subvertissent assassinat phagocytaire en limitant l&#39;acidification du phagosome, soulignant l&#39;importance du pH dans phagosome biologie. Nous décrivons ici une méthode pour mesurer phagosomale quotientométrique pH dans les neutrophiles en utilisant l&#39;isothiocyanate de fluorescéine (FITC) marqué au zymosan que phagocytaire targETS, et imagerie des cellules vivantes. Le dosage est basé sur les propriétés de fluorescence du FITC, qui est refroidi par un pH acide lorsqu&#39;il est excité à 490 nm mais non lorsqu&#39;il est excité à 440 nm, ce qui permet la quantification d&#39;un rapport dépendant du pH, au lieu de fluorescence absolue, d&#39;un seul colorant. Un protocole détaillé pour réaliser in situ colorant étalonnage et la conversion de rapport aux valeurs réelles de pH est également fourni. Simple-dye méthodes ratiométriques sont généralement considérés comme supérieurs à longueur d&#39;onde unique ou protocoles de pseudo-ratiométrique double teinture, car ils sont moins sensibles aux perturbations telles que le blanchiment, les changements de focus, les variations de laser, et l&#39;étiquetage inégale, qui faussent le signal mesuré. Ce procédé peut être facilement modifié pour mesurer le pH dans d&#39;autres types de cellules phagocytaires, et zymosan peut être remplacée par toute autre particule contenant une amine, à partir de billes inertes à des micro-organismes vivants. Enfin, ce procédé peut être adapté pour utiliser d&#39;autres sondes fluorescentes sensibles à des gammes de pH ou d&#39;autres phagosomactivités al, ce qui en fait un protocole généralisé pour l&#39;imagerie fonctionnelle de phagosomes.

Voici les résultats représentatifs pour une expérience où le phagosome pH de neutrophiles de souris primaires isolées de la moelle osseuse de type sauvage ou Hvcn1 - / - les souris ont été comparés. Pour une expérience réussie, il est important d&#39;obtenir suffisamment phagosomes dans le champ de vision pendant toute la durée du film time-lapse, tout en évitant de trop nombreux phagosomes, qui sera ensuite plus difficile de segmenter lors de l&#39;analyse d&#39;image. <strong...

Watch this Scientific Journal Video about Measuring Phagosome pH by Ratiometric Fluorescence Microscopy at JoVE.com

Measuring Phagosome pH by Ratiometric Fluorescence Microscopy

Phagosomal pH influences phagosome maturation, oxidant production, phagosomal killing as well as antigen presentation. Here we describe a ratiometric method for measuring time-course and endpoint pH changes in individual phagosomes in living phagocytes using fluorescence microscopy.

Mesure Phagosome pH par Ratiométrique microscopie à fluorescence

Phagocytosis is a fundamental process through which innate immune cells engulf bacteria, apoptotic cells or other foreign particles in order to kill or ...

measuring-phagosome-ph-by-ratiometric-fluorescence-microscopy

Research

JoVE Journal

Immunology and Infection

Microwave Assisted Rapid Diagnosis of Plant Virus Diseases by Transmission Electron Microscopy

Investigations of ultrastructural changes induced by viruses are often necessary to clearly identify viral diseases in plants. With conventional sample preparation for transmission electron microscopy (TEM) such investigations can take several days1,2 and are therefore not suited for a rapid diagnosis of plant virus diseases. Microwave fixation can be used to drastically reduce sample preparation time for TEM investigations with similar ultrastructural results as observed after conventionally sample preparation3-5. Many different custom made microwave devices are currently available which can be used for the successful fixation and embedding of biological samples for TEM investigations5-8. In this study we demonstrate on Tobacco Mosaic Virus (TMV) infected Nicotiana tabacum plants that it is possible to diagnose ultrastructural alterations in leaves in about half a day by using microwave assisted sample preparation for TEM. We have chosen to perform this study with a commercially available microwave device as it performs sample preparation almost fully automatically5 in contrast to the other available devices where many steps still have to be performed manually6-8 and are therefore more time and labor consuming. As sample preparation is performed fully automatically negative staining of viral particles in the sap of the remaining TMV-infected leaves and the following examination of ultrastructure and size can be performed during fixation and embedding.

This study describes a method that allows the rapid and clear diagnosis of plant virus diseases in about half a day by using a combination of microwave assisted plant sample preparation for transmission electron microscopy and negative staining methods.

Micro-ondes assistée diagnostic rapide des maladies virales des plantes par microscopie électronique à transmission

Investigations of ultrastructural changes induced by viruses are often necessary to clearly identify viral diseases in plants. With conventional sample ...

Recherche

Immunologie et infection

Visualization of Bacterial Toxin Induced Responses Using Live Cell Fluorescence Microscopy

Bacterial toxins bind to cholesterol in membranes, forming pores that allow for leakage of cellular contents and influx of materials from the external environment. The cell can either recover from this insult, which requires active membrane repair processes, or else die depending on the amount of toxin exposure and cell type1. In addition, these toxins induce strong inflammatory responses in infected hosts through activation of immune cells, including macrophages, which produce an array of pro-inflammatory cytokines2. Many Gram positive bacteria produce cholesterol binding toxins which have been shown to contribute to their virulence through largely uncharacterized mechanisms.
Morphologic changes in the plasma membrane of cells exposed to these toxins include their sequestration into cholesterol-enriched surface protrusions, which can be shed into the extracellular space, suggesting an intrinsic cellular defense mechanism3,4. This process occurs on all cells in the absence of metabolic activity, and can be visualized using EM after chemical fixation4. In immune cells such as macrophages that mediate inflammation in response to toxin exposure, induced membrane vesicles are suggested to contain cytokines of the IL-1 family and may be responsible both for shedding toxin and disseminating these pro-inflammatory cytokines5,6,7. A link between IL-1&beta; release and a specific type of cell death, termed pyroptosis has been suggested, as both are caspase-1 dependent processes8. To sort out the complexities of this macrophage response, which includes toxin binding, shedding of membrane vesicles, cytokine release, and potentially cell death, we have developed labeling techniques and fluorescence microscopy methods that allow for real time visualization of toxin-cell interactions, including measurements of dysfunction and death (Figure 1). Use of live cell imaging is necessary due to limitations in other techniques. Biochemical approaches cannot resolve effects occurring in individual cells, while flow cytometry does not offer high resolution, real-time visualization of individual cells. The methods described here can be applied to kinetic analysis of responses induced by other stimuli involving complex phenotypic changes in cells.

Methods for purifying the cholesterol binding toxin streptolysin O from recombinant E. coli and visualization of toxin binding to live eukaryotic cells are described. Localized delivery of toxin induces rapid and complex changes in targeted cells revealing novel aspects of toxin biology.

Visualisation des réponses toxine bactérienne induite en utilisant direct microscopie de fluorescence cellulaire

Bacterial toxins bind to cholesterol in membranes, forming pores that allow for leakage of cellular contents and influx of materials from the external ...

Study of Phagolysosome Biogenesis in Live Macrophages

Phagocytic cells play a major role in the innate immune system by removing and eliminating invading microorganisms in their phagosomes. Phagosome maturation is the complex and tightly regulated process during which a nascent phagosome undergoes drastic transformation through well-orchestrated interactions with various cellular organelles and compartments in the cytoplasm. This process, which is essential for the physiological function of phagocytic cells by endowing phagosomes with their lytic and bactericidal properties, culminates in fusion of phagosomes with lysosomes and biogenesis of phagolysosomes which is considered to be the last and critical stage of maturation for phagosomes. In this report, we describe a live cell imaging based method for qualitative and quantitative analysis of the dynamic process of lysosome to phagosome content delivery, which is a hallmark of phagolysosome biogenesis. This approach uses IgG-coated microbeads as a model for phagocytosis and fluorophore-conjugated dextran molecules as a luminal lysosomal cargo probe, in order to follow the dynamic delivery of lysosmal content to the phagosomes in real time in live macrophages using time-lapse imaging and confocal laser scanning microscopy. Here we describe in detail the background, the preparation steps and the step-by-step experimental setup to enable easy and precise deployment of this method in other labs. Our described method is simple, robust, and most importantly, can be easily adapted to study phagosomal interactions and maturation in different systems and under various experimental settings such as use of various phagocytic cells types, loss-of-function experiments, different probes, and phagocytic particles.

Étude de phagolysosome biogenèse dans les macrophages en direct

Phagocytic cells play a major role in the innate immune system by removing and eliminating invading microorganisms in their phagosomes. Phagosome ...

Measuring Physiological Responses of Drosophila Sensory Neurons to Lipid Pheromones Using Live Calcium Imaging

Unlike mammals, insects such as Drosophila have multiple taste organs. The chemosensory neurons on the legs, proboscis, wings and ovipositor of Drosophila express gustatory receptors1,2, ion channels3-6, and ionotropic receptors7 that are involved in the detection of volatile and non-volatile sensory cues. These neurons directly contact tastants such as food, noxious substances and pheromones and therefore influence many complex behaviors such as feeding, egg-laying and mating. Electrode recordings and calcium imaging have been widely used in insects to quantify the neuronal responses evoked by these tastants. However, electrophysiology requires specialized equipment and obtaining measurements from a single taste sensillum can be technically challenging depending on the cell-type, size, and position. In addition, single neuron resolution in Drosophila can be difficult to achieve since taste sensilla house more than one type of chemosensory neuron. The live calcium imaging method described here allows responses of single gustatory neurons in live flies to be measured. This method is especially suitable for imaging neuronal responses to lipid pheromones and other ligand types that have low solubility in water-based solvents.

Measuring Physiological Responses of Drosophila Sensory Neurons to Lipid Pheromones Using Live Calcium Imaging

The forelegs and proboscis of Drosophila contain a rich repertoire of gustatory sensory neurons. Here, we present a method using calcium imaging to measure physiological responses from sensory neurons in the foreleg and proboscis of live flies upon exogenous application of a gustatory pheromone.

Mesurer les réponses physiologiques de<em&gt; Drosophila</em&gt; Neurones sensoriels à Lipid Phéromones Utilisation en direct d&#39;imagerie de calcium

Unlike mammals, insects such as Drosophila have multiple taste organs. The chemosensory neurons on the legs, proboscis, wings and ovipositor of Drosophila ...

Ratiometric Imaging of Extracellular pH in Dental Biofilms

The pH in bacterial biofilms on teeth is of central importance for dental caries, a disease with a high worldwide prevalence. Nutrients and metabolites are not distributed evenly in dental biofilms. A complex interplay of sorption to and reaction with organic matter in the biofilm reduces the diffusion paths of solutes and creates steep gradients of reactive molecules, including organic acids, across the biofilm. Quantitative fluorescent microscopic methods, such as fluorescence life time imaging or pH ratiometry, can be employed to visualize pH in different microenvironments of dental biofilms. pH ratiometry exploits a pH-dependent shift in the fluorescent emission of pH-sensitive dyes. Calculation of the emission ratio at two different wavelengths allows determining local pH in microscopic images, irrespective of the concentration of the dye. Contrary to microelectrodes the technique allows monitoring both vertical and horizontal pH gradients in real-time without mechanically disturbing the biofilm. However, care must be taken to differentiate accurately between extra- and intracellular compartments of the biofilm. Here, the ratiometric dye, seminaphthorhodafluor-4F 5-(and-6) carboxylic acid (C-SNARF-4) is employed to monitor extracellular pH in in vivo grown dental biofilms of unknown species composition. Upon exposure to glucose the dye is up-concentrated inside all bacterial cells in the biofilms; it is thus used both as a universal bacterial stain and as a marker of extracellular pH. After confocal microscopic image acquisition, the bacterial biomass is removed from all pictures using digital image analysis software, which permits to exclusively calculate extracellular pH. pH ratiometry with the ratiometric dye is well-suited to study extracellular pH in thin biofilms of up to 75 &#181;m thickness, but is limited to the pH range between 4.5 and 7.0.

A pH-sensitive ratiometric dye is used in combination with confocal laser scanning microscopy and digital image analysis to monitor extracellular pH in dental biofilms in real-time.

Imagerie Ratiométrique du pH extracellulaire dans biofilms dentaires

The pH in bacterial biofilms on teeth is of central importance for dental caries, a disease with a high worldwide prevalence. Nutrients and metabolites ...

"Phagosome Closure Assay" to Visualize Phagosome Formation in Three Dimensions Using Total Internal Reflection Fluorescent Microscopy (TIRFM)

Phagocytosis is a mechanism used by specialized cells to internalize and eliminate microorganisms or cellular debris. It relies on profound rearrangements of the actin cytoskeleton that is the driving force for plasma membrane extension around the particle. In addition, efficient engulfment of large material relies on focal exocytosis of intracellular compartments. This process is highly dynamic and numerous molecular players have been described to have a role during phagocytic cup formation. The precise regulation in time and space of all of these molecules, however, remains elusive. In addition, the last step of phagosome closure has been very difficult to observe because inhibition by RNA interference or dominant negative mutants often results in stalled phagocytic cup formation. 
We have set up a dedicated experimental approach using total internal reflection fluorescence microscopy (TIRFM) combined with epifluorescence to monitor step by step the extension of pseudopods and their tips in a phagosome growing around a particle loosely bound to a coverslip. This method allows us to observe, with high resolution the very tips of the pseudopods and their fusion during closure of the phagosome in living cells for two different fluorescently tagged proteins at the same time.

&quot;Phagosome Closure Assay&quot; to Visualize Phagosome Formation in Three Dimensions Using Total Internal Reflection Fluorescent Microscopy TIRFM

We describe an experimental setup to visualize with unprecedented high resolution phagosome formation and closure in three dimensions in living macrophages, using total internal reflection fluorescence microscopy. It allows monitoring of the base of the phagocytic cup, the extending pseudopods, as well as the precise site of phagosome scission.

&quot;Phagosome Clôture Assay&quot; pour visualiser Formation Phagosome en trois dimensions en utilisant la réflexion interne totale Fluorescent Microscopy (TIRFM)

Phagocytosis is a mechanism used by specialized cells to internalize and eliminate microorganisms or cellular debris. It relies on profound rearrangements ...

Imaging the Neutrophil Phagosome and Cytoplasm Using a Ratiometric pH Indicator

Neutrophils are crucial to host innate defense and, consequently, constitute an important area of medical research. The phagosome, the intracellular compartment where the killing and digestion of engulfed particles take place, is the main arena for neutrophil pathogen killing that requires tight regulation. Phagosomal pH is one aspect that is carefully controlled, in turn regulating antimicrobial protease activity. Many fluorescent pH-sensitive dyes have been used to visualize the phagosomal environment. S-1 has several advantages over other pH-sensitive dyes, including its dual emission spectra, its resistance to photo-bleaching, and its high pKa. Using this method, we have demonstrated that the neutrophil phagosome is unusually alkaline in comparison to other phagocytes. By using different biochemical conjugations of the dye, the phagosome can be delineated from the cytoplasm so that changes in the size and shape of the phagosome can be assessed. This allows for further monitoring of ionic movement.

This manuscript describes a simple method to measure the phagosomal pH and area as well as the cytoplasmic pH of human and mouse neutrophils using the ratiometric indicator seminaphthorhodafluor (SNARF)-1, or S-1. This is achieved using live-cell confocal fluorescence microscopy and image analysis.

Imagerie du neutrophile Phagosome et Cytoplasme L&#39;utilisation d&#39;un pH Ratiométrique Indicateur

Neutrophils are crucial to host innate defense and, consequently, constitute an important area of medical research. The phagosome, the intracellular ...

Visualizing Intracellular SNARE Trafficking by Fluorescence Lifetime Imaging Microscopy

Soluble N-ethylmaleimide sensitive fusion protein (NSF) attachment protein receptor (SNARE) proteins are key for membrane trafficking, as they catalyze membrane fusion within eukaryotic cells. The SNARE protein family consists of about 36 different members. Specific intracellular transport routes are catalyzed by specific sets of 3 or 4 SNARE proteins that thereby contribute to the specificity and fidelity of membrane trafficking. However, studying the precise function of SNARE proteins is technically challenging, because SNAREs are highly abundant and functionally redundant, with most SNAREs having multiple and overlapping functions. In this protocol, a new method for the visualization of SNARE complex formation in live cells is described. This method is based on expressing SNARE proteins C-terminally fused to fluorescent proteins and measuring their interaction by F&#246;rster resonance energy transfer (FRET) employing fluorescence lifetime imaging microscopy (FLIM). By fitting the fluorescence lifetime histograms with a multicomponent decay model, FRET-FLIM allows (semi-)quantitative estimation of the fraction of the SNARE complex formation at different vesicles. This protocol has been successfully applied to visualize SNARE complex formation at the plasma membrane and at endosomal compartments in mammalian cell lines and primary immune cells, and can be readily extended to study SNARE functions at other organelles in animal, plant, and fungal cells.

This protocol describes a new method allowing for the quantitative visualization of complex formation of SNARE proteins, based on F&#246;rster resonance energy transfer, and fluorescence lifetime imaging microscopy.

Visualisation de SNARE intracellulaire traite par Fluorescence Lifetime Imaging Microscopy

Soluble N-ethylmaleimide sensitive fusion protein (NSF) attachment protein receptor (SNARE) proteins are key for membrane trafficking, as they catalyze ...

Measuring Deformability and Red Cell Heterogeneity in Blood by Ektacytometry

Decreased red cell deformability is characteristic of several disorders. In some cases, the extent of defective deformability can predict severity of disease or occurrence of serious complications. Ektacytometry uses laser diffraction viscometry to measure the deformability of red blood cells subject to either increasing shear stress or an osmotic gradient at a constant value of applied shear stress. However, direct deformability measurements are difficult to interpret when measuring heterogenous blood that is characterized by the presence of both rigid and deformable red cells. This is due to the inability of rigid cells to properly align in response to shear stress and results in a distorted diffraction pattern marked by an exaggerated decrease in apparent deformability. Measurement of the degree of distortion provides an indicator of the heterogeneity of the erythrocytes in blood. In sickle cell anemia, this is correlated with the percentage of rigid cells, which reflects the hemoglobin concentration and hemoglobin composition of the erythrocytes. In addition to measuring deformability, osmotic gradient ektacytometry provides information about the osmotic fragility and hydration status of erythrocytes. These parameters also reflect the hemoglobin composition of red blood cells from sickle cell patients. Ektacytometry measures deformability in populations of red cells and does not, therefore, provide information on the deformability or mechanical properties of individual erythrocytes. Regardless, the goal of the techniques described herein is to provide a convenient and reliable method for measuring the deformability and cellular heterogeneity of blood. These techniques may be useful for monitoring temporal changes, as well as disease progression and response to therapeutic intervention in several disorders. Sickle cell anemia is one well-characterized example. Other potential disorders where measurements of red cell deformability and/or heterogeneity are of interest include blood storage, diabetes, Plasmodium infection, iron deficiency, and the hemolytic anemias due to membrane defects.

Here we present techniques to measure red cell deformability and cellular heterogeneity by ektacytometry. These techniques are applicable to general investigations of red cell deformability and specific investigations of blood diseases characterized by the presence of both rigid and deformable red cells in circulation, such as sickle cell anemia.

Mesure de la déformabilité et hétérogénéité des globules rouges dans le sang par ektacytomètre

Decreased red cell deformability is characteristic of several disorders. In some cases, the extent of defective deformability can predict severity of ...

In Vitro Canine Neutrophil Extracellular Trap Formation: Dynamic and Quantitative Analysis by Fluorescence Microscopy

In response to invading pathogens, neutrophils release neutrophil extracellular traps (NETs), which are extracellular networks of DNA decorated with histones and antimicrobial proteins. Excessive NET formation (NETosis) and citH3 release during sepsis is associated with multiple organ dysfunction and mortality in mice and humans but its implications in dogs are unknown. Herein, we describe a technique to isolate canine neutrophils from whole blood for observation and quantification of NETosis. Leukocyte-rich plasma, generated by dextran sedimentation, is separated by commercially available density gradient separation media and granulocytes collected for cell count and viability testing. To observe real-time NETosis in live neutrophils, cell permeant and cell impermeant fluorescent nucleic acid stains are added to neutrophils activated either by lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA). Changes in nuclear morphology and NET formation are observed over time by fluorescence microscopy. In vitro NETosis is further characterized by co-colocalization of cell-free DNA (cfDNA), myeloperoxidase (MPO) and citrullinated histone H3 (citH3) using a modified double-immunolabelling protocol. To objectively quantify NET formation and citH3 expression using fluorescence microscopy, NETs and citH3-positive cells are quantified in a blinded manner using available software. This technique is a specific assay to evaluate the in vitro capacity of canine neutrophils to undergo NETosis.

In Vitro Canine Neutrophil Extracellular Trap Formation: Dynamic and Quantitative Analysis by Fluorescence Microscopy

We describe methods to isolate canine neutrophils from whole blood and visualize NET formation in live neutrophils using fluorescence microscopy. Also described are protocols to quantify NET formation and citrullinated histone H3 (citH3) expression using immunofluorescence microscopy.

In Vitro Formation canine piège extracellulaire neutrophiles : Analyse dynamique et Quantitative par microscopie de Fluorescence

In response to invading pathogens, neutrophils release neutrophil extracellular traps (NETs), which are extracellular networks of DNA decorated with ...