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.).

Etica Dichiarazione: Tutte le manipolazioni sugli animali sono state eseguite in stretta conformità con le linee guida del Comitato delle Università di Ginevra Animal Research. 1. Preparazione di obiettivi fagocitiche <ol><li> Aggiungere 20 mg di zimosan essiccata a 10 ml di fosfato sterile salina tamponata (PBS). Vortex e calore in un bagno di acqua bollente per 10 min. Raffreddare e centrifugare a 2000 xg per 5 min. </li><li> Rimuovere il surnatante, risospendere in 1 ml di PBS e ultrasuoni per 10 minuti in un bagno sonicatore acqua. Trasferire 500 microlitri di due provette da 1,5 ml. Centrifugare a 11.000 g per 5 min. </li><li> Ripetere il lavaggio con 500 microlitri di PBS. Il zymosan bollito può essere aliquotato, congelato e conservato a -20 ° C. </li><li> Lavare zymosan due volte in 500 microlitri preparate 0,1 M Na 2 CO 3, pH 9,3 come sopra (punto 1.2). </li><li> Risospendere in 490 microlitri dopo il lavaggio finale. Aggiungere 10 ml di 10 mg / ml FITC sciolto in dimetil sulfoxide (DMSO), vortice, coprire con un foglio, e incubare con agitazione per 4 ore a temperatura ambiente. </li><li> Per rimuovere il colorante, lavare come in precedenza (punto 1.2), prima con 0,5 ml di DMSO + 150 l di PBS, poi 0,5 ml di DMSO + 300 ml di PBS, poi 0,5 ml di DMSO + 450 l di PBS, poi PBS da solo. </li><li> Conte zymosan utilizzando un emocitometro. Aggiungere 1 ml di zymosan a 500 microlitri di PBS, vortex, quindi aggiungere 10 microlitri al bordo della camera dell&#39;emocitometro, dove incontra il coprioggetto posto sopra la griglia centrale. Montare il emocitometro su un microscopio in campo chiaro equipaggiato con un obiettivo 20X. </li><li> Focus su nell&#39;angolo in alto a sinistra contenente 16 piazze e contare tutte le particelle zymosan in questo settore con un contatore riscontro mano. Ripetere con l&#39;angolo in basso a destra. Calcolare la concentrazione zymosan utilizzando la seguente equazione: concentrazione Zymosan = Count / 2 x 500 x 10 4 zymosan / ml. Zymosan etichettati, possono essere aliquotato, congelato e conservato a -20 ° C. </li><li> Opsonize l&#39;etichetta wi zymosanTh A anticorpo anti-coniglio di zymosan a diluizione 1: 100. Vortex e incubare per 1 ora in un bagno d&#39;acqua a 37 ° C. Lavare con 500 microlitri di PBS come sopra (punto 1.2). Nota: Sonicazione è altamente raccomandato, in particolare dopo opsonizzazione, come zymosan tende a formare grumi che possono rendere l&#39;analisi più difficile in seguito. Opsonizzazione con il 65% v / v di ratto o siero umano può essere utilizzato in alternativa. </li><li> Conte zymosan utilizzando un emocitometro come descritto nei passaggi 1,7-1,8, e portare a 100 x 10 6 particelle / ml. Opsonizzazione con altri stimolatori fagocitosi, come complemento o no opsonizzazione, può essere effettuata in alternativa. </li></ol> 2. Live Video Microscopia <ol><li> Isolare neutrofili principale del mouse come descritto in dettaglio altrove 38. <ol><li> In alternativa, utilizzare qualsiasi tipo di cellula fagocitica. Mantenere neutrofili sul ghiaccio in Roswell Park Memorial Institute (RPMI) 1640 supplementato con 5% di siero fetale bovino (v / v), penicillina 200 U / streptomycin, ad una concentrazione di 10 x 10 6 cellule / ml fino al momento dell&#39;uso. Altri tipi di cellule possono essere seminate 1-4 giorni prima. </li></ol></li><li> Aggiungere 2 x 10 5 (20 ml) di neutrofili al centro di un piatto fondo di vetro 35 mm, diffondere il calo aggiungendo 50 ml di terreno ed incubare a 37 ° C per 5 minuti per consentire cellule di aderire. </li><li> Aggiungere 1 ml di soluzione salina bilanciata di Hank (HBSS) riscaldato a 37 ° C che contiene la specifica MPO idrazide inibitore 4-aminobenzoico (4-ABH, 10 micron). Non specifici inibitori MPO, come il sodio azide (5 mm), possono anche essere utilizzati, ma sono state recentemente suggerito di esercitare ulteriori effetti non specifici sul pH 39. </li><li> Montare il piatto su un microscopio a fluorescenza widefield dotato di un sistema di riscaldamento 37 ° C e un obiettivo 40X olio. Incubare le cellule senza l&#39;imaging per 10 minuti per consentire alle cellule e attrezzature equilibrare. </li><li> Regolare le impostazioni del microscopio per acquisire un&#39;immagine di trasmissione in campo chiaro [phase o il contrasto di interferenza differenziale (DIC), se disponibile] con 440 nm o 490 nm di eccitazione e 535 nm di emissione ogni 30 sec. </li><li> Regolare il tempo di esposizione e la frequenza di acquisizione secondo il sistema microscopio per evitare troppo photobleaching e fototossicità e seconda delle domande sperimentali viene chiesto. Inizia l&#39;acquisizione delle immagini. </li><li> Dopo 2 min, aggiungere 10 x 10 6 (50 microlitri) opsonizzati FITC-zymosan al centro del piatto. Regolare bersaglio: i rapporti di cellule a seconda del tipo di fagociti e target utilizzato. </li><li> Continuare di imaging per 30 min. Dopo 30 minuti fermare l&#39;acquisizione time-lapse e avviare un timer. Spostare lo stadio e catturare più di 10 istantanee in diversi campi di vista di immagine altri fagosomi, tutti a 5 minuti. </li></ol> 3. taratura e controllo Esperimenti <ol><li> Preparare le soluzioni di taratura pH (ricette sono descritti nella Tabella 1) prima del giorno di esperimento e congelare in 10 ml aliquote.Scongelare le soluzioni di taratura e la calda a 37 ° C in un bagno d&#39;acqua. Controllare il pH con un pHmetro e registrare il pH effettivo di soluzioni. </li><li> Montare una pompa peristaltica sul fondo piatto di vetro prima acquisizione dell&#39;immagine ed eseguire la microscopia video dal vivo come descritto sopra (sezione 2). </li><li> Alla fine del periodo di acquisizione 30 min accendere la pompa per rimuovere la soluzione all&#39;interno del piatto, aggiungere 1 ml della prima soluzione di calibrazione e arrestare la pompa. </li><li> Attendere che il segnale si stabilizza, di solito 5 min. Ripetere con ogni soluzione di calibrazione. <ol><li> Effettuare almeno una calibrazione al giorno sperimentale, e calibrare iniziando con il più alto pH e sequenzialmente lavorare al minimo, così come a partire dal pH basso e lavorando in sequenza verso l&#39;alto. </li></ol></li><li> Come controllo, aggiungere 100 ml di 100 mM inibitore NADPH ossidasi difenil propionium ioduro (DPI) diluiti in HBSS alle cellule in 900 microlitri HBSS nel piatto fondo di vetro, eincubare per 10 min. </li><li> Avviare l&#39;acquisizione e aggiungere zymosan come sopra (punto 2.7). Dopo 15 min di fagocitosi, aggiungere 10 ml di 10 mM inibitore V-ATPasi concanamycin A (ConcA) diluiti in HBSS e continuare l&#39;imaging per altri 15 min. </li></ol> 4. Analisi <ol><li> L&#39;analisi dei filmati time-lapse e istantanee phagosome. Nota: Le seguenti istruzioni sono specifici per ImageJ. Step-by-passo le istruzioni possono variare ampiamente a seconda del software utilizzato, ma le funzioni descritte in questa sezione sono disponibili nella maggior parte dei software di analisi immagine professionale. <ol><li> Aprire le immagini con il software di analisi di immagine professionale. Sottrarre il fondo nel canale 490 tracciando una piccola ROI piazza con lo strumento di selezione del poligono piazza in una zona dove non ci sono le cellule, e facendo clic su Plugins&gt; BG Sottrazione di ROI. Poi caricare lo stesso ROI sul canale 440 facendo clic su Modifica&gt; Selezione&gt; Ripristina selezione e ripetere. </li><li>Fare un rapporto di immagine a 32 bit del canale 490 diviso per il canale 440 cliccando processo&gt; Calcolatrice Immagine ..., selezionando le immagini appropriate nei menu a scorrimento visualizzati Image1 e Image2, quindi selezionando &#39;Divide&#39; nel menu a discesa Operazione , e controllando il risultato casella di controllo a 32 bit (float). </li><li> Cambia il look-up table colori per una codifica a colori compatibile rapporto facendo clic su Immagine&gt; tabelle di ricerca&gt; Arcobaleno RGB. Soglia l&#39;immagine rapporto di eliminare 0 e infinito pixel facendo clic su Immagine&gt; Regola&gt; Soglia .... Regolare le barre di scorrimento in modo che zymosan appare in rosso e fare clic su Applica, assicurandosi che i pixel dello sfondo Imposta la casella di controllo per NaN è selezionata. </li><li> Combinate questo rapporto stack con il canale in campo chiaro in un composito multi-canale cliccando Immagine&gt; Colore&gt; Unisci canali, e selezionando l&#39;immagine in campo chiaro nel menu a discesa dei canali grigio e l&#39;immagine il rapporto nel menu a discesa canale verde, e selezionando laMantenere immagini di origine check-box. Scansione film time-lapse o istantanee per determinare quale phagosomes devono essere analizzati. Il canale in campo chiaro è utile per questo. </li><li> Disegna regioni di interesse (ROI) utilizzando lo strumento di selezione ovale poligono attorno fagosomi, e aggiungerli al gestore ROI facendo clic su Analizza&gt; Strumenti&gt; ROI Manager&gt; Aggiungi. Misurare il loro rapporto di intensità zymosan facendo clic su Altro&gt; multimisura e de-selezionando l&#39;Una riga per fetta casella di controllo. </li><li> Per i filmati time-lapse, pista phagosomes uno alla volta disegnando un ROI, digitando CTRL + M per misurare ogni punto di tempo, e spostando il ROI in caso di necessità di monitorare i valori di intensità nel corso del tempo. Copiare le misurazioni dalla finestra Risultati in un foglio elettronico. Nota: Analisi di 15 (5 andamenti temporali per esperimento x 3) esperimenti indipendenti è ideale, ma più o meno può essere richiesta a seconda della variabilità osservata. Salvataggio delle ROI è sempre consigliato. Alcuni pacchetti software consentono regi immaginestrazione e aggiornamento dinamico di ROI, facilitare questo parte dell&#39;analisi. </li></ol></li><li> La conversione da fluorescenza a valori di pH <ol><li> Misurare il rapporto 490/440 per phagosomes nella calibrazione film time-lapse, come descritto nella sezione 4.1. </li><li> In un foglio di calcolo, tracciare i valori del rapporto nel corso del tempo, e calcolare i valori medi del rapporto da tutti i fagosomi all&#39;interno del campo di vista (di solito, tra 5-20) da 5 punti temporali entro la metà del periodo di tempo corrispondente ad ogni calibrazione pH soluzione. (Vedi anche le caselle rosse nella figura 5A.) </li><li> Tracciare questi medi 490/440 valori del rapporto contro il pH attuale di misura. Combina almeno 3 tarature indipendenti in un unico grafico. Utilizzare un pacchetto software statistico o numerico per eseguire una regressione lineare (migliore misura della curva), di solito per una equazione sigmoidale. Nota: per esempio, nella Figura 5B l&#39;equazione utilizzata era un sigmoidale Boltzmann [Y = inferiore + ((Alto-Basso)/ (1 + EXP ((V50-X) / Slope))], dove i valori di Y sono i rapporti 490/440, X sono i valori di pH e alto, in basso, i parametri V50 e pendenza sono calcolati dal software. </li><li> Usare l&#39;equazione ottenuto di trasformare valori di rapporto al pH. Nota: Per esempio, nella Figura 5B nell&#39;equazione ottenuto per la curva di calibrazione in presenza di sodio azide è 490/440 Ratio = 1.103 + [(2.89-1.103) / (1 ​​+ EXP ((6.993-pH) /0.9291)] . Risolvendo per pH dà la seguente equazione: pH = 6.993 - 0,9291 * [LN ((1.178 / (Ratio-1.103)) - 1))]. </li></ol></li></ol>

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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. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=gamma-Interferon-inducible+lysosomal+thiol+reductase+(GILT)+maintains+phagosomal+proteolysis+in+alternatively+activated+macrophages.">gamma-Interferon-inducible lysosomal thiol reductase (GILT) maintains phagosomal proteolysis in alternatively activated macrophages.</a> J Biol Chem. 289 (46), 31891-31904 (2014).</li><li>Sanjurjo, L., 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=The+scavenger+protein+apoptosis+inhibitor+of+macrophages+(AIM)+potentiates+the+antimicrobial+response+against+Mycobacterium+tuberculosis+by+enhancing+autophagy.">The scavenger protein apoptosis inhibitor of macrophages (AIM) potentiates the antimicrobial response against Mycobacterium tuberculosis by enhancing autophagy.</a> PLoS One. 8 (11), e79670 (2013).</li><li>Yuan, Z., Zhi, L., Li-Juan, Z., Hong-Tao, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Utility+of+Chloroquine+in+Cancer+Therapy.">The Utility of Chloroquine in Cancer Therapy.</a> Curr Med Res Opin. , 1-12 (2015).</li><li>Ohkuma, S., Poole, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescence+probe+measurement+of+the+intralysosomal+pH+in+living+cells+and+the+perturbation+of+pH+by+various+agents.">Fluorescence probe measurement of the intralysosomal pH in living cells and the perturbation of pH by various agents.</a> Proc Natl Acad Sci U S A. 75 (7), 3327-3331 (1978).</li><li>El Chemaly, 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=VSOP/Hv1+proton+channels+sustain+calcium+entry,+neutrophil+migration,+and+superoxide+production+by+limiting+cell+depolarization+and+acidification.">VSOP/Hv1 proton channels sustain calcium entry, neutrophil migration, and superoxide production by limiting cell depolarization and acidification.</a> J Exp Med. 207 (1), 129-139 (2010).</li><li>Levine, A. 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. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+and+regulation+of+the+cellular+responses+to+cold+shock:+the+responses+in+yeast+and+mammalian+systems.">Control and regulation of the cellular responses to cold shock: the responses in yeast and mammalian systems.</a> Biochem J. 397 (2), 247-259 (2006).</li><li>Yui, N., 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=Basolateral+targeting+and+microtubule-dependent+transcytosis+of+the+aquaporin-2+water+channel.">Basolateral targeting and microtubule-dependent transcytosis of the aquaporin-2 water channel.</a> Am J Physiol Cell Physiol. 304 (1), C38-C48 (2013).</li><li>Griffiths, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+phagosome+individuality+and+membrane+signalling+networks.">On phagosome individuality and membrane signalling networks.</a> Trends Cell Biol. 14 (7), 343-351 (2004).</li><li>Poburko, D., Santo-Domingo, J., Demaurex, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+regulation+of+the+mitochondrial+proton+gradient+during+cytosolic+calcium+elevations.">Dynamic regulation of the mitochondrial proton gradient during cytosolic calcium elevations.</a> J Biol Chem. 286 (13), 11672-11684 (2011).</li></ol>

The authors have nothing to disclose.

Sebbene più tempo rispetto metodi alternativi, come la spettroscopia e FACS, che impiegano una simile strategia di utilizzo di un colorante sensibile al pH accoppiato obiettivi ma misurano il pH medio di una popolazione di fagosomi, microscopia offre diversi vantaggi. Prima è che interno ed esterno vincolati, ma non interiorizzato, le particelle possono essere facilmente distinguibili, senza dover aggiungere altre sostanze chimiche, come trypan blu o di anticorpi, per placare o etichettare particelle esterne, rispetti...

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>Toxic, use gloves, various providers exist</td></tr><tr><td>Hank&#039;s balance salt solution</td><td>Life Technologies</td><td>14025092</td><td>Ringer&#039;s balanced salt solution or other clear physiological buffers may be substituted.</td></tr><tr><td>Sodium carbonate (Na&lt;sub&gt;2&lt;/sub&gt;CO&lt;sub&gt;3&lt;/sub&gt;)</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&amp;nbsp;</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&amp;nbsp;</td><td>Various providers exist</td></tr><tr><td>Ethylene glycol-bis(2-aminoethylether)-N,N,N&amp;prime;,N&amp;prime;-tetraacetic acid (EGTA)</td><td>Sigma-Aldrich</td><td>3777</td><td>Various providers exist</td></tr><tr><td>Tris(hydroxymethyl)aminomethane (Tris)</td><td>Sigma-Aldrich</td><td>T1503&amp;nbsp;</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 (MgCl&lt;sub&gt;2&lt;/sub&gt;)</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 &amp;micro;-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.&amp;nbsp;&amp;nbsp;</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

Fagocitosi è un processo fondamentale attraverso il quale le cellule immunitarie innate fagocitare batteri, cellule apoptotiche o altre particelle estranee al fine di uccidere o neutralizzare il materiale ingerito, o di presentarlo come antigeni e di avviare le risposte immunitarie adattive. Il pH di fagosomi è un parametro critico regolazione fissione o fusione con endomembrane e l&#39;attivazione degli enzimi proteolitici, eventi che permettono al vacuolo fagocitosi di maturare in un organello degradativa. Inoltre, è richiesto di traslocazione H + per la produzione di elevati livelli di specie reattive dell&#39;ossigeno (ROS), che sono essenziali per l&#39;uccisione efficiente e segnalazione ad altri tessuti dell&#39;ospite. Molti patogeni intracellulari sovvertono uccisione fagocitico limitando phagosomal acidificazione, sottolineando l&#39;importanza del pH in phagosome biologia. Qui si descrive un metodo per misurare raziometrica phagosomal pH nei neutrofili con fluoresceina isotiocianato (FITC) -labeled zymosan come phagocytic targETS e live-cell imaging. Il saggio si basa sulle proprietà di fluorescenza di FITC, che si spegne da pH acido quando eccitato a 490 nm ma non quando eccitato a 440 nm, permettendo la quantificazione di un rapporto pH-dipendente, piuttosto che di fluorescenza assoluta, di un singolo colorante. Viene inoltre fornito un protocollo dettagliato per l&#39;esecuzione in loco di calibrazione tintura e la conversione del rapporto di valori reali di pH. Single-dye metodi raziometriche sono generalmente considerati superiori a singola lunghezza d&#39;onda o protocolli pseudo-raziometrico dual-dye, in quanto sono meno sensibili alle perturbazioni, come lo sbiancamento, concentrarsi modifiche, variazioni laser, e l&#39;etichettatura irregolare, che distorcono il segnale misurato. Questo metodo può essere facilmente modificato per misurare il pH in altri tipi di cellule fagocitiche e zymosan può essere sostituita da qualsiasi altra particella contenente ammina, da perline inerti ai microrganismi viventi. Infine, questo metodo può essere adattato a fare uso di altre sonde fluorescenti sensibili a diversi intervalli di pH o altri phagosomattività al, rendendolo un protocollo generale per l&#39;imaging funzionale di fagosomi.

Di seguito sono riportati i risultati rappresentativi per un esperimento in cui il pH phagosomal dei neutrofili topo primari isolati dal midollo osseo di wild-type o Hvcn1 - / - sono stati confrontati topi. Per un esperimento riuscito, è importante ottenere abbastanza fagosomi all&#39;interno del campo visivo durante tutta la durata del film accelerato, evitando troppi fagosomi, che sarà poi essere più difficile segmento durante l&#39;analisi delle immagini. La figura 1 mostra</...

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.

Misurare phagosome pH Raziometrico microscopia a fluorescenza

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

Universidad de Cartagena UDEC

Research

JoVE Journal

Immunology and Infection

13.9K Views.  University of Geneva. 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. 

Video: Measuring Phagosome pH by Ratiometric Fluorescence Microscopy

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.

Studio di fagolisosoma Biogenesis nei macrofagi in diretta

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

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Immunologia e infezioni

High Throughput Fluorometric Technique for Assessment of Macrophage Phagocytosis and Actin Polymerization

The goal of fluorometric analysis is to serve as an efficient, cost effective, high throughput method of analyzing phagocytosis and other cellular processes. This technique can be used on a variety of cell types, both adherent and non-adherent, to examine a variety of cellular properties. When studying phagocytosis, fluorometric technique utilizes phagocytic cell types such as macrophages, and fluorescently labeled opsonized particles whose fluorescence can be extinguished in the presence of trypan blue. Following plating of adherent macrophages in 96-well plates, fluorescent particles (green or red) are administered and cells are allowed to phagocytose for varied amounts of time. Following internalization of fluorescent particles, cells are washed with trypan blue, which facilitates extinction of fluorescent signal from bacteria which are not internalized, or are merely adhering to the cell surface. Following the trypan wash, cells are washed with PBS, fixed, and stained with DAPI (nuclear blue fluorescent label), which serves to label nuclei of cells. By a simple fluorometric quantification through plate reading of nuclear (blue) or particle (red/green) fluorescence we can examine the ratio of relative fluorescence units of green:blue and determine a phagocytic index indicative of amount of fluorescent bacteria internalized per cell. The duration of assay using a 96-well method and multichannel pipettes for washing, from end of phagocytosis to end of data acquisition, is less than 45 min. Flow cytometry could be used in a similar manner but the advantage of fluorometry is its high throughput, rapid method of assessment with minimal manipulation of samples and quick quantification of fluorescent intensity per cell. Similar strategies can be applied to non adherent cells, live labeled bacteria, actin polymerization, and essentially any process utilizing fluorescence. Therefore, fluorometry is a promising method for its low cost, high throughput capabilities in the study of cellular processes.

Here we present a protocol to quantify phagocytosis of fluorescent particles by adherent macrophage cell line using a fluorometric method. This method facilitates a high throughput quantification of particle internalization as well as the resulting actin polymerization.

Alta Tecnica Throughput fluorometrica per la valutazione dei macrofagi fagocitosi e polimerizzazione

The goal of fluorometric analysis is to serve as an efficient, cost effective, high throughput method of analyzing phagocytosis and other cellular ...

"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.

"Phagosome Closure Assay" 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 chiusura Assay&quot; per visualizzare phagosome Formazione in tre dimensioni utilizzando la riflessione totale interna fluorescente 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.

Imaging dei neutrofili phagosome e nel citoplasma utilizzo di un indicatore di pH Raziometrico

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

Quantification of Efferocytosis by Single-cell Fluorescence Microscopy

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling and cellular processes that control efferocytosis. This quantification can be difficult to perform as apoptotic cells are often efferocytosed piecemeal, thus necessitating methods which can accurately delineate between the efferocytosed portion of an apoptotic target versus residual unengulfed cellular fragments. The approach outlined herein utilizes dual-labeling approaches to accurately quantify the dynamics of efferocytosis and efferocytic capacity of efferocytes such as macrophages. The cytosol of the apoptotic cell is labeled with a cell-tracking dye to enable monitoring of all apoptotic cell-derived materials, while surface biotinylation of the apoptotic cell allows for differentiation between internalized and non-internalized apoptotic cell fractions. The efferocytic capacity of efferocytes is determined by taking fluorescent images of live or fixed cells and quantifying the amount of bound versus internalized targets, as differentiated by streptavidin staining. This approach offers several advantages over methods such as flow cytometry, namely the accurate delineation of non-efferocytosed versus efferocytosed apoptotic cell fractions, the ability to measure efferocytic dynamics by live-cell microscopy, and the capacity to perform studies of cellular signaling in cells expressing fluorescently-labeled transgenes. Combined, the methods outlined in this protocol serve as the basis for a flexible experimental approach that can be used to accurately quantify efferocytic activity and interrogate cellular signaling pathways active during efferocytosis.

Efferocytosis, the phagocytic removal of apoptotic cells, is required to maintain homeostasis and is facilitated by receptors and signaling pathways that allow for the recognition, engulfment, and internalization of apoptotic cells. Herein, we present a fluorescence microscopy protocol for the quantification of efferocytosis and the activity of efferocytic signaling pathways.

Quantificazione del fagosoma da microscopia di fluorescenza di cella singola

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling ...

Measuring the pH, Redox Chemistries, and Degradative Capacity of Macropinosomes using Dual-Fluorophore Ratiometric Microscopy

In recent years, the field of macropinocytosis has grown rapidly. Macropinocytosis has emerged as a central mechanism by which innate immune cells maintain organismal homeostasis and immunity. Simultaneously, and in contrast to its homeostatic role, it can also drive various pathologies, including cancer and viral infections. Unlike other modes of endocytosis, the tools developed for studying the maturation of macropinosomes remain underdeveloped. Here the protocol describes newly developed tools for studying the redox environment within the lumen of early and maturing macropinosomes. Methodologies for using ratiometric fluorescence microscopy in assessing the pH, production of reactive oxygen species, and the degradative capacity within the lumen of individual macropinosomes in live cells are described. Single organelle measurements offer the advantage of revealing spatiotemporal heterogeneity, which is often lost with population-based approaches. Emphasis is placed on the basic principles of dual fluorophore ratiometric microscopy, including probe selection, instrumentation, calibration, and single-cell versus population-based methods.

We describe protocols for measuring pH, oxidative events, and protein digestion in individual macropinosomes in live cells. An emphasis is placed on dual-fluorophore ratiometric microscopy and the advantages it offers over population-based techniques.

Misurazione del pH, delle sostanze chimiche redox e della capacità degradativa dei macropinosomi utilizzando la microscopia a doppio fluoroforo

In recent years, the field of macropinocytosis has grown rapidly. Macropinocytosis has emerged as a central mechanism by which innate immune cells ...

Simultaneous pH Measurement in Endocytic and Cytosolic Compartments in Living Cells using Confocal Microscopy

Intracellular pH is tightly regulated and differences in pH between the cytoplasm and organelles have been reported1. Regulation of cellular pH is crucial for homeostatic control of physiological processes that include: protein, DNA and RNA synthesis, vesicular trafficking, cell growth and cell division. Alterations in cellular pH homeostasis can lead to detrimental functional changes and promote progression of various diseases2. Various methods are available for measuring intracellular pH but very few of these allow simultaneous measurement of pH in the cytoplasm and in organelles. Here, we describe in detail a rapid and accurate method for the simultaneous measurement of cytoplasmic and organellar pH by using confocal microscopy on living cells3. This goal is achieved with the use of two pH-sensing ratiometric dyes that possess selective cellular compartment partitioning. For instance, SNARF-1 is compartmentalized inside the cytoplasm whereas HPTS is compartmentalized inside endosomal/lysosomal organelles. Although HPTS is commonly used as a cytoplasmic pH indicator, this dye can specifically label vesicles along the endosomal-lysosomal pathway after being taken up by pinocytosis3,4. Using these pH-sensing probes, it is possible to simultaneously measure pH within the endocytic and cytoplasmic compartments. The optimal excitation wavelength of HPTS varies depending on the pH while for SNARF-1, it is the optimal emission wavelength that varies. Following loading with SNARF-1 and HPTS, cells are cultured in different pH-calibrated solutions to construct a pH standard curve for each probe. Cell imaging by confocal microscopy allows elimination of artifacts and background noise. Because of the spectral properties of HPTS, this probe is better suited for measurement of the mildly acidic endosomal compartment or to demonstrate alkalinization of the endosomal/lysosomal organelles. This method simplifies data analysis, improves accuracy of pH measurements and can be used to address fundamental questions related to pH modulation during cell responses to external challenges.

Several methods are available for measuring intracellular pH but very few of these allow simultaneous measurement of cytoplasmic and organellar pH. Here, we describe in detail a rapid and accurate methodology to simultaneously measure cytoplasmic and vesicular pH by ratiometric imaging of living cells.

La misurazione simultanea di pH in endocitosi e citosoliche scomparti nelle cellule viventi usando Microscopia confocale

Intracellular pH is tightly regulated and differences in pH between the cytoplasm and organelles have been reported1. Regulation of cellular pH is crucial ...

Biologia

In vitro Quantitative Imaging Assay for Phagocytosis of Dead Neuroblastoma Cells by iPSC-Macrophages

Microglia orchestrate neuroimmune responses in several neurodegenerative diseases, including Parkinson&#39;s disease and Alzheimer&#39;s disease. Microglia clear up dead and dying neurons through the process of efferocytosis, a specialized form of phagocytosis. The phagocytosis function can be disrupted by environmental or genetic risk factors that affect microglia. This paper presents a rapid and simple in vitro&#160;microscopy protocol for studying microglial efferocytosis in an induced pluripotent stem cell (iPSC) model of microglia, using a human neuroblastoma cell line (SH-SY5Y) labeled with a pH-sensitive dye for the phagocytic cargo. The procedure results in a high yield of dead neuroblastoma cells, which display surface phosphatidylserine, recognized as an &#34;eat-me&#34; signal by phagocytes. The 96-well plate assay is suitable for live-cell time-lapse imaging, or the plate can be successfully fixed prior to further processing and quantified by high-content microscopy. Fixed-cell high-content microscopy enables the assay to be scaled up for screening of small molecule inhibitors or assessing the phagocytic function of genetic variant iPSC lines. While this assay was developed to study phagocytosis of whole dead neuroblastoma cells by iPSC-macrophages, the assay can be easily adapted for other cargoes relevant to neurodegenerative diseases, such as synaptosomes and myelin, and other phagocytic cell types.

Neurodegenerative diseases are associated with dysregulated microglia functions. This article outlines an in vitro assay of phagocytosis of neuroblastoma cells by iPSC-macrophages. Quantitative microscopy readouts are described for both live-cell time-lapse imaging and fixed-cell high-content imaging.

Test di imaging quantitativo in vitro per la fagocitosi delle cellule morte del neuroblastoma da parte di iPSC-Macrophages

Microglia orchestrate neuroimmune responses in several neurodegenerative diseases, including Parkinson&#39;s disease and Alzheimer&#39;s disease. ...

Neuroscienze

Utilizing pHluorin-tagged Receptors to Monitor Subcellular Localization and Trafficking

Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular organelles and those localized on the plasma membrane. Traditional fluorescence-based measurements lack the capability to distinguish membrane proteins residing in different organelles. Cutting edge methodologies transcend traditional methods by coupling pH-sensitive fluorophores with total internal reflection fluorescence microscopy (TIRFM). TIRF illumination excites the sample up to approximately 150 nm from the glass-sample interface, thus decreasing background, increasing the signal to noise ratio, and enhancing resolution. The excitation volume in TIRFM encompasses the plasma membrane and nearby organelles such as the peripheral ER. Superecliptic pHluorin (SEP) is a pH sensitive version of GFP. Genetically encoding SEP into the extracellular domain of a membrane protein of interest positions the fluorophore on the luminal side of the ER and in the extracellular region of the cell. SEP is fluorescent when the pH is greater than 6, but remains in an off state at lower pH values. Therefore, receptors tagged with SEP fluoresce when residing in the endoplasmic reticulum (ER) or upon insertion in the plasma membrane (PM) but not when confined to a trafficking vesicle or other organelles such as the Golgi. The extracellular pH can be adjusted to dictate the fluorescence of receptors on the plasma membrane. The difference in fluorescence between TIRF images at neutral and acidic extracellular pH for the same cell corresponds to a relative number of receptors on the plasma membrane. This allows a simultaneous measurement of intracellular and plasma membrane resident receptors. Single vesicle insertion events can also be measured when the extracellular pH is neutral, corresponding to a low pH trafficking vesicle fusing with the plasma membrane and transitioning into a fluorescent state. This versatile technique can be exploited to study localization, expression, and trafficking of membrane proteins.

Labeling the extracellular domain of a membrane protein with a pH sensitive fluorophore, superecliptic pHluorin (SEP), allows subcellular localization, expression, and trafficking to be determined. Imaging SEP-labeled proteins with total internal reflection fluorescence microscopy (TIRFM) enables the quantification of protein levels in the peripheral ER and plasma membrane.

Utilizzando Recettori pHluorin-tag per il monitoraggio subcellulare localizzazione e il traffico

Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular ...

TIRF Microscopy-Based Visualization of Phagosome Formation and Closure

For non-covalent fixation of the SRBCs, pour 2 milliliters of the IgG-opsonized cells into each of the poly-lysine-coated dishes, and centrifuge the samples in a swinging rotor centrifuge. Discard the supernatants, and wash the particles one time with 2 milliliters of PBS plus 10% BSA.
Then, incubate the particles with 2 milliliters of fresh PBS plus 10% BSA for 30 minutes at room temperature, followed by three washes with 2 milliliters of PBS. After the last wash, replace the PBS with 2 milliliters of 37 degrees Celsius serum-free microscopy medium.
Place an SRBC-coded dish onto the microscope stage. Then, scrape the transfected cells of interest from the bottom of the culture dish and pipette the cells a few times to achieve a single-cell suspension. Add the transfected cells to the SRBC-coated dish.
Start the live acquisition software. Find a cell that expresses the fluorescently tagged proteins and adjust the position of the dish so that a cell of interest is in the middle of the field. Acquire 500 images at different angles from 0 to 5 degrees at 0.01-degree increments at one excitation wavelength.
To determine the critical angle for the incident light to be totally reflected at the glass-medium interface and generate an evanescent wave, open the image sequence in the appropriate imaging software. Select a region of interest in the cell with uniform fluorescence.
Then, under the Image tab, select Stacks and plot Z-axis profile. To plot the Z-axis profile mean fluorescence intensity measured in the region of interest with the function of the angles on the X-axis. Any angle value on the x-axis superior to the critical angle can then be used during the microscopy session to obtain a TIRF signal.

Misurare phagosome pH Raziometrico microscopia a fluorescenza

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