The authors would like to thank the following funding sources: RO1 DA 12104, RO1 DA 022935, RO1 DA031202, K05DA033881, P50 DA 011806, 1R01DA034582 (to S.R) and F31 DA026264-01A1, T32 DA07097 (to J.N.).

NOTE: This protocol can be used for multiple applications such as quantification of phagocytosis and actin polymerization as used in our previously published work12. The protocol lends itself to a variety of modification, and Table 1 lists cell types and particles successfully utilized in past studies. Standard use of this protocol for quantification of phagocytosis or actin polymerization is illustrated in Diagram 1.
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<ol>
	<li>Murphy, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Janeway's Immunobiology. , (2012).</li><li>Burke, D. W., O'Connor, D. O., Zalenski, E. B., Jasty, M., Harris, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micromotion+of+cemented+and+uncemented+femoral+components.">Micromotion of cemented and uncemented femoral components.</a> The Journal Of Bone And Joint Surgery. British Volume. 73 (1), 33-37 (1991).</li><li>Duan, X., 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=Resistance+to+malaria+by+enhanced+phagocytosis+of+erythrocytes+in+LMP7-deficient+mice.">Resistance to malaria by enhanced phagocytosis of erythrocytes in LMP7-deficient mice.</a> PloS One. 8 (3), 59633 (2013).</li><li>Dementhon, K., El-Kirat-Chatel, S., Noel, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+an+in+vitro+model+for+the+multi-parametric+quantification+of+the+cellular+interactions+between+Candida+yeasts+and+phagocytes.">Development of an in vitro model for the multi-parametric quantification of the cellular interactions between Candida yeasts and phagocytes.</a> PloS One. 7 (3), 32621 (2012).</li><li>Al-Bader, 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=Role+of+trehalose+biosynthesis+in+Aspergillus+fumigatus+development,+stress+response,+and+virulence.">Role of trehalose biosynthesis in Aspergillus fumigatus development, stress response, and virulence.</a> Infection And Immunity. 78 (7), 3007-3018 (2010).</li><li>Acosta-Iborra, B., 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=Macrophage+oxygen+sensing+modulates+antigen+presentation+and+phagocytic+functions+involving+IFN-gamma+production+through+the+HIF-1+alpha+transcription+factor.">Macrophage oxygen sensing modulates antigen presentation and phagocytic functions involving IFN-gamma production through the HIF-1 alpha transcription factor.</a> Journal Of Immunology. 182 (5), 3155-3164 (2009).</li><li>Ojielo, C. I., 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=Defective+phagocytosis+and+clearance+of+Pseudomonas+aeruginosa+in+the+lung+following+bone+marrow+transplantation.">Defective phagocytosis and clearance of Pseudomonas aeruginosa in the lung following bone marrow transplantation.</a> Journal Of Immunology. 171 (8), 4416-4424 (2003).</li><li>Neu, C., 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=CD14-dependent+monocyte+isolation+enhances+phagocytosis+of+listeria+monocytogenes+by+proinflammatory,+GM-CSF-derived+macrophages.">CD14-dependent monocyte isolation enhances phagocytosis of listeria monocytogenes by proinflammatory, GM-CSF-derived macrophages.</a> PloS One. 8 (6), 66898 (2013).</li><li>Sokolovska, 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=Activation+of+caspase-1+by+the+NLRP3+inflammasome+regulates+the+NADPH+oxidase+NOX2+to+control+phagosome+function.">Activation of caspase-1 by the NLRP3 inflammasome regulates the NADPH oxidase NOX2 to control phagosome function.</a> Nature Immunology. 14 (6), 543-553 (2013).</li><li>Janko, C., 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=CRP/anti-CRP+antibodies+assembly+on+the+surfaces+of+cell+remnants+switches+their+phagocytic+clearance+toward+inflammation.">CRP/anti-CRP antibodies assembly on the surfaces of cell remnants switches their phagocytic clearance toward inflammation.</a> Frontiers in Immunology. 2 (2), 70 (2011).</li><li>Clatworthy, M. 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=Systemic+lupus+erythematosus-associated+defects+in+the+inhibitory+receptor+FcgammaRIIb+reduce+susceptibility+to+malaria.">Systemic lupus erythematosus-associated defects in the inhibitory receptor FcgammaRIIb reduce susceptibility to malaria.</a> Proceedings of the National Academy of Sciences of the United States of America. 104 (17), 7169-7174 (2007).</li><li>Ninkovic, J., Roy, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphine+decreases+bacterial+phagocytosis+by+inhibiting+actin+polymerization+through+cAMP-,+Rac-1-,+and+p38+MAPK-dependent+mechanisms.">Morphine decreases bacterial phagocytosis by inhibiting actin polymerization through cAMP-, Rac-1-, and p38 MAPK-dependent mechanisms.</a> The American Journal Of Pathology. 180 (3), 1068-1079 (2012).</li><li>Nix, R. N., Altschuler, S. E., Henson, P. M., Detweiler, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemophagocytic+macrophages+harbor+Salmonella+enterica+during+persistent+infection.">Hemophagocytic macrophages harbor Salmonella enterica during persistent infection.</a> PLoS Pathogens. 3 (12), 193 (2007).</li><li>Xue, X., 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=Stable+gene+transfer+and+expression+in+cord+blood-derived+CD34++hematopoietic+stem+and+progenitor+cells+by+a+hyperactive+Sleeping+Beauty+transposon+system.">Stable gene transfer and expression in cord blood-derived CD34+ hematopoietic stem and progenitor cells by a hyperactive Sleeping Beauty transposon system.</a> Blood. 114 (7), 1319-1330 (2009).</li><li>Hed, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+distinguishing+ingested+from+adhering+particles.+Methods+in+Enzymology.">Methods for distinguishing ingested from adhering particles. Methods in Enzymology.</a> 132. , 198-204 (1986).</li><li>Scott, A. J., Woods, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monitoring+internalization+of+Histoplasma+capsulatum+by+mammalian+cell+lines+using+a+fluorometric+microplate+assay.">Monitoring internalization of Histoplasma capsulatum by mammalian cell lines using a fluorometric microplate assay.</a> Medical Mycology. 38 (1), 15-22 (2000).</li></ol>

The authors have no competing financial interests.

Major limitations of the fluorometric technique are experimental variance as well as cell loss associated with extensive washing and use of non-adherent cells.
Variance is observed largely due to the variation in fluorescent particles as weighing and pipetting during preparation of the stock solution is not an exact way of maintaining identical numbers of particles from experiment to experiment. To address the problem of variance between experiments, data can be expressed in relative terms, fo...

Quantification of fluorescent signal has been widely used in a multitude of scientific methods ranging from PCR, flow cytometry, confocal microscopy, and FRET analysis to multiplex ELISA. Fluorescence imaging and quantification has a broad application and can be a great tool for quantitative analysis of various cellular processes. Use of fluorescent markers and their signal has been revolutionized in the last decade, and emergence of fluorescent plate readers has facilitated the high throughput quantification of fluorescence emitted during cellular processes.
Fluorometric analysis can serve as a great tool in quantification of phagocytosis. Phagocytosis has been studied since the discovery of phagocytes by Metchnikoff in 18001. Over the years, a variety of methods have been utilized to examine this important process essential for innate immune defense against invading bacterial, viral, fungal and parasitic pathogens2-5. Previous methods of quantification utilized microscopy and stereological techniques in order to visualize cells that are phagocytosing, which were then quantified by counting of internalized particles (manually or with use of software)6-8. Some disadvantages to using microscopy alone for quantitative analysis are that manual counting of bacteria is labor intensive and more prone to observer bias. Another method used in quantification of phagocytosis is the microbiological technique of plating of bacteria from cell lysates (following phagocytosis) on bacterial culture plates, but this method can fail to account for bactericidal mechanisms and presence of partially internalized bacteria. This method is even more labor intensive compared to microscopy and takes several days to analyze. Flow cytometry seems to be the quickest, most effective way to quantify phagocytosis and has been utilized by many groups9-11, but the high cost commonly associated with the instrument needed for the analysis makes it the most expensive method when compared to the previously mentioned assays.
The fluorometric method is a good alternative to flow cytometry for analysis of particle internalization since it offers unbiased quantification of fluorescence using equipment that is not as cost prohibitive. Other added benefits of fluorometry are high efficiency, and high throughput capabilities for quantifying fluorescence emitted by the labeled internalized particles.
Benefits of fluorometry can be extrapolated to quantification of processes other than phagocytosis. For example, fluorometric analysis can be applied to study any process leading to changes in expression of intracellular or membrane-bound receptors, changes in cell permeability/viability, transfection efficacy, and modulation in actin polymerization. One downside of fluorometric technique is that, depending on the labels used, there may be a high experiment to experiment variability which can usually be resolved by demonstrating data through relative quantification, such as fold change or percent increase from control.

<table border="0" cellpadding="0" cellspacing="0" width="820">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Name of Material/ Equipment</td>
			<td style="width:131px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:255px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;"></td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="66">
			<td height="66" style="height:66px;width:315px;">1-&#956;m yellow-green fluorescent Fluo-Spheres;</td>
			<td style="width:131px;">Molecular Probes</td>
			<td style="width:119px;">F8852</td>
			<td style="width:255px;">combine 50&#956;l with 50&#956;l opsonizing reagent for 30 min at 37oC before use</td>
		</tr>
		<tr height="87">
			<td height="87" style="height:87px;">Heat killed E. coli BioParticles fluorescein conjugate</td>
			<td style="width:131px;">Molecular Probes</td>
			<td style="width:119px;">E2861</td>
			<td style="width:255px;">reconstitute (5 mg) in 50&#956;l of PBS and combine with 50&#956;l opsonizing reagent for 30 min at 37oC before use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Opsonizing reagent</td>
			<td style="width:131px;">Molecular Probes</td>
			<td style="width:119px;">E2870</td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Rhodamine phalloidin</td>
			<td style="width:131px;">Molecular Probes</td>
			<td style="width:119px;">R415</td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DAPI</td>
			<td>Sigma-Aldrich</td>
			<td>D9542</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Trypan blue</td>
			<td style="width:131px;">Gibco</td>
			<td style="width:119px;">15250-061</td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;"></td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;"></td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td colspan="4" height="21" style="height:21px;">the items below are available in many brands but the items we used in this study are from the following manufacturers</td>
		</tr>
		<tr height="66">
			<td height="66" style="height:66px;width:315px;">RPMI Cell growth media&#160;</td>
			<td style="width:131px;">Gibco</td>
			<td style="width:119px;"></td>
			<td style="width:255px;">Supplemented with 10% FBS and 1% pennicillin/Streptomycin; warm in 37oC before use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Fluorescent plate reader-Fluostar Omega</td>
			<td style="width:131px;">BMG Labtech</td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Paraformaldehyde (16%)</td>
			<td style="width:131px;">Fischer Scientific</td>
			<td>AA433689M</td>
			<td style="width:255px;">dilute to 4% before use</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:315px;">96 well plates</td>
			<td style="width:131px;">Greiner</td>
			<td style="width:119px;">655097</td>
			<td style="width:255px;">clear or black or clear bottom - black plates</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Multichannel pipette (8-12 channels)</td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Reagent reservoirs</td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">1x PBS</td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Microfuge tubes (0.6 ml)</td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">&#160;Conicles (10 ml)</td>
			<td style="width:131px;"></td>
			<td style="width:119px;"></td>
			<td style="width:255px;"></td>
		</tr>
	</tbody>
</table>

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.

Two major ways of quantifying phagocytosis and the subsequent actin polymerization through the use of this protocol is to observe continuous or synchronized phagocytosis.
Microscopic analysis (Figure 1B) illustrates fluorescent images comparable to what the fluorometer is recording (also see Diagram 1). In Figure 1B are red fluorescence of actin, green 268 fluorescence of FITC labels HKOP E. coli, nuclear DAPI stain, and the merged im...

Watch this Scientific Journal Video about High Throughput Fluorometric Technique for Assessment of Macrophage Phagocytosis and Actin Polymerization at JoVE.com

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

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.

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

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Immunology and Infection

14.5K Views.  University of Minnesota. 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.