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.
<img alt="Diagram 1" fo:content-width="4in" src="/files/ftp_upload/52195/52195diagram1.jpg" width="600" />
Diagram 1: Diagram of fluorometric assay for quantification of phagocytosis and actin polymerization. After the cells are plated, treated, and allowed to adhere, particles labeled with green fluorescence (FITC) are added to the cells for phagocytosis. Reaction is stopped by trypan or antibiotic wash (to eliminate non-internalized particles) and fixation is performed with 4% paraformaldehyde. Cells are subsequently stained with red fluorescent actin label (rhodamine phalloidin) and blue fluorescent label (DAPI). Indexes of phagocytosis and actin polymerization are quantified as a ratio of relative fluorescence units of green/blue (FITC/DAPI), or red/blue (rhodamine/DAPI) fluorescence.
1. Plating and Treating Cells
NOTE: Before beginning, consider running the treatments with at least 4 technical replicates, and include the following controls in the plate layout: cells only (unstained, with DAPI alone or rhodamine alone) and particle only.
<ol>
	<li>Conduct all addition of reagents in steps 1-4 in a sterile cell culture hood in order to protect the samples from contamination.</li>
	<li>Plate macrophages (murine J774 cell line) in a 96-well plate at 1-5 x 104 cells in 50 &#956;l (per well) of supplemented preheated media. Ideal plates for this method are black 96-well plates with clear or black bottoms, depending on reader capabilities.
	<ol>
		<li>For supplemented media, use 10% heat inactivated FBS to avoid interference of complement cascade, and 1% penicillin/streptomycin (if not using live bacteria for phagocytosis). If using adherent cells allow 1-2 hr for adhesion, and for non-adherent cells, spin down the plate with cells for 10 min at 500 x g.</li>
	</ol>
	</li>
	<li>Add desired agonists/antagonists or vehicle control at 2x concentration (resuspended in PBS or more preferably, in supplemented media) in 50 &#956;l for a final volume of 100 &#956;l (1x) and incubate for a desired amount of time. Multichannel pipette and reagent reservoirs will facilitate fastest processing.</li>
</ol>
2. Opsonization of Fluorescent Particles
<img alt="Table 1" fo:content-width="5in" src="/files/ftp_upload/52195/52195table1.jpg" width="500" /> 
Table 1: Tested cell types and fluorescent particles in fluorometric analysis of phagocytosis and actin polymerization. Table 1 illustrates combinations of cell types (cell lines, and primary cells) that our group has used via the fluorometric method. Other than looking at phagocytosis and actin polymerization by wild type cells, we have also utilized some of these particles for examination of phagocytosis by transfected cells expressing a GFP (green fluorescent protein). Fluorescence of the cells transfected with plasmids containing fluorescent reporters can also be used as a cellular marker in addition to DAPI. Table legend: A - actin polymerization; P - phagocytosis; PT - phagocytosis by GFP labeled transfected cells; OPDex - opsonized dextran bead; HKOP - heat killed opsonized.
<ol>
	<li>Ensure that fluorescent particles and labels are protected from light at all times, during processing, washing, as well as during the incubation in order to prevent photobleaching
	<ol>
		<li>For dry particles, weigh out fluorescent heat killed opsonized (HKOP) bacteria (E2861: E. coli K-12 strain), using manufacturer&#8217;s specifications. Take care to make sure the mass accounts for 10:1 - 20:1 bacteria:cell ratio (or at least a 10:1 ratio - commonly used in quantification of phagocytosis)13,14. Number of particles can be provided by the manufacturer or determined via couting serial dilutions of 1 mg/ml stock solution.</li>
		<li>Resuspend in 50 &#956;l PBS and vortex for 1 minute at highest setting. Ensure proper vortexing (here and throughout the protocol) as the particles tend to aggregate which may affect efficacy of opsonization.</li>
		<li>For particles in suspension such as fluorescently labeled dextran beads (DEX beads), vortex the stock solution for 1 min, take 50 &#956;l of suspension or depending on the bead concentration in the volume determine mount of beads to facilitate 10:1 bead:cell ratio.</li>
	</ol>
	</li>
	<li>Add an equal volume of the opsonizing reagent to the particles and vigorously vortex for another minute.</li>
	<li>Incubate the particles with opsonizing reagent at 37 &#176;C for 1 hr.</li>
	<li>Following the incubation, centrifuge the particles for 5 min at 500 x g, and remove the supernant containing excess opsonizing reagent. Wash the particles by adding 100 &#956;l of PBS, vortex to resuspend the pellet, and centrifugate for 5 min at 500 x g.
	<ol>
		<li>Repeat these steps two times to assure proper opsonization and removal of unbound antibody.</li>
	</ol>
	</li>
	<li>Prepare the working solution of opsonized particles by resuspending them in 5 ml of media (sufficient for one 96-well plate) and store away from light until addition to the cells.</li>
</ol>
3. Phagocytosis
<ol>
	<li>Place the working solution of particles in a sterile reagent reservoir. From here, add 50 &#956;l of opsonized particles to the cells prepared in step 1 (for a final concentration of 50 ng/ml) and allow phagocytosis to occur at standard cell culture conditions. Illustrated below are two methods of phagocytosis which can be assessed using this method (Diagram 2).</li>
</ol>
<img alt="Diagram 2" fo:content-width="4in" src="/files/ftp_upload/52195/52195diagram2.jpg" width="600" /> 
Diagram 2: Comparison of continuous versus synchronize phagocytosis. Continuous phagocytosis indicates continuous internalization of particles over time as they slowly reach the cells on the bottom of the well. A contrasting synchronization step (centrifugation) forces the particles to sink to the bottom, enhancing the particle contact with the cell, and leading to immediate internalization by the cells. Synchronized phagocytosis is a quicker process which more rapidly internalizes particles due to the increased cell:particle contact.
<ol>
	<li>
	<ol>
		<li>For the continuous phagocytosis method (Diagram 2) that allow cells to continuously phagocytose opsonized bacteria as they slowly sink to the bottom and come in contact with cells, utilize longer time frames to allow for the bacteria to reach the bottom of the well and get in touch with the cells. If conducting a timecourse experiment, add bacteria at different time intervals and stop the entire plate of reactions at the same time to enhance the speed of processing.</li>
		<li>For the synchronized phagocytosis method (Diagram 2) that enhances particle: cell contact via centrifugation, spin down the entire plate containing cells and particles (5 min at 500 x g) as soon as the particles are added, to facilitate synchronization of all time points and to expedite the particle: cell interaction.
		<ol>
			<li>Measure the time course starting right after the completion of the centrifugation step. If conducting a time course experiment, stop each time point independently at different time intervals as described below.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
NOTE: The synchronized phagocytosis method is somewhat more laborious from the previous one, but provides higher phagocytic index in a shorter time.
4. Stopping Phagocytosis
<ol>
	<li>For adherent cells, remove the supernatant and add 50 &#956;l of diluted trypan blue with PBS (1:2 dilution), in order to extinguish fluorescence of non-internalized bacteria.</li>
	<li>For non-adherent cells, spin down the plate and remove supernatant. Add 50 &#956;l of diluted trypan blue. Ensure to centrifuge the plate at (5-10 min at 500 x g) between each wash in order to minimize the cell loss and enable adequate washing.</li>
	<li>Following trypan incubation, wash cells two times with PBS to remove any residual trypan (until the PBS removed from the well turns clear). Trypan has been shown to quench fluorescence15,16 of non-internalized fluorescently labeled, heat killed, bacterial particles, but not for live bacteria or OPDex beads. For live bacteria, include a wash with antibiotics such as penicillin, streptomycin, or gentamicin instead of the trypan wash to avoid confounding effects of fluorescence from non-internalized particles.</li>
	<li>Fix cells with 100 &#956;l of 4% paraformaldehyde, and incubate for 15 min at room temperature, then wash with PBS (at 100 &#956;l per well for each wash). At this step, save the cells at 4 &#176;C for up to a week, or proceed directly to staining and quantification. 
	NOTE: All the subsequent steps form this point foreword can be done outside of the cell culture hood.</li>
	<li>Remove all liquid and add 50 &#956;l of DAPI at 5 ng/ml reconstituted in PBS. Allow 5 min for staining, and then wash twice with PBS. Following the wash step, add 50 &#956;l of PBS to each well and record phagocytosis.</li>
</ol>
5. Actin Staining
NOTE: In addition to phagocytosis, fluorometric method will enable quantification of actin polymerization by measuring intensity of actin, which is reduced during inhibition of lamellipodia, pseudopodiae, and membrane ruffling as a result of treatment with an inhibitor (Figure 1A). This is an optional step if interested in quantification of actin polymerization in addition to phagocytosis. If actin polymerization is the final goal, using fluorescent particles for phagocytosis is optional.
<ol>
	<li>Following paraformaldehyde fixation (step 4.3), wash the plate twice with PBS at 100 &#956;l per well for each wash. Add 50 &#956;l of 0.1% Triton X-100 in PBS for permeabilization and incubate for&#160; -5 min at RT.</li>
	<li>Wash out 0.1% Triton X-100 2 times with PBS (as above), and block with 1% bovine serum albumin (BSA) for 20 min to avoid non-specific binding of the label.</li>
	<li>Following blocking, remove the BSA solution and immediately add rhodamine phalloidin. To prepare the working solution of rhodamine stain, use 100 &#956;l of methanoic solution (provided by the manufacturer) in 5 ml of PBS (sufficient for one plate). From the working solution add 50 &#956;l per well and incubate for 20 min at room temperature. 
	NOTE: Following the washing steps and DAPI staining as in step 4.4 cells will be ready for quantification.</li>
</ol>
6. Quantification
<ol>
	<li>To quantify the phagocytosis using a fluorescent plate reader, record green fluorescence using excitation filter at &#955; = 488 nm and emission filter at &#955; = 518 nm, and blue fluorescence using excitation filter at &#955; = 355 nm and emission filter at &#955; = 460 nm.</li>
	<li>To quantify the actin polymerization using a fluorescent plate reader, record blue fluorescence via &#955; = 355 nm and &#955; = 460 nm (as above), and red fluorescence via excitation filter at &#955; = 584 nm and emission filter &#955; = 620 nm. 
	NOTE: Orbital or central detection is acceptable for recording. Some cell types gather more to the edge of the well than the center, in which case orbital recording can be of advantage. In particular, average of three points around the orbit could also be used to obtain more accurate results.</li>
	<li>Divide the total RFU of green or red fluorescence by blue fluorescence readout (from DAPI), depending on the particle label or phagocytic vs. actin quantification (Diagram 1). Due to high plate-to-plate variance, use relative indexes (such as relative to t = 0 control), to best illustrate trends observed and to facilitate more reliable statistical analysis.</li>
</ol>

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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>
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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...

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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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Research

JoVE Journal

Immunology and Infection

14.6K 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.

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

High-throughput Detection Method for Influenza Virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

A Microscopic Phenotypic Assay for the Quantification of Intracellular Mycobacteria Adapted for High-throughput/High-content Screening

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since several decades, the sudden burst of multi- and extensively-drug resistant strains is a serious threat for the control of tuberculosis. Therefore, it is essential to identify new targets and pathways critical for the causative agent of the tuberculosis, Mycobacterium tuberculosis (Mtb) and to search for novel chemicals that could become TB drugs. One approach is to set&#160;up methods suitable for the genetic and chemical screens of large scale libraries enabling the search of a needle in a haystack. To this end, we developed a phenotypic assay relying on the detection of fluorescently labeled Mtb within fluorescently labeled host&#160;cells using automated confocal microscopy. This in vitro assay allows an image based quantification of the colonization process of Mtb&#160;into the host and was optimized for the 384-well microplate format, which is proper for screens of siRNA-, chemical compound- or Mtb mutant-libraries. The images are then processed for multiparametric analysis, which provides read&#160;out inferring on the pathogenesis of Mtb&#160;within host cells.

Here, we describe a phenotypic assay applicable to the High-throughput/High-content screens of small-interfering synthetic RNA (siRNA), chemical compound, and Mycobacterium tuberculosis mutant libraries. This method relies on the detection of fluorescently labeled Mycobacterium tuberculosis within fluorescently labeled host&#160;cell using automated confocal microscopy.

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since ...

High-throughput Screening for Broad-spectrum Chemical Inhibitors of RNA Viruses

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat because of increased worldwide exchanges and human populations penetrating more and more natural ecosystems. A good example of such an emerging situation is chikungunya virus epidemics of 2005-2006 in the Indian Ocean. Recent progresses in our understanding of cellular pathways controlling viral replication suggest that compounds targeting host cell functions, rather than the virus itself, could inhibit a large panel of RNA viruses. Some broad-spectrum antiviral compounds have been identified with host target-oriented assays. However, measuring the inhibition of viral replication in cell cultures using reduction of cytopathic effects as a readout still represents a paramount screening strategy. Such functional screens have been greatly improved by the development of recombinant viruses expressing reporter enzymes capable of bioluminescence such as luciferase. In the present report, we detail a high-throughput screening pipeline, which combines recombinant measles and chikungunya viruses with cellular viability assays, to identify compounds with a broad-spectrum antiviral profile.

In vitro assays to measure virus replication have been greatly improved by the development of recombinant RNA viruses expressing luciferase or other enzymes capable of bioluminescence. Here we detail a high-throughput screening pipeline that combines such recombinant strains of measles and chikungunya viruses to isolate broad-spectrum antivirals from chemical libraries.

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat ...

Macrophage Cholesterol Depletion and Its Effect on the Phagocytosis of Cryptococcus neoformans

Cryptococcosis is a life-threatening infection caused by pathogenic fungi of the genus Cryptococcus. Infection occurs upon inhalation of spores, which are able to replicate in the deep lung. Phagocytosis of Cryptococcus by macrophages is one of the ways that the disease is able to spread into the central nervous system to cause lethal meningoencephalitis. Therefore, study of the association between Cryptococcus and macrophages is important to understanding the progression of the infection. The present study describes a step-by-step protocol to study macrophage infectivity by C. neoformansin vitro. Using this protocol, the role of host sterols on host-pathogen interactions is studied. Different concentrations of methyl--cyclodextrin (MCD) were used to deplete cholesterol from murine reticulum sarcoma macrophage-like cell line J774A.1. Cholesterol depletion was confirmed and quantified using both a commercially available cholesterol quantification kit and thin layer chromatography. Cholesterol depleted cells were activated using Lipopolysacharide (LPS) and Interferon gamma (IFN&#947;) and infected with antibody-opsonized Cryptococcus neoformans wild-type H99 cells at an effector-to-target ratio of 1:1. Infected cells were monitored after 2 hr of incubation with C. neoformans and their phagocytic index was calculated. Cholesterol depletion resulted in a significant reduction in the phagocytic index. The presented protocols offer a convenient method to mimic the initiation of the infection process in a laboratory environment and study the role of host lipid composition on infectivity.

Macrophage Cholesterol Depletion and Its Effect on the Phagocytosis of Cryptococcus neoformans

In this article, a protocol for infection of macrophages with Cryptococcus neoformans is described. Also, a method for sterol depletion from the macrophages is explained. These protocols provide a guide to study fungal infections in vitro and examine the role of sterols in such infections.

Cryptococcosis is a life-threatening infection caused by pathogenic fungi of the genus Cryptococcus. Infection occurs upon inhalation of spores, which are ...

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to effectiveness in the clinical setting. This is likely due to a lack of consideration for the physiologically relevant cellular penetration barriers that exist in the infected host. We recently established an alternative infection model that generates large macrophage aggregate structures containing densely packed M. tuberculosis (Mtb) at its core, which was suitable for drug susceptibility testing. This infection model is inexpensive, rapid, and most importantly BSL-2 compatible. Here, we describe the experimental procedures to generate Mtb/macrophage aggregate structures that would produce macrophage-passaged Mtb for drug susceptibility testing. In particular, we demonstrate how this infection system could be directly adapted to the 96-well plate format showing throughput capability for the screening of compound libraries against Mtb. Overall, this assay is a valuable addition to the currently available Mtb drug discovery toolbox due to its simplicity, cost effectiveness, and scalability.

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

New models and assays that would improve the early drug development process for next-generation anti-tuberculosis drugs are highly desirable. Here, we describe a quick, inexpensive, and BSL-2 compatible assay to evaluate drug efficacy against Mycobacterium tuberculosis that can be easily adapted for high-throughput screening.

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to ...

Cell-free Biochemical Fluorometric Enzymatic Assay for High-throughput Measurement of Lipid Peroxidation in High Density Lipoprotein

Low high-density lipoprotein cholesterol (HDL-C) levels are one of the most powerful independent negative predictors of atherosclerotic cardiovascular disease (CVD). The structure and function of HDL rather than HDL-C may more accurately predict atherosclerosis. Several HDL protein and lipid compositional changes that impair HDL function occur in inflammatory states such as atherosclerosis. HDL function is usually determined by cell based assays such as cholesterol efflux assay but these assays have numerous drawbacks lack of standardization. Cell-free assays may give more robust measures of HDL function compared to cell-based assays. HDL oxidation impairs HDL function. HDL has a major role in lipid peroxide transport and high amount of lipid peroxides is related to abnormal HDL function. Lipid-probe interactions should be considered when interpreting the results of non-enzymatic fluorescence assays for measuring the lipid oxidative state. This motivated us to develop a cell-free biochemical enzymatic method to assess HDL lipid peroxide content (HDLox) that contributes to HDL dysfunction. This method is based on the enzyme horseradish peroxidase (HRP) and the fluorochrome Amplex Red that can quantify (without cholesterol oxidase) the lipid peroxide content per mg of HDL-C. Here a protocol is describedfor determination of HDL-lipid peroxidation using the fluorochrome reagent. Assay variability can be reduced by strict standardization of experimental conditions. Higher HDLox values are associated with reduced HDL antioxidant function. The readout of this assay is associated with readouts of validated cell-based assays, surrogate measures of cardiovascular disease, systemic inflammation, immune dysfunction, and associated cardiovascular and metabolic risk phenotypes. This technical approach is a robust method to assess HDL function in human disease where systemic inflammation, oxidative stress and oxidized lipids have a key role (such as atherosclerosis).

We describe here a fluorometric cell-free biochemical assay for determination of HDL-lipid peroxidation. This rapid and reproducible assay can be used to determine HDL function in large scale studies and can contribute to our understanding of HDL function in human disease.

Low high-density lipoprotein cholesterol (HDL-C) levels are one of the most powerful independent negative predictors of atherosclerotic cardiovascular ...

Using Enhanced Green Fluorescence Protein-expressing Escherichia Coli to Assess Mouse Peritoneal Macrophage Phagocytosis

This manuscript describes a simple and reproducible method to perform a phagocytosis assay. The first part of this method involves building a pET-SUMO-EGFP vector (SUMO = small ubiquitin-like modifier) and expressing enhanced green fluorescence protein (EGFP) in Escherichia coli (BL21DE). EGFP-expressing E. coli is coincubated with macrophages for 1 h at 37 &#176;C; the negative control group is incubated on ice for the same amount of time. Then, the macrophages are ready for assessment. The advantages of this technique include its simple and straightforward steps, and phagocytosis can be measured by both flow cytometer and fluorescence microscope. The EGFP-expressing E. coli are stable and display a strong fluorescence signal even after the macrophages are fixed with paraformaldehyde. This method is not only suitable for the assessment of macrophage cell lines or primary macrophages in vitro but also suitable for the evaluation of granulocyte and monocyte phagocytosis in peripheral blood mononuclear cells. The results show that the phagocytic capability of peritoneal macrophages from young (eight-week-old) mice is higher than that of macrophages from aged (16-month-old) mice. In summary, this method measures macrophage phagocytosis and is suitable for studying the innate immune system function.

Using Enhanced Green Fluorescence Protein-expressing Escherichia Coli to Assess Mouse Peritoneal Macrophage Phagocytosis

Here, we present a protocol to assess mouse peritoneal macrophage phagocytosis using enhanced green fluorescence protein-expressing Escherichia coli.

This manuscript describes a simple and reproducible method to perform a phagocytosis assay. The first part of this method involves building a ...

High Throughput In Vitro Assessment of Latency Reversing Agents on HIV Transcription and Splicing

HIV remains incurable due to the existence of a reservoir of cells that harbors stable and latent form of the virus, which stays invisible to the immune system and is not targeted by the current antiretroviral therapy (cART). Transcription and splicing have been shown to reinforce HIV-1 latency in resting CD4+ T cells. Reversal of latency by the use of latency reversal agents (LRAs) in the &#34;shock and kill&#34; approach has been studied extensively in an attempt to purge this reservoir but has thus far not shown any success in clinical trials due to the lack of development of adequate small molecules that can efficiently perturb this reservoir. The protocol presented here provides a method for reliably and efficiently assessing latency reversal agents (LRAs) on HIV transcription and splicing. This approach is based on the use of an LTR-driven dual color reporter that can simultaneously measure the effect of an LRA on transcription and splicing by flow cytometry. The protocol described here is adequate for adherent cells as well as the cells in suspension. It is useful for testing a large number of drugs in a high throughput system. The method is technically simple to implement and cost-effective. In addition, the use of flow cytometry allows the assessment of cell viability and thus drug toxicity at the same time.

A high throughput protocol for functional assessment of HIV efficient reactivation and clearance of latent proviruses is described and applied by testing the impact of interventions on HIV transcription and splicing. Representative results of the effect of latency reversing agents on LTR-driven transcription and splicing are provided.

HIV remains incurable due to the existence of a reservoir of cells that harbors stable and latent form of the virus, which stays invisible to the immune ...

Alveolar Macrophage Phagocytosis and Bacteria Clearance in Mice

Alveolar macrophages (AMs) guard the alveolar space of the lung. Phagocytosis by AMs plays a critical role in the defense against invading pathogens, the removal of dead cells or foreign particles, and in the resolution of inflammatory responses and tissue remodeling, processes that are mediated by various surface receptors of the AMs. Here, we report methods for the analysis of the phagocytic function of AMs using in vitro and in vivo assays and experimental strategies to differentiate between the pattern recognition receptor-, complement receptor-, and Fc gamma receptor-mediated phagocytosis. Finally, we discuss a method to establish and characterize a P. aeruginosa pneumonia model in mice to assess bacterial clearance in vivo. These assays represent the most common methods to evaluate AM functions and can also be used to study macrophage function and bacterial clearance in other organs.

Here we report common methods to analyze the phagocytic function of murine alveolar macrophages and bacterial clearance from the lung. These methods study in vitro phagocytosis of fluorescein isothiocyanate beads and in vivo phagocytosis of Pseudomonas aeruginosa Green Fluorescent Protein. We also describe a method for clearing P. aeruginosa in mice.

Alveolar macrophages (AMs) guard the alveolar space of the lung. Phagocytosis by AMs plays a critical role in the defense against invading pathogens, the ...

In Vivo Assessment of Alveolar Macrophage Efferocytosis Following Ozone Exposure

Ozone (O3) is a criteria air pollutant that exacerbates and increases the incidence of chronic pulmonary diseases. O3 exposure is known to induce pulmonary inflammation, but little is known regarding how exposure alters processes important to the resolution of inflammation. Efferocytosis is a resolution process, whereby macrophages phagocytize apoptotic cells. The purpose of this protocol is to measure alveolar macrophage efferocytosis following O3-induced lung injury and inflammation. Several methods have been described for measuring efferocytosis; however, most require ex vivo manipulations. Described in detail here is a protocol to measure in vivo alveolar macrophage efferocytosis 24 h after O3 exposure, which avoids ex vivo manipulation of macrophages and serves as a simple technique that can be used to accurately represent perturbations in this resolution process. The protocol is a technically non-intensive and relatively inexpensive method that involves whole-body O3 inhalation followed by oropharyngeal aspiration of apoptotic cells (i.e., Jurkat T cells) while under general anesthesia. Alveolar macrophage efferocytosis is then measured by light microscopy evaluation of macrophages collected from bronchoalveolar (BAL) lavage. Efferocytosis is finally measured by calculating an efferocytic index. Collectively, the outlined methods quantify efferocytic activity in the lung in vivo while also serving to analyze the negative health effects of O3 or other inhaled insults.

This manuscript describes a protocol for determining whether exposure to ozone, a criteria air pollutant, impairs alveolar macrophage efferocytosis in vivo. This protocol utilizes commonly used reagents and techniques and can be adapted to multiple models of pulmonary injury to determine effects on alveolar macrophage efferocytosis.