Name: assessing retinal microglial phagocytic function in vivo using a flow cytometry-based assay
Uploaded: 2016-10-18T15:00:00
Description: Watch this Scientific Journal Video about Assessing Retinal Microglial Phagocytic Function In Vivo Using a Flow Cytometry-based Assay at JoVE.com

Salome Murinello is supported by American Diabetes Association grant #1-16-PDF-072. This work was supported by grants to Martin Friedlander from the National Institutes of Health (National Eye Institute EY11254 and EY22025) and the Lowy Medical Research Institute.

All animals were treated in accordance with the ethical guidelines established by the Scripps Research Institute.
1. Preparation of Materials for Injection
<ol>
	<li>Sterilize a 33 G needle and syringe: disassemble and autoclave at 115&#160; &#959;C. Prepare needles for injection by rising in sterile phosphate buffered saline (PBS).</li>
	<li>Thaw fluorescently labeled particles at room temperature for 5 - 10 min. Prepare particle solution for injection by reconstituting to a 50 mg/ml solution in ster...

<ol>
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P., 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=Microglia+sculpt+postnatal+neural+circuits+in+an+activity+and+complement-dependent+manner.">Microglia sculpt postnatal neural circuits in an activity and complement-dependent manner.</a> Neuron. 74, 691-705 (2012).</li><li>Sierra, 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=Microglia+shape+adult+hippocampal+neurogenesis+through+apoptosis-coupled+phagocytosis.">Microglia shape adult hippocampal neurogenesis through apoptosis-coupled phagocytosis.</a> Cell Stem Cell. 7, 483-495 (2010).</li><li>Sierra, A., Abiega, O., Shahraz, A., Neumann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Janus-faced+microglia:+beneficial+and+detrimental+consequences+of+microglial+phagocytosis.">Janus-faced microglia: beneficial and detrimental consequences of microglial phagocytosis.</a> Front Cell Neurosci. 7 (6), (2013).</li><li>Chan, G., 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=CD33+modulates+TREM2:+convergence+of+Alzheimer+loci.">CD33 modulates TREM2: convergence of Alzheimer loci.</a> Nat Neurosci. 18, 1556-1558 (2015).</li><li>Murinello, S., Mullins, R. 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J., 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=Inhibition+of+microglial+phagocytosis+is+sufficient+to+prevent+inflammatory+neuronal+death.">Inhibition of microglial phagocytosis is sufficient to prevent inflammatory neuronal death.</a> J Immunol. 186, 4973-4983 (2011).</li><li>Fricker, M., 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=MFG-E8+mediates+primary+phagocytosis+of+viable+neurons+during+neuroinflammation.">MFG-E8 mediates primary phagocytosis of viable neurons during neuroinflammation.</a> J Neurosci. 32, 2657-2666 (2012).</li><li>Mildner, 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=Distinct+and+non-redundant+roles+of+microglia+and+myeloid+subsets+in+mouse+models+of+Alzheimer's+disease.">Distinct and non-redundant roles of microglia and myeloid subsets in mouse models of Alzheimer's disease.</a> J Neurosci. 31, 11159-11171 (2011).</li><li>Neher, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagocytosis+executes+delayed+neuronal+death+after+focal+brain+ischemia.">Phagocytosis executes delayed neuronal death after focal brain ischemia.</a> Proc Natl Acad Sci U S A. 110, E4098-E4107 (2013).</li><li>Perego, C., Fumagalli, S., De Simoni, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+pattern+of+expression+and+colocalization+of+microglia/macrophage+phenotype+markers+following+brain+ischemic+injury+in+mice.">Temporal pattern of expression and colocalization of microglia/macrophage phenotype markers following brain ischemic injury in mice.</a> J Neuroinflammation. 8, 174-174 (2011).</li><li>Preissler, J., 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=Altered+microglial+phagocytosis+in+GPR34-deficient+mice.">Altered microglial phagocytosis in GPR34-deficient mice.</a> Glia. 63, 206-215 (2015).</li><li>Hughes, M. M., Field, R. H., Perry, V. H., Murray, C. L., Cunningham, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglia+in+the+degenerating+brain+are+capable+of+phagocytosis+of+beads+and+of+apoptotic+cells,+but+do+not+efficiently+remove+PrP(Sc),+even+upon+LPS+stimulation.">Microglia in the degenerating brain are capable of phagocytosis of beads and of apoptotic cells, but do not efficiently remove PrP(Sc), even upon LPS stimulation.</a> Glia. 58, 2017-2030 (2010).</li><li>Westenskow, P. D., 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=Using+flow+cytometry+to+compare+the+dynamics+of+photoreceptor+outer+segment+phagocytosis+in+iPS-derived+RPE+cells.">Using flow cytometry to compare the dynamics of photoreceptor outer segment phagocytosis in iPS-derived RPE cells.</a> Invest Ophthalmol Vis Sci. 53, 6282-6290 (2012).</li><li>London, A., Benhar, I., Schwartz, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+retina+as+a+window+to+the+brain-from+eye+research+to+CNS+disorders.">The retina as a window to the brain-from eye research to CNS disorders.</a> Nat Rev Neurol. 9, 44-53 (2013).</li><li>Fritzenwanger, M., Jung, C., Goebel, B., Lauten, A., Figulla, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+short-term+systemic+hypoxia+on+phagocytosis,+cytokine+production,+and+transcription+factor+activation+in+peripheral+blood+cells.">Impact of short-term systemic hypoxia on phagocytosis, cytokine production, and transcription factor activation in peripheral blood cells.</a> Mediators Inflamm. , 429501 (2011).</li><li>Ragsdale, R. L., Grasso, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+spectrofluorometric+assay+for+quantitating+yeast+phagocytosis+in+cultures+of+murine+peritoneal+macrophages.">An improved spectrofluorometric assay for quantitating yeast phagocytosis in cultures of murine peritoneal macrophages.</a> J Immunol Methods. 123, 259-267 (1989).</li><li>Stokes, L., Surprenant, A. <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+P2X4+receptor+in+alveolar+macrophages+by+phagocytosis+and+classical+activation.">Dynamic regulation of the P2X4 receptor in alveolar macrophages by phagocytosis and classical activation.</a> Eur J Immunol. 39, 986-995 (2009).</li><li>Kotani, 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=Intraoperative+modulation+of+alveolar+macrophage+function+during+isoflurane+and+propofol+anesthesia.">Intraoperative modulation of alveolar macrophage function during isoflurane and propofol anesthesia.</a> Anesthesiology. 89, 1125-1132 (1998).</li><li>Xu, X., Feng, J., Zuo, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isoflurane+preconditioning+reduces+the+rat+NR8383+macrophage+injury+induced+by+lipopolysaccharide+and+interferon+gamma.">Isoflurane preconditioning reduces the rat NR8383 macrophage injury induced by lipopolysaccharide and interferon gamma.</a> Anesthesiology. 108, 643-650 (2008).</li><li>abd-el-Basset, E., Fedoroff, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+bacterial+wall+lipopolysaccharide+(LPS)+on+morphology,+motility,+and+cytoskeletal+organization+of+microglia+in+cultures.">Effect of bacterial wall lipopolysaccharide (LPS) on morphology, motility, and cytoskeletal organization of microglia in cultures.</a> J Neurosci Res. 41, 222-237 (1995).</li><li>Menon, V., Thomas, R., Ghale, A. R., Reinhard, C., Pruszak, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+cytometry+protocols+for+surface+and+intracellular+antigen+analyses+of+neural+cell+types.">Flow cytometry protocols for surface and intracellular antigen analyses of neural cell types.</a> J Vis Exp. , (2014).</li><li>Jackson, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+vulnerability+to+neurodegenerative+disease:+the+curious+case+of+Prion+Protein.">Selective vulnerability to neurodegenerative disease: the curious case of Prion Protein.</a> Dis Model Mech. 7, 21-29 (2014).</li><li>O'Koren, E. G., Mathew, R., Saban, D. 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There are three critical steps in this method: (1) intravitreal injection of fluorescently labeled particles; (2) harvesting and preparation of retinal tissue; and (3) flow cytometric analysis. We recommend that researchers practice intravitreal injections prior to performing the method we present here. Albino mice (e.g., BALB/c) and a colored solution (e.g., fluorescently labeled particles) can be used for easy visualization of the needle and injected solution. Intravitreal injections are challenging a...

The overall goal of this method is to accurately assess and quantify in vivo microglial phagocytosis. Microglia are the tissue resident macrophages of the central nervous system (CNS). They perform a variety of functions to ensure maintenance of tissue homeostasis. These include immune surveillance, secretion of neurotrophic factors and, of pivotal importance, phagocytosis1. Microglial phagocytosis is key in several important events during development of the brain and retina, such as phagocytosis of irrelevant synapses (synaptic pruning) and removal of apoptotic neurons2-4. Furthermore, microglial phagocytosis of damaged or apoptotic neurons, cellular debris, and invading microbes has been shown to be essential for maintaining CNS homeostasis through adulthood5. Finally, microglial phagocytosis has been implicated in the pathogenesis of several neurodegenerative diseases, including Alzheimer&#39;s disease and age-related macular degeneration, where it has been suggested that defective or insufficient phagocytic capacity may contribute to the build-up of amyloid-&#946; (A&#946;) plaques and drusen, respectively6,7.
Microglial function is tightly regulated by their microenvironment, notably by soluble factors such as tumor-growth factor &#946; or cell-cell interactions. Neurons constitutively express several cell surface ligands, such as CD200 and CX3CL1, while microglia exclusively express the respective receptors CD200R and CX3CR1. These receptors contain immunoreceptor tyrosine-based inhibition motifs (ITIMs) in their intracellular portion. These inhibitor receptors are critical for preventing the over-stimulation of microglia, which can contribute to neuroinflammation. Thus, under normal physiological conditions, cell-cell interactions between neurons and microglia keep microglia in a quiescent state. During tissue injury, however, neurons can down-regulate expression of these ligands, removing their inhibitory effect on microglia activation. Microglial function (including phagocytosis) is thus tightly linked to their microenvironment8. Nevertheless, to date, there are no standardized assays to study microglia phagocytosis in a physiological context or in a way that fully replicates their CNS microenvironment.
Several assays have been developed to measure phagocytic activity of microglia in vitro, where primary microglia or microglia cell lines are cultured with target cells (e.g., apoptotic neurons) or fluorescently labeled beads. Target uptake is then assessed using fluorescent imaging microscopy or flow cytometry9-12. These assays allow testing of how pharmacological or genetic manipulation may affect microglial phagocytosis and, while informative, fail to fully replicate the complex in vivo environment. Indirect methods for examining microglial phagocytosis in vivo have been reported: these are accomplished by staining of molecules thought to be involved in phagocytosis (e.g., CD68), assessing physical proximity of microglia and targets for phagocytosis (e.g., compromised neurons or synaptic elements), or by immunohistochemical detection of phagocytic targets within microglial cells (e.g., A&#946;)13-17. Two studies have used more direct approaches to assess microglia phagocytosis in vivo. Hughes and colleagues have used imaging techniques to measure microglial uptake of beads delivered via the intracranial route18. Sierra et al. developed a refined method to quantitatively assess microglia phagocytosis of apoptotic cells using complex imaging techniques4. However, these methods involve complicated protocols for tissue preparation, sectioning, imaging, and analysis. We have previously used flow cytometric analysis to assess phagocytosis of photoreceptor outer segments by retinal pigmented epithelium (RPE) cells in culture19. Here, we describe a protocol to rapidly assess uptake of fluorescently labeled particles by retinal microglia as a quantitative measure of in vivo microglia phagocytosis.
The protocol we describe here allows for reliable and quantitative measurement of retinal microglial phagocytosis in just under six hours in three critical steps: (1) intravitreal delivery of fluorescently labeled particles, (2) harvest and preparation of retinal tissue, and (3) flow cytometric analysis. The method we have developed is a robust method to assess microglial phagocytosis in the retina, and it can be successfully used to test how various compounds or genetic manipulation alter this key microglial function in physiological settings. As a specialized area of the CNS, the retina is an easily accessible model system to study microglia function20. While this method was developed in the eye, we believe it can be useful for all neuroscientists investigating microglia phagocytic function.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Stereomicroscope</td>
			<td>Nikon</td>
			<td>Discontinued</td>
			<td></td>
		</tr>
		<tr>
			<td>Hamilton&#160;syringe, 600 series</td>
			<td>Sigma</td>
			<td>26702</td>
			<td></td>
		</tr>
		<tr>
			<td>33 gauge, Small Hub RN NDL, 0.5 in, point style 4 - 12o</td>
			<td>Hamilton</td>
			<td>7803-05</td>
			<td></td>
		</tr>
		<tr>
			<td>Zymosan A (S. cerevisiae) BioParticles, Alexa Fluor 488 conjugate</td>
			<td>ThermoFisher Scientific</td>
			<td>Z-23373</td>
			<td>Prepare immediately before injection</td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Corning</td>
			<td>21-030-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #5/45 Forceps</td>
			<td>Fine Science Tools</td>
			<td>11251-35</td>
			<td>Need two</td>
		</tr>
		<tr>
			<td>Dumont #5SF Forceps</td>
			<td>Fine Science Tools</td>
			<td>11252-00</td>
			<td></td>
		</tr>
		<tr>
			<td>Vannas Spring Scissors - 3mm Cutting Edge</td>
			<td>Fine Science Tools</td>
			<td>15000-10</td>
			<td>Curved</td>
		</tr>
		<tr>
			<td>Neural Tissue Dissociation Kit &#8211; Postnatal Neurons</td>
			<td>Miltenyi Biotec</td>
			<td>130-094-802</td>
			<td></td>
		</tr>
		<tr>
			<td>5 mL Polystyrene Round-bottom Tube</td>
			<td>Falcon</td>
			<td>352054</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well U-bottom plate</td>
			<td>Falcon</td>
			<td>353077</td>
			<td></td>
		</tr>
		<tr>
			<td>Stain Buffer (BSA)</td>
			<td>BD Biosciences</td>
			<td>554657</td>
			<td></td>
		</tr>
		<tr>
			<td>CD11b-BV650 Antibody</td>
			<td>BioLegend</td>
			<td>101259</td>
			<td></td>
		</tr>
		<tr>
			<td>Ly6C-APC-Cy7</td>
			<td>BioLegend</td>
			<td>128025</td>
			<td></td>
		</tr>
		<tr>
			<td>Ly6G-PE-Cy7</td>
			<td>BioLegend</td>
			<td>127617</td>
			<td></td>
		</tr>
		<tr>
			<td>Propidium Iodide</td>
			<td>BD Biosciences</td>
			<td>556463</td>
			<td></td>
		</tr>
		<tr>
			<td>Purified anti-mouse CD16/32 Antibody</td>
			<td>BioLegend</td>
			<td>101301</td>
			<td></td>
		</tr>
	</tbody>
</table>

assessing retinal microglial phagocytic function in vivo using a flow cytometry-based assay

Microglia are the tissue resident macrophages of the central nervous system (CNS) and they perform a variety of functions that support CNS homeostasis, including phagocytosis of damaged synapses or cells, debris, and/or invading pathogens. Impaired phagocytic function has been implicated in the pathogenesis of diseases such as Alzheimer's and age-related macular degeneration, where amyloid-&#946; plaque and drusen accumulate, respectively. Despite its importance, microglial phagocytosis has been challenging to assess in vivo. Here, we describe a simple, yet robust, technique for precisely monitoring and quantifying the in vivo phagocytic potential of retinal microglia. Previous methods have relied on immunohistochemical staining and imaging techniques. Our method uses flow cytometry to measure microglial uptake of fluorescently labeled particles after intravitreal delivery to the eye in live rodents. This method replaces conventional practices that involve laborious tissue sectioning, immunostaining, and imaging, allowing for more precise quantification of microglia phagocytic function in just under six hours. This procedure can also be adapted to test how various compounds alter microglial phagocytosis in physiological settings. While this technique was developed in the eye, its use is not limited to vision research.

Here we describe a method to rapidly and reliably quantify the number of phagocytic retinal microglia in a physiological setting using flow cytometric analysis (Figure 2). This method can be adapted to test the effect of compounds and/or genetic manipulation on the phagocytic capacity of microglia (Figures 3A, 3B). It can also be used in young (10 - 20 days postnatal) or adult mice (Figure 3C). Varying doses of lipopolysaccharide...

Watch this Scientific Journal Video about Assessing Retinal Microglial Phagocytic Function In Vivo Using a Flow Cytometry-based Assay at JoVE.com

Assessing Retinal Microglial Phagocytic Function In Vivo Using a Flow Cytometry-based Assay

Microglial phagocytosis is critical for the maintenance of tissue homeostasis and inadequate phagocytic function has been implicated in pathology. However, assessing microglia function in vivo is technically challenging. We have developed a simple but robust technique for precisely monitoring and quantifying the phagocytic potential of microglia in a physiological setting.

Assessing Retinal Microglial Phagocytic Function In Vivo Using a Flow Cytometry-based Assay

Microglia are the tissue resident macrophages of the central nervous system (CNS) and they perform a variety of functions that support CNS homeostasis, ...

The overall goal of this procedure is to assess the phagocytic function of retinal microglia in vivo. This method can help answer key questions in the ophthalmology field, such as whether certain compounds alter microglia phagocytic function in a physiological setting. The main advantage of this technique is that it uses flow cytometry, allowing a fast and precise quantitative analysis of microglial phagocytosis.Helping me to demonstrate the procedure will be Susumu Sakimoto, a postdoc from my laboratory. Begin by loading a 33-gauge needle and syringe with 0.5 microliters of fluorescently labeled particle solution. Then place an anesthetized mouse sideways on soft material under a surgical microscope and confirm the appropriate level of sedation by a lack of response to toe pinch.Next, use forceps to carefully apply pressure around one eyelid, so that the eye ball pops slightly out of the socket. Then grasp the head with two fingers just above the ear and by the animal's jaw, and gently stretch the skin parallel to the eyelids to keep the eye slightly bulged out of the socket. Intravitreal injections are challenging, and if not performed correctly will lead to biased and variable results.To reduce trauma to the eye, hold the animal in a stable position with minimal head movement. To puncture the eyeball, gently grasp the mouse with one hand. Then locate the corneal limbus where the cornea and sclera connect, which is visible as a gray circle in pigmented mice.Holding the syringe in the other hand, insert the needle into the limbus. Then retract the needle slightly to expel a small volume of vitreous fluid, and slowly depress the plunger to inject the particles. When all of the beads have been delivered, slowly withdraw the syringe to avoid reflux of the injected material and apply moisturizing drops to keep the eye hydrated once the eye has retracted back into place.Then place the animal on a heating pad in its own cage with monitoring until it is fully recovered. Three hours after intravitreal injection, use 45 degree angle forceps to gently press against the eyelid to proptose the eyeball. Position the forceps behind the eyeball and pull.Then transfer the eyeball to the dry area of a petri dish, containing a small volume of PBS with calcium and magnesium under a dissecting microscope. And use one tip of a superfine forceps to perforate the eye in the corneal limbus. Next, holding the eyeball with fine 45-degree angled forceps, use spring scissors to cut around the corneal limbus until roughly half of the circumference is cut.Transfer the eyeball into PBS and use a second pair of fine 45-degree angled forceps to tear the cornea and sclera apart. The lens and retina will come out intact. Ensure the lens and retina are separated and transfer the retina to a 5.4 milliliter polystyrene test tube, containing two milliliters of PBS with calcium and magnesium.To obtain a single cell suspension of the retinal cells, use a neuronal tissue dissociation kit according to the manufacturer's instructions and resuspend the cells in 200 microliters of staining buffer. Then transfer the sample to one well of a 96-well U-bottom plate. After centrifugation, invert the plate to discard the supernatant and block the FC receptors with 25 microliters of stain buffer containing CD16, CD32 antibody per well for five minutes at room temperature.Next label the cells with the antibodies of interest for 15 minutes at room temperature in the dark. Then pellet the cells and follow this by a wash in 200 microliters of fresh staining buffer per well. Now resuspend the pellets in 200 microliters of stain buffer and viability dye and transfer the samples to 1.2 milliliter microtiter tubes.Then wash the wells with an additional 100 microliters of staining buffer and viability dye and pool the washes with the corresponding samples for analysis by flow cytometry. This method can be used in 10 to 20-day old postnatal or adult mice and can be adapted to test the effect of compounds and/or the genetic manipulation of microglial phagocytosis. For example, in this experiment after intraperitoneal challenge with varying doses of LPS, a 1.42 milligram per kilogram dose of LPS was determined to induce a statistically significant increase in the percentage of phagocytic microglia, compared to vehicle challenged controls.Once mastered, this technique can be completed in six hours if it is performed properly. Following this procedure, other methods like cell sorting followed by qPCR or proteomic analysis, can be used to answer further questions about the differences between phagocytic and non phagocytic microglia in the retina. In developing this technique, it's our expectation that we can now make it possible for vision and neuro scientists to further explore microglial phagocytic function in situ and in a physiologically relevant context.

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Research

JoVE Journal

Immunology and Infection

Image-based Flow Cytometry Technique to Evaluate Changes in Granulocyte Function In Vitro

Granulocytes play a key role in the body&#8217;s innate immune response to bacterial and viral infections. While methods exist to measure granulocyte function, in general these are limited in terms of the information they can provide. For example, most existing assays merely provide a percentage of how many granulocytes are activated following a single, fixed length incubation. Complicating matters, most assays focus on only one aspect of function due to limitations in detection technology. This report demonstrates a technique for simultaneous measurement of granulocyte phagocytosis of bacteria and oxidative burst. By measuring both of these functions at the same time, three unique phenotypes of activated granulocytes were identified: 1) Low Activation (minimal phagocytosis, no oxidative burst), 2) Moderate Activation (moderate phagocytosis, some oxidative burst, but no co-localization of the two functional events), and 3) High Activation (high phagocytosis, high oxidative burst, co-localization of phagocytosis and oxidative burst). A fourth population that consisted of inactivated granulocytes was also identified. Using assay incubations of 10, 20, and 40-min the effect of assay incubation duration on the redistribution of activated granulocyte phenotypes was assessed. A fourth incubation was completed on ice as a control. By using serial time incubations, the assay may be able to able to detect how a treatment spatially affects granulocyte function. All samples were measured using an image-based flow cytometer equipped with a quantitative imaging (QI) option, autosampler, and multiple lasers (488, 642, and 785 nm).

Image-based Flow Cytometry Technique to Evaluate Changes in Granulocyte Function In Vitro

This method demonstrates a technique for assessing granulocyte function by simultaneously measuring phagocytosis of bacteria and oxidative burst. Image-based flow cytometry allowed for the identification of three distinct subsets of activated granulocytes that all differed in their relative functional capacity.

Granulocytes play a key role in the body&#8217;s innate immune response to bacterial and viral infections. While methods exist to measure granulocyte ...

Flow Cytometry-based Assay for the Monitoring of NK Cell Functions

Natural killer (NK) cells are an important part of the human tumor immune surveillance system. NK cells are able to distinguish between healthy and virus-infected or malignantly transformed cells due to a set of germline encoded inhibitory and activating receptors. Upon virus or tumor cell recognition a variety of different NK cell functions are initiated including cytotoxicity against the target cell as well as cytokine and chemokine production leading to the activation of other immune cells. It has been demonstrated that accurate NK cell functions are crucial for the treatment outcome of different virus infections and malignant diseases. Here a simple and reliable method is described to analyze different NK cell functions using a flow cytometry-based assay. NK cell functions can be evaluated not only for the whole NK cell population, but also for different NK cell subsets. This technique enables scientists to easily study NK cell functions in healthy donors or patients in order to reveal their impact on different malignancies and to further discover new therapeutic strategies.

A simple and reliable method is described here to analyze a set of NK cell functions such as degranulation, cytokine and chemokine production within different NK cell subsets.

Natural killer (NK) cells are an important part of the human tumor immune surveillance system. NK cells are able to distinguish between healthy and ...

A Flow Cytometry-Based Cytotoxicity Assay for the Assessment of Human NK Cell Activity

Within the innate immune system, effector lymphocytes known as natural killer (NK) cells play an essential role in host defense against aberrant cells, specifically eliminating tumoral and virally infected cells. Approximately 30 known monogenic defects, together with a host of other pathological conditions, cause either functional or classic NK cell deficiency, manifesting in reduced or absent cytotoxic activity. Historically, cytotoxicity has been investigated with radioactive methods, which are cumbersome, expensive and potentially hazardous. This article describes a streamlined, clinically applicable flow cytometry-based method to quantify NK cell cytotoxic activity. In this assay, peripheral blood mononuclear cells (PBMCs) or purified NK cell preparations are co-incubated at different ratios with a target tumor cell line known to be sensitive to NK cell-mediated cytotoxicity (NKCC). The target cells are pre-labeled with a fluorescent dye to allow their discrimination from the effector cells (NK cells). After the incubation period, killed target cells are identified by a nucleic acid stain, which specifically permeates dead cells. This method is amenable to both diagnostic and research applications and, thanks to the multi-parameter capabilities of flow cytometry, has the added advantage of potentially enabling a deeper analysis of NK cell phenotype and function.

A flow cytometry-based method to quantitatively determine the cytotoxic activity of human natural killer cells is shown here.

Within the innate immune system, effector lymphocytes known as natural killer (NK) cells play an essential role in host defense against aberrant cells, ...

In Vivo Assay for Detection of Antigen-specific T-cell Cytolytic Function Using a Vaccination Model

Current methodologies for antigen-specific killing are limited to in vitro use or utilized in infectious disease models. However, there is not a protocol specifically intended to measure antigen-specific killing without an infection. This protocol is designed and describes methods to overcome these limitations by allowing for the detection of antigen-specific killing of a target cell by CD8+ T cells in vivo. This is accomplished by merging a vaccination model with a traditional CFSE-labeled target killing assay. This combination allows the researcher to assess the antigen-specific CTL potential directly and quickly as the assay is not dependent upon tumor growth or infection. In addition, the readout is based on flow cytometry and so should be readily accessible to most researchers. The major limitation of the study is identifying the timeline in vivo that is appropriate to the hypothesis being tested. Variations in antigen strength and mutations in the T cells that may result in differential cytolytic function need to be carefully assessed to determine the optimal time for cell harvest and assessment. The appropriate concentration of peptide for vaccination has been optimized for hgp10025-33 and OVA257-264, but further validation would be needed for other peptides that may be more appropriate to a given study. Overall, this protocol allows a quick assessment of killing function in vivo and can be adapted to any given antigen.

In Vivo Assay for Detection of Antigen-specific T-cell Cytolytic Function Using a Vaccination Model

The goal of this protocol is to allow for detection of in vivo antigen-specific killing of a target cell in a murine model.

Current methodologies for antigen-specific killing are limited to in vitro use or utilized in infectious disease models. However, there is not a protocol ...

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

Antibody dependent enhancement of infection has been shown to play a major role in Dengue viral pathogenesis. Traditional assays that measure the capacity of antibodies or serum to enhance infection in impermissible cell lines have relied on using viral output in the media followed by plaque assays to quantify infection. More recently, these assays have examined Dengue virus (DENV) infection in the cell lines using fluorescently labeled antibodies. Both these approaches have limitations that restrict the widespread use of these techniques. Here, we describe a simple in vitro assay using Dengue virus reporter viral particles (RVPs) that express green fluorescent protein and K562 cells to examine antibody dependent enhancement (ADE) of DENV infection using serum that was obtained from rhesus macaques 16 weeks after infection with Zika virus (ZIKV). This technique is reliable, involves minimal manipulation of cells, does not involve the use of live replication competent virus, and can be performed in a high throughput format to get a quantitative readout using flow cytometry. Additionally, this assay can be easily adapted to examine antibody dependent enhancement (ADE) of other flavivirus infections such as Yellow Fever virus (YFV), Japanese Equine Encephalitis virus (JEEV), West Nile virus (WNV) etc. where RVPs are available. The ease of setting up the assay, analyzing the data, and interpreting results makes it highly amenable to most laboratory settings.

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

We describe a simple and easy protocol for measuring antibody dependent enhancement of infection by Zika virus convalescent serum using Dengue virus Reporter Viral Particles.

Antibody dependent enhancement of infection has been shown to play a major role in Dengue viral pathogenesis. Traditional assays that measure the capacity ...

Multicolor Flow Cytometry-based Quantification of Mitochondria and Lysosomes in T Cells

T cells utilize different metabolic programs to match their functional needs during differentiation and proliferation. Mitochondria are crucial cellular components responsible for supplying cell energy; however, excess mitochondria also produce reactive oxygen species (ROS) that could cause cell death. Therefore, the number of mitochondria must constantly be adjusted to fit the needs of the cells. This dynamic regulation is achieved in part through the function of lysosomes that remove surplus/damaged organelles and macromolecules. Hence, cellular mitochondrial and lysosomal contents are key indicators to evaluate the metabolic adjustment of cells. With the development of probes for organelles, well-characterized lysosome or mitochondria-specific dyes have become available in various formats to label cellular lysosomes and mitochondria. Multicolor flow cytometry is a common tool to profile cell phenotypes, and has the capability to be integrated with other assays. Here, we present a detailed protocol of how to combine organelle-specific dyes with surface markers staining to measure the amount of lysosomes and mitochondria in different T cell populations on a flow cytometer.

This article illustrates a powerful method to quantify mitochondria or lysosomes in living cells. The combination of lysosome- or mitochondria-specific dyes with fluorescently conjugated antibodies against surface markers allows the quantification of these organelles in mixed cell populations, like primary cells harvested from tissue samples, by using multicolor flow cytometry.

T cells utilize different metabolic programs to match their functional needs during differentiation and proliferation. Mitochondria are crucial cellular ...

Assessing the Cellular Immune Response of the Fruit Fly, Drosophila melanogaster, Using an In Vivo Phagocytosis Assay

In all animals, innate immunity provides an immediate and robust defense against a broad spectrum of pathogens. Humoral and cellular immune responses are the main branches of innate immunity, and many of the factors regulating these responses are evolutionarily conserved between invertebrates and mammals. Phagocytosis, the central component of cellular innate immunity, is carried out by specialized blood cells of the immune system. The fruit fly, Drosophila melanogaster, has emerged as a powerful genetic model to investigate the molecular mechanisms and physiological impacts of phagocytosis in whole animals. Here we demonstrate an injection-based in vivo phagocytosis assay to quantify the particle uptake and destruction by Drosophila blood cells, hemocytes. The procedure allows researchers to precisely control the particle concentration and dose, making it possible to obtain highly reproducible results in a short amount of time. The experiment is quantitative, easy to perform, and can be applied to screen for host factors that influence pathogen recognition, uptake, and clearance.

Assessing the Cellular Immune Response of the Fruit Fly, Drosophila melanogaster, Using an In Vivo Phagocytosis Assay

This protocol describes an in vivo phagocytosis assay in adult Drosophila melanogaster to quantify phagocyte recognition and clearance of microbial infections.

In all animals, innate immunity provides an immediate and robust defense against a broad spectrum of pathogens. Humoral and cellular immune responses are ...

Measuring Naturally Acquired Phagocytosis-Inducing Antibodies to Plasmodium falciparum Parasites by a Flow Cytometry-Based Assay

The protocol describes how to set up and run a flow cytometry-based phagocytosis assay of Plasmodium falciparum-infected erythrocytes (IEs) opsonized by naturally acquired IgG antibodies specific for VAR2CSA. VAR2CSA is the parasite antigen that mediates the selective sequestration of IEs in the placenta that can cause a severe form of malaria in pregnant women, called placental malaria (PM). Protection from PM is mediated by VAR2CSA-specific antibodies that are believed to function by inhibiting placental sequestration and/or by opsonizing IEs for phagocytosis. The assay employs late-stage-synchronized IEs that have been selected in vitro to express VAR2CSA, plasma/serum-antibodies from women with naturally acquired PM-specific immunity, and the phagocytic cell line THP-1. However, the protocol can easily be modified to assay the functionality of antibodies to any parasite antigen present on the IE surface, whether induced by natural exposure or by vaccination. The assay offers simple and high-throughput evaluation, with good reproducibility, of an important functional aspect of antibody-mediated immunity in malaria. It is, therefore, useful when evaluating clinical immunity to P. falciparum malaria, a major cause of morbidity and mortality in the tropics, particularly in sub-Saharan Africa.

Measuring Naturally Acquired Phagocytosis-Inducing Antibodies to Plasmodium falciparum Parasites by a Flow Cytometry-Based Assay

The overall goal of this protocol is to provide instruction on how to measure the capacity of antibodies present in sera or plasma of individuals, naturally exposed to Plasmodium falciparum infection, to opsonize and induce phagocytosis of the parasite-infected erythrocytes (IEs).

The protocol describes how to set up and run a flow cytometry-based phagocytosis assay of Plasmodium falciparum-infected erythrocytes (IEs) opsonized by ...

Assessing Respiratory Immune Responses to Haemophilus Influenzae

Haemophilus influenzae (Hi) is a prevalent bacterium found in a range of respiratory conditions. A variety of different assays/techniques may be used to assess the respiratory immune/inflammatory response to this bacterium. Flow cytometry and confocal microscopy are fluorescence-based technologies that allow detailed characterization of biological responses.&#160;Different forms of Hi antigen can be used, including cell wall components, killed/inactivated preparations, and live bacteria. Hi is a fastidious bacterium that requires enriched media but is generally easy to grow in standard laboratory settings. Tissue samples for stimulation with Hi may be obtained from peripheral blood, bronchoscopy, or resected lung (e.g., in patients undergoing surgery for the treatment of lung cancer). Macrophage and neutrophil function may be comprehensively assessed using flow cytometry with a variety of parameters measured, including phagocytosis, reactive oxygen species, and intracellular cytokine production. Lymphocyte function (e.g., T cell and NK cell function) may be specifically assessed using flow cytometry, principally for intracellular cytokine production. Hi infection is a potent inducer of extracellular trap production, both by neutrophils (NETs) and macrophages (METs). Confocal microscopy is arguably the most optimal way to assess NET and MET expression, which may also be used to assess protease activity. Lung immunity to Haemophilus influenzae can be assessed using flow cytometry and confocal microscopy.

Assessing Respiratory Immune Responses to Haemophilus Influenzae

Haemophilus influenzae induces inflammation in the respiratory tract. This article will focus on the use of flow cytometry and confocal microscopy to define immune responses by phagocytes and lymphocytes in response to this bacterium.

Haemophilus influenzae (Hi) is a prevalent bacterium found in a range of respiratory conditions. A variety of different assays/techniques may be used to ...

Flow Cytometry-Based Quantification and Analysis of Myocardial B-Cells

A growing body of evidence shows that B-lymphocytes play an important role in the context of myocardial physiology and myocardial adaptation to injury. However, the literature reports contrasting data on the prevalence of myocardial B-cells. B-cells have been reported to be both among the most prevalent immune cells in the rodent heart or to be present, but at a markedly lower prevalence than myeloid cells, or to be quite rare. Similarly, several groups have described that the number of myocardial B-cells increases after acute ischemic myocardial injury, but one group reported no changes in the number of B-cells of the injured myocardium. Implementation of a shared, reproducible method to assess the prevalence of myocardial B-cells is critical to harmonize observations from different research groups and thus promote the advancement of the study of B-cell myocardial interactions. Based on our experience, the seemingly contrasting observations reported in the literature likely stem from the fact that murine myocardial B-cells are mostly intravascular and connected to the microvascular endothelium. Therefore, the number of B-cells recovered from a murine heart is exquisitely sensitive to the perfusion conditions used to clean the organ and to the method of digestion used. Here we report an optimized protocol that accounts for these two critical variables in a specific way. This protocol empowers reproducible, flow cytometry-based analysis of the number of murine myocardial B-cells and allows researchers to distinguish extravascular vs. intravascular myocardial B-cells.

Here we report a protocol for the quantification and differentiation of myocardial B-lymphocytes based on their location in the intravascular or endothelial space using flow cytometry.

A growing body of evidence shows that B-lymphocytes play an important role in the context of myocardial physiology and myocardial adaptation to injury. ...