This work was supported by NIEHS R01ES014470 (KMZ).

&#160;Prior to starting this protocol, collect neonatal mice at postnatal days 1-3 (P1-3) in a sterile container nested with original cage bedding for protection and warmth. It is important to work quickly and efficiently through this protocol to optimize microglial yield. Please see Table 1 for complete reagent list.
1.&#160;Preparation of instruments, Culture Media, and Dishes
<ol>
	<li>Prepare 10 ml/pup Microglia Complete Media (MCM; 1x Minimal Essential Medium Earle&#39;...

<ol>
	<li>Ranshoff, R. M. P. V. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglia+Physiology:+Unique+Stimuli,+Specialized+Responses.">Microglia Physiology: Unique Stimuli, Specialized Responses.</a> Annu. Rev. Immunol. 27, 119-145 (2009).</li><li>Lawson, L. J., Perry, V. H., Dri, P., Gordon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heterogeneity+in+the+distribution+and+morphology+of+microglia+in+the+normal+adult+mouse+brain.">Heterogeneity in the distribution and morphology of microglia in the normal adult mouse brain.</a> Neuroscience. 39, 151-170 (1990).</li><li>Gomez Perdiguero, E., Schulz, C., Geissmann, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+homeostasis+of+&amp;#34;resident&amp;#34;+myeloid+cells:+The+case+of+the+microglia.">Development and homeostasis of &amp;#34;resident&amp;#34; myeloid cells: The case of the microglia.</a> Glia. 61, 112-120 (2013).</li><li>Kierdorf, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglia+emerge+from+erythromyeloid+precursors+via+Pu.1-+and+Irf8-dependent+pathways.">Microglia emerge from erythromyeloid precursors via Pu.1- and Irf8-dependent pathways.</a> Nat. 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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=CD36+ligands+promote+sterile+inflammation+through+assembly+of+a+Toll-like+receptor+4.">CD36 ligands promote sterile inflammation through assembly of a Toll-like receptor 4.</a> 11, 155-161 (2010).</li><li>Beraud, 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=alpha-Synuclein+Alters+Toll-Like+Receptor+Expression.">alpha-Synuclein Alters Toll-Like Receptor Expression.</a> Front. Neurosci. 5, 80 (2011).</li><li>Banati, R. B., Gehrmann, J., Schubert, P., Kreutzberg, G. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cytotoxicity+of+microglia..">Cytotoxicity of microglia..</a> Glia. 7, 111-118 (1993).</li><li>Combs, C. K., Karlo, J. C., Kao, S. 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Phenotypic differences defined and direct ex vivo antigenpresentation to myelin basic protein-reactive CD4+ T cells compared.</a> J. Immunol. 154, 4309-4321 (1995).</li><li>Ford, A. L., Foulcher, E., Goodsall, A. L., Sedgwick, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+digestion+with+dispase+substantially+reduces+lymphocyte+and+macrophage+cell-surface+antigen+expression.">Tissue digestion with dispase substantially reduces lymphocyte and macrophage cell-surface antigen expression.</a> J. Immunol. Methods. 194, 71-75 (1996).</li><li>Pino, P. A., Cardona, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+brain+and+spinal+cord+mononuclear+cells+using+percoll+gradients.">Isolation of brain and spinal cord mononuclear cells using percoll gradients.</a> J. Vis. 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The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The present procedure offers an effective method for the isolation of cortical microglia from neonatal mice. This procedure has a two-fold benefit of 1) preserving microglia immunophenotype and functionality, as determined by fluorescent imaging, immunocytochemistry, and ELISA; and, 2) allowing microglia to mature in the presence of other glial cells (astrocytes and oligodentrocytes) prior to isolation, which may facilitate important cell-cell interactions during the glial culture maturation period. Importantly, isolated...

Microglial cells, the surveillance macrophages of the CNS parenchyma, comprise approximately 12% of the total cell population of the adult mammalian brain. Microglia are derived from yolk sac myeloid precursor cells&#160;and vary in cell density and morphology in different cytoarchitectural regions within the adult CNS1-5. In a healthy adult brain, microglia are small, ramified or polar cells with fine, dynamic processes. In contrast to peripheral macrophage morphology, microglia demonstrate a quiescent, low-profile phenotype in healthy brains that may appear as cellular inactivity; however, in vivo imaging studies demonstrate that microglial processes dynamically extend and retract to monitor their microenvironment in a manner reminiscent of &#34;sampling and surveying&#34;6,7.
Microglia are highly and differentially responsive to environmental and pathophysiological alterations in the brain, switching from a surveillant to an effector state&#8212;commonly regarded as their resting and activated states, respectively. This switch in activation can be mediated by engagement of membrane-bound pattern recognition receptors (PRRs), such as toll-like receptors (TLRs), which respond to pathogen-associated molecular patterns (PAMPs), namely bacterial- and viral-derived lipoproteins, nucleic acids, and carbohydrates8-11. In addition to PAMPs, PRRs have also been shown to induce microglial activation against sterile, nonpathogenic molecules known as danger/damage-associated molecular patterns (DAMPs), which represent a perturbation in CNS homeostasis, such as cellular damage12-16. Once engaged, PRRs initiate an intracellular signaling cascade that results in changes in microglial cell morphology and gene expression; specifically, activated microglia adapt an amoeboid-like phenotype, translocate the p65 NF-&#954;B subunit (p65) to the cell nucleus, and upregulate the production and secretion of proinflammatory cytokines, such as tumor necrosis factor-&#945; (TNF-&#945;), interleukin-1 &#946; (IL-1&#946;), along with reactive oxygen species (ROS)16-24. Although integral in the innate immune response of the CNS, these secreted molecules have also been found to increase neuronal oxidative stress, thereby inducing and exacerbating neurodegeneration in diseased states such as Parkinson&#39;s and Alzheimer&#39;s disease25-29.
However, the mechanisms of microglial activation in pathological states are not completely understood. Therefore, isolation of microglia is a powerful investigative tool into these biological processes, as many in vivo features of microglial activation can be recapitulated in culture. Several methods are available for isolating microglia, including isolation via a Percoll gradient following enzymatic digestion of CNS tissue30,31. However, enzymatic digestion can alter the immunophenotype of the cells by reducing cell-surface antigen expression32, and results in lower cell yield per animal than the method described herein. Specifically, we report an average microglia yield per pup cortex of 7.5 x 105 cells, while previously reported isolation methods from whole CNS via a Percoll gradient yield 3-5 x 105 cells30,33,34. The present procedure circumvents the use of digestion enzymes by isolating microglia based on their low-adherence properties, thereby preserving the microglial immunophenotype and functionality.
In the present study, we describe the isolation of microglial cells from mixed glial cultures derived from neonatal heterozygous CX3CR1-GFP (CX3CR1-GFP+/-), and C57BL/6 murine cortices via mechanical agitation on a rotary shaker, an extension of previously published method24,35. We utilize the former mouse strain for easy visualization of microglia, as these mice express GFP under the control of the endogenous Cx3Cr1 locus -&#160;a monocyte-specific promoter36-38. This method produces highly pure microglial cultures with a preserved immunophenotype ex vivo as demonstrated by morphological changes, nuclear translocation of p65, and secretion of TNF-&#945; when challenged with bacterial lipopolysaccharide (LPS) or Pam3CSK4, TLR4 and TLR1/2 agonists, respectively.

<table border="0" cellpadding="0" cellspacing="0" width="680">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="160">
			<td height="160" style="height:160px;width:233px;">Glucose</td>
			<td style="width:149px;">Sigma</td>
			<td style="width:155px;">G8270</td>
			<td style="width:143px;">Make 20% Stock Solution with MilliQ water; filter sterilize; store at 4 &#176;C; shelf life: 3-6 months. Used to make MCM and MGM.</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:233px;">Sodium pyruvate 100 mM (100x)</td>
			<td style="width:149px;">Hyclone</td>
			<td style="width:155px;">SH30239.01</td>
			<td style="width:143px;">Store at 4 &#176;C. Used to make MCM and MGM.</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">Penicillin/Streptomycin 10,000 units/ml (100x)</td>
			<td style="width:149px;">Gibco</td>
			<td style="width:155px;">15140-122</td>
			<td style="width:143px;">Store at -20 &#176;C. Used to make MCM, MGM, MM, and DM.</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:233px;">L-glutamine 200 mM (100x)</td>
			<td style="width:149px;">Gibco</td>
			<td style="width:155px;">25030-081</td>
			<td style="width:143px;">Store at -20 &#176;C. Used to make MCM and MGM.</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">Fetal Bovine Serum (Defined)</td>
			<td style="width:149px;">Hyclone</td>
			<td style="width:155px;">SH30070.03</td>
			<td style="width:143px;">Filter sterilize; store at -20 &#176;C. Used to make MCM and MGM.</td>
		</tr>
		<tr height="120">
			<td height="120" style="height:120px;width:233px;">Minimum Essential Medium Earle&#39;s (MEM)</td>
			<td style="width:149px;">Cellgro</td>
			<td style="width:155px;">15-010-CV</td>
			<td style="width:143px;">Without L-glutamine. Contains Earle&#39;s salts. Used to make MCM, MGM, and DM.</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">Horse Serum</td>
			<td style="width:149px;">Gibco</td>
			<td style="width:155px;">16050</td>
			<td style="width:143px;">Filter sterilize; store at -20 &#176;C. Used to make MCM and MGM.</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">Hanks&#39; Balanced Salt Solution (HBSS)</td>
			<td style="width:149px;">Cellgro</td>
			<td style="width:155px;">21-021-CV</td>
			<td style="width:143px;">Without calcium and magnesium. Store at 4 &#176;C. Used to make MM.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">HEPES 1 M</td>
			<td style="width:149px;">Gibco</td>
			<td style="width:155px;">15630-031</td>
			<td style="width:143px;">Store at 4 &#176;C. Used to make MM.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:233px;">T-75 Flask</td>
			<td style="width:149px;">Corning</td>
			<td style="width:155px;">430641</td>
			<td style="width:143px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">4&#39;,6-Diamidino-2-Phenylindole, dilactate (DAPI)</td>
			<td style="width:149px;">Invitrogen</td>
			<td style="width:155px;">D3571</td>
			<td style="width:143px;">Used to stain cell nucleus.</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:233px;">Rabbit anti-Iba1</td>
			<td style="width:149px;">Wako</td>
			<td style="width:155px;">019-19741</td>
			<td style="width:143px;">Used at 1/750 dilution for ICC staining of Iba1.&#160;</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:233px;">Rabbit anti-NF&#954;B (p65)</td>
			<td style="width:149px;">Abcam</td>
			<td style="width:155px;">7970</td>
			<td style="width:143px;">Used at 1/1250 dilution for ICC staining for p65.</td>
		</tr>
		<tr height="100">
			<td height="100" style="height:100px;width:233px;">Alexafluor 594 Goat anti-Rabbit IgG (H+L)</td>
			<td style="width:149px;">Invitrogen</td>
			<td style="width:155px;">A11012</td>
			<td style="width:143px;">Used at 1/1000 dilution for visualization of antigen:antibody complex in ICC.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">10 ml Disposable Serological Pipet</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td style="width:155px;">13-678-11E</td>
			<td style="width:143px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">50 ml Disposable Centrifuge Tube</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td style="width:155px;">05-539-8</td>
			<td style="width:143px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">15 ml Disposible Centrifuge Tube</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td style="width:155px;">05-539-12</td>
			<td style="width:143px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:233px;">Sterile Polystyrene Petri Dish</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td style="width:155px;">875713</td>
			<td style="width:143px;">100 mm x 15 mm</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Scissor: Straight Metzembaum (scissor #1)</td>
			<td style="width:149px;">Roboz Surgical</td>
			<td style="width:155px;">RS-6010</td>
			<td style="width:143px;">1; 5 inch; used for removing head</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">Scissor: Vannas 
			(scissor #2)</td>
			<td style="width:149px;">Fine Science Tools</td>
			<td style="width:155px;">15000-08</td>
			<td style="width:143px;">1; non-angled; 2.5mm cutting edge; used to open scalp</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Scissor: Student Vannas (scissor #3)</td>
			<td style="width:149px;">Fine Science Tools</td>
			<td style="width:155px;">91501-09</td>
			<td style="width:143px;">1; curved; used to mince brain tissue</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:233px;">Forcep: Dumont #7 
			(forcep #1)</td>
			<td style="width:149px;">Fine Science Tools</td>
			<td style="width:155px;">91197-00</td>
			<td style="width:143px;">2; used to secure nose and remove cortices&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Forcep: Dumont #2 
			(forcep #2)</td>
			<td style="width:149px;">Fine Science Tools</td>
			<td style="width:155px;">11223-20</td>
			<td style="width:143px;">1; used to remove scalp</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Forcep: Dumont #3 
			(forcep #3)</td>
			<td style="width:149px;">Fine Science Tools</td>
			<td style="width:155px;">11231-30</td>
			<td style="width:143px;">1; used to remove skull</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Forcep: Dumont #5a 
			(forcep #4)</td>
			<td style="width:149px;">Fine Science Tools</td>
			<td style="width:155px;">11253-21</td>
			<td style="width:143px;">1; used to remove meninges</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Table of specific equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:233px;">Name of Equipment</td>
			<td style="width:149px;">Name of Company</td>
			<td style="width:155px;">Catalogue Number</td>
			<td style="width:143px;">Comments</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">Zoom Stereo Dissection Microscope&#160;</td>
			<td style="width:149px;">Olympus</td>
			<td style="width:155px;">SZ4060</td>
			<td style="width:143px;">Microscope is placed inside Laminar-Horizontal Flow Cabinet</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Laminar-Horizontal Flow Cabinet</td>
			<td style="width:149px;">Nuaire</td>
			<td style="width:155px;">NU-201-330</td>
			<td style="width:143px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:233px;">Biological Safety Cabinet</td>
			<td style="width:149px;">Labconco</td>
			<td style="width:155px;">3440001</td>
			<td style="width:143px;">Class II</td>
		</tr>
		<tr height="46">
			<td height="46" style="height:46px;width:233px;">Water-Jacketed CO2 Incubator</td>
			<td style="width:149px;">VWR</td>
			<td>97025-836</td>
			<td style="width:143px;">Set to 37 &#176;C, 5% CO2</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Swing-out buckets</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td>75006441</td>
			<td style="width:143px;">To be used with Swing-out rotor</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Swing-out Rotor</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td>75006445</td>
			<td style="width:143px;">Max Radius: 19.2 (cm)</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:233px;">Sorvall Legend RT+ Centrifuge 
			(clinical centrifuge)</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td>75-004-377</td>
			<td style="width:143px;">With swing-out rotor</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:233px;">AccuSpin Micro 17 microcentrifuge 
			(tabletop microcentrifuge)</td>
			<td style="width:149px;">Fisher Scientific</td>
			<td>S98645</td>
			<td style="width:143px;">With microliter rotor (24 x 1.5/2.0 ml; 
			Cat #: 75003524)&#160;&#160;</td>
		</tr>
	</tbody>
</table>

isolation of cortical microglia with preserved immunophenotype and functionality from murine neonates

Isolation of microglia from CNS tissue is a powerful investigative tool used to study microglial biology ex vivo. The present method details a procedure for isolation of microglia from neonatal murine cortices by mechanical agitation with a rotary shaker. This microglia isolation method yields highly pure cortical microglia that exhibit morphological and functional characteristics indicative of quiescent microglia in normal, nonpathological conditions in vivo. This procedure also preserves the microglial immunophenotype and biochemical functionality as demonstrated by the induction of morphological changes, nuclear translocation of the p65 subunit of NF-&#954;B (p65), and secretion of the hallmark proinflammatory cytokine, tumor necrosis factor-&#945; (TNF-&#945;), upon lipopolysaccharide (LPS) and Pam3CSK4 (Pam) challenges. Therefore, the present isolation procedure preserves the immunophenotype of both quiescent and activated microglia, providing an experimental method of investigating microglia biology in ex vivo conditions.

Retaining the immunophenotype and functionality of microglia ex vivo during isolation is critical to be able to utilize these cells as an investigatory model for microglial biology. In order to demonstrate the successful preservation of microglia immunofunctionality using the present method, we isolated cortical microglia from P3 neonates (CX3CR1-GFP+/-and C57BL/6) and treated cultures with either LPS or Pam.
As illustrated in Figure 1A, isolation of microg...

Watch this Scientific Journal Video about Isolation of Cortical Microglia with Preserved Immunophenotype and Functionality From Murine Neonates at JoVE.com

Isolation of Cortical Microglia with Preserved Immunophenotype and Functionality From Murine Neonates

One key to successful investigation of microglial biology is the preservation of microglial immunofunction ex vivo during isolation from CNS tissue. Isolating microglia via rotary shaking results in highly pure and immunofunctional cell cultures as assessed by fluorescent imaging, immunocytochemistry, and ELISA following microglia activation with the proinflammatory stimuli lipopolysaccharide (LPS) and Pam3CSK4 (Pam).

Isolation of microglia from CNS tissue is a powerful investigative tool used to study microglial biology ex vivo. The present method details a procedure ...

isolation-cortical-microglia-with-preserved-immunophenotype

Research

JoVE Journal

Immunology and Infection

15.6K Views.  Georgetown University Medical Center. One key to successful investigation of microglial biology is the preservation of microglial immunofunction ex vivo during isolation from CNS tissue. Isolating microglia via rotary shaking results in highly pure and immunofunctional cell cultures as assessed by fluorescent imaging, immunocytochemistry, and ELISA following microglia activation with the proinflammatory stimuli lipopolysaccharide (LPS) and Pam3CSK4 (Pam).