Figures were created using BioRender. Research is funded by Inserm, Universit&#233; de Paris, Horizon 2020 (PREMSTEM-874721), Fondation de France, Fondation ARSEP, Fondation pour la Recherche sur le Cerveau, Fondation Grace de Monaco, and an additional grant from Investissement d&#39;Avenir -ANR-11-INBS-0011-NeurATRIS and Investissement d&#39;Avenir -ANR-17-EURE-001-EUR G.E.N.E.

The protocol was approved, and all the animals were handled according to the institutional guidelines of Institut National de la Sante&#769; et de la Recherche Scientifique (Inserm, France). Magnetic isolation of microglia from the brains of 24 OF1 mouse pups (both male and female) at P8, divided into 6-well, 12-well, or 96-well plates, are presented. The experimental work was performed under a hood to maintain sterile conditions.
1. Preparation of sterile solutions for isolation and cell culture
<ol>
	<li>Prepare 50 mL of 1x Hanks&#39; Balanced Salt Solution (HBSS) without Ca2+ and Mg2+ (HBSS-/-) from the commercially available 10x solution (see Table of Materials).</li>
	<li>Prepare dissociation mixture according to the composition provided in Table 1 using a commercially available tissue dissociation kit (see Table of Materials).</li>
	<li>Prepare 200 mL of 1x HBSS with Ca2+ and Mg2+ (HBSS+/+) from the commercially available 10x solution.</li>
	<li>Prepare 200 mL of 1x PBS + 0.5% BSA (referred to as cell sorting buffer).</li>
	<li>Prepare CD11b-microbeads according to Table 2.</li>
	<li>Prepare 500 mL of macrophage serum-free culture medium (SFM) + 1% of Penicillin-Streptomycin (P/S). Make aliquots of 50 mL tubes and store them at 4 &#176;C. This is referred to as the microglia medium later in the text. 
	NOTE: All isolation solutions must be freshly prepared under sterile conditions on experimentation day and kept on ice. Microglia cell culture medium can be prepared, aliquoted in 50 mL tubes, and kept at 4 &#176;C for future use. Filtration is not needed.</li>
</ol>
2. Brain dissection
<ol>
	<li>Decapitate the pup&#39;s head using large scissors without previous general anesthesia.</li>
	<li>Cut the skin from the neck to the nose following the sagittal suture (15-20 mm) with small scissors (Figure 1A-C).</li>
	<li>Insert a small scissor&#39;s tips within the Foramen magnum parallel to the skull. Cut from each side carefully to the eyes (Figure 1D,E).</li>
	<li>Cut between the eyes with small scissors to detach the skull and brain from the head (Figure 1F).</li>
	<li>With two forceps, grab the skull close to the olfactory bulbs and tear the skull carefully, taking care not to damage the underlying brain (Figure 1G-I).</li>
	<li>Remove cerebellum and olfactive bulb with a razor blade and cut the brain into two pieces (Figure 1J).</li>
	<li>Place the brain pieces in a Petri dish containing 30-40 mL of HBSS-/- (Figure 1K).</li>
</ol>
3. Brain dissociation and magnetic microglial isolation
NOTE: All cell manipulations and resuspensions must be performed with a 1,000 &#181;L pipette with great caution. Applying a high mechanical action may activate or kill microglia cells.
<ol>
	<li>Transfer 12 brain pieces (~1.2 g) per dissociation tube containing dissociation mixture according to Table 1. For 24 pups, four C-Tubes were needed (Figure 2A-B).</li>
	<li>Place C-Tubes on the dissociator (with the heating mode). Start the optimized NTDK program in the equipment according to the manufacturer&#39;s instruction (Figure 2D).</li>
	<li>Centrifuge at 300 x g for 20 s (at 4 &#176;C) to collect all the cells. Complete the mechanical dissociation by pipetting three times up and down with a 1,000 &#181;L pipette (Figure 2E).</li>
	<li>Transfer the cells to four 15 mL tubes + strainers. Rinse the strainers with 10 mL of HBSS+/+ (Figure 2F).</li>
	<li>Centrifuge at 300 x g for 10 min&#160;(at 4 &#176;C) and remove the supernatant. Carefully resuspend the pellet with 10 mL of HBSS+/+ (Figure 2G).</li>
	<li>Centrifuge at 300 x g for 10 min&#160;(at 4 &#176;C) and remove the supernatant. Carefully resuspend the pellet with 6 mL of sorting buffer (step 1.4) (Figure 2H).</li>
	<li>Centrifuge at 300 x g for 10 min&#160;(at 4 &#176;C) and remove the supernatant. Add 200 &#181;L of CD11b-microbead solution (step 1.5) per tube and resuspend carefully (Figure 2I).</li>
	<li>Incubate the tubes for 15-20 min at 4 &#176;C. Carefully resuspend the pellet with 6 mL of sorting buffer (Figure 2I-J).</li>
	<li>Centrifuge at 300 x g for 10 min&#160;(at 4 &#176;C) and remove the supernatant. Carefully resuspend the pellet with 8 mL of sorting buffer (Figure 2K).</li>
	<li>Follow the POSSEL program on the separator (see Table of Materials) to prepare eight columns. Transfer cells 1 mL by 1 mL on the column. Wait for all the cells to pass through before adding another mL. Elute CD11b+ cells on sterile elution plate with 1 mL of sorting buffer (Figure 2L).</li>
	<li>Pool CD11b+ cells in a new 50 mL tube (Figure 2M).</li>
	<li>Centrifuge at 300 x g for 10 min&#160;(at 4 &#176;C) and remove the supernatant. Carefully resuspend the pellet with 10 mL of cold microglia medium (step 1.6) (Figure 2N).</li>
	<li>Count the CD11b+ cells. At P8, one should obtain ~650,000 cells per brain. 
	NOTE: In the present protocol, the cells were counted using an automated cell counter (see Table of Materials).</li>
	<li>Resuspend the cells in cold microglia medium to a final concentration of 650,000-700,000 cells/mL and dispense in cell culture plates. 
	NOTE: The 6-well plates are for Western Blot&#160;(2 mL per well); the 12-well plates are for RT-qPCR analysis (1 mL per well), and the 96-well plates are for phagocytic assay (250 &#181;L per well); all three were used for this work. However, in this manuscript, the results from the Western Blot analysis are not shown, but it is possible to perform with this protocol.</li>
	<li>Place the plates at 37 &#176;C with 5% CO2&#160;overnight. Change the medium carefully with a 1,000 &#181;L pipette with pre-heated microglia medium.</li>
	<li>Place the plates at 37 &#176;C with 5% CO2&#160;overnight before stimulation. 
	NOTE: Isolating microglia from more than 36 pups and after P9 are not recommended. This will increase the risk of contamination and accumulation of cell debris to activate microglia.</li>
</ol>
4.&#160;Cell stimulations
<ol>
	<li>Prepare stimulation reagents according to Table 3 using the commercially available reagents (see Table of Materials).</li>
	<li>Add the appropriate volume in each stimulated well. 
	NOTE: The appropriate volume depends on the concentration of the stimulus and the size of the well.</li>
	<li>Place the plates at 37 &#176;C with 5% CO2until the end of stimulation at 6 h, 24 h, or 48 h.</li>
	<li>For the Western Blot analysis, aspirate the supernatant and add 50 &#181;L of protein lysis buffer (see Table of Materials) with a pipette. Using tips, scratch the bottom of the plate to detach the lysed cells and transfer them to 1.5 mL tubes. Store at -80 &#176;C. 
	NOTE: The culture plates can be stored for years at -80 &#176;C if the supernatant is aspirated correctly.</li>
	<li>For RT-qPCR analysis6,31, aspirate the supernatant and store the culture plates directly at -80 &#176;C until mRNA extraction (step 5).</li>
	<li>For the phagocytic assay, please see step 6.</li>
</ol>
5. mRNA extraction and RT-qPCR analysis
<ol>
	<li>Perform RNA extraction, RT-PCR, and RT-qPCR following the manufacturer&#39;s protocol (see Table of Materials). Refer to Table 4 for the primer sequences5,6,31.</li>
	<li>Perform RT-qPCR analysis by following the previously published report5.</li>
</ol>
6. Phagocytic assay
<ol>
	<li>Stimulate the cells and perform phagocytic assay during the last 3 h of the stimulation. For example, for stimulation of 6 h, start the phagocytic assay after 3 h of stimulation; and for stimulation of 12 h, start the phagocytic assay 9 h after the beginning of the stimulation.</li>
	<li>Calculate the number of beads needed to prepare considering the ratio (1 cell: 50 beads). For one well of the 96-well plate, 8.1 x 106 beads are required. Prepare the beads mixture according to Table 5. 
	NOTE: Carefully vortex the beads stock vial before adding to the PBS/FBS mixture.</li>
	<li>Incubate for 1 h in a water bath at 37 &#176;C. Vortex every 10 min.</li>
	<li>Calculate the solution volume to add to each well. Add the solution and incubate for 3 h.</li>
	<li>Rinse the wells three times with 1x PBS. Read the fluorescence emission at 550 nm (Cy3 emission wavelength).</li>
</ol>
7. Purity quality control
<ol>
	<li>Evaluate the purity of CD11b magnetic isolation by flow cytometry (FACS) (before and after cell sorting), and then perform the RT-qPCR.
	<ol>
		<li>Count the cells and resuspend in FACS buffer (PBS + 2 mM of EDTA + 0.5% of Bovine Serum Albumin) in order to obtain a dilution of 10 x 106 cells/mL after step 3.5 and step 3.14.</li>
		<li>After 15 min of the conventional Fc blocking32,33, incubate the cells for 15 min with viability probe (FVS780) and fluorophore-conjugated antibodies against mouse CD45, CD11b, CX3CR1, ACSA-2, O4 or their corresponding control isotypes32,33&#160;at the concentration recommended by the manufacturers (see Table of Materials).</li>
		<li>Wash the cells with FACS buffer, fix, and permeabilize with a commercially available permeabilization kit (see Table of Materials).</li>
		<li>Perform Fc blocking again on the permeabilized cells, and then incubate with fluorophore-conjugated antibody against NeuN (see Table of Materials) or its control isotype for 15 min.</li>
		<li>Perform FACS analysis after washing with FACS buffer.</li>
		<li>After excluding the doublets and the dead cells based on morphological parameters and FVS780 staining, respectively, select the gating strategy for the surface expression of CX3CR1 (microglia), ACSA-2 (astrocytes), O4 (oligodendrocytes), and intracellular presence of NeuN (neurons) for the analysis of the percentage of positive cells.</li>
	</ol>
	</li>
	<li>Following step 5, extract mRNA and perform RT-qPCR to quantify Itgam (CD11b), Cx3cr1, Olig2, Synaptophysin, and Gfap mRNA. Normalize Cq using Rpl13a mRNA as a reporter, and perform a relative expression to Itgam mRNA.</li>
</ol>

The authors declare no conflicts of interest.

The current work presents a primary microglial cell culture using magnetically sorted CD11b+ cells. In addition to the microglial functional evaluation (RT-qPCR and phagocytic assays), microglial culture purity was also determined.
Classical microglia cell cultures are commonly generated from P1 or P2 rodent neonate brain and co-culture with astrocytes for at least 10 days. Microglia are then separated mechanically using an orbital shaker. The method to isolate and culture microglia in vitro was described for the first time at the end of the 1990s from the brains of neonate rats40,41. Since then, it has been widely used to analyze microglial phenotypes such as activated/resting microglia or pro-inflammatory/anti-inflammatory microglia. Furthermore, this experiment has been fundamental to defining microglia as neurotoxic cells co-cultured with neurons. However, in 2014, Biber and collaborators described three significant disadvantages of studying microglia in vitro using classical methods42. (1) The experiment uses rat/mouse neonate brains (P1/P2), and these cells did not pass through all the maturation processes that can occur in vivo. (2) In the co-culture medium, 10% FBS is used; however, in vivo, microglia never encounter such components in a &#34;normal&#34; environment. (3) Recent studies demonstrate that in vivo microglia are restrained by several inhibitory components not present in the culture43,44. Moreover, many studies (electrophysiological45&#160;and transcriptomic46,47) described non-stimulated primary microglia as &#34;activated&#34;.
The present method proposes an alternative technique to generate microglia cultures using magnetically cell sorted technology. With this protocol, microglia are harvested only a few hours after the animal dies without any co-culture step. Moreover, microglia are only cultured 2 days in vitro (DIV) before stimulation compared to 10-14 DIV, including co-culture in other protocols. This allows getting closer to the microglial physiological conditions. This procedure of culturing microglia in vitro was previously published25,26,27,28,29. The current work presented an optimized protocol for neonate mice, standardized for reducing the number of animals used and without myelin removal step.
To reduce the number of mice used for primary microglia culture, we decided to work at P8 in the OF1 strain. At this stage of brain development in OF1 strain, up to 750,000 microglial cells per brain was obtained, in opposition to 500,000 microglial cells per C57BL6/J strain mouse brain at the same age. C57BL6/J strain has been published at a different developmental stage for microglia culture27,28. The present protocol has also been used with Fmr1KO mice to evaluate phagocytic properties of microglia linked to this mutation and LysMCre: Dicerfl/+ mice to assess microglial activation phenotypes by RT-qPCR. Thus, working with C57BL/6 J mouse strain is a little more challenging than working on OF1 strain due to (1) fewer microglial cells per brain at the same developmental stage and (2) fragility of microglia that are more prone to die due to mechanical activation (see the troubleshooting section).
Depending on the developmental stage chosen for primary microglia culture, myelination must be considered since it starts around P5. In a classical microglial culture (at P0-2), myelination is not an issue; however, in other published methods to isolate microglia, myelin is removed using Percoll gradient or anti-myelin antibodies25,26,28,29. In the present protocol, animals are euthanized at P8 when myelination has already begun; large volumes are used to rinse pellets, and the newly formed myelin can be removed without any additional procedure. This can be one troubleshooting method (see the Debris section).
The manufacturer and previously published microglial magnetic isolation used DMEM F-12 media supplemented with 10% FBS - 1% P/S25,26,27,28,29. Biber et al.42&#160;described that microglia rarely contact serum in vivo. Indeed, the central nervous system&#39;s extracellular fluid rarely contains protein and bioactive factors29. That is why serum-free macrophage (SFM) medium + 1% P/S is used in the present protocol.
Magnetic-activated cell sorting (MACS) protocol can also isolate and culture postnatal rat microglia with some modifications25,29. Rat microglia are indeed isolated using Microbead-coated anti-rat CD11b/c. However, due to the brain size being bigger than P8 mice, only one brain per dissociation tube per column should be used. Microglia were isolated from P10-14 rat brains in previously published protocols, including the myelination removal step29. Despite the previous comments on culture medium, for rat microglial culture, F-12 media + 10% FBS and 550,000-600,000 cells per 12-well plate are recommended for downstream applications.
Troubleshooting 
Dissociation: The dissociation mixture as described in Table 1&#160;is calculated for the maximal amount of brain that can be dissociated and proceed at P8 in OF1 mice. If more brain is added, dissociation cannot be completed at the end of step 3.2, and non-dissociated brain tissue will be found. In this case, it is recommended to run the NTDK program on the tube with non-dissociated tissue and keep the other tubes at 4 &#176;C.
Clogged strainer and/or column: As described before, the dissociation mixture is calculated for the maximal amount of brain tissue that can pass through the strainer during step 3.5. If more brain is added, the filtration may take longer, but eventually, it will pass through. It is recommended to carefully resuspend cell suspension on the top of the strainer until all cell suspension is filtered.
During step 3.12, the experimenter must pass labeled cell suspension through a column inside the magnetic field. The column can be clogged at this stage of the procedure (1) if too much brain tissue is dissociated per tube, (2) if resuspension volume is not correct, or (3) if there is some mechanically induced cell death (some DNA can be present); in that case, it is recommended to remove the visible DNA with a 200 &#181;L tip carefully.
Mechanically induced cell death and/or activation: The protocol described here presents one main challenge: avoiding mechanical activation. To do so, it is critical to pipette gently and keep the centrifugation speed low. If not, immature microglia can die due to the mechanical stress or get activated, leading to high variability in RT-qPCR results.
Debris: In this procedure, animals are euthanized at P8 when myelination is just beginning, and therefore there is no procedure to precisely remove myelin. At this stage of development, myelin can easily be removed by centrifugation. Resuspension volumes described in this procedure are calculated to remove the maximum myelin. If not respected, myelin could appear as cell debris in culture wells. The experimenter cannot completely remove it when observed in culture wells by changing the medium on day 2. Microglial cells tend to phagocyte this debris, which may affect the microglial activation state before stimulation and thus affect experimental reproducibility.
All previously described troubleshooting (Dissociation, Clogged strainer and/or column, Mechanically induced cell death and/or activation, and debris) can lead to variability in the number of CD11b+ cells obtained when cell counting (Figure 5B). We recommend paying great attention to this to optimize the final cell yield.
Contamination: In this protocol, microglial cells are cultured in SFM medium + 1% P/S. SFM medium can easily be contaminated. Therefore, it is recommended to aliquot the medium in 50 mL tubes after adding P/S to avoid medium contamination. Moreover, all experimentation needs to be performed as much as possible under sterile conditions.
mRNA quantity/quality: Our team works on miRNA or siRNA transfections. The present protocol is highly compatible with such applications using magnetic transfection with a slight modification of the protocol; the experimenter needs to harvest 700,000 cells per 12-well plate to get high-quality mRNA for RT-qPCR. Although RNAseq is not performed in the present study, previously, our team performed mRNA extraction for RNAseq using 500,000 cells per 12-well plate48.
In conclusion, this protocol can be reproduced, and it is expected to be a new standard for isolating microglia at a juvenile developmental stage.

Microglia are the central nervous system resident macrophage-like cells derived from erythropoietic precursors of the yolk sac that migrate to the neuroepithelium during early embryonic development1. Apart from their immunity functions, they also play a significant role during neurodevelopment, particularly for synaptogenesis, neuronal homeostasis, and myelination2. In adulthood, microglia develop long cellular processes to scan the environment continuously. In case of homeostasis ruptures such as brain injury or brain disease, microglia can change their morphological appearance to adopt an amoeboid shape, migrate to the injured area, increase and release many cytoprotective or cytotoxic factors. Microglia have heterogeneous activation states depending on their developmental stage and the type of injury sustained3,4,5. In this study, these activation states are broadly classified into three different phenotypes: pro-inflammatory/phagocytic, anti-inflammatory, and immuno-regulatory, keeping in mind that in reality, the situation is likely to be more complex6.
Studying in vivo microglial activation and screening for neuroprotective strategies at early stages of brain development can be challenging due to (1) the fragility of animals before weaning and (2) the low number of microglial cells. Therefore in vitro studies on microglia are widely used for toxicity7,8,9, neuroprotective strategies5,10,11,12,13,14, and co-cultures15,16,17,18,19,20,21. In vitro studies can use either microglial cell lines, stem-cell-derived microglia, or primary microglia culture. All these approaches have advantages and disadvantages, and the choice depends on the initial biological question. The benefits of using primary microglia cultures are the homogenous genetic background, pathogen-free history, and control of the time when the microglia are stimulated after animal death22.
Over the years, different methods (flow cytometry, shaking, or magnetic labeling) were developed for culturing primary microglia from rodents, both neonate and adult23,24,25,26,27,28,29. In the present work, microglia isolation from mouse neonate pups is performed using previously described magnetic-activated cell sorting technology using microbead-coated anti-mouse CD11b25,27,29. CD11b is an integrin-receptor expressed at the surface of myeloid cells, including microglia. When there is no inflammatory challenge within the brain, almost all CD11b+ cells are microglia30. Compared to other previously published methods23,24,25,26,27,28,29, the present protocol balances immediate ex vivo microglial activation analyses and common in vitro primary microglial culture. Thus, microglia are (1) isolated at postnatal day (P)8 without myelin removal, (2) cultured without serum, and (3) exposed either to siRNA, miRNA, pharmacological compound, and/or inflammatory stimuli only 48 h after brain isolation. Each of these three aspects makes the current protocol relevant and rapid. First of all, the use of pediatric microglia allows obtaining dynamic and reactive viable cells in culture without requiring an additional demyelination step that could potentially modify microglial reactivity in vitro. The present protocol aims to get as close as possible to the physiological environment of microglia. Indeed, microglia never encounter serum, and this protocol does not require the use of serum either. Moreover, exposing microglia as early as 48 h after culture prevents them from losing their physiological faculties.

<table><tbody><tr><td>Anti mouse ACSA-2 PE Vio 615</td><td>Miltenyi Biotec</td><td>130-116-246</td><td></td></tr><tr><td>Anti mouse CD11b BV421</td><td>Sony Biotechnology</td><td>1106255</td><td></td></tr><tr><td>Anti mouse CD45 BV510</td><td>Sony Biotechnology</td><td>1115690</td><td></td></tr><tr><td>Anti mouse CX3CR1 PE Cy7</td><td>Sony Biotechnology</td><td>1345075</td><td></td></tr><tr><td>Anti mouse NeuN PE</td><td>Milli-Mark</td><td>FCMAB317PE</td><td></td></tr><tr><td>anti mouse O4 Vio Bright B515</td><td>Miltenyi Biotec</td><td>130-120-016</td><td></td></tr><tr><td>BD Cytofix/Cytoperm permeabilization kit</td><td>BD Biosciences</td><td>554655</td><td></td></tr><tr><td>Bovine Serum Albumin</td><td>Miltenyi Biotec</td><td>130-091-376</td><td></td></tr><tr><td>CD11b (Microglia) MicroBeads, h, m</td><td>Miltenyi Biotec</td><td>130-093-634</td><td></td></tr><tr><td>Confocal microscope</td><td>Leica TCS SP8</td><td></td><td></td></tr><tr><td>D-PBS (10x)</td><td>Thermo Scientific</td><td>14200067</td><td></td></tr><tr><td>EDTA</td><td>Sigma-Aldrich</td><td>E1644</td><td></td></tr><tr><td>Falcon Cell culture 12-well plate, flat bottom + lid</td><td>Dutscher</td><td>353043</td><td></td></tr><tr><td>Falcon Cell culture 96-well plate, flat bottom + lid</td><td>Dutscher</td><td>353072</td><td></td></tr><tr><td>Falcon tubes 50 mL</td><td>Dutscher</td><td>352098</td><td></td></tr><tr><td>Fc blocking reagent (Mouse CD16/32)</td><td>BD Biosciences</td><td>553142</td><td></td></tr><tr><td>Fluorescence microscope</td><td>Nikon ECLIPSE TE300</td><td></td><td></td></tr><tr><td>gentleMACS C Tubes (4 x 25 tubes)</td><td>Miltenyi Biotec</td><td>130-096-334</td><td></td></tr><tr><td>gentleMACS Octo Dissociator with Heaters</td><td>Miltenyi Biotec</td><td>130-096-427</td><td></td></tr><tr><td>Hanks&#039; Balanced Salt Solution (HBSS) +CaCl&lt;sub&gt;2&lt;/sub&gt; +MgCl&lt;sub&gt;2&lt;/sub&gt; 10x</td><td>Thermo Scientific</td><td>14065049</td><td></td></tr><tr><td>Hanks&#039; Balanced Salt Solution (HBSS) -CaCl&lt;sub&gt;2&lt;/sub&gt; -MgCl&lt;sub&gt;2&lt;/sub&gt; 10x</td><td>Thermo Scientific</td><td>14185045</td><td></td></tr><tr><td>iQ SYBR&amp;nbsp;Green Supermix</td><td>Bio-rad</td><td>1725006CUST</td><td></td></tr><tr><td>Iscript c-DNA synthesis</td><td>Bio-rad</td><td>1708890</td><td></td></tr><tr><td>Latex beads, amine-modified polystyrene, fluorescent red</td><td>Sigma-Aldrich</td><td>L2776-1mL</td><td></td></tr><tr><td>Lipopolysaccharides (LPS) from&amp;nbsp;Escherichia coli&amp;nbsp;O55:B5</td><td>Sigma-Aldrich</td><td>L2880</td><td></td></tr><tr><td>Macrophage-SFM serum-free medium</td><td>Thermo Scientific</td><td>12065074</td><td></td></tr><tr><td>MACS BSA Stock Solution</td><td>Miltenyi Biotec</td><td>130-091-376</td><td></td></tr><tr><td>MACS SmartStrainers (70 &amp;mu;m), 4 x 25 pcs</td><td>Miltenyi Biotec</td><td>130-110-916</td><td></td></tr><tr><td>Mouse IgG1 PE</td><td>Millipore</td><td>MABC002H</td><td></td></tr><tr><td>Mouse IgG2a PE Cy7</td><td>Sony Biotechnology</td><td>2601265</td><td></td></tr><tr><td>Mouse IL1 beta</td><td>Miltenyi Biotec</td><td>130-101-684</td><td></td></tr><tr><td>Multi-24 Column Blocks</td><td>Miltenyi Biotec</td><td>130-095-691</td><td></td></tr><tr><td>MultiMACS Cell24 Separator</td><td>Miltenyi Biotec</td><td></td><td></td></tr><tr><td>Neural Tissue Dissociation Kit - Papain</td><td>Miltenyi Biotec</td><td>130-092-628</td><td></td></tr><tr><td>Nucleocounter NC-200</td><td>Chemometec</td><td></td><td></td></tr><tr><td>Nucleospin RNA Plus XS</td><td>Macherey Nagel</td><td>740990.5</td><td></td></tr><tr><td>Nun EZFlip Top Conical Centrifuge Tubes</td><td>Thermo Scientific</td><td>362694</td><td></td></tr><tr><td>OPTILUX Petri dish - 100 x 20 mm</td><td>Dutscher</td><td>353003</td><td></td></tr><tr><td>P&amp;eacute;nicilline-streptomycine (10 000 U/mL)</td><td>Thermo Scientific</td><td>15140122</td><td></td></tr><tr><td>Rat IgG2b, k BV421</td><td>BD Biosciences</td><td>562603</td><td></td></tr><tr><td>Rat IgG2b, k BV510</td><td>Sony Biotechnology</td><td>2603230</td><td></td></tr><tr><td>REA control (S) PE vio 615</td><td>Miltenyi Biotec</td><td>130-104-616</td><td></td></tr><tr><td>REA control (S) Vio Bright B515</td><td>Miltenyi Biotec</td><td>130-113-445</td><td></td></tr><tr><td>Recombinant Mouse IFN-gamma Protein</td><td>R&amp;amp;D System</td><td>485-MI</td><td></td></tr><tr><td>Recombinant Mouse IL-10 Protein</td><td>R&amp;amp;D System</td><td>417-ML</td><td></td></tr><tr><td>Recombinant Mouse IL-4 Protein</td><td>R&amp;amp;D System</td><td>404-ML</td><td></td></tr><tr><td>RIPA Buffer</td><td>Sigma-Aldrich</td><td>R0278</td><td></td></tr><tr><td>Viability probe (FVS780)</td><td>BD Biosciences</td><td>565388</td><td></td></tr></tbody></table>

magnetic isolation of microglial cells from neonate mouse for primary cell cultures

Microglia, as brain resident macrophages, are fundamental to several functions, including response to environmental stress and brain homeostasis. Microglia can adopt a large spectrum of activation phenotypes. Moreover, microglia that endorse pro-inflammatory phenotype is associated with both neurodevelopmental and neurodegenerative disorders. In vitro studies are widely used in research to evaluate potential therapeutic strategies in specific cell types. In this context studying microglial activation and neuroinflammation in vitro using primary microglial cultures is more relevant than microglial cell lines or stem-cell-derived microglia. However, the use of some primary cultures might suffer from a lack of reproducibility. This protocol proposes a reproducible and relevant method of magnetically isolating microglia from neonate pups. Microglial activation using several stimuli after 4 h and 24 h by mRNA expression quantification and a Cy3-bead phagocytic assay is demonstrated here. The current work is expected to provide an easily reproducible technique for isolating physiologically relevant microglia from juvenile developmental stages.

Microglia is the CNS resident macrophage that gets activated when exposed to environmental challenges (trauma, toxic molecules, inflammation )4,5,6,34&#160;(Figure 3A). In vitro studies on microglia are commonly used to evaluate cell-autonomous mechanisms related to those environmental challenges and characterize activation state after pharmacological or genetic manipulation. Here, an approach is presented to isolate primary microglia at the juvenile stage using magnetic coupled beads.
An easy readout for microglial activation in vitro is to quantify mRNA expression of several microglial reactivity markers associated with a pro-inflammatory phenotype (Cd86, Nos2, Ptgs2, Tnf) or an anti-inflammatory phenotype (Cd206, Igf1, Arg1, Lgasl3)5,6,31. These phenotypes were described depending on mRNA expression after pro-inflammatory (IL-1&#946;, LPS) or anti-inflammatory (IL-4 or IL-10) stimulus. Some markers are classified as immuno-regulatory markers because they are upregulated through pro- and anti-inflammatory stimulation (Figure 3A). This classification was described previously by our team5,6,31. After 48 h, isolated microglial were stimulated with pro- and anti-inflammatory stimulus for 4 h or 24 h. mRNA were extracted, and RT-qPCR quantified gene expression. At 4 h and 24 h, pro-inflammatory and immuno-regulatory markers are induced by IL-1&#946;, IL-1&#946; + IFN-&#947;, and LPS5,6,31. At 4 h, IL-4 stimulation also induces the immuno-regulatory marker Il-1rn6. They are induced strongly at 4 h after IL-4 stimulation regarding anti-inflammatory markers. Interestingly, Cd206 is also significantly upregulated 24 h after IL-1&#946; stimulation6&#160;(Figure 3B).
To evaluate the phagocytic activity of microglia in vitro, fluorescent Cy3 PVC beads were used. They were pre-treated with fetal bovine serum (FBS) to facilitate their phagocytosis by microglia. Microglia were polarized toward pro-inflammatory phenotype by stimulation with IL-1&#946; + IFN-&#947; or LPS for 3 h or 21 h. Three hours before the end of stimulation, Cy3-beads were incubated with microglial cells. After rinsing with 1x PBS, the fluorescence intensity in each well was quantified. Quantification relative to wells with no beads was expressed, and representative images were taken (Figure 4). After 6 h stimulation, microglia start to phagocyte Cy3-beads only under IL-1&#946; + IFN-&#947;. After a 24 h stimulation, there is an increase of Cy3 fluorescence for both kinds of stimulation. That increase of Cy3 fluorescence highlights increased phagocytic activity (Figure 4C).
Flow cytometry (FACS) and RT-qPCR were performed to evaluate the microglial culture&#39;s purity. Different brain cellular populations can be distinguished by flow cytometry: CX3CR135&#160;for microglia, O4 for oligodendrocytes36, NeuN for neurons37, and ACSA-2 for astrocytes38. After dissociation, all brain cells are present; however, after cell sorting using CD11b antibody, only microglia and small amounts of O4 cells are present (Figure 5A). 48 h after primary cell culture, only microglia markers are found as evaluated by RT-qPCR (Figure 5B).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62964/62964fig01.jpg" /> 
Figure 1: Step-by-step representation showing the removal of the brain from the skull. (A-C) Small scissors were used to cut the skin from the neck to the nose following the sagittal suture. (D-E) The small scissor&#39;s tips were inserted within the Foramen magnum parallel to the skull, and from each side to the eyes were carefully cut. (F) The skull and brain were detached from the head by cutting between the eyes with small scissors. (G-I) The skull was grabbed close to the olfactive bulbs with two forceps and torn carefully not to damage the underlying brain. (J) The cerebellum and the olfactive bulb were removed with a razor blade, and the brain was cut into two pieces. (K) The brain pieces were placed in a Petri dish containing 30-40 mL of HBSS-/-. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62964/62964fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62964/62964fig02.jpg" /> 
Figure 2: Schematic representation of brain dissociations and microglial cells isolation. (A-C) After P8 mouse brain dissection and removing olfactive bulbs and cerebellum, brains were first transferred to a Petri dish with HBSS+/+, and then to dissociation tubes containing the dissociation mixture. The C-tubes were placed on the dissociator (with the heating mode), and the NTDK program was started (D). (E) At the end of the program, tubes were centrifuged at 300 x g for 20 s at 4 &#176;C; dissociation was then completed by pipetting three times up and down with a 1,000 &#181;L pipette. (F) Cells were then transferred to 15 mL tubes + strainers of 70 &#181;m and rinsed with 10 mL of HBSS+/+. (G) Samples were then centrifuged at 300 x g for 10 min at 4 &#176;C, the supernatant was removed, and the pellet was resuspended with 10 mL of HBSS+/+. (H) Tubes were again centrifuged at 300 x g for 10 min at 4 &#176;C; the supernatant was removed, and then the pellet was resuspended in 6 mL of sorting buffer. (I) Tubes were centrifuged at 300 x g for 10 min at 4 &#176;C, the supernatant was removed, and the CD11b-microbead (200 &#181;L) solution was added. Tubes were incubated for 15-20 min at 4 &#176;C, and then resuspended in 6 mL of sorting buffer (J) and centrifuged at 300 x g for 10 min&#160;at 4 &#176;C. (K) The supernatant was removed, and the pellet was carefully resuspended in 8 mL of sorting buffer. (L) Then, launch the POSSEL program on the separator to prepare columns. Cells were transferred 1 mL by 1 mL on the column, and CD11b cells were eluted on a sterile elution plate with 1 mL of sorting buffer. (M) CD11b cells were pooled in a new 50 mL tube and centrifuged at 300 x g for 10 min at 4 &#176;C, and the supernatant was removed. (N) The pellet was carefully resuspended in 10 mL of cold microglia medium in the last step. The cells were counted and diluted in the microglial medium to a final concentration of 650,000-700,000 cells/mL dispensed in cell culture plates. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62964/62964fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62964/62964fig03.jpg" /> 
Figure 3: Microglial activation following exposition to environmental challenges. (A) Simplified schematic representation of microglial activation spectrum. (B) Relative quantification of microglial activation markers after 4 h or 24 h stimulation. Two-way ANOVA followed by Dunnett&#39;s multiple comparisons test39&#160;(n = 5-15); error bars represent SEM; *p &#60; 0.05, **p &#60; 0.01, ***p &#60; 0.001. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62964/62964fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62964/62964fig04.jpg" /> 
Figure 4: Evaluation of the phagocytic activity of microglia in vitro. (A) Representative images of microglia Cy3-beads (in red) phagocytosis after stimulation of 6 h or 24 h. The images were acquired using 20x objective of the fluorescence microscope. Scale bar = 100 &#956;m. (B) Relative quantification of fluorescence emits per well. Statistics was performed using two-way ANOVA followed by Dunnett&#39;s multiple comparisons test (n = 4-7); error bars represent SEM; *p &#60; 0.05, ** p &#60; 0.01, ***p &#60; 0.001. (C) Representative picture of microglia (IBA-1 + cells in green) Cy3-beads (in red) phagocytosis after 6 h stimulation. The images are acquired using a 40x objective of the confocal microscope. Scale bar = 300 &#956;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62964/62964fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62964/62964fig05.jpg" /> 
Figure 5: Evaluation of CD11b magnetic isolation purity by flow cytometry before and after cell sorting. (A) Reports examples from the cell counter before and after cell sorting, highlighting cell concentration and viability. (B) The x-axis represent cell concentration (cell/mL) and viability (%) after CD11b cell sorting. Column bar graph; error bars represent SEM (n = 16). Phenotypic and gene expression analysis of cell population markers before and after CD11b+ cell sorting. After dissociation, CD11b+ cells from P8 mice brains were magnetically sorted. Expression of microglia (CX3CR1), oligodendrocytes (O4 or Olig2&#160;mRNA), neurons (NeuN or Synaptophysin mRNA)), and astrocytes (ACSA-2 or Gfap mRNA) markers was analyzed before and after sorting. (C) FACS analysis of CX3CR1, O4, NeuN, and ACSA-2 expression. The x-axis represents the percentage of alive cells and cell numbers. (D) Relative quantification of CD11b+ cells expression of Cx3cr1, Olig2, Synaptophysin, and Gfap mRNA (x-axis represent relative target mRNA expression to Itgam mRNA). Column bar graph; error bars represent SEM (n = 7). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62964/62964fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Solution</td>
			<td>For one C-Tube (&#181;L)</td>
			<td>For four C-tubes (&#181;L)</td>
		</tr>
		<tr>
			<td>Buffer X</td>
			<td>2850</td>
			<td>11400</td>
		</tr>
		<tr>
			<td>Enzyme P (Papain)</td>
			<td>75</td>
			<td>300</td>
		</tr>
		<tr>
			<td>Enzyme A (DNAse)</td>
			<td>15</td>
			<td>60</td>
		</tr>
		<tr>
			<td>Buffer Y</td>
			<td>30</td>
			<td>120</td>
		</tr>
		<tr>
			<td>Total</td>
			<td>2970</td>
			<td>11880</td>
		</tr>
	</tbody>
</table>
Table 1: Preparation of the dissociation mixture.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Solution</td>
			<td>For one tube (&#181;L)</td>
			<td>For four tubes (&#181;L)</td>
		</tr>
		<tr>
			<td>CD11b Microbeads</td>
			<td>20</td>
			<td>80</td>
		</tr>
		<tr>
			<td>Sorting Buffer</td>
			<td>180</td>
			<td>720</td>
		</tr>
		<tr>
			<td>Total</td>
			<td>200</td>
			<td>800</td>
		</tr>
	</tbody>
</table>
Table 2: Preparation of the CD11b microbead solution.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Stimulation</td>
			<td>Concentration (ng/mL)</td>
		</tr>
		<tr>
			<td>IL-1&#946;</td>
			<td>50</td>
		</tr>
		<tr>
			<td>IFN-&#947;</td>
			<td>20</td>
		</tr>
		<tr>
			<td>LPS</td>
			<td>10</td>
		</tr>
		<tr>
			<td>IL-4</td>
			<td>30</td>
		</tr>
		<tr>
			<td>IL-10</td>
			<td>20</td>
		</tr>
	</tbody>
</table>
Table 3: The stimulation reagents.
<table fo:font-size="9px" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Genes</td>
			<td>Protein</td>
			<td>Forward</td>
			<td>Reverse</td>
		</tr>
		<tr>
			<td>Arg1</td>
			<td>Arginase 1</td>
			<td>GTG AAG AAC CCA CGG TCT GT</td>
			<td>GCC AGA GAT GCT TCC AAC TG</td>
		</tr>
		<tr>
			<td>Cd206</td>
			<td>Cluster of differentiation 206</td>
			<td>CTT CGG GCC TTT GGA ATA AT</td>
			<td>TAG AAG AGC CCT TGG GTT GA</td>
		</tr>
		<tr>
			<td>Cd32</td>
			<td>Cluster of differentiation 32</td>
			<td>CTG GAA GAA GCT GCC AAA AC</td>
			<td>CCA ATG CCA AGG GAG ACT AA</td>
		</tr>
		<tr>
			<td>Cd86</td>
			<td>Cluster of differentiation 86</td>
			<td>GAG CGG GAT AGT AAC GCT GA</td>
			<td>GGC TCT CAC TGC CTT CAC TC</td>
		</tr>
		<tr>
			<td>Gfap</td>
			<td>Glial fibrillary acidic protein</td>
			<td>AAGCCAAGCACGAAGCTAAC</td>
			<td>CTCCTGGTAACTGGCCGACT</td>
		</tr>
		<tr>
			<td>Igf-1</td>
			<td>Insulin like growth factor 1</td>
			<td>TGG ATG CTC TTC AGT TCG TG</td>
			<td>GCA ACA CTC ATC CAC AAT GC</td>
		</tr>
		<tr>
			<td>Il1-rn</td>
			<td>Interleukine 1 receptor antagonist</td>
			<td>TTG TGC CAA GTC TGG AGA TG</td>
			<td>TTC TCA GAG CGG ATG AAG GT</td>
		</tr>
		<tr>
			<td>Il4-ra</td>
			<td>Interleukine 4 receptor antagonist</td>
			<td>GGA TAA GCA GAC CCG AAG C</td>
			<td>ACT CTG GAG AGA CTT GGT TGG</td>
		</tr>
		<tr>
			<td>Itgam</td>
			<td>Integrin alpha M</td>
			<td>CTGGTGCTCTTGGCTCTCAT</td>
			<td>GGCAGCTTCATTCATCATGT</td>
		</tr>
		<tr>
			<td>Lgals3</td>
			<td>Lectin Glactoside-Binding soluble 3</td>
			<td>GAT CAC AAT CAT GGG CAC AG</td>
			<td>ATT GAA GCG GGG GTT AAA GT</td>
		</tr>
		<tr>
			<td>Nos2</td>
			<td>Nitric oxide synthase 2</td>
			<td>CCC TTC AAT GGT TGG TAC ATG G</td>
			<td>ACA TTG ATC TCC GTG ACA GCC</td>
		</tr>
		<tr>
			<td>Olig2</td>
			<td>Oligodendrocyte transcription factor 2</td>
			<td>CAGCGAGCACCTCAAATCTA</td>
			<td>GATGGGCGACTAGACACCAG</td>
		</tr>
		<tr>
			<td>Ptgs2</td>
			<td>Prostaglandin endoperoxide synthase 2</td>
			<td>TCA TTC ACC AGA CAG ATT GCT</td>
			<td>AAG CGT TTG CGG TAC TCA TT</td>
		</tr>
		<tr>
			<td>Rpl13</td>
			<td>Ribosomal protein L13a</td>
			<td>ACA GCC ACT CTG GAG GAG AA</td>
			<td>GAG TCC GTT GGT CTT GAG GA</td>
		</tr>
		<tr>
			<td>Socs3</td>
			<td>Suppressor of cytokine 3</td>
			<td>CGT TGA CAG TCT TCC GAC AA</td>
			<td>TAT TCT GGG GGC GAG AAG AT</td>
		</tr>
		<tr>
			<td>Sphk1</td>
			<td>Sphingosine kinase 1</td>
			<td>TCC AGA AAC CCC TGT GTA GC</td>
			<td>CAG CAG TGT GCA GTT GAT GA</td>
		</tr>
		<tr>
			<td>Syp</td>
			<td>Synaptophysin</td>
			<td>ATCTCAGTGTCCCGATCCCA</td>
			<td>GCTGTCTTCCTGGTGGGTAC</td>
		</tr>
		<tr>
			<td>Tnf-&#945;</td>
			<td>Tumor necrosis factor &#945;</td>
			<td>GCC TCT TCT CAT TCC TGC TT</td>
			<td>AGG GTC TGG GCC ATA GAA CT</td>
		</tr>
	</tbody>
</table>
Table 4: RT-qPCR primer sequences.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Stimulation</td>
			<td>For 1-well</td>
			<td>For n-wells</td>
		</tr>
		<tr>
			<td>Cy3 Beads (1 cell : 50 beads)</td>
			<td>8, 100, 000</td>
			<td>X = (8, 100, 000) x n</td>
		</tr>
		<tr>
			<td>1x PBS</td>
			<td rowspan="2">Y =(100+X)/n</td>
			<td>50</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>50</td>
		</tr>
	</tbody>
</table>
Table 5: Preparation of the beads mixture for phagocytic assay.

Watch this Scientific Journal Video about Magnetic Isolation of Microglial Cells from Neonate Mouse for Primary Cell Cultures at JoVE.com

Magnetic Isolation of Microglial Cells from Neonate Mouse for Primary Cell Cultures

Primary microglia cultures are commonly used to evaluate new anti-inflammatory molecules. The present protocol describes a reproducible and relevant method to magnetically isolate microglia from neonate pups.

Microglia, as brain resident macrophages, are fundamental to several functions, including response to environmental stress and brain homeostasis. ...

magnetic-isolation-microglial-cells-from-neonate-mouse-for-primary

Nanyang Technological University

Research

JoVE Journal

Neuroscience

2.9K Views.  Université de Paris. Dit protocol stelt ons in staat om microglia te kweken in omstandigheden die de in vivo kenmerken nauw nabootsen. Met behulp van magnetische celsorteertechnologie stelt ons protocol ons in staat om microglia slechts twee dagen in vitro te stimuleren, zonder serum in het kweekmedium te gebruiken. Gebruik om te beginnen een kleine schaar om de huid van de nek naar de neus te knippen, volgens de sagittale hechting van 15 tot 20 millimeter.Plaats de uiteinden met het foramen magnum paralle...

Video: Magnetic Isolation of Microglial Cells from Neonate Mouse for Primary Cell Cultures

Primary Microglia Isolation from Mixed Glial Cell Cultures of Neonatal Rat Brain Tissue

Microglia account for approximately 12% of the total cellular population in the mammalian brain. While neurons and astrocytes are considered the major cell types of the nervous system, microglia play a significant role in normal brain physiology by monitoring tissue for debris and pathogens and maintaining homeostasis in the parenchyma via phagocytic activity 1,2. Microglia are activated during a number of injury and disease conditions, including neurodegenerative disease, traumatic brain injury, and nervous system infection 3. Under these activating conditions, microglia increase their phagocytic activity, undergo morpohological and proliferative change, and actively secrete reactive oxygen and nitrogen species, pro-inflammatory chemokines and cytokines, often activating a paracrine or autocrine loop 4-6. As these microglial responses contribute to disease pathogenesis in neurological conditions, research focused on microglia is warranted.
	Due to the cellular heterogeneity of the brain, it is technically difficult to obtain sufficient microglial sample material with high purity during in vivo experiments. Current research on the neuroprotective and neurotoxic functions of microglia require a routine technical method to consistently generate pure and healthy microglia with sufficient yield for study. We present, in text and video, a protocol to isolate pure primary microglia from mixed glia cultures for a variety of downstream applications. Briefly, this technique utilizes dissociated brain tissue from neonatal rat pups to produce mixed glial cell cultures. After the mixed glial cultures reach confluency, primary microglia are mechanically isolated from the culture by a brief duration of shaking. The microglia are then plated at high purity for experimental study.
	The principle and protocol of this methodology have been described in the literature 7,8. Additionally, alternate methodologies to isolate primary microglia are well described 9-12. Homogenized brain tissue may be separated by density gradient centrifugation to yield primary microglia 12. However, the centrifugation is of moderate length (45 min) and may cause cellular damage and activation, as well as, cause enriched microglia and other cellular populations. Another protocol has been utilized to isolate primary microglia in a variety of organisms by prolonged (16 hr) shaking while in culture 9-11. After shaking, the media supernatant is centrifuged to isolate microglia. This longer two-step isolation method may also perturb microglial function and activation. We chiefly utilize the following microglia isolation protocol in our laboratory for a number of reasons: (1) primary microglia simulate in vivo biology more faithfully than immortalized rodent microglia cell lines, (2) nominal mechanical disruption minimizes potential cellular dysfunction or activation, and (3) sufficient yield can be obtained without passage of the mixed glial cell cultures.
	It is important to note that this protocol uses brain tissue from neonatal rat pups to isolate microglia and that using older rats to isolate microglia can significantly impact the yield, activation status, and functional properties of isolated microglia. There is evidence that aging is linked with microglia dysfunction, increased neuroinflammation and neurodegenerative pathologies, so previous studies have used ex vivo adult microglia to better understand the role of microglia in neurodegenerative diseases where aging is important parameter. However, ex vivo microglia cannot be kept in culture for prolonged periods of time. Therefore, while this protocol extends the life of primary microglia in culture, it should be noted that the microglia behave differently from adult microglia and in vitro studies should be carefully considered when translated to an in vivo setting.

Isolating primary microglia from the cellular heterogeneity of the brain is essential to investigate their role in both physiological and pathological conditions. This protocol describes a mechanical isolation and mixed cell culture technique that provides high yield and high purity, viable primary microglial cells for in vitro study and downstream applications.

Microglia account for approximately 12% of the  total cellular population in the mammalian brain. While neurons and astrocytes are considered  the major ...

Immunology and Infection

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.

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 ...

Rapid and Refined CD11b Magnetic Isolation of Primary Microglia with Enhanced Purity and Versatility

Microglia are the primary responders to central nervous system insults; however, much remains unknown about their role in regulating neuroinflammation. Microglia are mesodermal cells that function similarly to macrophages in surveying inflammatory stress. The classical (M1-type) and alternative (M2-type) activations of macrophages have also been extended to microglia in an effort to better understand the underlying interplay these phenotypes have in neuroinflammatory conditions such as Parkinson&#39;s, Alzheimer&#39;s, and Huntington&#39;s Diseases. In vitro experimentation utilizing primary microglia offers rapid and reliable results that may be extended to the in vivo environment. Although this is a clear advantage over in vivo experimentation, isolating microglia while achieving adequate yields of optimal purity has been a challenge. Common methods currently in use either suffer from low recovery, low purity, or both. Herein, we demonstrate a refinement of the column-free CD11b magnetic separation method that achieves a high cell recovery and enhanced purity in half the amount of time. We propose this optimized method as a highly useful model of primary microglial isolation for the purposes of studying neuroinflammation and neurodegeneration.

Here, we present a protocol to isolate microglia from postnatal mouse pups (day 1) for in vitro experimentation. This improvised method of isolation generates both high yield and purity, a significant advantage over alternate methods that allows broad range experimentation for the purposes of elucidating microglial biology.

Microglia are the primary responders to central nervous system insults; however, much remains unknown about their role in regulating neuroinflammation. ...

Characterization and Isolation of Mouse Primary Microglia by Density Gradient Centrifugation

Microglia, the resident immune cells in the brain, are the first responders to inflammation or injury in the central nervous system. Recent research has revealed microglia to be dynamic, capable of assuming both pro-inflammatory and anti-inflammatory phenotypes. Both M1 (pro-inflammatory) and M2 (pro-reparative) phenotypes play an important role in neuroinflammatory conditions such as perinatal brain injury, and exhibit differing functions in response to certain environmental stimuli. The modulation of microglial activation has been noted to confer neuroprotection thus suggesting microglia may have therapeutic potential in brain injury. However, more research is required to better understand the role of microglia in disease, and this protocol facilitates that. The protocol described below combines a density gradient centrifugation process to reduce cellular debris, with magnetic separation, producing a highly pure sample of primary microglial cells that can be used for in vitro experimentation, without the need for 2-3 weeks culturing. Additionally, the characterization steps yield robust functional data about microglia, aiding studies to better our understanding of the polarization and priming of these cells, which has strong implications in the field of regenerative medicine.

A protocol for the isolation of primary microglia from murine brains is presented. This technique aids in furthering the current understanding of neurological conditions. Density gradient centrifugation and magnetic separation are combined to produce sufficient yield of a highly pure sample. Furthermore, we outline the steps for characterization of microglia.

Microglia, the resident immune cells in the brain, are the first responders to inflammation or injury in the central nervous system. Recent research has ...

Isolation and Culture of Rodent Microglia to Promote a Dynamic Ramified Morphology in Serum-free Medium

Microglia represent 5 - 10% of all central nervous system (CNS) cells and are increasingly drawing attention due to their contributions during development, homeostasis, and disease. Although macrophages have been studied in detail for decades, specialized features of microglia, the tissue-resident macrophages of the CNS, have remained largely mysterious, in part due to limitations in the ability to recapitulate mature microglial properties in culture. Here, we illustrate a straightforward procedure for the rapid isolation of pure microglia from the mature rodent brain. We also describe serum-free culture conditions that support high levels of microglial viability over time. Microglia cultured under these defined-medium conditions exhibit elaborate ramified processes and dynamic surveillance behavior. We illustrate some effects of serum exposure on cultured microglia and discuss how these serum-free cultures compare to both serum-exposed cultures as well as microglia in vivo.

Efforts to understand microglial function in detail have been hindered by the lack of microglial culture models that recapitulate the properties of mature in vivo microglia. This protocol describes an isolation and culture approach designed to maintain robust survival of highly ramified mature rat microglia under defined-medium conditions.

Microglia represent 5 - 10% of all central nervous system (CNS) cells and are increasingly drawing attention due to their contributions during ...

Primary Microglia Isolation from Postnatal Mouse Brains

Microglia are the mononuclear phagocytes in the central nervous system (CNS), which play key roles in maintaining homeostasis and regulating the inflammatory process in the CNS. To study the microglial biology in vitro, primary microglia show great advantages compared to immortalized microglial cell lines. However, microglia isolation from the postnatal mouse brain is relatively less efficient and time-consuming. In this protocol, we provide a quick and easy-to-follow method to isolate primary microglia from the neonatal mouse brain. The overall steps of this protocol include brain dissection, primary brain cell culture, and microglia isolation. Using this approach, researchers can obtain primary microglia with high purity. In addition, the harvested primary microglia were able to respond to the lipopolysaccharides challenge, indicating they retained their immune function. Collectively, we developed a simplified approach to efficiently isolate primary microglia with high purity, which facilitates a wide range of microglial biology investigations&#160;in vitro.

Primary cell culture is one of the primarily used approaches for studying microglial biology in vitro. Here, we developed a method for simple and rapid microglia isolation from the mouse postnatal day 1 (P1) to P4.

Microglia are the mononuclear phagocytes in the central nervous system (CNS), which play key roles in maintaining homeostasis and regulating the ...

Isolation of Mouse Primary Microglia by Magnetic-Activated Cell Sorting in Animal Models of Demyelination

Microglia, the resident innate immune cells in the brain, are the primary responders to inflammation or injury in the central nervous system (CNS). Microglia can be divided into resting state and activated state and can rapidly change state in response to the microenvironment of the brain. Microglia will be activated under different pathological conditions and exhibit different phenotypes. In addition, there are many different subgroups of activated microglia and great heterogeneity between different subgroups. The heterogeneity mainly depends on the molecular specificity of microglia. Studies have revealed that microglia will be activated and play an important role in the pathological process of inflammatory demyelination. To better understand the characteristics of microglia in inflammatory demyelinating diseases such as multiple sclerosis and neuromyelitis optica spectrum disorder, we propose a perilesional primary microglial sorting protocol. This protocol utilizes columnar magnetic-activated cell sorting (MACS) to obtain highly purified primary microglia and preserve the molecular characteristics of microglia to investigate the potential effects of microglia in inflammatory demyelinating diseases.

Here, we present a protocol to isolate and purify primary microglia in animal models of demyelinating diseases, utilizing columnar magnetic-activated cell sorting.

Microglia, the resident innate immune cells in the brain, are the primary responders to inflammation or injury in the central nervous system (CNS). ...

Isolation of Hypothalamic Microglia from Mice Using MACS for In Vitro Assays

Isolation of Hypothalamic Microglia from Freshly Perfused Adult Mouse Brain by Magnetic-Activated Cell Sorting

Microglia, as the resident macrophages of the brain, are essential for maintaining brain homeostasis. They shape neuronal circuits during development, survey their environment for debris or dead cells, as well as respond to infection and injury in the brain, among many other functions. However, their important role in neurodevelopment and synaptic plasticity and pathophysiology has not been fully defined, highlighting the need for further investigation. To gain a more comprehensive understanding of the role of microglia in these processes, we need to isolate microglia and characterize them genetically, metabolically, and functionally. However, the isolation of microglia from adult mice, especially from small brain structures, is challenging as they represent a small percentage of the total brain cells, and the yield of isolated microglia is often too low. Here, the magnetic isolation of microglia using CD11b+ microbeads allows us to sort microglial cells from the hypothalamus of a freshly perfused adult mouse brain. The current method allows us to achieve relatively high purity and yield in a short period while maintaining cell viability.

Author Spotlight: Investigating the Impact of Nutrition on Mouse Brain Function and Metabolic Disorders 

We describe a protocol for isolating microglial cells from the mouse hypothalamus (or equivalent small brain structures) using magnetically activated cell sorting (MACS), in a relatively short time. The MACS-sorted hypothalamic microglia can be used for ex vivo analysis and can be plated to perform in vitro assays.

Microglia, as the resident macrophages of the brain, are essential for maintaining brain homeostasis. They shape neuronal circuits during development, ...

Magnetic Isolation of Microglia from Mouse Pup Brains

Source: Bokobza, C. et al., <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/62964">Magnetic Isolation of Microglial Cells from Neonate Mouse for Primary Cell Cultures.</a> J. Vis. Exp. (2022)
In this video, we describe a protocol for isolating CD11b cells, including microglia, from mouse pup brains using magnetic-activated cell sorting. The brain tissues are homogenized to obtain single-cell suspensions, which are incubated with anti-CD11b antibody-coated microbeads, followed by a magnetic column-based separation to purify the CD11b+ cell population.

Source: Bokobza, C. et al., Magnetic Isolation of Microglial Cells from Neonate Mouse for Primary Cell Cultures. J. Vis. Exp. (2022)
In this video, we ...

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Cell Isolation and Culture

Isolating Microglia from Mouse Brain Demyelinating Lesions Using Magnetic Activated Cell Sorting

Source: Zhang, H. et al. <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/63511">Isolation of Mouse Primary Microglia by Magnetic-Activated Cell Sorting in Animal Models of Demyelination.</a> J. Vis. Exp. (2022).
This video demonstrates a protocol for extracting microglial cells from demyelinating lesions in mouse brains using magnetic cell sorting. The protocol involves dissecting the lesioned brain tissue containing microglial cells, treating the tissue with specific enzymes to obtain a single-cell suspension, and utilizing microglial receptor-specific magnetic beads to isolate the microglial cells.

 All procedures involving animal samples have been reviewed and approved by the appropriate animal ethical review committee. 
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Magnetic Isolation of Microglial Cells from Neonate Mouse for Primary Cell Cultures

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