Analysis of Microglia and Monocyte-derived Macrophages from the Central Nervous System by Flow Cytometry

Summary

This protocol provides an analysis of the macrophage subpopulations in the adult mouse central nervous system by flow cytometry and is helpful for the study of multiple markers expressed by these cells.

Abstract

Numerous studies have demonstrated the role of immune cells, in particular macrophages, in central nervous system (CNS) pathologies. There are two main macrophage populations in the CNS: (i) the microglia, which are the resident macrophages of the CNS and are derived from yolk sac progenitors during embryogenesis, and (ii) the monocyte-derived macrophages (MDM), which can infiltrate the CNS during disease and are derived from bone marrow progenitors. The roles of each macrophage subpopulation differ depending on the pathology being studied. Furthermore, there is no consensus on the histological markers or the distinguishing criteria used for these macrophage subpopulations. However, the analysis of the expression profiles of the CD11b and CD45 markers by flow cytometry allows us to distinguish the microglia (CD11b⁺CD45^med) from the MDM (CD11b⁺CD45^high). In this protocol, we show that the density gradient centrifugation and the flow cytometry analysis can be used to characterize these CNS macrophage subpopulations, and to study several markers of interest expressed by these cells as we recently published. Thus, this technique can further our understanding of the role of macrophages in mouse models of neurological diseases and can also be used to evaluate drug effects on these cells.

Introduction

The microglia are the parenchymal tissue-resident macrophages of the central nervous system (CNS). They play two key functional roles: immune defense and maintenance of the CNS homeostasis. In contrast to the MDM, which are renewed continually from the hematopoietic stem cells in the bone marrow, the microglial cells differentiate from primitive hematopoietic progenitor cells originating in the yolk sac (YS) that colonized the brain during embryonic development^1,2,3. In rodents, the transcription factor Myb plays a crucial role in the development of all bone marrow derived mo....

Protocol

All methods described here have been approved by the Institutional Animal Care and Use Committee at the ICM Institute and by the Darwin French Ethic Animal Committee, and are covered under the protocol 01407.02.

1. Preparation

1. Prepare the digestion cocktail in a 1.5 mL tube by combining the following for each mouse: 1 mL Phosphate Buffered Saline (PBS); 123 µL digestion enzyme (see table of materials) at 13 wunsch/mL (stock solution), final concentration 1.6 wunsch/mL; and 5 µL DNase I (see table of materials) at 100 mg/mL (stock solution), final concentration 0.5 mg/mL.

2. Perfusion an....

Results

After the density gradient centrifugation and antibody staining, the cells were acquired on a flow cytometer and analyzed using a morphological gating strategy as follows. A first gate was defined in the dot plot Forward-Scattered-Area (FSC-A) versus Forward-Scattered-Height (FSC-H) to discriminate single cells from doublets (Figure 3A). The single cells were then gated on FSC-A versusSide-Scattered-Area (SSC-A) dot plots to exclude cell deb.......

Discussion

It has been demonstrated that the microglia and MDM have different functions and phenotypes in the CNS, and thus the identification and the analysis of these macrophage subpopulations are essential in order to better understand neurological diseases^9,18,25. Flow cytometry analysis using two markers (CD11b and CD45) allows for the distinction between each subpopulation (Figure 3C). This strategy was .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
5 month-old Mice	Janvier	C57BL/6J
Liberase TL Research Grade	Sigma-Aldrich	5401020001	Digestion enzyme
Deoxyribonuclease I from bovine pancreas	Sigma-Aldrich	DN25
Percoll	GE Healthcare Life Sciences	17-0891-01	Density gradient medium
Cell Strainer size 70 µm Nylon	Corning	731751
Venofix 25 G	BRAUN	4056370
Piston syringe 10 mL	Terumo	SS+10ES1
Pasteur pipette 230 mm	Dustcher	20420
1.5 mL tube	Eppendorf	0030 123.328
15 mL tube	TPP	91015
50 mL tube	TPP	91050
5 mL polystyrene round bottom tube	BD Falcon	352054
D-PBS (1x) without Ca2+/Mg2+	Thermo Fisher Scientific	14190-094
D-PBS (10x) without Ca2+/Mg2+	Thermo Fisher Scientific	14200-067
Fetal bovine serum	Thermo Fisher Scientific	10270-106
EDTA	Sigma-Aldrich	E4884
Bovine Serum Albumin solution 30%	Sigma-Aldrich	A7284
Paraformaldehyde 32% Solution	Electron Microscopy Sciences	15714-S	Caution -Toxic
Saponin	Sigma-Aldrich	S2002
Sodium Azide	Sigma-Aldrich	47036
PerCPCy5.5 Rat anti-mouse CD11b (clone M1/70)	eBioscience	45-0112
Rat IgG2b K Isotype Control PerCP-Cyanine5.5	eBioscience	45-4031
BV421 Rat anti-mouse CD45 (clone 30-F11)	BD Biosciences	563890
BV421 Rat IgG2b, κ Isotype Control RUO	BD Biosciences	562603
Rabbit anti-mouse TMEM119 (clone28 - 3)	Abcam	ab209064
AlexaFluor 647 Donkey anti-rabbit IgG	Life Technologies	A31573
Anti-Mouse CD16/CD32 Purified	eBioscience	14-0161	Mouse Fc Block
Fixable Dead Cell Stain Kits	Invitrogen	L34969
Mouse CCR2 APC-conjugated Antibody	R&D	FAB5538A
Rat IgG2B APC-conjugated Isotype Control	R&D	IC013A
Mouse CX3CR1 PE-conjugated Antibody	R&D	FAB5825P
Goat IgG PE-conjugated Antibody	R&D	IC108P
Centrifuge	Eppendorf	5804R
Cell analyzer	BD Biosciences	BD FACSVERSE
Data Analysis Software	FlowJo LLC	FlowJo
Fine scissors	F.S.T	14090-11
Standard Pattern Forceps	F.S.T	11000-13
Mayo Scissors	F.S.T	14010-15
Dumont #5 Forceps	F.S.T	11251-20