This manuscript presents a protocol to induce active experimental autoimmune encephalomyelitis (EAE) in mice. A method for the isolation and characterization of the infiltrated lymphocytes in the central nervous system (CNS) is also presented to show how lymphocytes are involved in the development of CNS autoimmune disease.
Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) caused by the combination of environmental factors and susceptible genetic background. Experimental autoimmune encephalomyelitis (EAE) is a typical disease model of MS widely used for investigating the pathogenesis in which T lymphocytes specific for myelin antigens initiate an inflammatory reaction in CNS. It is very important to assess how lymphocytes in the CNS regulate the development of disease. However, the approach for measuring the quantity and quality of infiltrated lymphocytes in the CNS is very limited due to the difficulties in isolating and detecting infiltrated lymphocytes from the brain. This manuscript presents a protocol for that is useful for the isolation, identification, and characterization of infiltrated lymphocytes from the CNS and will be helpful for our understanding of how lymphocytes are involved in the development of the CNS autoimmune disease.
As a chronic demyelinating disease of the CNS, MS affects about 2.5 million people worldwide and lacks curative treatments1. It is also considered an autoimmune disease, in which myelin antigen specific T lymphocytes initiate an inflammatory reaction and lead to demyelination and axonal injury in the CNS2. Experimental autoimmune encephalomyelitis (EAE) has been widely used to investigate pathogenic mechanisms of MS as a classic autoimmune demyelination disease model in CNS3. There are two ways to induce EAE: one is to induce EAE actively by immunizing animals with myelin components, another is adoptive transfer by transferring encephalitogenic T cells into receptor2,4,5. The susceptibilities to EAE are different in different animal strains6. In C57BL/6 mice, myelin oligodendrocyte glycoprotein (MOG) 35–55 challenge induces a monophasic disease with extensive demyelination and inflammation in the CNS, which is frequently used in experiments with gene-targeted mice7.
The generation of myelin-specific reactive T cells is required for the occurrence and development of disease in EAE and is an immunological sign of both EAE and MS. Activated autoreactive T lymphocytes cross the blood brain barrier (BBB) into the healthy CNS and initiate EAE disease. When MOG 35–55 Ag is encountered, these T lymphocytes induce inflammation and the recruitment of effector cells into the CNS, resulting in demyelination and axon destruction8,9. In the EAE model, there is ample evidence that neuroantigen-specific CD4+ T cells can initiate and sustain neuroinflammation and pathology3,10. Depending on the major cytokines produced, CD4+ T lymphocytes have been classified into different subsets: Th1 (characterized by the production of interferon-γ), Th2 (characterized by the production of interleukin 4), and Th17 (characterized by the production of interleukin 17). It is believed that activation of Th1 and Th17 cells contribute to the induction, maintenance, and regulation of inflammatory demyelination in EAE and MS by secreting effector cytokines IFN-γ and IL-17, which are capable of activating macrophages and recruiting neutrophils to the inflammatory sites to accelerate the lesions11.
Because autoreactive T cells cross the BBB into the CNS and induce the development of disease in MS and EAE, it is very important to analyze T cells in the CNS. However, there are very few established protocols for the isolation of lymphocytes from the CNS12. Therefore, a method optimized for isolating mononuclear cells from the brain and analyzing T lymphocytes with markers CD45, CD11b, CD3, CD4, INF-g, and IL-17 for flow cytometry was developed. The method uses MOG35–55 adjuvant Mycobacterium tuberculosis H37 Ra and Pertussis Toxin Working Solution (PTX) to induce an active immunization model of EAE in mice. Then, mechanical separation and density gradient centrifugation methods are used for the isolation of CNS mononuclear cells. Finally, an optimized flow cytometry gating strategy is used to identify T lymphocytes and subsets from the brain by staining multiple markers.
All methods described here have been approved by the animal committee of the School of Basic Medical Sciences, Shanghai Jiao Tong University.
1. Preparation of the materials
2. Housing of C57BL/6 mice
3. Immunization of C57BL/6 mice
4. Single-cell suspension preparation from brain
5. Flow cytometric analysis of single cells from brain
6. Data analysis
After immunization of C57BL/6 mice, all mice were weighed, examined, and graded daily for neurological signs. The representative clinical course of EAE should result in a disease curve as presented in Figure 2A and a change of body weight in the mouse as presented in Figure 2B. C57BL/6 mice immunized with MOG35-55 usually started to develop disease symptoms around day 10–12 and achieved the peak of disease around day 15–21 after active immunization (Figure 2A). Weight change was a valuable indicator in the EAE model. Before the onset of disease, the body weight of immunized mice gradually increased, then typically decreased correlating to the increasing disease symptoms. At the peak of EAE, mice also showed the lowest body weight (Figure 2B). Then body weight recovered slightly as clinical symptoms decreased. However, the mice usually did not fully recover. C57BL/6 mice developed a monophasic chronic disease pathology upon MOG35–55 challenge (Figure 2A).
The clinical severity of EAE is directly associated with autoreactive T cell activation14. Neuroantigen-specific CD4+ T cells are capable of initiating and sustaining neuroinflammation and pathology in EAE3. The typical characteristics of CD4+T cells in the peak of EAE are shown in Figure 3. Further, the proportion of Th1 and Th17 subsets in encephalitogenic cells, which are the major pathogenic cells mediating EAE, was analyzed by flow cytometry. Following the separation of a single-cell suspension from brain, the cells were stained with CD45, CD11b, CD3, CD4, IFN-γ, and IL-17 antibodies, which are expressed by T lymphocytes. FSC-A vs. FSC-H and SSC-A vs. SSC-H were used to gate singlets (Figure 3A, B), then FSC-A vs. SSC-A were used to gate live cells based on size and granularity (Figure 3C). After, CD45+ CD11b– cells were gated to identify leukocytes excluding monocytes (Figure 3D). Then, the gate was set on CD3+CD4+ to identify CD4+ T lymphocytes (Figure 3E). Finally, IFN-γ and IL-17 were used to identify Th1 and Th17 subsets and assess the functional effect according to effector cytokines (Figure 3F). According to the clinical severity of disease, representative results showed that IFN-γ–producing Th1 and IL-17–producing Th17 cells significantly increased in the encephalitogenic cells from EAE mice.
Grade | Clinical sign |
0 | no disease |
1 | decreased tail tone or slightly clumsy gait |
2 | tail atony and moderately clumsy gait and/or poor righting ability |
3 | limb weakness |
4 | limb paralysis |
5 | moribund state. |
Table 1: Clinical scoring system. C57BL/6 mice were immunized with the MOG35–55 peptide. Then, neurological signs were recorded. A 5-point scoring system was used to assess the severity of EAE.
Figure 1: Schematic of the Percoll gradient setup for isolation of mononuclear cells. Please click here to view a larger version of this figure.
Figure 2: Representative course of EAE. EAE was induced in C57BL/6 mice by injection of MOG35–55 as described in the protocol. The clinical score (A) and change of body weight (B) were determined in these mice. Data are presented as mean ± SEM; n = 8 for each group. Please click here to view a larger version of this figure.
Figure 3: Representative flow cytometry analysis of lymphocytes in brain. A single-cell suspension was isolated from the brain in the peak of EAE. The gating strategy of T lymphocytes is shown. Singlets were gated as FSC-A vs. FSC-H and SSC-A vs. SSC-H (A,B). Live cells were gated as FSC-A vs. SSC-A (C). Leukocytes excluding monocytes were gated as CD45+ CD11b– (D). CD4+ T lymphocytes were gated as CD3+CD4+ (E). Th1 and Th17 subsets were gated as IFN-γ+ and IL-17+ (F). Please click here to view a larger version of this figure.
This study presents a protocol to induce and monitor EAE using MOG35-55 in C57BL/6 mice, which are considered a typical neuroimmunological experimental animal model of MS. EAE can be induced varying the mice strains or the type of protein used for induction according to the purpose of the study. For example, using PLP139–151 peptide in SJL mice can induce a relapsing-remitting EAE disease course that is especially well-suited for assessing therapeutic effects on relapses15. The experimental procedure outlined here can be also applied to other EAE protocols7. In this model, C57BL/6 mice are immunized with MOG35–55 peptide and develop a monophasic disease. A 5-point scoring system is used to assess the severity of EAE. Although several scoring systems ranging from 0–3 points or 0–10 points are employed to score disease severity7,16,17, these results show that a 5-point scoring system is capable of determining statistically significant differences in disease scores between groups and other EAE scoring systems do not lead to obvious improvement.
EAE severity is generally evaluated by an EAE clinical score taking into account the severity of neurological dysfunction11,13. To ensure the comparability of the experiment for all mice, it is important to keep them under the same conditions, including changes of cage, administration of food and water, and especially mouse housing conditions. In addition, cross-immunization should be also performed to avoid cage-specific phenomena induced by the investigator.
This study provides a method to separate mononuclear cells from the CNS that is suitable for FACS analysis or functional study. To ensure that the blood is removed from the CNS tissue, the mice should be perfused prior to dissociating the tissue. The purification of the mononuclear cells on a density gradient centrifugation is a key step in the isolation. To ensure a separation effect, the acceleration and deceleration of the centrifuge should be set to 1 and 0, respectively. Using this method, the single cell yields are usually low from normal brain, but higher from diseased brain with EAE. Representative results show that there is an obvious increase in CD3+CD4+ T lymphocytes, especially the IFN-γ producing cells and IL-17 producing cells, which are considered to contribute to the worsened disease.
There are some limitations of this protocol. The EAE model induced with MOG35–55 shows mainly a CD4+ T cell-driven immunological response. If the role of CD8+ T cells and B cells needs to be analyzed, alternative protocols should be considered. As a CNS inflammatory disease, a severe pathological phenotype is also found in the spinal cord in the EAE model. However, due to the presence of large amounts of myelin, it is difficult to get enough single cells from the spinal cord for FACS analysis. In that case, using immunohistochemistry or immunofluorescence to analyze spinal cord tissue is needed. There are also researchers that put the brain and spinal cord together to separate mononuclear cells for FACS analysis12. This protocol separates single cells from the brain for FACS analysis and spinal cord tissue for immunohistochemistry and immunofluorescence analysis.
The importance of T lymphocytes in immune regulation of MS and EAE has received more and more attention recently. Much of the published literature focuses on spleen and lymph nodes11; however, lymphocytes are found throughout the CNS of EAE mice and, thus, the characteristic analysis of T lymphocytes in the CNS is necessary. Immunohistological staining of sections can identify infiltrating cells in the CNS. However, phenotypic and functional analysis is limited. Following isolation of the immune cells from the CNS of normal or diseased mice, the analysis of more detailed phenotypes becomes possible. With this method, T lymphocytes in the brain can be studied on a cell-by-cell basis, and the expression of different surface markers, cytokines, chemokines, and transcription factors (e.g., intracellular proteins) can be analyzed better. The protocol will be useful for future studies to assess the phenotype and function of T lymphocytes in the brain during the course of MS and EAE.
The authors have nothing to disclose.
This research was supported by National Natural Science Foundation of China grant (31570921 to ZJ, 81571533 to LS), Shanghai Municipal Commission of Health, and Family Planning (201540206 to ZJ), Ruijin Hospital North research grant (2017ZX01 to ZJ).
Alexa Fluor700 anti-mouse CD45.2 | eBioscience | 56-0454-82 | |
Anti-Mouse CD16/CD32 Fc block | BioLegend | 101302 | |
APC anti-mouse IFN-g | eBioscience | 17-7311-82 | |
BD LSRFortessa X-20 | BD | ||
Dounce homogenizer | Wheaton | 353107542 | |
eBioscience Cell Stimulation Cocktail (plus protein transport inhibitors) (500X) | eBioscience | 00-4975-03 | |
eBioscience Intracellular Fixation & Permeabilization Buffer Set | eBioscience | 88-8824-00 | |
FITC anti-mouse CD3 | BioLegend | 100203 | |
FITC Rat IgG2b, κ Isotype Ctrl Antibody | BioLegend | 400605 | |
Freund's Adjuvant Complete (CFA) | Sigma-Aldrich | F5881 | |
Mouse IgG2a kappa Isotype Control (eBM2a), Alexa Fluor 700, eBioscience | eBioscience | 56-4724-80 | |
Mycobacterium tuberculosis H37 Ra | Difco Laboratories | 231141 | |
PE anti-mouse IL-17A | eBioscience | 12-7177-81 | |
PE/Cy7 anti-mouse CD4 | BioLegend | 100422 | |
PE/Cy7 Rat IgG2b, κ Isotype Ctrl Antibody | BioLegend | 400617 | |
Percoll | GE | 17-0891-01 | |
PerCP/Cy5.5 anti-mouse CD11b | BioLegend | 101228 | |
PerCP/Cy5.5 Rat IgG2b, κ Isotype Ctrl Antibody | BioLegend | 400631 | |
pertussis toxin (PTX) | Sigma-Aldrich | P-2980 | |
Rat IgG1 kappa Isotype Control (eBRG1), APC, eBioscience | eBioscience | 17-4301-82 | |
Rat IgG2a kappa Isotype Control (eBR2a), PE, eBioscience | eBioscience | 12-4321-80 | |
Rat MOG35–55 peptides | Biosynth International | MEVGWYRSPFSRVVHLYRNGK |