资料来源: 穆尼尔·西尔万1,2,3,佩尔切特·蒂鲍特1,2,3,苏菲·诺沃4,雷切尔·戈卢布1,2,3
1法国巴黎巴斯德研究所免疫学系淋巴病系
2 INSERM U1223, 巴黎, 法国
3巴黎迪德罗大学,索邦巴黎城,大提琴巴斯德,巴黎,法国
4流式细胞测定,细胞学和生物标志物 UtechS,转化科学中心,巴斯德研究所,法国巴黎
预防病原体取决于免疫系统的监测。该系统很复杂,包括许多细胞类型,每种类型都有特定的功能。这种复杂的组成能够对大量病原体和损伤进行免疫反应。适应性免疫允许对特定病原体作出特定反应。负责这种免疫的大多数细胞是淋巴细胞(B细胞和T细胞)。通常,B细胞对细胞外感染(如细菌感染)作出反应,T细胞对细胞内感染(如病毒感染)作出反应。淋巴细胞群中不同类型的细胞可以通过它们表达的细胞表面蛋白和/或分泌细胞因子的面板的组合来表示。
磁性分选允许使用磁性特性和一个或多个细胞表面蛋白的表达来丰富目标细胞群(1,2)。此技术包括三个步骤。首先,细胞用磁珠孵育,磁珠与一个或多个单克隆特异性抗体结合。表达与这些抗体结合的表面蛋白的细胞附着在磁珠上。然后,用磁铁捕获目标细胞群。最后,目标细胞从磁铁中洗脱。最后,获得两个分拣产品,一个包含未标记的细胞,第二个包含与磁珠结合的目标细胞。列可用于提高磁分拣效率。在列中,非磁性元素延长细胞穿过列的路径。因此,细胞流减慢,促进细胞捕获的磁铁。
图1:磁分离的原理表示。双核白细胞被染色的抗CD3生物素化抗体。洗涤后,链球菌(SAV)耦合珠子在抗CD3抗体上专门固定生物链。(1) 单元格在列中传输。(2) 磁体不保留未标记的细胞,而CD3阳性细胞则保留在柱中。最后,将柱与磁体分离,(3)CD3阳性细胞在介质中洗脱。请点击此处查看此图的较大版本。
有两种类型的磁性分拣 (3)。在正排序中,感兴趣的细胞被磁珠捕获。在负排序中,通过捕获携带相应抗体的磁珠来去除不需要的细胞。这种MACS技术允许目标细胞的良好富集,并将器官中回收的细胞的百分比从1-20%提高到60-98%。分拣后,有必要用不同的方法(例如流式细胞测定)验证细胞纯度和分拣。MACS 技术是丰富目标人群的理想,用于其他实验,如细胞培养或细胞周期分析。
在本实验练习中,我们演示如何分离胸腺白细胞,然后使用磁细胞分选技术从混合物中丰富胸腺CD3阳性细胞。
1. 准备
2. 解剖
3. 免疫细胞分离
4. 免疫细胞的磁性标记
混合 | 标记试剂 | 稀释 |
1 | 抗CD3生物仿当抗体 | 1/400 (在哈佛商学院 2% FCS) |
2 | 链球菌结合珠 | 1/5 (在哈佛商学院 2% FCS) |
3 | 防 CD3 BV421 | 1/200 (在哈佛商学院 2% FCS) |
表1:抗体混合组合。混合1和2用于磁分离。混合3用于评估磁分离后的细胞富集。
5. CD3-正细胞的磁性分离
6. 流量细胞测定对靶细胞富集的评价
7. 数据分析
磁活细胞分类(MACS)是一种技术,允许研究人员根据表面表达的特定表位分离细胞。
这个过程通常从提取器官或组织开始,如胸腺。然后,细胞被机械地分离,通常是通过粉碎,直到组织分离成单个细胞。在这个阶段,可以通过添加化学物质来去除不需要的细胞。例如,氯化铵-钾,或ACK缓冲液,可用于解说不需要的红细胞。
接下来,与一种称为生物锡的分子结合的抗体被添加到悬浮液中,这些复合物与目标细胞表面的表皮结合。生物锡对另一种叫做链球菌的分子具有很高的亲和力。在下一步中,与磁珠融合的链球菌分子被添加到抗体标记细胞中。当生物锡和链球菌接触时,它们紧密结合。结果是感兴趣的细胞被涂上磁珠。这个复合物有时被称为三明治。在这种情况下,CD3在细胞膜的底部,然后抗CD3结合生物素,最后,链球菌素结合磁珠。
这些标记的细胞现在可以放入一个包含矩阵的列中,在重力的辅助下,允许细胞通过磁铁缓慢地通过。当它们这样做时,磁珠标记的细胞将粘在离磁铁最近的管的边缘,而未标记的细胞将继续进入下面的收集管中。接下来,只需去除磁铁、添加润液和用柱塞施加温和压力,将标记的细胞从柱状物中排出并放入新的收集管,即可从柱状体中取出标记的细胞。最终,这个过程允许60-98%的感兴趣的细胞检索。
在此过程中,我们将从小鼠中分离胸腺白细胞,并使用 MACS 对 CD3 阳性 T 细胞进行排序,然后再确认使用 FACS 进行分拣的效率。
首先,穿上任何适当的防护设备,包括实验室外套和手套。接下来,用70%乙醇洗一把解剖剪刀和钳子,用干净的纸巾擦干。然后,通过将 4 毫升 FCS 与 196 毫升 HBSS 混合,制备 200 毫升 HBSS 2% 胎儿小牛血清(FCS)。
将安乐死小鼠固定在解剖板上的苏平位置。使用剪刀和钳子,进行纵向腹腔切除术进入胸腔。首先,取出心脏,以进入位于心脏上方的胸腺。然后识别胸腺,由两个白色叶组成。使用钳子,小心地分离胸腺,并将其放在五毫升的HBSS 2%FCS的培养皿上。
要分离免疫细胞,首先将胸腺放在培养皿中的40微米细胞过滤器上。用柱塞粉碎组织,将其分离到盘子里。在此之后,用 HBSS 2% FCS 冲洗柱塞和滤网,以恢复任何粘附细胞。然后,将分离的胸腺细胞和液体从培养皿移入15毫升的离心管中。用5毫升的HBSS 2%FCS清洗培养皿,并将这种洗涤溶液转移到15毫升的离心管中。
接下来,在20摄氏度的温度下,以370次g将管离心7分钟。丢弃上清液,将颗粒重新悬浮在两毫升ACK解毒缓冲液中,以赖解红细胞。在室温下在台面孵育两分钟。然后,使用 HBSS 2% FCS 将音量调至 14 毫升。在20摄氏度下,以370次g将管离心7分钟。然后,丢弃上清液,将细胞重新悬浮在5毫升的HBSS 2%FCS中。
使用 Malasez 幻灯片估计细胞浓度,如 B 淋巴细胞 FACS 分离协议所示,并使用 HBSS 2% FCS 将细胞浓度调整到每毫升 10 至第 7 个细胞。
将500微升的细胞溶液转移到两个FACS管中。将一管非富集T细胞和另一管富集T细胞贴上标签,使用磁性标记分离。
在20摄氏度下,以370次g将浓缩T细胞管离心3分钟。在 HBSS 2% FCS 中,丢弃上清液并重新悬浮在 250 微升生物蛋白结合抗 CD3 抗体中稀释的 400 分之一的颗粒。在冰上和黑暗中孵育细胞20分钟。在管中加入三毫升HBSS 2%FCS,并在20摄氏度下以370次g再次离心3分钟。丢弃上清液,在 250 微升链球蛋白耦合珠中重新悬浮在 HBSS 2% FCS 中五分之一稀释的颗粒中。在冰上孵育细胞和珠子的混合物20分钟。接下来,在管中加入三毫升的HBSS 2%FCS,上下移液混合,并在20摄氏度的温度下以370次g再次离心3分钟。将颗粒重新悬浮在两毫升的 HBSS 2% FCS 中。
将柱放在磁铁上,加入三毫升的 HBSS 2% FCS 来加湿系统。然后,将染色的细胞移入柱中。细胞悬浮液通过柱后,用三毫升的HBSS 2%FCS清洗柱三次。接下来,从磁铁上取下柱子,并将其放入 15 毫升的管子中。要洗去目标细胞,在柱中加入五毫升的HBSS 2%FCS,用柱塞冲洗柱塞。再用五毫升的哈佛商学院 2% FCS 重复此步骤。
为了评估靶细胞分离的有效性,首先将500微升的洗脱细胞悬浮液转移到FACS管中,并将其标记为富集T细胞。然后,在20摄氏度的温度下,以370倍g将浓缩管和非富集管离心7分钟。丢弃上清液,然后将100微升荧光抗体稀释在HBSS 2%FCS中的200分之一添加到两个管中。在冰上和黑暗中孵育细胞20分钟。接下来,在管中加入三毫升HBSS 2%FCS,在20摄氏度的温度下以370次g将其离心3分钟。丢弃上清液,然后重新悬浮在 250 微升的 HBSS 2% FCS 中的颗粒。现在,使用流式细胞测定法评估CD3阳性细胞富集率,如FACS协议所示。
现在,我们将确定从小鼠胸腺分离的所有胸腺细胞中CD3阳性淋巴细胞的频率。要开始,双击 FlowJo 图标,并拖动所有示例窗口中每个管的文件。然后,双击富集的 T 细胞文件,在显示 x 轴上的正向散点、FSCA 和 y 轴上的侧散射 SSCA 的点图上显示从该样本记录的单元格。
单击多边形以圈出淋巴细胞群。接下来,双击圆圈填充以创建新窗口。在 y 轴上选择 FSC-W,在 x 轴上选择 FSC-A,然后圈出 FSA-W 负数。在子人口标识窗口中,命名单元格填充单个单元格。接下来,单击子填充标识窗口上的”确定”,然后双击圈填充以创建新窗口。在 y 轴上选择 CD3,然后圈出 CD3 阳性细胞。在子总体标识窗口中,命名单元格群 T 细胞。对未富集的 T 细胞文件重复上述操作。要可视化单元格群,请单击”布局编辑器”,并将丰富的 T 细胞和未富集的 T 细胞文件中的 T 细胞填充拖动到选项卡中。
将显示表示 CD3 阳性淋巴细胞的点图。CD3阳性细胞应只出现在CD3阳性浓缩管的感兴趣人群中。要评估已排序细胞中 CD3 阳性淋巴细胞的富集性,请单击表编辑器,然后将富集的 T 细胞和非富集 T 细胞文件中的 T 细胞群拖到表中。在统计菜单上,选择淋巴细胞的频率以检查所有淋巴细胞中CD3阳性细胞的百分比。然后,单击”创建表”。参数值将显示在新表中。对于富集的T细胞,CD3阳性细胞的频率应在80%或以上。
在此协议中,CD3阳性细胞通过磁细胞分拣从胸腺白细胞中富集(图1)。在磁细胞富集CD3阳性细胞之前,CD3阳性细胞占胸腺细胞总数的53.6%(图2,顶部面板)。磁细胞富集后,CD3阳性细胞的百分比增加到95%(图2,底部面板)。因此,MACS是一种简单、快速、高效的细胞浓缩技术,用于从细胞悬浮混合物中丰富所需的细胞群。
图2:浇注策略和纯度测试排序。首先根据细胞的形态(左:FSC-A、SSC-A)对细胞进行封闭,然后根据CD3(右图:CD3,SSC-A)绘制细胞。顶部面板表示细胞富集前的胸腺细胞悬浮液。底部面板表示磁细胞分类后的胸腺细胞悬浮液。请点击此处查看此图的较大版本。
磁分离技术是方便快速地对目标细胞群进行分类的常用方法。使用T细胞特异性抗体和磁珠,我们丰富了样品中的T细胞频率。实验结束时的纯度取决于初始细胞悬浮液中目标细胞的百分比。磁细胞分类后获得的细胞可用于各种用途,如细胞转移或细胞周期分析。另一种排序方法,使用流细胞测定法,可用于丰富细胞。这种技术在细胞分类后具有非常高的纯度,但它需要更多的步骤,需要更多的时间。
Magnetic-activated cell sorting, or MACS, is a technique that allows researchers to separate cells based on specific epitopes expressed on their surfaces.
The process typically begins with extraction of an organ or tissue, such as the thymus. Then, the cells are mechanically separated, usually by crushing, until the tissue is dissociated into single cells. Unwanted cells can be removed at this stage via the addition of chemicals. For example, ammonium-chloride-potassium, or ACK buffer, can be used to lyse unwanted erythrocytes.
Next, an antibody conjugated to a molecule called biotin is added to the suspension, and these complexes bind to the epitopes of the surface of the target cells. Biotin has a high affinity for another molecule called streptavidin. In the next step, streptavidin molecules fused to magnetic beads are added to the antibody labeled cells. When the biotin and streptavidin come into contact, they tightly bind. The result is that the cells of interest are coated with magnetic beads. This complex is sometimes referred to as a sandwich. In this case, CD3 on the cell membrane on the bottom, then anti-CD3 conjugated to biotin, and finally, streptavidin conjugated to magnetic beads.
These labeled cells can now be placed into a column containing a matrix which, assisted by gravity, allows the cells to pass slowly by a magnet. As they do so, the magnetic bead-labeled cells will stick to the edge of the tube nearest the magnet, while the non-labeled cells will continue on into a collection tube below. Next, the labeled cells can be removed from the column by simply removing the magnet, adding an eluent solution, and applying gentle pressure with a plunger to flush them out of the column and into a fresh collection tube. Ultimately, this process allows for 60 to 98% retrieval of the cells of interest.
In this procedure, we will isolate thymic leukocytes from a mouse and use MACS to sort out CD3-positive T-cells before confirming the efficiency of sorting using FACS.
To begin, put on any appropriate protective equipment including a lab coat and gloves. Next, wash a pair of dissecting scissors and forceps with 70% ethanol and dry them with a clean paper towel. Then prepare 200 milliliters of HBSS 2% fetal calf serum, or FCS, by mixing four milliliters of FCS with 196 milliliters of HBSS.
Pin a euthanized mouse in a supine position on a dissection plate. Using scissors and forceps, perform a longitudinal laparotomy to access the chest cavity. First, remove the heart to gain access to the thymus, which is located above the heart. Then identify the thymus, which is composed of two white lobes. Using forceps, carefully detach the thymus and place it on a Petri dish with five milliliters of HBSS 2% FCS.
To isolate the immune cells, first place the thymus on a 40 micrometer cell strainer in the Petri dish. Crush the tissue with a plunger to dissociate it into the dish. After this, rinse the plunger and strainer with HBSS 2% FCS to recover any adhered cells. Then, pipette the dissociated thymus cells and fluid from the Petri dish into a 15 milliliter centrifuge tube. Wash the Petri dish with five milliliters of HBSS 2% FCS and transfer this wash solution to the 15 milliliter centrifuge tube also.
Next, centrifuge the tube at 370 times g for seven minutes at 20 degrees Celsius. Discard the supernatant and resuspend the pellet in two milliliters of ACK lysing buffer to lyse the erythrocytes. Incubate for two minutes at room temperature on the bench top. Then, bring the volume to 14 milliliters with HBSS 2% FCS. Centrifuge the tube at 370 times g for seven minutes at 20 degrees Celsius. Then, discard the supernatant and resuspend the cells in five milliliters of HBSS 2% FCS.
Estimate the cell concentration using a Malassez slide as shown in the protocol for FACS isolation of B lymphocytes and adjust the cell concentration to 10 to the seventh cells per milliliter with HBSS 2% FCS.
Transfer 500 microliters of cell solution into two FACS tubes. Label one tube non-enriched T-cells and the other tube enriched T-cells, which will be separated using magnetic labeling.
Centrifuge the enriched T-cells tube at 370 times g for three minutes at 20 degrees Celsius. Discard the supernatant and resuspend the pellet in 250 microliters of biotin coupled anti CD3 antibody diluted one in 400 in HBSS 2% FCS. Incubate the cells for 20 minutes on ice and in the dark. Add three milliliters of HBSS 2% FCS to the tubes and centrifuge them again at 370 times g for three minutes at 20 degrees Celsius. Discard the supernatant and resuspend the pellet in 250 microliters of streptavidin-coupled beads diluted one in five in HBSS 2% FCS. Incubate the mixture of cells and beads for 20 minutes on ice. Next, add three milliliters of HBSS 2% FCS to the tube, pipette up and down to mix, and centrifuge again at 370 times g for three minutes at 20 degrees Celsius. Resuspend the pellet in two milliliters of HBSS 2% FCS.
Place the column on the magnet and add three milliliters of HBSS 2% FCS to humidify the system. Then, pipette the stained cells into the column. After the cell suspension passes through the column, wash the column three times with three milliliters of HBSS 2% FCS. Next, remove the column from the magnet and place it in a 15 milliliter tube. To elute the target cells, add five milliliters of HBSS 2% FCS to the column and flush the column with a plunger. Repeat this step with another five milliliters of HBSS 2% FCS.
To evaluate the effectiveness of target cell isolation, first transfer 500 microliters of eluted cell suspension to a FACS tube and label it enriched T-cells. Then, centrifuge both the enriched and non-enriched tubes at 370 times g for seven minutes at 20 degrees Celsius. Discard the supernatant, then add 100 microliters of fluorescent antibody diluted one in 200 in HBSS 2% FCS to both tubes. Incubate the cells for 20 minutes on ice and in the dark. Next, add three milliliters of HBSS 2% FCS to the tubes and centrifuge them at 370 times g for three minutes at 20 degrees Celsius. Discard the supernatant, then resuspend the pellets in 250 microliters of HBSS 2% FCS. Now, evaluate the CD3-positive cell enrichment rate using flow cytometry as shown in the FACS protocol.
Now, we will determine the frequency of CD3-positive lymphocytes among all thymocytes that were isolated from the mouse thymus. To start, double click on the FlowJo icon and drag the files for each tube in the all sample window. Then, double click on the enriched T-cells file to display the cells recorded from that sample on a dot plot that displays forward scatter, FSCA, on the x-axis, and side scatter, SSCA, on the y-axis.
Click on polygon to circle the lymphocyte populations. Next, double click on the circled population to create a new window. Select FSC-W on the y-axis, and FSC-A on the x-axis and circle the FSA-W negative cells. In the sub population identification window, name your cell population Single Cells. Next, click on OK on the sub population identification window, then double click on the circled population to create a new window. Select CD3 on the y-axis, and circle the CD3-positive cells. In the sub population identification window, name your cell population T-cells. Repeat with the non-enriched T-cells file. To visualize your cell population, click Layout Editor and drag the T-cell population from enriched T-cells and non-enriched T-cells files into the tab.
Dot plots representing CD3-positive lymphocytes will appear. CD3-positive cells should only appear in the population of interest in the CD3-positive enriched tube. To evaluate the enrichment of CD3-positive lymphocytes in the sorted cells, click on Table Editor and then drag the T-cells population from enriched T-cells and non-enriched T-cells files into the table. On the statistic menu, select Frequency of Lymphocyte Cells to check the percentage of CD3-positive cells in all lymphocytes. Then, click on Create Table. Parameter values will appear in a new table. For the enriched T-cells, the frequency of CD3-positive cells should be around 80% or above.
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