In this animation, we will explain what antibodies are, 在这个动画中，我们将解释什么是抗体，
how they are made and how they are most commonly used 它们是如何制作的以及它们最常用的方式
in laboratory research. 在实验室研究。
Antibodies are proteins that can specifically 抗体是特异性的蛋白质
recognize foreign invaders or pathogens, 认识外国入侵者或病原体，
such as viruses, bacteria and parasites. 如病毒，细菌和寄生虫。
All pathogens express a unique combination 所有病原体都表达出独特的组合
of molecules, both inside and outside their cell membranes. 细胞膜内外的分子。
These are called antigens. 这些被称为抗原。
Antibodies can serve two functions. 抗体可以起到两种功能。
Antibodies can neutralize pathogens 抗体可以中和病原体
by binding to their antigens and blocking their action, 通过与他们的抗原结合并阻止他们的行为，
such as preventing a virus from entering a cell 例如防止病毒进入细胞
or blocking a bacterial toxin. 或阻断细菌毒素。
Antibodies also mediate the destruction of pathogens 抗体也介导病原体的破坏
by acting as markers that other cells in the immune system 通过充当免疫系统中其他细胞的标志物
recognize. 认识。
Antibodies are produced by specialized cells 抗体由特化细胞产生
within the immune system called B lymphocytes or B cells. 在免疫系统内称为B淋巴细胞或B细胞。
The immune system recognizes a wide array of antigens 免疫系统识别多种抗原
by producing millions of different types of antibodies, 通过产生数百万种不同类型的抗体，
each recognizing a different antigen, 每个识别不同的抗原，
with each B cell producing only one particular antibody. 每个B细胞仅产生一种特定抗体。
Antibodies are Y-shaped proteins and are made up 抗体是Y形蛋白质并且是组成的
of four polypeptides or protein chains: 四个多肽或蛋白质链：
two identical shorter chains called light chains 两条相同的较短链称为轻链
and two identical longer chains called heavy chains. 和两条相同的长链称为重链。
The N-terminus of the four polypeptide chains 四条多肽链的N-末端
vary significantly in sequence from one antibody to the next 从一种抗体到下一种抗体的序列显着不同
and are called variable regions. 并称为可变区域。
Variable regions are involved in antigen binding. 可变区参与抗原结合。
The other regions of the polypeptide chains 多肽链的其他区域
vary very little in sequence among different antibodies 在不同抗体之间的序列变化非常小
from the same species and are called constant regions. 来自同一物种，被称为恒定区域。
The constant regions are responsible for interacting 恒定区域负责交互
with effector proteins that mediate the immune response. 与效应蛋白质介导免疫反应。
Antibodies are produced by B cells 抗体由B细胞产生
through a process of recombination 通过重组过程
where the genes that code for portions of the antibody 其中编码抗体部分的基因
protein are recombined or shuffled 蛋白质重组或改组
to create many different variations 创造许多不同的变化
of the final protein. 最终的蛋白质。
Antibodies are first expressed on the cell membrane 首先在细胞膜上表达抗体
of immature or naïve B cells that have not yet encoutered 尚未成熟的未成熟或幼稚B细胞
antigens. 抗原。
Recognition of the antigen by an antibody 通过抗体识别抗原
leads to B cell activation, which 导致B细胞活化，这
results in its differentiation and clonal expansion. 导致其分化和克隆扩展。
Differentiated B cells or plasma cells in turn 依次分化的B细胞或浆细胞
produce and secrete large amounts 产生和分泌大量的
of the respective antibody, which 各自的抗体，哪个
is released into the blood stream 被释放到血液中
to aid in the finding and targeting 帮助发现和定位
of additional pathogens of the same type. 相同类型的其他病原体。
Upon antigen binding, B cells can 抗原结合后，B细胞可以
be induced to produce additional antibody variation 被诱导产生额外的抗体变异
through a process called somatic hypermutation, where 通过一个称为体细胞超突变的过程，其中
the DNA sequences that code for the antibody's variable regions 编码抗体可变区的DNA序列
can rapidly mutate. 可以迅速变异。
Antibodies with higher affinity cause further B cell 具有更高亲和力的抗体引起进一步的B细胞
activation, which results in the selection and production 激活，这导致选择和生产
of highly specific antibodies to the antigen in question. 对所述抗原的高度特异性抗体
Because of their ability to bind proteins 因为它们能够结合蛋白质
with exquisite specificity, antibodies 具有精确的特异性，抗体
are routinely used in research to (1) quantify the relative 通常用于研究（1）量化相对
amount of protein present in a sample, (2) 样品中存在的蛋白质含量，（2）
to detect the addition of a covalent modification 检测共价修饰的添加
and the binding of other proteins to the protein 以及其他蛋白质与蛋白质的结合
of interest, (3) to isolate a protein 感兴趣的，（3）分离蛋白质
or protein complex from a cell lysate, 或来自细胞裂解物的蛋白质复合物，
and (4) to visualize proteins, cell structures and processes （4）使蛋白质，细胞结构和过程可视化
under the microscope. 在显微镜下。
To produce antibodies against an antigen of interest, 要产生针对目标抗原的抗体，
researchers inject the antigen in question or a fragment of it 研究人员注射了有问题的抗原或其片段
into a mammal such as a rabbit, sheep or goat. 进入哺乳动物，如兔子，绵羊或山羊。
The resulting antibodies are isolated. 分离所得抗体。
A polyclonal antibody preparation 多克隆抗体制剂
contains a mixture of heterogeneous antibodies 含有异质抗体的混合物
against multiple sites of the antigen. 针对多个抗原位点。
A monoclonal antibody preparation 单克隆抗体制剂
contains an antibody that recognizes only one 含有仅识别一种的抗体
site on the antigen. 抗原上的位点。
Polyclonal and monoclonal antibodies 多克隆和单克隆抗体
have different strengths and weaknesses. 有不同的优点和缺点。
Long-term production of polyclonal antibodies 长期生产多克隆抗体
requires the use of multiple individual animals resulting 需要使用多个单独的动物
in differences between different batch preparations. 在不同的批次准备之间的差异。
In contrast, monoclonals can be continuously produced 相反，可以连续生产单克隆抗体
from a clonal cell population, and are 来自克隆细胞群，并且是
less subject to changes. 较少受到变化的影响。
Since polyclonals can recognize multiple sites 由于polyclonals可以识别多个站点
within a protein, they can amplify detection signals, 在蛋白质中，它们可以放大检测信号，
but they also then cross-react more 但他们也会交叉反应更多
with non-specific proteins. 与非特异性蛋白质。
Monoclonals, on the other hand, do not 另一方面，Monoclonals却没有
amplify detection signals as well 也放大检测信号
but provide a lower signal to noise ratio 但提供较低的信噪比
due to their higher specificity. 由于它们的特异性较高。
As a result, polyclonals are better 因此，多面体更好
suited for detecting proteins that 适合检测蛋白质
are expressed at low levels. 以低水平表示。
They are also used to effectively 它们也被用于有效
detect different isoforms or versions of a protein 检测不同的同种型或蛋白质的形式
or to screen for the presence of the protein of interest 或筛选感兴趣的蛋白质的存在
in other species. 在其他物种。
Monoclonals are more commonly used 单克隆抗体更常用
when purifying a protein from a mixture where specificity 从特异性混合物中纯化蛋白质时
is important or when detection of a very specific portion 很重要或当检测到非常特定的部分时
of a protein or modification is desired. 需要蛋白质或修饰物。
When detection or isolation of a protein is desired, 当需要检测或分离蛋白质时，
researchers commonly use a combination of two antibodies: 研究人员通常使用两种抗体的组合：
primary and secondary antibodies. 一抗和二抗。
Primary antibodies bind to specific antigens 一抗与特异性抗原结合
while secondary antibodies are made to recognize 而二抗则被识别
and bind to the constant region of primary antibodies, which 并与一抗的恒定区结合
is the same within a given species. 在给定的物种中是相同的。
Depending on the application, secondary antibodies 根据应用，二抗
might be conjugated to marker or a bead, which 可以与标记物或珠子缀合，其中
allows for easy detection or isolation, 便于检测或隔离，
of the protein of interest. 感兴趣的蛋白质。
The use of a secondary antibody leads 使用二抗导致
to amplification in signal since multiple secondary antibodies 由于多种二抗，因此可以扩增信号
can bind to a primary antibody. 可以与一抗结合。