视听｜免疫系统是如何工作的？
How Does the Immune System Work
免疫系统是如何工作的
里面一A mosquito lands on your arm, injects its chemicals into your skin, and begins to feed. You wouldn’t even know it was there, if not for the red lump that appears, accompanied by a telltale itch. It’s a nuisance, but that bump is an important signal that you’re protected by your immune system, your body’s major safeguard against infection, illness, and disease.
一只蚊子落到了你的手臂上，把化学物质注射到皮肤中，然后大快朵颐。如果没有出现奇痒无比的红色肿块，你甚至不会察觉它来过。尽管很烦人，可这个包是重要的信号，表示你正受到免疫系统保护。免疫系统是身体的重要保镖，保护其免受感染和疾病侵害。
This system is a vast network of cells, tissues, and organs that coordinate your body’s defenses against any threats to your health. Without it, you’d be exposed to billions of bacteria, viruses, and toxins that could make something as minor as a paper cut or a seasonal cold fatal.
免疫系统是一张巨大的网络，由细胞、组织和器官组成，负责协调身体防御机制，抵御可能危害健康的外来入侵者。没有它，你将会暴露在数以亿计的细菌、病毒和毒素中，甚至连被纸划伤和季节性感冒这样的小伤小病都会变得非常致命。
The immune system relies on millions of defensive white blood cells, also known as leukocytes, that originate in our bone marrow. These cells migrate into the bloodstream and the lymphatic system, a network of vessels which helps clear bodily toxins and waste. Our bodies are teeming with leukocytes: there are between 4 000 and 11 000 in every microliter of blood.
白细胞是免疫系统中不可或缺的成员，也被称作白血球，从骨髓中产生，并分散到血液和淋巴系统等用于清除毒素和废物的管道系统中。我们的身体里有大量白血球，每1微升血液中就有4 000到11 000个。
As they move around, leukocytes work like security personnel, constantly screening the blood, tissues, and organs for suspicious signs. This system mainly relies on cues called antigens. These molecular traces on the surface of pathogens and other foreign substances betray the presence of invaders. As soon as the leukocytes detect them, it takes only minutes for the body’s protective immune response to kick in.
它们在身体里散开后，作用类似保安，会持续不断地在血液、组织和器官中搜查可疑迹象。免疫系统主要以抗原为线索，搜查病原体。这些病原体和外来物质表面的分子痕迹会暴露入侵者。白血球发现它们之后，只需要几分钟，就会触发身体的免疫反应。
Threats to our bodies are hugely variable, so the immune response has to be equally adaptable. That means relying on many different types of leukocytes to tackle threats in different ways.
对我们有威胁的物质种类繁多，相应地，免疫反应必须随机应变。这意味着，要依靠许多种类的白血球，以不同的方式抵御入侵者。
Despite this diversity, we classify leukocytes in two main cellular groups, which coordinate a two-pronged attack. First, phagocytes trigger the immune response by sending macrophages and dendritic cells into the blood. As these circulate, they destroy any foreign cells they encounter, simply by consuming them. That allows phagocytes to identify the antigen on the invaders they just ingested and transmit this information to the second major cell group orchestrating the defense, the lymphocytes.
尽管白血球种类繁多，但是我们仍可以分为两个主要细胞组，它们能双管齐下地攻击敌人。首先，吞噬细胞把巨噬细胞和树突状细胞输送到血液里，触发免疫反应。这些细胞在血液循环中会以吞噬的方法将遇到的外来细胞消灭。这使吞噬细胞能够辨别入侵者身上携带的抗原，然后把信息传送给第二个主要细胞组，即负责组织身体防御的淋巴细胞。
A group of lymphocyte cells called T-cells go in search of infected body cells and swiftly kill them off. Meanwhile, B-cells and helper T-cells use the information gathered from the unique antigens to start producing special proteins called antibodies. This is the pièce de résistance: Each antigen has a unique, matching antibody that can latch onto it like a lock and key, and destroy the invading cells. B-cells can produce millions of these, which then cycle through the body and attack the invaders until the worst of the threat is neutralized.
一群叫做“T细胞”的淋巴细胞开始搜索被感染的身体细胞，然后迅速地消灭它们。与此同时，B细胞和辅助T细胞利用从抗原处收集的信息，制造被称为“抗体”的特殊蛋白质。抗体可不容小觑：每个抗原都有一个独特抗体与之相匹配，就像锁和钥匙一样，当抗体附着其上，就能够摧毁入侵细胞。B细胞能生产数以百万计的抗体，这些抗体在身体里循环，并攻击入侵者，直到解除对身体的严重威胁。
While all of this is going on, familiar symptoms, like high temperatures and swelling, are actually processes designed to aid the immune response. A warmer body makes it harder for bacteria and viruses to reproduce and spread because they’re temperature-sensitive. And when body cells are damaged, they release chemicals that make fluid leak into the surrounding tissues, causing swelling. That also attracts phagocytes, which consume the invaders and the damaged cells.
与此同时，人们熟知的症状，比如发烧和肿胀，其实是为了帮助免疫反应而产生的。因为细菌和病毒对温度很敏感，较高的体温能够使它们更难繁殖和扩散。当身体细胞受损时，它们会释放一种能让体液渗入周围组织的化学物质，从而造成肿胀。这也会吸引吞噬细胞来吞食入侵者和受伤的细胞。
Usually, an immune response will eradicate a threat within a few days. It won’t always stop you from getting ill, but that’s not its purpose. Its actual job is to stop a threat from escalating to dangerous levels inside your body. And through constant surveillance over time, the immune system provides another benefit: it helps us develop long-term immunity.
通常来说，免疫反应能在几天内根除威胁，但它不能让你免受疾病之苦，那并不是它的职责。它真正的职责是阻止威胁在身体中升级成危险。另外，通过对身体持续不断的监视，免疫系统还有另一个好处：帮助我们构建长期免疫力。
When B-cells and T-cells identify antigens, they can use that information to recognize invaders in the future. So, when a threat revisits, the cells can swiftly deploy the right antibodies to tackle it before it affects any more cells. That’s how you can develop immunity to certain diseases, like chickenpox.
当B细胞和T细胞识别出抗原，它们能通过这些信息识别未来的入侵者。因此，当相同的威胁再次到来时，这些细胞就能快速地调动相应的抗体，在感染扩散之前进行拦截。这就是我们能对水痘等特定疾病产生免疫力的原因。
It doesn’t always work so well. Some people have autoimmune diseases, which trick the immune system into attacking the body’s own perfectly healthy cells. No one knows exactly what causes them, but these disorders sabotage the immune system to varying degrees, and underlie problems like arthritis, Type I diabetes, and multiple sclerosis.
但这并非总是有效。一些人患有自体免疫疾病，他们的免疫系统会变得敌我不分，攻击正常而健康的身体细胞。尽管病因不得而知，但是这些疾病会在不同程度上影响免疫系统，并引发像关节炎、I型糖尿病和多发性硬化症等疾病。
For most individuals, however, a healthy immune system will successfully fight off an estimated 300 colds and innumerable other potential infections over the course of a lifetime. Without it, those threats would escalate into something far more dangerous. So the next time you catch a cold or scratch a mosquito bite, think of the immune system. We owe it our lives.
不过，就大多数人而言，健康的免疫系统能在其一生中成功抵御大约300次感冒和不计其数的其他潜在感染。没有免疫系统，这些威胁就会发展成更危险的疾病。所以，你下次得感冒或挠蚊子包时，想想你的免疫系统，我们的生命全靠它保障。
原文、译文转自TED-Ed官网
大连外国语大学高级翻译学院实习生
祁玥 整理
(Credit: VoiceTube)