How does your immune system work? - Emma Bryce

翻译人员: Jian Wang 校对人员: Riley WANG

A mosquito lands on your arm,

一只蚊子落到了你的手臂上，

injects its chemicals into your skin, and begins to feed.

把化学物质注射到你的皮肤内， 然后开始大快朵颐。

You wouldn’t even know it was there, if not for the red lump that appears,

如果没有在叮咬后出现又红又痒的包，

你甚至不会察觉它的存在。

accompanied by a telltale itch.

It’s a nuisance, but that bump is an important signal

虽然很烦人 ， 可这个包是一个是重要的信号，

that you’re protected by your immune system,

它表示你正被你的免疫系统保护着。

your body’s major safeguard against infection, illness, and disease.

免疫系统是你身体的保镖， 使你的身体免受感染和疾病的侵害。

This system is a vast network of cells, tissues, and organs

免疫系统是由细胞、组织 和器官形成的巨大网络，

that coordinate your body’s defenses against any threats to your health.

负责组织身体防御 可能危害健康的外来入侵者。

Without it, you’d be exposed to billions of bacteria, viruses, and toxins

没有它，你将会暴露在 数以亿计的细菌、病毒和毒素之中，

that could make something as minor as a paper cut or a seasonal cold fatal.

这些病原体能让 一个小割伤或小感冒变得致命。

The immune system relies on millions of defensive white blood cells,

白细胞是免疫系统中 一个不可或缺的成员，

also known as leukocytes,

它们也被称作白血球，

that originate in our bone marrow.

由我们的骨髓产生。

These cells migrate into the bloodstream and the lymphatic system,

这些细胞在血液和淋巴系统中游荡，

a network of vessels which helps clear bodily toxins and waste.

血液和淋巴系统是 用于清除毒素和废物的管道系统。

Our bodies are teeming with leukocytes:

我们的身体里有大量白血球，

there are between 4,000 and 11,000 in every microliter of blood.

每微升血液中就有 4000 到 11000 个白血球。

As they move around, leukocytes work like security personnel,

它们在身体里的作用如同保安，

constantly screening the blood, tissues, and organs for suspicious signs.

持续不断地在血液、组织 和器官中搜查可疑迹象。

This system mainly relies on cues called antigens.

免疫系统主要依靠抗原 作为搜查病原体的线索。

These molecular traces on the surface of pathogens and other foreign substances

这些在病原体和外来物质 表面上的分子痕迹

betray the presence of invaders.

标示着入侵者的存在。

As soon as the leukocytes detect them,

白血球发现它们之后，

it takes only minutes for the body’s protective immune response to kick in.

只需要几分钟 ， 身体的免疫反应就会被触发。

对我们有威胁的物质种类繁多，

Threats to our bodies are hugely variable,

so the immune response has to be equally adaptable.

所以免疫反应必须随机应变。

That means relying on many different types of leukocytes

这意味着，要依靠许多 不同种类的白血球，

to tackle threats in different ways.

通过不同的方式抵御入侵者。

Despite this diversity, we classify leukocytes in two main cellular groups,

尽管白血球种类繁多，我们仍可以 把它们分为两个主要细胞组，

which coordinate a two-pronged attack.

它们能双管齐下地攻击敌人。

首先，吞噬细胞输送 巨噬细胞和树突状细胞

First, phagocytes trigger the immune response

by sending macrophages and dendritic cells into the blood.

到血液里，进而触发免疫反应。

As these circulate, they destroy any foreign cells they encounter,

这些细胞在血液循环中 会通过吞噬的方法

simply by consuming them.

将遇到的外来细胞消灭。

That allows phagocytes to identify

这让吞噬细胞能够辨别

the antigen on the invaders they just ingested

入侵者身上携带的抗原，

and transmit this information to the second major cell group

然后把信息传送给第二个主要细胞组，

orchestrating the defense,

即 淋巴细胞，

the lymphocytes.

它们负责组织身体的防御。

A group of lymphocyte cells called T-cells go in search of infected body cells

一群叫做“T 细胞”的淋巴细胞 开始搜索被感染的身体细胞，

and swiftly kill them off.

然后迅速地消灭它们。

Meanwhile, B-cells and helper T-cells

与此同时，B 细胞和辅助 T 细胞

use the information gathered from the unique antigens

使用从抗原处收集的信息

to start producing special proteins called antibodies.

来制造被称为“抗体”的特殊蛋白质。

This is the pièce de résistance:

它们可不容小觑：

Each antigen has a unique, matching antibody that can latch onto it

每个抗原都有一个独特抗体 附着其上，与之相匹配，

like a lock and key,

就像锁和钥匙一样，

and destroy the invading cells.

能够摧毁入侵细胞。

B-cells can produce millions of these,

B 细胞能生产数以百万计的抗体，

which then cycle through the body and attack the invaders

这些抗体在身体里循环 ， 并攻击入侵者，

until the worst of the threat is neutralized.

直到解除对身体的威胁。

While all of this is going on, familiar symptoms,

与此同时，令人熟悉的症状，

like high temperatures and swelling,

比如发烧和肿胀，

are actually processes designed to aid the immune response.

其实是为了帮助免疫反应而产生的。

A warmer body makes it harder for bacteria and viruses to reproduce and spread

较高的体温能够 使细菌和病毒更难繁殖和扩散，

because they’re temperature-sensitive.

因为它们对温度很敏感。

And when body cells are damaged,

当身体细胞受损时，

they release chemicals that make fluid leak into the surrounding tissues,

它们会释放一种能让 体液渗入周围组织的化学物质，

causing swelling.

从而造成肿胀。

That also attracts phagocytes,

这也会吸引吞噬细胞

which consume the invaders and the damaged cells.

来吞食入侵者和受伤的细胞。

Usually, an immune response will eradicate a threat within a few days.

通常来说 ，免疫反应 能在几天内根除威胁。

It won’t always stop you from getting ill, but that’s not its purpose.

它不会总让你免受疾病之苦， 那并不是它的职责。

Its actual job is to stop a threat

它真正的职责是

阻止威胁在你的身体中 上升到危险的程度。

from escalating to dangerous levels inside your body.

And through constant surveillance over time,

另外，通过对身体持续不断的监视，

the immune system provides another benefit:

免疫系统还能提供另一个好处：

it helps us develop long-term immunity.

那就是帮助我们构建长期免疫力。

When B- and T-cells identify antigens,

当 B 细胞和 T 细胞识别出抗原，

they can use that information to recognize invaders in the future.

它们能使用这些信息 识别未来的入侵者。

So, when a threat revisits, the cells can swiftly deploy the right antibodies

所以，当相同威胁再次到来时， 这些细胞就能快速地调动相应的抗体，

to tackle it before it affects any more cells.

在感染扩散之前进行拦截。

That’s how you can develop immunity to certain diseases, like chickenpox.

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.

但这并不总能一劳永逸。

Some people have autoimmune diseases,

一些人患有自体免疫疾病，

which trick the immune system

他们的免疫系统会变得敌我不分，

into attacking the body’s own perfectly healthy cells.

并开始攻击正常而健康的身体细胞。

No one knows exactly what causes them,

这种病的病因不得而知，

but these disorders sabotage the immune system to varying degrees,

但是这些疾病会在 不同程度上影响免疫系统，

and underlie problems like arthritis,

并引发像关节炎，

Type I diabetes,

1型糖尿病，

and multiple sclerosis.

和多发性硬化症等问题。

For most individuals, however,

不过，对于大多数人来说，

a healthy immune system will successfully fight off an estimated 300 colds

健康的免疫系统能在一生中

成功抵御大约 300 次感冒 和不计其数的其他潜在感染。

and innumerable other potential infections over the course of a lifetime.

Without it, those threats would escalate into something far more dangerous.

没有免疫系统，这些威胁 就会发展成更危险的疾病。

So the next time you catch a cold or scratch a mosquito bite,

所以，你下次得感冒或被蚊子咬时，

think of the immune system.

想想你的免疫系统，

We owe it our lives.

我们的生命全靠它保障。