Name: 免疫系統，第二部分：速成班 A&P #46 (Immune System, part 2: Crash Course A&P #46)
Uploaded: 2021-01-14T06:04:44.000Z
Duration: 9 min 44 s
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What’s true in World of Warcraft is also true in your immune system:

To defeat your enemy, you have to know your enemy.

Uncover its weaknesses. Learn how to see it, before it sees you.

We’ve already talked about how your innate defense system keeps out, or quietly neutralizes,

pathogens without much too much fuss. But sooner or later, a threat’s gonna come along

that’s stronger than what the first-responders can handle. That’s when it’s time for

the adaptive, or acquired immune system to step in.

While your innate system takes its zero-tolerance policy very seriously, and tries to toast

any foreign microbe that it encounters, your adaptive system does things differently.

It has to be expressly introduced to a specific pathogen, and recognize it as a threat, before it will attack.

As its name suggests, you’re not born with a working adaptive immune system -- it’s

slow to act, in part because it takes time for it to shake hands with so many pathogens

These introductions may be organic -- like touching a dirty faucet in the bathroom or

Or they may be premeditated, which is why vaccination is pretty much the greatest thing

But once it’s been introduced to a potential threat, your adaptive defenses never forget

it. And this ability to remember specific pathogens is one of the key differences between

Another main difference is that adaptive immunity is systemic -- rather than being restricted

to a particular infection in, say, a sinus or a sliced finger, your adaptive system can

fight throughout your whole body at once.

And it does this by deploying one or both of its separate, but cooperating, defenses

-- your humoral immunity and your cellular defenses.

Your humoral immunity -- which you might not have heard of before -- works by dispatching

important proteins that I’m sure you have heard of: antibodies.

They’re made by special white blood cells, and they patrol the body’s “humors”

or fluids like blood and lymph, where they combat viruses and bacteria moving around

the interstitial space between your cells.

Much of what you know, or have heard about, or think of, when your immune system comes

up actually has to do with your humoral immunity.

It’s why, if you had mumps as a kid, you probably don’t have to worry about getting

It’s also why doctors and nurses and patients who have been infected with the ebola virus

-- a disease once thought to be incurable -- have lived to tell about it.

Whether you’re protecting yourself from infections or playing an MMO, one of the first

steps in any good defensive strategy is to be able to tell your friend from your foe.

And in the case of your immune system, that means being able to identify antigens.

An antigen could be an invader from the outside world, like a bacterium, virus, or fungus.

Or it could be a toxin or a diseased cell within your own body.

But in any case, antigens are large signalling molecules not normally found in the body,

and they act as flags that get the adaptive immune system riled up.

So let’s say a flu virus gets inside of you, and it’s floating around trying to

find a good host cell to start multiplying inside of.

Before it finds that cell, hopefully it will be paid a visit by one of the stars of your

Like all blood cells, these guys originate in your bone marrow. But unlike other white

blood cells, they also mature in the bone marrow too.

And as a B cell matures, it develops the ability to determine friend from foe, developing both

immunocompetence -- or how to recognize and bind to a particular antigen -- as well as

self-tolerance, or knowing how to NOT attack your body’s own cells.

Once it’s fully mature, a B lymphocyte displays at least 10,000 special protein receptors

on its surface -- these are its membrane-bound antibodies.

All B lymphocytes have them, but the cool thing is, every individual lymphocyte has

its own unique antibodies, each of which is ready to identify and bind to a particular kind of antigen.

That means that, with all of your B lymphocytes together, it’s like having 2 billion keys

on your immune system’s keychain, each of which can only open one door.

So, part of your immune system’s strategy is just to win with overwhelming odds: The

more unique antibodies your lymphocytes have, the more likely it is that one will eventually

find, bind to, and mark a particular antigen.

Once they’ve matured, B cells colonize or “seed” your secondary lymphoid organs,

like your lymph nodes, and start roaming around in your blood and lymph.

At this point they’re still naive and untested, and they won’t truly be activated until

When the right B cell finally bumps into an antigen it has antibodies for -- usually in

a lymph node or in the spleen -- and recognizes it, it binds to it. This summons the full

power of the humoral immune response, and the cell basically goes into berserker mode.

Once activated, the B cell starts cloning itself like crazy, quickly producing an army

of similar cells, all with the instructions for the exact same antibodies that are designed

Most of these clones become active fighters, or effector cells. But a few become long-lived

memory cells that preserve the genetic code for that specific, successful antibody.

This ensures that, if and when the antigen returns, there will be a prepared secondary

immune response that’s both stronger and faster than the first.

This is key to why vaccinations are so brilliant and important, which I’ll come back to in a minute.

But while the memory cells are just there to hang back and record things, the effector,

or plasma cells, are packed with extra amounts of rough endoplasmic reticulum, which acts

These cells can mass-produce the same antibodies over and over for that particular invader,

spitting them out into the humor at a rate of around 2,000 antibodies per second for

And the antibodies they make work the same way that the membrane-bound ones do; they’re just free-floating.

So they ride the tides of blood and lymph, binding to all the antigens they can find,

Now, antibodies can’t really do the killing themselves, but they do have a few moves that

could make it hard for intruders to take hold.

One of their most effective and common strategies is neutralization, where antibodies physically

block the binding sites on viruses or bacterial toxins, so they can’t hook up to your tissues.

And because antibodies have more than one binding site, they can bind to multiple antigens

at the same time, in a process called agglutination.

The resulting clumps can’t get around easily, which makes it easier for macrophages

And not only that, but while all this is going on, antibodies are also ringing a chemical

dinner bell, calling in phagocytes from the innate immune system, and special lymphocytes

from the adaptive system, to destroy these messy little antigen-antibody clumps.

So, the point of all this in the short term is to keep you healthy. But in the long term,

this process also adds to your overall immunity.