Billions of bacteria, viruses, and fungi are trying to make you their home.

數以10億計的細菌、病毒和真菌們想要將你的身體變成它們的溫床

So our bodies have developed a super complex little army with guards, soldiers, intelligence, weapons factories,

所以我們的身體發展出一套包含守衛、士兵、情報、武器工廠和聯絡系統等構成的

and communicators to protect you from... Well, dying.

超級複雜的系統來保護你免於...嗯，死亡

For this video, let's assume the immune system has twelve different jobs, for example, kill enemies, communicate, etc.

在這部影片中，我們假設免疫系統有12種不同的工作，舉例來說，殺死敵人、聯繫溝通等等

And it has 21 different cells and 2 protein forces.

且它包含21種不同的細胞和兩種不同的蛋白質生力軍

These cells have up to 4 different jobs.

這些細胞有多至4種不同工作

Let's assign them, here are the interactions.

我們來指派一下其間的互動關係

Now let's make this understandable.

現在我們來讓這變得好懂一點

First of all, let's add colors to the jobs,

首先，我們來替不同的工作進行顏色標記

now let's illustrate the cells.

現在我們來以圖像方式來說明這些細胞

The central color represent the main job of the cell,

中間的顏色代表這個細胞的主要工作

while the surrounding ones represents secondary duties.

而周圍的代表次要的責任

Now the immune system looks like this...

現在免疫系統看起來像是這樣...

Now the interactions.

現在來看其間的相互關係

Isn't this complexity just awesome?

如此複雜的系統看起來是不是很棒阿？

For this video we will only talk about these cells and ignore the rest.

這部影片我們就只會談到這一些細胞而其他的就略過不談

So, what happens in the case of an infection?

所以，感染發炎到底是怎麼一回事？

It's a beautiful day, when suddenly, a wild rusty nail appears and you cut yourself.

這是一個美好的一天，但突然，一個野外生鏽的釘子割傷了你

The first barrier of the immune system is breached: your skin.

免疫系統的第一道防線，你的皮膚已被攻破

Nearby bacteria seizes on the opportunity and enter your wound.

附近的細菌抓住機會從傷口進入你的體內

They start using up the body's resources and double their numbers about every 20 minutes

它們開始利用你身體內的資源，然後在約每20分鐘數量就翻一倍

At first, they fly under the radar, but when a certain bacteria population is reached

一開始，它們能夠躲過身體免疫系統的偵測，但當細菌的數量到達一定程度時

they change their behavior and start to damage the body by changing the environment around them.

它們的整體行為將會改變，且開始去傷害其附近的體內環境

The immune system has to stop them as fast as possible.

免疫系統這時要越快阻止它們越好

First of all, your guard cells, known as macrophages intervene.

首先，你的守衛細胞，即大家熟知的巨噬細胞介入其中

They are huge cells that guard every border region of the body.

它們是一群很巨大的細胞，在身體每個邊界區域守衛著

Most of the time they alone can suffocate an attack,

大多數時間靠它們就能夠阻止細菌的攻擊

because they can devour up to 100 intruders each.

因為它們一個巨噬細胞能夠吞噬掉多至100個入侵者

They swallow the intruder whole and trap it inside a membrane.

它們會將入侵者整個吞噬且困在一個細胞膜內

Then the enemy gets broken down by enzymes and is killed.

然後酵素會將其分解並殺死

On top of that, they cause inflammation by ordering the blood vessels to release water into the battlefield,

除此之外，它們會命令血管釋出水份造成發炎反應

so fighting becomes easier.

讓這場戰爭變得容易對付

You notice this as a very mild swelling.

你會發現有輕微的腫脹反應

When the macrophages fight for too long,

而若是巨噬細胞已經讓這場仗拖了太久

they call in heavy backup by releasing messenger proteins that communicate location and urgency.

它們就會以釋出信息蛋白告知戰鬥地點以緊急程度來請求強力支援

Neutrophils leaves their patrol routes in the blood and move to the battlefield.

中性粒胞體離開了巡邏路線進到血液中移動到戰鬥場地

The neutrophils fight so furiously that they kill healthy cells in the process.

中性粒胞體在戰鬥中是十分的兇猛的，它們會連健康的細胞都一併在過程中殺死

On top of that, they generates barriers that trap and kill the bacteria.

此外，它們也會築起屏障來捕獲細菌然後把它們殺死

They are, indeed, so deathly that they evolved to commit suicide after five days to prevent them from causing too much damage.

它們的確是十分致命的，它們甚至演化到為了避免造成太多傷害，所以在生成五天之後就會啟動自殺機制

If this is not enough to stop the invasion, the brain of the immune system kicks in.

若這還不足以阻擋入侵，則免疫系統的大腦就會開始運作

The dendritic cell gets active, it reacts to the signals of the soldiers and starts collecting samples from the enemies.

樹狀細胞就會開始活化，會對於自方士兵的信號做出反應以及開始蒐集敵軍的樣本

They rip them into pieces and present the parts on their outer layer.

它們會將細菌們撕裂成好幾塊然後將它們的部份展示在自己的外層以供快速辨識

Now the dendritic cell makes a crucial decision.

這個時候樹狀細胞要做一個關鍵的決定

Should they call for anti-virus forces that eradicates infected body cells...

它們是該叫對抗病毒的武力來根除受感染的細胞體...

or an army of bacteria killers?

還是請出細菌殺手大軍呢？

In this case, anti-bacteria forces are necessary.

在這個案例中，對抗細菌的武力則是必要的

It then travels to the closest lymph node in about a day.

它們會在約一天的時間內移動至最近的淋巴結

Here, billion of helper and killer T cells are waiting to be activated.

在這，數以10億計的幫手和殺手T細胞在這裡等待指揮

When T cells are born they go trough a difficult and complicated training process

當T細胞生成之後，它們會經過一段很艱難和複雜的訓練過程

and only a quarter survives.

且只會有4分之1存活下來

The surviving cells are equipped with a specific set-up.

存活下來的細胞都具備了一套很特別的裝備

And the denditric cell is on its way looking for a helper T cell with the set-up that's just right.

而樹狀細胞會在路上尋找具備它們想要的裝備的幫手T細胞

It's looking for a helper T cell that combined the parts of the intruders which the dendritic cell has presented on its membrane.

它在尋找一個有結合能幫助辨識敵軍的、帶有一部分入侵者特徵在其細胞膜上的幫手T細胞

When it finally finds one, the chain reaction takes place.

一旦發現了一個，連鎖效應就開始發生

The helper T cell is activated, it quickly duplicates thousands of time.

幫手T細胞被活化，它們開始以數以千倍計的數量複製

Some become memory T cells that stay in the lymph node and will make you practically immune against this enemy,

它們有些變成了記憶T細胞留在淋巴結中，會讓你對於敵人的攻擊免疫

some travel to the field of battle to help out.

有些會移動到戰場去幫忙

And the third group goes on to travel to the center of the lymph node

而第三類群會移動至淋巴結的中心處

to activate a very powerful weapons factory.

去啟動一個非常強大的武器工廠

Like the T cells they are born with a specific set-up

正如那些天生具有特殊裝備的T細胞一樣

and when the B cell and the T cell with the same set-up meet, hell breaks loose.

當B細胞和有相同裝備的T細胞相遇，一股巨大力量迸發

The B cell duplicates rapidly and starts producing millions of little weapons.

B細胞快速地複製且開始製造數以百萬計的小型武器

They work so hard that they will literally die from exhaustion very fast.

由於它們過度認真地工作，所以實際上它們過勞死的速度非常快

Here helper T cells play another important role, they stimulate the hard working factories and tell them:

這裡幫手T細胞扮演了另一個重要角色，它們刺激勵了生產力旺盛的工廠且告訴它們說：

"don't die yet, we still need you, keep going!"

「先別掛掉阿，我們還需要你們呀，繼續工作！」

This also ensures that the factories die if the infection is over so the body doesn't waste energy or hurt itself.

這也確保了當感染消除後這些工廠會自動瓦解以節省身體的能量或者傷害到自己

But what is produced by the B cells?

但B細胞產出了什麼？

You've heard of them of course, antibodies,

你絕對有聽過它們：抗體

little proteins that are engineered to bind to the surface of the specific intruder.

它們是一群結合在入侵者標面的小型蛋白質

They're even different kinds of antibodies that have slightly different jobs.

甚至有不同功能的抗體執行細微差異的工作

The helper T cells tell the plasma cells which type is needed the most in this particular invasion.

幫手T細胞會告訴血漿細胞去製造哪些需要在這個特定入侵事件下的蛋白質種類

Millions of them flood the blood and saturate the body.

數以百萬計的抗體流經血液且充斥著身體

Meanwhile, at the site of infection, the situation is getting dire.

與此同時，在發炎的地方，情勢一發不可收拾

The intruders have multiplied in number and start hurting the body.

入侵者數量翻了好幾倍且開始傷害身體

Guard and attack cells fight hard but also die in the process.

守衛以及攻擊細胞奮戰也在過程中死傷不少

Helper T cells support them by ordering them to be more aggressive and to stay alive longer.

幫手T細胞藉由指揮它們變得更加有侵略性以支持它們撐的更久

But without help they can't overwhelm the bacteria.

但若缺少支援它們就無法戰勝細菌大軍

But now, the second line of defense arrives.

但現在，第二波防禦抵達了

Billions of antibodies flood the battlefield and disable lots of the intruders,

數以十億計的抗體流入戰場中，且使得許多入侵者喪失作戰能力

rendering them helpless or killing them in the process.

讓它們變得無助或者在過程中殺死它們

They also stun the bacteria and make them an easy target.

它們也震攝著細菌大軍且讓它們變成籠中鳥、甕中鱉

Their back is built to connect to killer cells so they can connect and kill the enemy more easily,

它們的後部是為了連結殺手細胞而造，所以它們能夠更輕易地連接上且殺死敵人

macrophages are specially good at nomming up the bacteria which antibodies have attached to.

巨噬細胞特別擅於在抗體吸付在細菌上時吞噬細菌

Now the balance shifts, in a team effort the infection is wiped out.

現在，局勢翻轉，在團隊合作努力下，感染就被除去了

At this point, millions of body cells have already died, no big deal, the losses are quickly replenished.

在這個階段，數以百萬計的體細胞已然死亡，這沒什麼大不了，這些損失迅速地被補上

Most immune cells are now useless and without the constant signals they commit suicide, so is not to waste any resources.

大多數的免疫細胞現在都沒有用處且在沒有持續的指示之下，它們開始執行自殺動作，才不會浪費任何資源

But some stay behind: the memory cells.

但是其中有些轉居幕後：記憶細胞

If this enemy is encountered ever again in the future, they will be ready for it and probably kill it before you even notice.

若這的敵人於未來再度捲土重來時，這些記憶細胞會準備好，也許在我們發現之前就殺光敵人了

This was a very very simplified explanation of parts of the immune system at work.

以上就是對於免疫系統部分功能的非常、非常簡化的解釋

Can you imagine how complex this system is, even at this level, when we ignore so many players and all the chemistry.

即使在我們省略掉其中很多角色以及參與的所有化學反應後，試圖以簡化方式來理解，依然難以想像這個系統的複雜程度

Life is awfully complicated, but if we take the time to understand it, we'll always encounter endless wonders and great beauty.

生命是十分的複雜難懂，但我們若花時間來了解它，我們會發現其中數不盡的驚喜與美麗