and yet most of us never learn how it works.

その仕組みを知ることはあまりない

Or, what it is.

免疫自体を知らない人もいる

Your immune system consists of hundreds of tiny—and two large—organs.

免疫系は何百もの小さな臓器と ２つの大きな臓器からなり

It has its own transport network spread throughout your body.

全身に張り巡らされた 独自の輸送系をもっている

Every day, it makes hundreds of billions of fresh cells organized like an army.

毎日、何千億もの細胞が作られ 軍隊のように組織されている

With soldiers, captains, intelligence officers, heavy weapons, and crazy suicide bombers.

兵士、隊長、諜報員、重火器 そして狂気の自爆テロリスト

It's not some sort of abstract entity.

免疫系は抽象的な存在ではなく

Your immune system is you.

自分自身のことなのだ

Your biology protecting you from the billions of microorganisms that want to consume you,

あなたを消費しようとする何十億もの微生物や 自身のガン細胞から、生物学的メカニズムは防衛する

and from your own perverted cells that turn into cancer.

免疫系はあまりにも多岐にわたり 一つの動画には収まらないので

It's so manifold that it's impossible to cover in one video,

シリーズ化して多面的にみていこう

so we'll make a series looking at different aspects of it.

今回は、人体が侵略を受け、あなたの第一防衛ラインが 生死をかけて戦う際に何が起きるのかについて

Today: What happens when your body is invaded

何の変哲もない日

and your first lines of defenses are engaged in a fight for life and death.

突如、世界が爆発し 小惑星が空を切り裂いた

It's been a normal day,

無数のエイリアンが侵入し 都市やインフラを破壊し、市民を捕食する…

when suddenly the world explodes and an asteroid rips the sky open.

あなたの細胞が経験することだ

Countless alien life forms invade,

あなたは親指からの出血を見ている さっき公園の汚い小枝で切ってしまった

ready to destroy cities and infrastructure, and eat civilians...

ムカつきますね！

Or, this is what your cells experience.

しかし傷の内側では恐るべき大惨事が起きている

You look at your bleeding thumb that you just cut on a dirty twig in the park.

死んだ細胞、血とゴミがそこら中にあり

How annoying!

さらに、無数の細菌が無力な細胞の あたたかな隙間に侵入し

But inside the wound, a horrible catastrophe has happened.

定住先を探し、資源を盗み フンをまき散らしている

There are dead cells, and blood and dirt everywhere.

直ちに、防衛の第一段階が始まる

Even worse, countless bacteria invade the warm caverns between your helpless cells

生き延びた細胞、傷ついた細胞 死んだ細胞がパニック状態で悲鳴をあげ

to explore their new home, steal your resources, and poop everywhere.

免疫システムを目覚めさせる 化学的な信号を大量放出する

Immediately, the first stage of your defense kicks in.

まず登場するのがマクロファージだ

The cells that survive the impact, or are hurt or dying, scream in panic

平均的なサイズの細胞を人間とすると マクロファージはクロサイの大きさになる

releasing an onslaught of chemical alarm signals that awaken your immune system.

原理的にはストイックな細胞だが 怒らせたくはないだろう

The first cells to show up are macrophages.

だが細菌は怒らせてしまう

If an average cell were the size of a human, a macrophage would be the size of a black rhino.

数秒で、マクロファージは容赦なく殺し始める

A stoic cell in principle but you wouldn't want to annoy it.

タコの腕のようなパーツを伸ばし つかんで細菌を丸のみにし

Bacteria -do- annoy them.

生きたまま消化する

Within seconds, the large cells attack and begin killing them without mercy.

マクロファージは消耗しきるまでに 100個の細菌を食べられる

They stretch out parts like the arms of an octopus,

しかし敵はあまりに多く、 マクロファージは援軍を呼ぶ

and grab the bacteria to swallow them whole and digest them alive.

血中には何十万もの好中球がおり 信号に反応して戦場に移る

A macrophage can eat 100 bacteria before it's exhausted.

好中球は細菌を殺すことに特化した 強烈な特攻隊員だ

But there are too many enemies, so the macrophages call for reinforcements.

殺しへの熱意のあまり、生後数日で自殺してしまう

In your blood, hundreds of thousands of neutrophils pick up their signals and move to the battlefield.

だから誤ってあなたの身体を 内側から破壊するだけの時間もない

Neutrophils are intense suicide warriors that only live to kill.

到着するやいなや、致命的な化学物質を吐き出したり 食い殺したりし始める

They're so enthusiastic about killing that they kill themselves a few days after birth,

攻撃は配慮無く行われ あなたの細胞にも害がおよぶ

so they don't have time to accidentally destroy your body from the inside.

だが今は巻き添えもやむを得ない いや、配慮したことないけど

As soon as neutrophils arrive, they begin vomiting deadly chemicals at bacteria, or devour them.

好中球の中には自爆するものまでいる

They are so careless in their attacks that they are causing real damage to your own cells.

化学物質で満たされたDNAが 広く有毒な網を張り、細菌を捉えて殺す

But collateral damage is not their concern now,

この時点で瀕死なのだが さらに戦い続けることもある

or ever.

殺すことを楽しんでいるのだ

Some neutrophils go so far to push their suicide button and explode,

戦いの最中、ダムからの放流のごとく 血管から体液が流れ込む

casting a wide and toxic net made from their own DNA filled with deadly chemicals that trap and kill bacteria.

これが炎症だ

Sometimes, they can continue fighting after that, even though they're sort of dead already.

親指が少し膨らみ 赤く、暖かくなる

This is how much fun they have killing!

体液は戦場に静かな殺し屋を連れてくる 数百万もの補体タンパク室だ

While the battle rages, your blood vessels let fluid stream into the battlefield like a dam opening up towards a valley.

自動化された液体兵器のたぐいで 細菌に穴をあけ、気絶か死をもたらす

You notice this as inflammation.

補体については詳細な動画を作っている

Your thumb swells up a little and gets red and warm.

ここが分岐点だ

The fluid brings a silent killer into the battle zone, millions of complement proteins.

うまく行けば、第一防衛ラインで 速やかに侵入者を殺すことができる

A sort of automated liquid weapon that stuns and kills bacteria by ripping holes into them.

一方で侵入者が強すぎて 最終的に防御が圧倒されることもあり

We made a whole video explaining them in detail.

あなたの確実な死を意味する

We are reaching a crossroad now.

ここで免疫系の諜報員 樹状細胞の出番だ

If things go well, your first line of defense kills the invaders quickly.

戦いの傍らで、細菌を細かく砕いてサンプルを集め 身体に被せていた

But sometimes, the enemies are too strong and would overwhelm your defenses eventually,

兵士が敵の死体の内臓で 死んだふりをするように

which means certain death for you, the human.

樹状細胞は戦場を離れ、全ての組織と免疫の本部をつなぐ 免疫系の高速道路に入る

This is the hour of the dendritic cell, your immune system's intelligence officer.

リンパ節だ

While your soldiers were bashing in heads,

到着した樹状細胞は ヘルパーT細胞を探す

it was collecting samples by ripping bacteria into tiny parts and covering itself in it.

免疫系という軍の 万能な司令官だ

Like a soldier decorating itself in the guts of a dead enemy.

感染した細菌にピッタリの武器を偶然持つ 特定のヘルパーT細胞が必要である

The cell leaves the battlefield and enters the superhighway of your immune system

樹状細胞は、身体につけた細菌の一部を ヘルパーT細胞にこすりつけてまわる

that connects all your tissues with your immune headquarters.

ほとんどは嫌そうにするか、興味を示さない

Your lymph nodes.

数時間後、該当者が出てくる

The dendritic cell coming from the battlefield is looking for a helper T cell,

ヘルパーT細胞は細菌の一部を認識する

which is a sort of all-purpose commander cell within your immune army.

この細胞こそ、今必要な武器だ

But not any helper T cell.

樹状細胞が大喜びで活性化させる

One that happens to have just the right weapon for the bacteria that infected your wound.

うん、待って

So it goes around and rubs itself, still covered in bacteria parts, against every helper T cell it meets.

たまたま感染してきた特定の細菌に なぜピッタリの武器が準備されているの？

Most T cells are a bit disgusted and not interested.

免疫系は宇宙に存在しうる全ての病気に対し 完璧な武器を持っている

But after a few hours, something clicks.

黒死病、コロナウイルス あるいは100年後の火星に出現する感染症にも

A helper T cell recognizes the bacteria parts.

これは非常に複雑なので 次の動画でもう少し詳しく扱う

This cell is the weapon that's needed right now.

さしあたり、数十億種類の ヘルパーT細胞がいて

The dendritic cell is overjoyed and activates the helper T cell.

それぞれであらゆる敵への武器を持っていると 理解してほしい

Okay, wait.

適切なT細胞が活性化されると

How come your immune system has a cell that has a weapon against the specific bacteria that infected you?

第二防衛ラインが目覚め 登校日の10代ぐらいのように立ち上がる

Well, your immune system has a perfect weapon against every possible disease in the universe.

ごくゆっくりと

Against the Black Death, the Coronavirus, or an infection that will emerge in 100 years on Mars.

重火器は極めて効果的だが 速くはない

We'll talk about this a bit more in the next video because it's very complex.

活性化されたヘルパーT細胞は 何度も分裂を繰り返す

So, for now, just know that you have billions of unique helper T cells

1つから2つ、2つから4つと 数千クローンに達するまで

that each have weapons against every possible enemy.

そして2グループに分かれる

After the right T cell is activated, your second line of defense awakes

第一のグループは戦線に急行する

and rises like a teenager that needs to get up on a school day...

戦場は手の付けられない状況で

Very slowly.

何日も闘い、疲弊したマクロファージは もう眠りにつきたがっている

Your heavy weapons are incredibly effective but they're not fast.

戦友たちがそうしているように

The activated helper T cell begins to clone itself over and over again.

そこにヘルパーT細胞が到着し

One becomes two, two become four, until there are thousands of them.

マクロファージに駆け寄り特別な化学信号で 何かをささやく

Now, they split into two groups.

失意の兵士は、瞬く間に新鮮な気持ちになる

The first group quickly moves to help out your soldiers.

加えて、白くて熱い怒りもこみあげてくる

At the battlefield, things are getting out of hand.

何をすべきか マクロファージは知っている

A tired macrophage is ready to give up.

殺せ

After fighting for days, it just wants to go to sleep like many of its buddies have done already.

活性化されたマクロファージは 敵中に再び身を投じる

But now the helper T cells arrive.

これが戦場のあちこちで始まる

One of them comes to the tired macrophage and whispers something using special chemical signals.

一方、ヘルパーT細胞の第二グループは もう一つの防衛ライン、B細胞の活性化に向かう

In a heartbeat, the demoralized soldier feels fresh again.

抗体の工場だ

But there's something else.

抗体はタンパク質製の超兵器で 2本の爪をもつ小さいカニのようだ

A hot white anger.

ヘルパーT細胞と同様、あらゆる敵に対し ピッタリの抗体を作成できるB細胞が存在する

The macrophage knows what it needs to do...

まさにこのB細胞を ヘルパーT細胞は探すのだ

Kill.

1日か2日で適切なB細胞が見つかり 分裂を始める

Invigorated, it throws itself against the enemies once again.

十分な数まで達するとすぐに、各B細胞は 最大2000個/秒で抗体を送り出し始める

All over the battlefield, this begins to happen.

ケガをして細菌が侵入してから1週間ほどで

Meanwhile, the second group of helper T cells was working on activating another line of defense:

第二防衛ラインはようやく戦力を整える

B cells, your antibody factories.

小さな軍隊が戦場を満たし 抗体は細菌をつまみ、まとめ、無力化する

Antibodies are protein super weapons that look like tiny crabs with two pincers to grab enemies.

そして戦闘部隊が 無防備な細菌を虐殺する

Just like the helper T cells, there are B cells in your body

戦局は忙しく変化する

that are able to make just the right antibodies for every possible enemy.

敵が一掃されると、兵士たちは 自分たちがもはや必要ないと悟り

And the helper T cell is looking for exactly these B cells.

資源節約のため、自殺する

After a day or two, the right B cell is found, and begins to clone itself.

全員ではなく

As soon as enough clones have been made,

少数のヘルパーT細胞は残り 記憶細胞となる

each B cell begins pumping out up to 2,000 antibodies per second!

それらは数年にわたって組織を守り 同じ細菌が二度と足場を築かないようにする

About a week after you injured yourself and bacteria invaded,

同様に、いくらかのB細胞は生き残り、 少量の抗体を産生し続ける

your second line of defense finally arrives in full force.

この細菌への免疫を おそらく一生作り続けてくれる

The tiny army begins to saturate the battlefield, pinching and stunning desperate bacteria.

ある日目覚めると、傷口が再生を終え かすかな赤い跡しか残っていないと気付くだろう

The antibodies clump them together and make them unable to move or fight,

あなたは自身の細胞が試練を乗り越えるドラマに 全く気付かず、少しイラっとしただけだった

while your soldiers massacre the defenseless victims.

一方、数百万の細胞にとって それは生死をかけた決死の戦いだったのだ

The tide is turning fast.

だがこれも体内で日々展開される 壮大な物語の一部に過ぎず、その全容は

As the last enemies are cleaned up, your soldiers realize they are no longer needed,

『Immune: A Journey into the Mysterious System That Keeps You Alive』という書籍で語られます

and begin to kill themselves to save resources.

著者のPhilipp Dettmerは Kurzgesagtの創設者でありヘッドライターです

But not all of them.

この本は重要性のわりに理解が不十分な免疫系を 美麗なイラストで掘り下げ

A few helper T cells remain and turn into memory cells.

身体への理解を不可逆的に変えます

They will guard the tissue for years,

できるだけシンプルに楽しく書いていますが 約10年にわたり情熱を傾けました

making sure the same bacteria will never again gain a foothold here.

免疫系は最も驚異的で 魅力的なトピックだからです

Similarly, a few B cells will stay alive

さあ、自分の身体を知る旅に出ましょう

and keep producing a low amount of antibodies,

謎の臓器、殺人を学ぶ大学 そして宇宙で最大の図書館まで

making you immune against this bacteria,

信じられないほど広大な免疫システムと その実際の働きを紹介します

maybe for the rest of your life.

ガンやHIV、インフルエンザなどの敵と どう戦っているのか

One day you wake up and notice that the wound has grown over

免疫の高め方と、その妥当性を学びます

and left nothing but a faint red mark.

発売は6週後ですが、予約をしていただけると 私たちとPhilippにとって非常にありがたいです

You were completely unaware of the drama your cells had to deal with.

本の世界では予約はとても重要で

For you, the whole ordeal was a slight annoyance.

ゲームとは違って、書籍は完成を保証できますし 初日にパッチが出ることもありません

While for millions of cells, it was a desperate fight for life and death.

詳細欄にリンクがあります

But this is just the beginning of the epic story that unfolds inside you every day,

これは10年にわたる個人的な旅の終わりで 皆さんのご感想をとても楽しみにしています

and is told in full in

ご視聴ありがとうございました

"Immune: A Journey into the Mysterious System That Keeps You Alive",

written by Philipp Dettmer, the founder and head writer of Kurzgesagt.

The book is a beautifully illustrated deep dive into the immune system,

the most important thing you don't know enough about,

that will forever change how you think about your body.

Written to be as simple and fun as possible,

it's been an ongoing passion project for almost a decade

because the immune system is just about the most amazing and fascinating topic there is.

So, go on a journey and get to know your own body.

From mystery organs, murder universities, to the largest library in the universe.

Explore how incredibly vast your immune system is and how it actually works.

How it fights enemies from cancer to HIV, or just the flu.

Learn how you can boost it and if that's actually a good idea.

The book will be out in six weeks

and it would mean the world to us and Philipp if you could pre-order it.

Pre-ordering is super important in the world of books,

and in contrast to games, we can guarantee that it's actually finished

and there will be no day one patch.

There's a link in the description.

This is the end of a decade-long personal journey and we'd love to see what you think.

Thank you for watching.