Every living being needs to fight off other living beings that want to feast on them.​

Every living being needs to fight off other living beings that want to feast on them.​

So as multicellular life evolved over billions of years, it came up with ways to defend itself.​

So as multicellular life evolved over billions of years, it came up with ways to defend itself.​

So as multicellular life evolved over billions of years, it came up with ways to defend itself.​

Today humans have a sophisticated defense network,​

Today humans have a sophisticated defense network,​

Today humans have a sophisticated defense network,​

like physical barriers, defense cells, and weapons factories.​

like physical barriers, defense cells, and weapons factories.​

like physical barriers, defense cells, and weapons factories.​

But one of the most important defenses of our body is largely unknown:​

But one of the most important defenses of our body is largely unknown:​

But one of the most important defenses of our body is largely unknown:​

The Complement System​

The Complement System​

The Complement System​

It evolved over 700 million years ago and is an army of over 30 different proteins​

It evolved over 700 million years ago and is an army of over 30 different proteins​

It evolved over 700 million years ago and is an army of over 30 different proteins​

that work together in a complex and elegant dance to stop intruders.​

that work together in a complex and elegant dance to stop intruders.​

that work together in a complex and elegant dance to stop intruders.​

All in all, about 15 quintillion of them are saturating every fluid in your body right now.​

All in all, about 15 quintillion of them are saturating every fluid in your body right now.​

All in all, about 15 quintillion of them are saturating every fluid in your body right now.​

Guided by nothing but chemistry,​

Guided by nothing but chemistry,​

Guided by nothing but chemistry,​

these proteins are one of the most effective weapons we have against invaders.​

these proteins are one of the most effective weapons we have against invaders.​

these proteins are one of the most effective weapons we have against invaders.​

Many other parts of the immune system are just tools to activate the Complement System.​

Many other parts of the immune system are just tools to activate the Complement System.​

Many other parts of the immune system are just tools to activate the Complement System.​

But it's also really dangerous.​

But it's also really dangerous.​

But it's also really dangerous.​

Imagine having trillions of little bombs inside your blood that could go off at any moment.​

Imagine having trillions of little bombs inside your blood that could go off at any moment.​

Imagine having trillions of little bombs inside your blood that could go off at any moment.​

So our cells use numerous mechanisms to prevent​ ​complement from accidentally attacking ​​them​.​

So our cells use numerous mechanisms to prevent​ ​complement from accidentally attacking ​​them​.​

So our cells use numerous mechanisms to prevent​ ​complement from accidentally attacking ​​them​.​

Okay, what exactly does it do and what makes it so dangerous?​

Okay, what exactly does it do and what makes it so dangerous?​

Okay, what exactly does it do and what makes it so dangerous?​

In a nutshell, The Complement System does three things:​

In a nutshell, The Complement System does three things:​

In a nutshell, The Complement System does three things:​

it cripples enemies, it activates the immune system, and it rips holes in things until they die.​

it cripples enemies, it activates the immune system, and it rips holes in things until they die.​

it cripples enemies, it activates the immune system, and it rips holes in things until they die.​

But, how?​

But, how?​

But, how?​

After all, these are mindless proteins randomly drifting around without will or direction.​

After all, these are mindless proteins randomly drifting around without will or direction.​

After all, these are mindless proteins randomly drifting around without will or direction.​

Well, this is actually part of the strategy.​

Well, this is actually part of the strategy.​

Well, this is actually part of the strategy.​

Complement proteins float around in a sort-of passive mode.​

Complement proteins float around in a sort-of passive mode.​

Complement proteins float around in a sort-of passive mode.​

They do nothing, until they get activated and change their shape.​

They do nothing, until they get activated and change their shape.​

They do nothing, until they get activated and change their shape.​

In the world of proteins, your shape determines what you can and cannot do.​

In the world of proteins, your shape determines what you can and cannot do.​

In the world of proteins, your shape determines what you can and cannot do.​

Because shape determines what you can interact with and in what way.​

Because shape determines what you can interact with and in what way.​

Because shape determines what you can interact with and in what way.​

For example, in your passive shape you might do nothing.​

For example, in your passive shape you might do nothing.​

For example, in your passive shape you might do nothing.​

In your active shape, however, you might, for example, change the shape of other proteins​

In your active shape, however, you might, for example, change the shape of other proteins​

In your active shape, however, you might, for example, change the shape of other proteins​

activating them so they can activate others.​

activating them so they can activate others.​

activating them so they can activate others.​

Mechanisms like this one can start cascades that spread very quickly.​

Mechanisms like this one can start cascades that spread very quickly.​

Mechanisms like this one can start cascades that spread very quickly.​

Imagine the complement proteins as being like millions of matches very close together.​

Imagine the complement proteins as being like millions of matches very close together.​

Imagine the complement proteins as being like millions of matches very close together.​

Once one catches fire, it ignites the ones around it.​

Once one catches fire, it ignites the ones around it.​

Once one catches fire, it ignites the ones around it.​

They ignite more and suddenly you have a big fire.​

They ignite more and suddenly you have a big fire.​

They ignite more and suddenly you have a big fire.​

To show the actual mechanisms of The Complement System is a tad complicated and overwhelming.​

To show the actual mechanisms of The Complement System is a tad complicated and overwhelming.​

To show the actual mechanisms of The Complement System is a tad complicated and overwhelming.​

So, we'll simplify here.​

So, we'll simplify here.​

So, we'll simplify here.​

Now, let's imagine you cut yourself and a bunch of bacteria enter the wound​

Now, let's imagine you cut yourself and a bunch of bacteria enter the wound​

Now, let's imagine you cut yourself and a bunch of bacteria enter the wound​

and make it into the surrounding tissue.​

and make it into the surrounding tissue.​

and make it into the surrounding tissue.​

Our complement attack begins with C3.​

Our complement attack begins with C3.​

Our complement attack begins with C3.​

C3 is the first match, the initial spark that will start our fire.​

C3 is the first match, the initial spark that will start our fire.​

C3 is the first match, the initial spark that will start our fire.​

And to do that, C3 needs to switch from passive to active.​

And to do that, C3 needs to switch from passive to active.​

And to do that, C3 needs to switch from passive to active.​

How this happens is complex, but let's just say it can happen randomly​

How this happens is complex, but let's just say it can happen randomly​

How this happens is complex, but let's just say it can happen randomly​

through other complement proteins that bind to enemies or through antibodies.​

through other complement proteins that bind to enemies or through antibodies.​

through other complement proteins that bind to enemies or through antibodies.​

All you really need to know is that C3 breaks into two smaller proteins,​

All you really need to know is that C3 breaks into two smaller proteins,​

All you really need to know is that C3 breaks into two smaller proteins,​

C3a and C3b, that are now activated.​

C3a and C3b, that are now activated.​

C3a and C3b, that are now activated.​

One of these parts, the C3b protein, is like a seeker missile specialized in bacteria, fungi, and viruses.​

One of these parts, the C3b protein, is like a seeker missile specialized in bacteria, fungi, and viruses.​

One of these parts, the C3b protein, is like a seeker missile specialized in bacteria, fungi, and viruses.​

It has a fraction of a second to find a victim or it will be neutralized by water molecules.​

It has a fraction of a second to find a victim or it will be neutralized by water molecules.​

It has a fraction of a second to find a victim or it will be neutralized by water molecules.​

If C3b does find a target, it anchors itself very tightly to its surface and doesn't let go.​

If C3b does find a target, it anchors itself very tightly to its surface and doesn't let go.​

If C3b does find a target, it anchors itself very tightly to its surface and doesn't let go.​

By doing so, the protein changes its shape again.​

By doing so, the protein changes its shape again.​

By doing so, the protein changes its shape again.​

In its new shape, it's now able to grab other proteins and start a small cascade,​

In its new shape, it's now able to grab other proteins and start a small cascade,​

In its new shape, it's now able to grab other proteins and start a small cascade,​

changing its shape multiple times, adding other complement proteins to itself.​

changing its shape multiple times, adding other complement proteins to itself.​

changing its shape multiple times, adding other complement proteins to itself.​

Finally, it transforms itself into a recruiting platform known as C3 Convertase.​

Finally, it transforms itself into a recruiting platform known as C3 Convertase.​

Finally, it transforms itself into a recruiting platform known as C3 Convertase.​

This platform is an expert at activating more C3 proteins that start the whole cycle anew.​

This platform is an expert at activating more C3 proteins that start the whole cycle anew.​

This platform is an expert at activating more C3 proteins that start the whole cycle anew.​

An amplification loop begins.​

An amplification loop begins.​

An amplification loop begins.​

Soon, thousands of proteins cover the bacteria.​

Soon, thousands of proteins cover the bacteria.​

Soon, thousands of proteins cover the bacteria.​

For the bacteria, this is very bad.​

For the bacteria, this is very bad.​

For the bacteria, this is very bad.​

It can cripple the bacteria and make them helpless, or slow them down.​

It can cripple the bacteria and make them helpless, or slow them down.​