Your immune system is an omnipresent, terrifying entity made of billions of nuclear weapons and kamikaze bombers, saturating every little tissue, bone and fluid in your body.
It scans, patrols, and when it finds an enemy, it kills.
But what if it suddenly decides that you are the enemy?
This is the betrayal of autoimmunity.
Diseases like type 1 diabetes, multiple sclerosis, celiac disease, lupus and Crohn's disease, and many more.
Literally every tissue can be affected, from your nerves to your thyroid or joints.
They are all unique and different kinds of bad, from manageable to life-changing to deadly.
All share one fundamental property, your immune system thinks some healthy part of you is the enemy.
It's like a country attacking itself.
Fighter jets bomb roads, snipers hunt doctors and baristas, artillery levels daycare centers.
While there's usually a certain amount of genetic risk for autoimmunity, to get an actual autoimmune disease you also need a colossal case of bad luck on top of that.
How does this work?
The shape of life.
The fundamental building blocks of life are proteins.
Like ultra-complex Lego blocks, each of them has a precise shape allowing them to perform highly specific tasks like breaking down food or transcribing DNA.
In total, your body produces about 100,000 different proteins or shapes.
Your immune system evolved to constantly check the proteins of your cells and look for shapes that are not you, and to kill whatever's attached to them violently and brutally.
Autoimmunity is when your soldier cells suddenly think that your own healthy and natural proteins belong to an enemy.
We explained this in more detail in this video but, in a nutshell, this is such a critical danger to your survival that your body created an entire murder university to prevent this from happening.
Here, young immune cells go through ruthless training.
If they recognize the shapes of your own proteins, they're executed immediately.
But sometimes, through sheer dumb luck, one makes it through.
Right at this moment, you probably have a few million cells patrolling your body with the potential to trigger an autoimmune disease.
Another way to trigger autoimmunity is through your enemies.
Some bacteria and viruses have evolved proteins that are extremely similar to the ones in your own body, because they just have to if they want to interact with your cells and to stay hidden.
We see this everywhere in nature, from moths that look like bark or crocodiles that disappear in muddy water.
For bacteria, your tissue is a hostile jungle full of angry predators looking for them.
So they try to cover themselves in shapes that are very similar to your proteins.
But both of these things are not enough.
The final ingredient is a trigger event and a colossal case of bad luck.
The war that never ends.
The trigger can be anything that activates your defenses.
A common cold, the flu, a tiny wound.
Any sort of infection floods your body with cytokines, signals that tell your body this is a real fight, take this seriously, which truly wakes up your immune system.
Intelligent cells start to gather proteins, shapes, from the battlefield.
These shapes are the physical information of what's going on and are carried to your lymph nodes.
Information distribution centers.
Here your heavy weapons T-cells pass through.
Taking a look at the shapes that are being presented here.
If they recognize the shape of an invader, they activate the whole immune system and a few days later the attacker will be wiped out.
But this time, the worst things happen in the worst kind of way.
Maybe an intelligence officer picked up a piece of one of your healthy cells that died in the battle, or maybe a bacteria had a protein pretty similar to one of yours.
And by sheer extremely bad luck, a few months ago a single T-cell that can recognize this shape survived the murder university.
And today, exactly this T-cell happened to pass exactly this lymph node and is activated.
This single T cell now starts a big immune reaction against your own body.
It clones itself thousands of times, gathers other cells for support, and streams into your tissue.
When the misguided immune cells arrive, they see nothing but enemies.
The proteins they're looking for are everywhere, which can only mean that there's a full-on invasion going on.
They spread out and start attacking and killing your tissue.
How bad is this?
Well, it depends.
There are more than 100 different autoimmune diseases and basically any tissue can be affected.
In multiple sclerosis your immune cells are attacking the insulation of your nerve cells, making them sort of short circuit or slow down dramatically, causing numbness, muscle cramps, problems with your vision and concentration.
In type 1 diabetes, your immune system kills the cells that produce your insulin in your pancreas, starving your cells of glucose and turning your blood into acid.
In rheumatoid arthritis, angry cells invade your joints and literally start to dissolve cartilage and bone.
Lupus is a body-wide blitzkrieg that attacks literally every part of your body, causing painful, unpredictable and widespread destruction with a variety of bad symptoms.
And almost all autoimmune diseases come with crushing fatigue and exhaustion.
Because when you're sick, your immune system tells your body to shut down and rest.
Even if the immune system is itself the attacker, it still sends out the same orders.
It feels like you have the flu, but the real enemy is your own body.
The worst part about autoimmunity is that it never stops.
Your immune system is a self-enforcing machine of destruction.
The more enemies your initial autoimmunity cells encounter, the more cells they clone and activate.
So its nature prevents lasting peace.
Why is your body allowing this?
Most, if not all, autoimmune diseases have a genetic component, but this is kind of weird.
If some variants of genes are actively harmful to us, evolution should weed them out and make them less common.
But up to 1 in 10 people in the industrialized world suffers from them.
So why did they stick around?
Well, when it comes to genes, we often have to work with trade-offs.
At their core, autoimmune diseases always mean that your immune system is more aggressive.
And while this is mostly bad, until recently in human history, this was pretty great.
In the past, infectious diseases were the most common cause of death.
Terrible pandemics ravaged our cities regularly, sometimes decimating communities.
Researchers analyzed DNA samples from London cemeteries before, during and after the Black Death pandemic that killed about half of the population.
They found that individuals with gene variants that increased the risk for Crohn's disease seemed to have died at a much lower rate.
What helped them against a deadly disease back then might make us vulnerable to autoimmunity today.
Evolution doesn't care about perfect solutions.
It's only looking for good enough.
If variants made it more likely to survive the deadliest diseases, why care if, down the line, this might lead to something else?
If you have an autoimmune disease, you may only be alive because your ancestors carried these genes and survived a pandemic that wiped out their neighbors.
And then, a hot second ago, we changed our world.
Hygiene, antibiotics, vaccines and modern medicine revolutionized our lives and how we die.
So much so that most of us don't even think a lot about infectious diseases.
And this is great.
But now we're left with genes that make our immune systems more aggressive for no good reason.
Add a bit of bad luck, and all these billions of nuclear weapons and kamikaze bombers take aim at the wrong target.
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