You Are Immune Against Every Disease

You Are Immune Against Every Disease

You are not a man, but a planet. Composed of about 40 billion cells. There is so much in your body that if your cells were human-sized, you would be as tall as 20 Mount Everest. For your creeping inhabitants, your body is an ecosystem, rich in resources, warm and vast. Great place to move and start a family.

Some of these guests are welcome, but most are not. Your immune system is the guardian of this planet, the forces that protect you from the constant risk of invasion. But your enemies in the microworld have a huge advantage. Think about how much effort it takes to create a copy of yourself with your billions of cells.

First you have to find someone to like you, to go out together, to behave strangely, and if all goes well, two of your cells will merge.

Then you have to wait months for the cell to multiply in large numbers, and finally, it emerges as a human being. Even it is only a small copy that needs years of care to become useful. A bacterium consists of a single cell. It can be completely copied in half an hour. A virus can turn into hundreds per hour and billions per day.

Your enemies multiply, much faster than you. Worse, for a bacterium or virus, your body is a hostile ecosystem with natural selection.

They go through so many generations so fast that, by chance, by chance, an individual can mutate and adapt in the exact way it needs to hold on to your defenses and multiply again quickly. In short, you are facing an immense variety of different enemies and you are too slow to catch up with their evolution. This is bad.

Fortunately, your immune system is just the coolest thing. The second most complex biological system we know, after the human brain, is so sophisticated that we have not yet discovered all its secrets. Therefore, we need to simplify things and focus on things one by one. If you want the whole story, wait for the notification at the end of the video! Well, why aren’t there any new bacteria and viruses that are constantly killing us?

In short, you actually have two immune systems: the innate and the adaptive immune system. The innate immune system is ready from birth.

Mostly there are general-purpose soldiers, we introduced them in the last video in the series. The adaptive immune system has two types of cells – T and B cells – which are your superweapons and are incredibly deadly and effective against your enemies. The production of these cells is complicated and takes a long time, but once they are ready, they strike hard.

What makes the adaptive immune system so strong is that it has the largest library in the universe. There is an answer to everything! You have at least one of these superweapon cells in you with the right answer against the black death, the coronavirus, and against an infection that will appear in a century on Mars. This gives you the ability to fight the ability of viruses and bacteria to change so quickly. How is that possible?

To understand, we must take a step back. All organisms on Earth are made up of the same basic parts, mostly proteins. Proteins are like the constructor of life and can have billions of different shapes, you can imagine them as parts of a 3D puzzle.

There are billions of different proteins that enemies can use to build their bodies. This is important because proteins are, in a way, the “language” of the microverse.

The cells do not have eyes and ears. To distinguish friends from enemies, they must touch them and distinguish whether the protein is part of a friend or an enemy. Therefore, cells have countless small devices called receptors that can connect to a specific piece of the puzzle. That is, your cells have small proteins on their membranes that can bind to or differentiate other proteins. When a cell connects with a protein and distinguishes it as enemy, it knows it must attack.

Only when cells can differentiate between friend and foe is the immune system able to fight off an invader. But because there are billions of possible proteins, there are billions that enemies can use. That’s why diseases like the flu come back every year: The influenza virus mutates very quickly and the proteins on the skin are constantly changing a little.

Soldiers in the innate immune system have memorized many of the proteins for common bacteria and viruses, so they are your general-purpose weapons. But they are not effective against the billions of gadgets and mutations that enemies can develop.

Therefore, the reason you are alive is that the adaptive immune system can recognize between a billion and 10 billion different enemy proteins. That’s enough to be prepared for any possible enemy. But how is this possible? How is it possible that the immune system is so diverse, and prepared for every possible enemy protein? Well.

Cells in the adaptive immune system have a trick: they mix and match their own genetic code to create this huge variety of receptors. The details are too complicated for this video, but in short, the cells of the adaptive immune system are allowed to take some of their genetic code and mix it randomly to create billions of different receptors. A good way to understand this is to imagine an army of crazy chefs where everyone wants their own special recipe.

They can choose from 100 different ingredients. Each ingredient is a tiny part of the genetic code in this metaphor. So, each chef takes a few random ingredients and mixes them randomly.

Maybe an appetizer of tomatoes, chicken, rice, and half an onion, and marshmallows, peppers, strawberries, and a quarter banana for dessert. Or cucumber, beef, potatoes, and two carrots, and blueberries, chocolate, cream with a pinch of cinnamon.

Even with small changes and only 100 ingredients, there are billions of recipes. Similarly, with few gene fragments, your cells make billions of receptors. The details are so cool that they deserve a whole video dedicated to them. Or a whole chapter in a book. However, by mixing gene fragments, you can get up to 10 billion different combinations.

Finally, you get billions of immune cells, each of which has a unique receptor – the dish of our metaphor – that is able to recognize a specific protein. In total, you have at least one cell for every enemy that could exist. But here we come across a very dangerous problem. Once the adaptive immune system creates superweapons for every possible protein in the universe.

. won’t it create some that will recognize your cells? Yes, it happens all the time.

It’s so ingrained in your survival that you have a whole body working just to prevent it: Thymus Murder University. The thymus is a chicken wing-like organ located above your heart.

You probably haven’t heard it. Interestingly, the thymus is one of the reasons that the immune system weakens as you age because it constantly deteriorates as you go through puberty. But what does the thymus do? At the University of Murder, adaptive immune cells must undergo intensive and lethal training.

In short, their immune system shows them all the proteins that your cells use to see how they will react.

If a young cell recognizes a protein used by your body and wants to attack it, their teachers order them to commit suicide and they are swallowed and recycled. The immune system is so strict that about 98% of the adaptive immune cells that enter this university die there. 2% complete the training and start their work: to protect you. If something goes wrong and cells come out that can recognize your proteins, it can lead to autoimmune diseases in which the immune system attacks your body from within. And this, again, is a fairy tale for another time.

Okay, let’s summarize. The immune system has two parts. One protects you from birth, and the other carries the largest library of superweapons in the universe but must be loaded first. To create billions of different superweapons, adaptive immune cells recombine part of their own genetic code and create a great variety of weapons.

Then, they enter a homicide university, which only 2% survive so they don’t attack you.

And so you have billions of different cells that are able to protect you against every possible enemy in the universe. I’m waiting. If this is true, why do we get sick at all? Why do new diseases like Covid-19 appear and kill millions? All we have learned is just a tiny part of the struggle for survival that happens in your body every day, and there are many more great details and questions: how does your body manage to find the right cell in time, to protect you?

How do your enemies manage to fight your immune system? What about the things that didn’t fit in this video? [A book on the immune system written by the founder of the Kurzgesagt was published on 2021-11-02! Link in the description.]

As found on YouTube

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