You are not a human being, but a planet of about 40 trillion cells. Your cells are so numerous that if they were the size of a human, you would be as large as 20 Mount Everest. For reptiles, this is an ecosystem rich in resources, heat and space for your body. It is a perfect place to move and get married. Although some of these guests are welcomed, most are not accepted. Your immune system is the guardian of this planet, a force responsible for protecting yourself from the constant threat of occupation. Unfortunately, your enemies in a small world have a great advantage. Think of the effort it takes to create a copy of yourself and trillions of cells. First, you need to find someone who thinks you are beautiful, then go to a meeting with him and sit there anxiously, and if he goes to work in a complicated dance, your two cells will unite. Then you have to wait for months until the cell multiplies many times and opens its eyes to the world as a human being.
Even then, it will take years for your mini copy to become less useful. The bacterium consists of one cell. He can create a fully mature copy of himself in about half an hour. A virus can turn into hundreds of hours and billions of days. Your enemies are multiplying faster than you. Worse, it is an hostile ecosystem in which your body exerts selective pressure on a bacterium or virus. Because they change generations so rapidly, they will eventually become individuals who, by chance, mutate and adapt properly to resist your defenses, and then multiply rapidly again. In other words, you encounter an infinite number of different enemies and you are too slow to keep up with their evolution. This is bad. Fortunately, your immune system is the most amazing thing that has ever existed. It is the second most complex biological system known to us after the human brain, and it is so complex that we have not yet discovered all its secrets.
Because it is so complex, we need to simplify it and focus on only one thing at a time. If you want the whole story, wait for the announcement at the end of the video! So why aren't we all killed by some new bacteria or viruses? In short, you actually have two immune systems, the innate and the adaptive immune system. Your innate immune system was ready when you were born. It consists mainly of general-purpose soldiers, which we presented in our last immune video. The adaptive immune system is your super weapon and carries two types of cells: T cells and B cells, which are incredibly effective and deadly for your enemies. The production of these cells is complex and takes a long time to place, but once ready, they strike a real blow. What makes your adaptive immune system so strong is that it has the largest library in the universe.
He has the answer to everything. At least one of these super-weapon cells is present inside you to fight black death, the coronavirus, and the first deadly bacteria that will appear in any city on Mars a hundred years from now. This allows you to resist the rapid change of bacteria and viruses. How is this possible? We need to take a step back to understand what is happening here. All organisms on Earth are made up of the same basic components, especially proteins. Proteins are the cornerstones of life and can take billions of different shapes – you can imagine them as pieces of a 3D puzzle. There are billions of different puzzle pieces that your enemies can use to build their bodies. Why is this important? Because proteins are, in a sense, the "language" of the microcosm.
Cells do not have eyes or ears, so they must touch them to distinguish a friend from an enemy, and understand that their protein is part of a friend or foe. Recognition means that cells have countless tiny devices called receptors that can communicate with a particular protein puzzle piece. That is, the outer parts of your cells have small puzzle parts that can connect to each other or recognize other protein puzzle parts. The cell knows that it must attack when it combines with a protein and recognizes it as an "enemy." Only if your cells can make this difference between friend or foe can your immune system fight the invader. However, since there are billions of possible protein puzzle pieces, this means that there are billions of possible enemy puzzles. This is also one of the reasons why we still have to fight diseases like the flu every year – the flu virus mutates very quickly, and therefore the proteins that make up its body are constantly changing. Soldiers of your innate immune system have many puzzle pieces for common bacteria and viruses, so they are your all-round weapons. But they are ineffective against billions of mutations and adaptations that your enemies can develop.
So the reason you still survive is that your adaptive immune system can recognize between one billion and tens of billions of different enemy protein puzzle pieces, which is enough to be ready for any possible enemy. But how is this possible? How can your immune system be so diverse to be prepared for every possible protein puzzle? The cells of your adaptive immune system have found a trick code: they mix and match their genetic codes to create receptors for this amazing variety. The details are too complicated for this video, but in short, your adaptive immune cells have official permission to take a small fraction of their genetic code and mix them randomly in order to create billions of different receptors.
A good way to explain this is to imagine an army of chefs who want each to have their own recipe. They have 100 different ingredients to choose from. Each ingredient refers to a small piece of genetic code in this metaphor. Thus, each cook takes a few random ingredients and mixes them at random. Maybe a quarter of tomatoes, chicken, rice and half an onion as a meal, marshmallows, peppers, strawberries and a quarter of a banana as a dessert.
Or cream with cucumber, beef, potatoes and two carrots, blueberries, chocolate and a pinch of cinnamon. Even with a small assortment and only 100 ingredients, billions of possible recipes can be prepared. Similarly, with a small selection of gene fragments, your cells create billions of receptors. The details are so beautiful that they need to have a separate video or chapter in the book. In any case, by mixing gene fragments, you get up to tens of billions of different combinations.
As a result, you get billions of immune cells, and each of them has a special and unique receptor, that is, they have food, as in our metaphor, they are also able to recognize a particular piece of protein puzzle. In total, you get at least one cell for each enemy that may exist. But here we face a very dangerous problem – if your adaptive immune system produces weapons that can attack all the possible protein puzzles in the universe …
Doesn't it also create those that attack your own cells? Yes, it always happens. It is so dangerous for your survival that you simply have an organ working to prevent it: the University of the Thymus Murder. Your thymus is a chicken wing-sized organ above your heart, and you've probably never heard of it. Interestingly, the thymus gland is one of the reasons for the weakening of your immune system as you age, as it constantly begins to decline after puberty. What does the thymus gland do? At your university of murder, your immune system places your adaptive immune cells in a tight and deadly curriculum. Basically, all kinds of protein puzzles used by your own cells show them how to react. When a young cell recognizes a part of the body puzzle and wants to attack it, the teacher commands the cells to kill themselves, and they are eaten and processed.
The immune system is so special in this process that about 98% of the adaptive immune cells that enter the university of murder die there. Only 2% graduate and do their job to really protect you. If this process goes wrong and cells that can recognize your own protein puzzles escape, it can lead to an autoimmune disease in which your immune system attacks your body from within. And this is a different story to be told about another time. Well, let's summarize. Your immune system is made up of two parts, one that protects you immediately after birth, and the other that carries the largest library of super weapons in the universe, but it must first be activated. To create billions of different super weapons, your adaptive immune cells reunite part of their genetic code to create a variety of deadly attack weapons. Then they enter a murder university where only 2% survive to make sure they don't attack you. And then you get billions of different cells that can generally protect you from every possible enemy in the universe.
Now wait a second. If all this is true, then why do we get sick in general? Why did a new disease like Covid-19 kill millions? Everything we have just learned is a very small window into the amazing life-and-death struggle that takes place in your body every day, and there are many amazing details and questions: How does your body actually find the right cell to protect you in time? How do your enemies resist and overpower your immune system? What about all the things that aren't in this video? Finally, today is the release of the book "Journey to the mysterious system that keeps you alive" written by Philipp Dettmer, founder and editor-in-chief of Kurzgesagt. At first we had to delay the release due to a cargo problem, and then we didn't have enough copies for the original release date because many of you had pre-ordered! Thank you very much for that! Immunity tells the epic story of your immune system and will forever change the way you think about your body, how you experience being sick and healthy.
The book is written to be as entertaining and easy to understand as Kurzgesagt's videos, but it can delve deeper into the subject. So, travel in your secret micro-universe. Witness the deadly wars between billions of invaders and cells, learn how your immune system actually works and how it protects you from cuts, cancer and Jovid. Never before has there been such an urgent need to learn how immunity works. Immune is fun, great to look at and even smells good. To order today, check the link in the description. This is the end of our decade-long personal journey, and we thank each and every one of you for your support. Thank you very much for watching and reading..