You are Immune.

You’re not an individual but a planet for microorganisms; comprised of around 40 trillion cells. If your cells were human-sized, you would be as giant as 20 Mount Everests. For the weird residents in your body, your body works as an ecosystem, affluent in latitude, warmth, and resources: an ideal place to move into and maintain a family. While some of these visitors are welcome, most are not. Your immune system is the protector of this planet: your body, the force charged with protecting yourself against the ongoing threat of attack. Unfortunately, your enemies in the tiny world have a lot of benefits.

Suppose all the struggle requires to produce a single copy of yourself and your trillions of cells. The bacterium is composed of one cell. It divides too fast; it can make a fully grown copy in about half an hour. The viruses can turn into hundreds within hours and billions within days. Your foes reproduce in orders of volume faster than you. For a bacterium or virus, your body is an ecosystem facing certain pressure because microorganisms go through so many generations so fast. The microbe will be an individual who mutates and acclimates in just the suitable way to oppose your defenses and then breed quickly again. In simple words, you're encountering a mere infinite mixture of different opponents, and you’re too gradual to compete with their evolution.

Your immune system is one of the most marvelous things ever. The human immune system is the second most complicated natural process known to us after the human brain, and the developed humans still have not discovered all its mysteries. The question arises here, if there are so many microbes that are dividing at a faster rate in our body, then how are we still alive? The answer is that human has two immune systems, the innate and the adaptive immune system.

• The innate immune system was ready at the time of your birth. It consists of general-purpose fighters, mostly.
• The adaptive immune system carries two types of cells; T cells and B cells. Both the T and B cells are superweapons any human has and are extremely effective and deadly for the enemies. Those cells are difficult to create, and they carry a lot of time to deploy, but once they get ready, they're real threat for microbes.

The adaptive immune system evolves so powerfully because it holds the greatest library of cells in the universe. You have at least one of these superweapon cells inside you to combat the black demise, the coronavirus.

All living organisms on the ground are made up of the identical basic components: mostly proteins. Proteins are the building blocks of life and can have billions of different shapes. You may take proteins as 3D puzzle pieces, and there are billions of multiple puzzle pieces your enemies can use to create their bodies. Proteins are, in a way, the speech that the microworld uses, most often. Cells don’t contain eyes or ears, so to differentiate friends from foe, they have to connect them and identify if the protein is part of a friend or part of an enemy. Identifying means that cells have countless tiny receptors that can connect with a specific protein puzzle piece. So your cells have little puzzle parts on their exteriors that can connect together or recognize other protein puzzle pieces. When a cell connects with a protein and recognizes it as an enemy, it starts to attack.

Only if your cells can create this difference between friend or enemy then your immune system becomes able to combat an invader. But since there are billions of possible protein puzzle pieces: there are billions of possible enemy puzzle pieces. This is also one of the causes we still have to deal with infections like the flu every year — the influenza virus mutates very quickly, and the proteins that create up its hull frequently alter. The soldiers of your innate immune system have a large number of the puzzle pieces for common bacteria and viruses learned. But they are inadequate against billions of transformations and adaptions that your foes can evolve. So the reason you're still alive is that your adaptive immune system can identify between one billion and ten billion diverse enemy protein puzzle pieces, which is sufficient to be readied for every possible opponent. The cells of your adaptive immune system found a cheat code: mixing and matching their genetic code to create this stunning variety of receptors. The facts are too complex for this article, but, in a nutshell, your adaptive immune cells have official approval to take a tiny part of their genetic code and mix it in haphazardly to create billions of various receptors.

A better way to describe this is by requesting you to imagine an army of cooks, with each of them desiring their unique recipe. They have 100 different ingredients to choose from, and each ingredient stands for one tiny fragment of genetic code in this metaphor. So each cook takes a few unplanned ingredients, and randomly combines them. Maybe tomato, chicken, rice, onion, marshmallow, pepper, strawberries, and a quarter banana as a dessert, or cucumber, beef, potatoes, carrots, blueberries, chocolate, and cream with a pinch of cinnamon. Even with little divergence and with only 100 ingredients, there are billions of possible recipes. And likewise, with just a small sample of gene fragments, your cells create billions of receptors. In any case, by combining up gene segments, you get up to ten billion different varieties. So, in the end, you reach billions of immune cells, and each of them has one specific and unique receptor that can recognize one specific protein puzzle piece. In aggregate you end up with at least one cell for every enemy that could exist.

But, here we run into a pretty dangerous problem if your adaptive immune system is making weapons that can attack every possible protein puzzle piece in the universe, wouldn’t it also make some that can attack your cells? Yes, it happens all the time. This is so fundamentally dangerous to your survival that you have a whole organ that does nothing but work on preventing this: The Murder University of your Thymus. Your thymus is a chicken wing-sized organ above your heart, and you’ve probably never heard of it. Interestingly, your thymus is one of the reasons why your immune system weakens as you age because it is in a constant state of decline once you reach puberty.

What's the function of the thymus? In your murder university, your immune system is putting your adaptive immune cells through an intense and deadly curriculum. It is showing them all sorts of protein puzzle pieces that are used by your cells to see how they react. When a young cell recognizes a body puzzle piece and wants to attack it, the teacher cells order them to kill themselves, and they're eaten up and recycled. The immune system is so particular about this process that around 98% of your adaptive immune cells that enter murder university die there. 2% graduate and get to do their job of protecting you for the real. If this process goes wrong and cells escape that can recognize your protein puzzle pieces, this can lead to autoimmune disease, where your immune system strikes your own body from the inside.

A quick recap: your immune system has two parts, one that defends you right after birth and one that carries the huge library of superweapons in the universe but needs to boot up first. Your adaptive immune cells recombine a portion of their genetic code to construct a stunning combination of attack weapons; to create billions of different superweapons. Then they enter a slain university where only 2% endure to make sure they don't shoot you. And then you end up with billions of different cells that on whole can shield you against every potential opponent in the universe.

Now, wait a moment. If this is all correct, why do we get sick at all? Why was a new disease like Covid-19 able to kill millions of people? Everything we just learned about is just a tiny window into the amazing struggle for life and death; that recreates every day inside your body, in addition, there are so many interesting details and questions here: How does your body find the exact cell in time to rescue you? How do your opponents combat back and crush your immune system nonetheless?

And what about all the things that are not included in this article?

Disclaimer: The original version of this story's published on another platform.