Immune: A Journey Into the Mysterious System That Keeps You Alive

by Philipp Dettmer

Unfortunately, the immune system is very complicated, although that is not strong enough a word. The immune system is complicated in the sense that climbing Mount Everest is a nice stroll through nature. It is intuitive like reading the Chinese translation of the tax code of Germany is a fun Sunday afternoon. The immune system is the most complex biological system known to humanity, other than the human brain.

At its very core, the immune system is a tool to distinguish the other from the self.

How crucial health is becomes the most apparent when it is missing. Health is really an abstract concept because it describes the absence of something. The absence of suffering and pain, the absence of limitations. If you are healthy, you feel normal, you feel right. Once you witness your health go away, even for a brief time, it is hard to forget how fragile you are and how much you are living on borrowed time. Disease is an unavoidable fact of life. If you have been lucky, you have not had to face it up to this point. If you or one of your loved ones has had to deal with it already, you know that nothing is more elemental for a pleasant life than being healthy.

In fact, while you were reading the last few pages, somewhere inside you a young cancer cell was quietly eliminated by your immune cells.

An allergic shock shows strikingly how truly powerful your defense system is and how horribly it can go wrong: it may take a disease days to kill you—your immune system can do so in minutes.

The collateral damage your defense networks dish out against you can build up over time and today it is thought that many deadly diseases start with your immune system working as intended. So as important as it is for your health to have an immune system that is fast and brutal, it is just as important to keep it in check and prevent it from becoming unhinged and destructive. Just like in the human world, if you need to go to war, you at least want your wars to be over quickly and end with a clean victory. You don’t want decades of occupation or conflict that eat up resources and leave destroyed infrastructure.

If you were the size of one of your cells, the body of a human would be in the area of fifteen to twenty Mount Everests stacked on top of each other.

Overall, an average square centimeter of your skin is home to around a million bacteria.

pH is one of those things that is often not properly explained or quickly forgotten once it is. For once, scientists gave something a great name: pH is short for POWER OF HYDROGEN, which is exciting and easy to remember. But then scientists decided to abbreviate it. Disappointing to say the least. Without getting too deep into it, the POWER OF HYDROGEN is a scale that describes how many hydrogen ions are present in a water-based solution.

You probably learned in school that mitochondria, the powerhouse of the cell, were ancient bacteria that merged with the ancestors of your cells to become a symbiotic organism. Today they are organelles inside your cells that provide the cell with useful energy. Your immune system still remembers them as bacteria though, as intruders that have no business being outside cells. So if your cells burst and your immune system detects mitochondria floating around, your immune cells will react super alarmed.

Sperm cells do use a long and powerful flagellum to move forward (which are technically different structures that work differently but are called the same because hey, biology is not confusing enough apparently). But sperm is a fascinating example in any case. Think about it, why does the body of a woman not recognize sperm cells as other and kill them right away? Well, it does! This is one of the reasons you need about 200 million sperm cells to fertilize a single egg!

Right now your Adaptive Immune System has a specific weapon against every possible enemy in the universe. For every single infection that has ever existed in the past, for all of them in the world right now, and for every single one that might emerge in the future but does not even exist yet. In a way, the largest library in the universe.

while your adaptive immune system has billions of different cells, each with a receptor for every possible enemy, it only has maybe ten to a dozen cells with each unique receptor.

You find potential partners with MHC molecules that are different from yours more attractive! OK wait, what? How would you even know this? Well, you can literally smell the difference! The shape of your MHC molecules does influence a number of special molecules that are secreted by your body—which we pick up subconsciously, from the body odor of other people—so you communicate what type of immune system you have through your individual smell!

In German there is even a popular saying “Jemanden gut riechen können,” literally translated “being able to smell someone very well,” which means “liking someone on an intuitive level.” This smell thing is a real thing!

Saliva contains a number of chemicals that help break down your food, so digestion really begins right after you begin eating. This makes sense, because as food is funneled through you, there is only a limited time window to extract the resources, so better start as soon as possible.

So a lot of IgA can create huge clumps of helpless bacteria that are transported out of the body as part of your poop. All in all, around 30% of your poop consists of bacteria—and a lot of them have been clumped up by IgA Antibodies (most disturbingly, around 50% of them are still alive when they leave you).

There is evidence that thousands of years ago eating the feces of animals was used to treat stomach and gut-related problems and diseases.

Though it’s fun to imagine, your lungs are actually not big balloons, but in a way much like dense sponges with countless nooks and crannies. The parts of your lungs that do the actual breathing have an enormous surface area, in excess of 145 square yards (120 square meters)—more than sixty times the surface of your skin.

We talked about cytokines a bunch in this book—the amazing proteins that transmit information, activate cells, lead cells to the site of a skirmish, or make immune cells change their behavior. In short, cytokines are the molecules that activate and guide your immune system.

There is the common wisdom that the color of your snot can tell what kind of infection you have and if it is just a cold or a flu, but that is not true: the color just tells you how severe the inflammatory reaction inside your nose is, not what caused it. The more colorful, the more Neutrophils have given their life.

Why do you lose your appetite when you are sick? Well, you can blame the onslaught of cytokines that your immune system releases for that. The cytokines signal your brain that a serious defense is happening at that very moment that the body needs to conserve energy for. Because as you may imagine, mobilizing millions or billions of cells for a fight is a pretty resource-heavy operation. Digesting food actually requires a lot of energy too, so shutting these processes down is freeing up your system to focus on the defense. It also reduces the availability of certain nutrients in your blood that your invaders would love to get their tiny pathogenic hands on. This does not mean that you should actively try to starve out a disease. Not digesting is a short-term strategy not a long term solution and in chronically ill people, the lack of appetite can lead to dangerous weight loss. So if you feel hungry again you can eat something to refill your energy storage.

So you have an immune memory, and it is a living thing! Or many living things, as we introduced briefly before: Memory Cells. Approximately 100 billion living beings, 100 billion parts of YOU, sitting all over your body, doing nothing but remembering what you went through. Isn’t this a tiny bit poetic, the fact that being immune means that there is a part of you remembering your struggles and making you stronger by its presence?

The human genome project found the genetic remains, living fossils, of thousands of viruses in our DNA, comprising up to 8% of our genetic code. So in a sense you are 8% virus.

your immune system is much more dangerous to your survival than any pathogen ever could be. Think of Ebola, even this pretty disgusting and horrible disease needs about six days to kill you. Your immune system has the power to kill you in about fifteen minutes.

So what can you take away from this chapter? Wash your hands at least every time you use the restroom, clean your apartment but don’t try to sterilize it, and clean the tools you use to prepare food properly. But let your kids play in the forest.

All in all, the easiest way to get cancer is to be alive long enough. It is statistically impossible to not develop some cancer at some point in your life, even if it ends up not being the cause of your death.

by being told that you are supposed to be positive to get well, you are told that you are not allowed to feel how you feel. But expressing how unwell you are and asking for an open ear or love is important because it can help you deal with very strong negative emotions caused by fear and very unpleasant treatments that you have to endure. Being more positive and having a good attitude towards life and its challenges makes your life better.