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

Book Preface

IMAGINE WAKING UP TOMORROW, FEELING a bit under the weather. An annoying pain in your throat, your nose is runny, you cough a bit. All in all, not bad enough to skip work, you think, as you step into the shower, pretty annoyed about how hard your life is. While you are totally not being a whiny little baby, your immune system is not complaining. It is busy keeping you alive so you can live to whine another day. And so, while intruders roam your body, killing hundreds of thousands of your cells, your immune system is organizing complex defenses, communicating over vast distances, activating intricate defense networks, and dishing out a swift death to millions, if not billions, of enemies. All while you are standing in the shower, mildly annoyed.
But this complexity is largely hidden.
Which is a real shame because there are not many things that have such a crucial impact on the quality of your life as your immune system. It is all-embracing and all-encompassing, protecting you from bothersome nuisances like the common cold, scratches, and cuts, to life-threatening stuff from cancer and pneumonia to deadly infections like COVID-19. Your immune system is as indispensable as your heart or your lungs. And actually, it is one of the largest and most widespread organ systems throughout your body, although we don’t tend to think about it in these terms.
For most of us, the immune system is a vague and cloud-like entity that follows strange and untransparent rules, and which seems to sometimes work and sometimes not. It is a bit like the weather, extremely hard to predict and subject to endless speculations and opinions, resulting in actions that feel random to us. Unfortunately many people speak about the immune system with confidence but without actually understanding it, it can be hard to know which information to trust and why. But what even is the immune system and how does it actually work?

Understanding the mechanisms that are keeping you alive as you read this is not just a nice exercise in intellectual curiosity; it is desperately needed knowledge. If you know how the immune system works, you can understand and appreciate vaccines and how they can save your life or the lives of your children, and approach disease and sickness with a very different mindset and far less fear. You become less susceptible to snake oil salesmen who offer wonder drugs that are entirely devoid of logic. You get a better grasp on the kinds of medication that might actually help you when you are sick. You get to know what you can do to boost your immune system. You can protect your kids from dangerous microbes while also not being too stressed-out if they get dirty playing outside. And in the very unlikely case of, say, a global pandemic, knowing what a virus does to you and how your body fights it, might help you understand what the public health experts say.
Besides all these practical and useful things, the immune system is also simply beautiful, a wonder of nature like no other. The immune system is not a mere tool to make your cough go away. It is inextricably tied into almost all other processes in your body—and while it is centrally important to keeping you alive, it is likely that it may also be the part of your body that causes your untimely death, either by failing or by being too active.
I have been fascinated and obsessed by the incredible complexity of the human immune system for the better part of a decade now. It began in university where I was studying information design and was looking for a semester project and the immune system seemed like a good idea. So I got a large pile of books about immunology and began digging in, but no matter how much I read, things just did not get less complicated. The more I learned the more impossible it seemed to simplify the immune system as every layer revealed more mechanisms, more exceptions, more complexity.
And so a project that was supposed to last the spring took over the summer and then the fall and the winter. The interactions of the parts of the immune system were too elegant and the dance they danced was too beautiful to stop learning about them. This progress fundamentally changed how I experienced and felt about my body.
When I got the flu I could no longer just complain, but had to look at my body, touch my swollen lymph nodes, and visualize what my immune cells were doing right then, which part of the network was activated, and how T Cells killed millions of intruders to protect me. When I cut myself while being careless in the forest I felt gratitude for my Macrophages, large immune cells hunting scared bacteria and ripping them into pieces to protect the open wound from infection. After taking a bite of the wrong granola bar and suffering an allergic shock, while being rushed to the hospital, I thought about Mast Cells and IgE Antibodies and how they had almost killed me in a misguided attempt to protect me from scary foodstuffs!
When I was diagnosed with cancer at the age of thirty-two and had to undergo a couple of operations and then chemotherapy, my obsession with immunology became even more intense. One of the jobs of my immune system is to kill cancer. In this case, it had failed.
But I somehow could not be angry or too upset as I had learned how hard of a job this was for my immune cells and how hard cancer had to work to keep them in check. And as the chemo melted the cancer my thoughts again went to my immune cells invading the dying tumors and eating them up one cell after another.
Disease and sickness are scary and unsettling and I’ve had plenty of that in my life. But knowing how my cells, my immune system, this integral and personal part of myself, defended the entity that is me, how it fought and died and healed and restored this body I inhabit, always gave me a lot of comfort. Learning about the immune system made my life better and more interesting and it alleviated a lot of the anxiety that comes with being sick. Knowing about the immune system always put things in perspective.
So because of this positive effect and just because of the fun of learning and reading about the immune system, it became an ongoing hobby, as I eventually became a science communicator and explaining complex things became my purpose in life. About eight years ago I started Kurzgesagt—In a Nutshell, a YouTube channel dedicated to making information easy to understand and beautiful, while trying to be as true to the science as possible. In early 2021 the Kurzgesagt team has grown to over forty people working on this vision, while the channel has attracted over fourteen million subscribers and reaches about thirty million viewers each month. So if this large platform exists, why go through the horrible process of writing this book? Well, while some of our most successful videos have been about the immune system, it has always bugged me that I could not explore this wonderful topic in the depth it deserves. A ten-minute video is simply not the right medium for that. So this book is a way to turn my decade-long love affair with the immune system into something tangible that will hopefully be a helpful and entertaining way to learn about the stunning and beautiful complexity that makes it possible for you to survive each day.
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.
The bigger the immunology textbook you read, the more layers of detail start piling on, the more exceptions to rules appear, the more intricate the system becomes, the more specific it seems to be for every possible eventuality. Every single one of its many parts has multiple jobs and functions and areas of expertise that overlap and influence each other. Even if you make it past these challenges and still want to understand the immune system, you will encounter another problem: The humans who described it.
Scientists have laid the foundation for the amazing modern world we get to enjoy today through hard work and endless curiosity and we owe them a great deal of gratitude. Unfortunately, though, many scientists are really bad at choosing good names and coming up with accessible language for the things they discover. The science of immunology is one of the worst culprits of any scientific discipline in this regard. An already breathtakingly complex field is spiked with words like Major Histocompatibility Complex class I and II, gamma delta T Cells, interferon alpha, beta, gamma, and kappa, and the complement system, with actors named C4b2a3b complex. None of this makes it a pleasure to pick up a textbook and learn about the immune system on your own. But even without this barrier, the complex relationships of the many different actors of the immune system, with countless exceptions and unintuitive rules, are a challenge all by themselves. Immunology is hard even for the people working in public health, even for the people studying immunology, even for the foremost experts in the field.

All of this makes the immune system horrible to explain. If you venture too far into simplification you deprive the learner of the beauty and wonder that lie in the evolutionary genius of the sheer endless complexity that deals with the most crucial problems of living beings. But if you include too much detail, it quickly becomes mind-numbingly hard to keep up with. Listing everything, every part of the immune system, is just too much. It would be like telling someone your whole life story on the first date: Overwhelming and very likely to make them less interested in dating you.
So my aim for this book is to try to carefully dance around all these problems. It will use human language and use complicated words only when necessary. Where appropriate, processes and interactions will be simplified while staying as true to the science as possible. Complexity between chapters will go up and down, so after you are fed a lot of information, there will be more chill parts to relax a bit. And we will summarize what we learned in regular intervals. I want this book to make it possible for everybody to understand their own immune system and have a bit of fun doing so. And since this complexity and beauty are deeply connected to your health and survival, you might actually learn something useful. And of course, the next time you are sick or have to deal with disease, you hopefully can look at your body from a different perspective.
Also, the obligatory disclaimer: I’m not an immunologist, but a science communicator and immune system enthusiast. This book will not make every immunologist happy—what became obvious right from the start of the research is that there are a lot of different ideas and concepts about the details of the immune system and there is a lot of disagreement between the scientists holding these ideas. (Which is how science is supposed to work!) For example, some immunologists consider certain cells useless fossils, while others think they are crucial for your defenses. So as much as possible this book is based on conversations with scientists, the current literature that is used to teach immunology, and peer-reviewed papers.
Still, at some point in the future, parts of this book will need an update. Which is a good thing! The science of immunology is a dynamic field where a lot of amazing things are happening and different theories and ideas are in flux with each other. The immune system is a living topic where great discoveries are still happening. Which is great, because it means we are learning more about ourselves and the world we live in.
OK! Before we jump in and explore what your immune system is doing, let us define the premise first, so we have solid ground to stand on. What is the immune system, what is the context it works in, and what are the tiny parts that do the actual work? After we have covered these basics we will explore what happens if you hurt yourself and how your immune system rushes in to defend you. Then we’ll explore your most vulnerable parts and see how your body scrambles to protect from a serious infection. And lastly, we’ll take a look at different immune disorders like allergies and autoimmune disease and discuss how you can boost your immune system. But now let us get to the very beginning of this story.