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NEW YORK TIMES BESTSELLER A gorgeously illustrated deep dive into the immune system that will forever change how you think about your body, from the creator of the popular science YouTube channel Kurzgesagt In a Nutshell
 
Through wonderful analogies and a genius for clarifying complex ideas, Immune is a truly brilliant introduction to the human body s vast system for fighting infections and other threats. John Green, #1 New York Times bestselling author of The Fault in Our Stars

You wake up and feel a tickle in your throat. Your head hurts. You re mildly annoyed as you get the kids ready for school and dress for work yourself. Meanwhile, an epic war is being fought, just below your skin. Millions are fighting and dying for you to be able to complain as you head out the door.
 
 But most of us never really stop to ask: What even is our immune system?

Second only to the human brain in its complexity, it is one of the oldest and most critical facets of life on Earth. Without it, you would die within days. In Immune, Philipp Dettmer, the brains behind the most popular science channel on YouTube, takes readers on a journey through the fortress of the human body and its defenses. There is a constant battle of staggering scale raging within us, full of stories of invasion, strategy, defeat, and noble self-sacrifice. In fact, in the time you ve been reading this, your immune system has probably identified and eradicated a cancer cell that started to grow in your body.

Each chapter delves into an element of the immune system, including defenses like antibodies and inflammation as well as threats like bacteria, allergies, and cancer, as Dettmer reveals why boosting your immune system is actually nonsense, how parasites sneak their way past your body s defenses, how viruses work, and what goes on in your wounds when you cut yourself.

Enlivened by engaging full-color graphics and immersive descriptions, Immune turns one of the most intricate, interconnected, and confusing subjects immunology into a gripping adventure through an astonishing alien landscape. Immune is a vital and remarkably fun crash course in what is arguably, and increasingly, the most important system in the body.

Immune is science communication at its most lucid and exhilarating, a tour de force of demystification. Dettmer maintains an intimate relationship with the reader while revealing the Homeric dramas that routinely unfold within us. It has a vivid clarity that never comes at the expense of the science or the wonder, as if an entire scientific field had been translated into human. Ann Druyan, author of Cosmos: Possible Worlds

Philipp Dettmer has a unique skill to show us the beauty and complexity of our world as it is revealed through a scientific understanding of it. In Immune he takes us on a tour through our own body and allows us to see and understand how our immune system actually works. A beautiful book about a complex system that our life depends on. Max Roser, founder of Our World in Data

Immune reads like it s a riveting sci-fi novel, as Philipp Dettmer takes you on a journey into the body for an up-close look at the armies of expert warriors, rogue gladiators, and stealthy detectives that protect you in the daily war against trillions of ruthless microbe enemies. By the end of the book, I understood my entire body far better than I ever had before. Immune is a delightful treat for the curious. Tim Urban, creator of Wait But Why

Bringing both insight and humor to an important and relevant topic, Dettmer s book is essential reading, especially in light of the COVID-19 pandemic. Library Journal

1

What Is the Immune System?

The story of the immune system begins with the story of life itself, almost 3.5 billion years ago, in some strange puddle on a hostile and vastly empty planet. We don t know what these first living beings did, or what their deal was, but we know they very soon started to be mean to each other. If you think life is hard because you need to get up early in the morning to get your kids ready for the day, or because your burger is only lukewarm, the first living cells on earth would like a word with you. As they figured out how to transform the chemistry around them into stuff they could use while also acquiring the energy needed to keep going, some of the first cells took a shortcut. Why bother with doing all the work yourself if you could just steal from someone else? Now, there were a number of different ways to do that, like swallowing someone else whole, or ripping holes into them and slurping out their insides. But this could be dangerous, and instead of getting a free meal, you could end up as the meal of your intended victim, especially if they were bigger and stronger than you. So another way to get the prize with less of the risk might be to just get inside them and make yourself comfortable. Eat what they eat and be protected by their warm embrace. Kind of beautiful, if it wasn t so horrible to the host.

As it became a valid strategy to become good at leeching from others, it became an evolutionary necessity to be able to defend yourself against the leeches. And so microorganisms competed and fought each other with the weapons of equals for the next 2.9 billion years. If you had a time machine and went back to marvel at the wonders of this competition, you would be pretty bored, as there was nothing big enough to see other than a few faint films of bacteria on some wet rocks. Earth was a pretty dull place for the first few billion years. Until life made, arguably, the single largest jump in complexity in its history.

We don t know what exactly started the shift from single cells that were mostly on their own to huge collectives working closely together and specializing.

Around 541 million years ago, multicellular animal life suddenly exploded and became visible. And not only that, it became more and more diverse, extremely quickly. This, of course, created a problem for our newly evolved ancestors. For billions of years the microbes living in their tiny world had competed and fought for space and resources in every ecosystem available. And what are animals really to a bacteria and other critters if not a very nice ecosystem? An ecosystem filled top to bottom with free nutrients. So from the very start intruders and parasites were an existential danger to the existence of multicellular life.

Only multicellular beings that found ways to deal with this threat would survive and get the chance to become even more complex. Unfortunately, since cells and tissues do not really preserve well over hundreds of millions of years, we can t look at immune system fossils. But through the magic of science we can look at the diverse tree of life and the animals that are still around today and study their immune systems. The farther separated two creatures are on the tree of life and still share a trait of the immune system, the older that trait must generally be.

So the great questions are: Where is the immune system different, and what are the common denominators between animals? Today virtually all living beings have some form of internal defense, and as living things become more complex, so do their immune systems. We can learn a lot about the age of the immune system by comparing the defenses in very distantly related animals.

Even on the smallest scale, bacteria possess ways to defend against viruses, as they can t get taken over without a fight. In the animal world, sponges, the most basic and oldest of all ani

Philipp Dettmer is the founder and head writer of Kurzgesagt, one of the largest science channels on YouTube with over fourteen million subscribers and one billion views. After dropping out of high school at age fifteen, Dettmer met a remarkable teacher who inspired in him a passion for learning and understanding the world. He went on to study history and information design with a focus on infographics. Dettmer started Kurzgesagt as a passion project to explain complicated ideas from a holistic perspective. When the channel took off, Dettmer dedicated himself full-time to making difficult ideas engaging and accessible.