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

by Philipp Dettmer

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.

sponges, the most basic and oldest of all animals, which have existed for more than half a billion years, possess something that probably was the first primitive immune response in animals.

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

If the other is not on a very exclusive guest list that grants free passage, it has to be attacked and destroyed because the other might harm you.

The goal above all things is maintaining and establishing homeostasis: the equilibrium between all the elements and cells in the body.

But health is a hard thing to maintain because every day of your life you are in contact with hundreds of millions of bacteria and viruses that would love to make your body their home,

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

many deaths from COVID-19 come from the immune system doing its job with too much enthusiasm.

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. It would be a mountain of flesh at least sixty miles (a hundred kilometers) tall, reaching into space. If you are near a window take a second and look into the sky. Try to imagine this for a moment, a giant so large that passenger planes would crash against its lower legs, its head so far above you that you would not be able to see it.

Your real weak points to infections are your mucous membranes—the surface that lines your windpipe and lungs, eyelids, mouth, and nose, your stomach and intestines, your reproductive tracts and bladder.

there are about 200 square yards (meters) of mucous membranes in a healthy adult (about the same as a tennis court), most of them being your lungs and your digestive tract.

For your cells, the surface area of the mucous membranes is as big as Central Europe

your immune system. It makes you a fortress. And even more, a fortress filled with billions of the most effective and fierce soldiers in the universe. They have countless weapons at their disposal and they use them without mercy. Your immune system army has already killed billions of enemies and parasites in your life, and it is ready to kill billions or trillions more.

A single human cell is filled up with dozens of millions of individual molecules.