PREFACE
Our Hidden Army

Every epic tale needs a hero. Ours is 12 microns tall and lives for a matter of hours; it's called a neutrophil and your life depends on it. Don't be deceived by its tiny stature and minuscule lifespan; this cell can capture bubonic plague in a web of its own DNA, spew out enzymes to digest anthrax and die in a kamikaze blaze of microbe-massacring glory. The neutrophil is a key soldier in an eternal war between our bodies and the legions of bacteria, viruses, fungi and parasites that surround us. From having sex to cleaning the kitchen sink, everything we do exposes us to millions of potential invaders. Yet we are safe. Most of the time these invaders' attempts are thwarted. This is because the human body is like an exceedingly well-fortified castle, defended by billions of soldiers. Some live for less than a day, others remember battles for years, but all are essential in protecting us. This is the hidden army that we all have inside of us, and I'd like to reveal its myriad of miracles and secrets to you.

Our adventure tour will begin with a jaunt through our key defences, which include tears, snot, stomach acid and a cast of killer cells. Drawing on everything from the history of medicine to cutting-edge science, we'll explore the incredible arsenal that lives within us and how it kills off a plethora of diseases, from the common cold to the plague.

Next we'll rattle through the past, present and future of organ transplants – from the first heart transplant to lab-grown vaginas – and the vital role the immune system plays in their success or failure. While organ transplants are needed by very few of us, the truth is every single one of us is dependent on foreign cells to thrive. This will be our focus in'Outnumbered' ( Chapter 5 ) as we'll unveil the emerging evidence on the immune system's relationship with the body's billions of resident bacteria.

We'll follow this dirty revelation with some sexy science looking at the role of the immune system in our brief encounters, and maybe even love, as we dance the 'Immunological Tango'( Chapter 6 ). The chapter that follows, appropriately, will cover pregnancy. Having grown my own cutie of a parasite while writing this book, this chapter is particularly close to my heart as it tells the tale of how the immune system allows, and actually encourages, a baby to thrive, despite being a foreign invader.

Of course not all parasites are cute or precious, and in'A Palace for Parasites'( Chapter 8 ) we'll meet the creepy critters that like to call us home and the ways our immune system tries to show them the door. This includes worms that can live in your brain and how one parasite might make you want to skydive. Having come across such unpleasantries it will be a relief to read about our adaptive assassins, our T and B cells, and how we can make as many different antibodies as there are stars in the galaxy. We'll follow this by looking at how we can train these cells to do our bidding as we look at vaccines, a triumph of mankind's manipulation of the immune system that has enabled us to prevent and treat a legion of serious diseases.

However, our story won't all be rainbows and unicorns, as we will also uncover the itchy truth behind allergies and see what happens when the body overreacts to harmless things like strawberries, latex and even exercise. Continuing to cast the immune system as the villain of the piece, we will then investigate its dark side, and see what happens when it turns on the very body it exists to protect. Before we get too down on our defences, we will move to 'Defenceless'( Chapter 13 ) and dedicate ourselves to understanding the terrible consequences of a weakened immune system and how it makes a normal life near impossible.

From there we will springboard to some of the immune system's most aggressive adversaries. First up is cancer, an opponent worthy of its own chapter as we'll review why the immune system finds it such a difficult challenge and how modern medicine is trying to change that. Then in 'Killer Bugs'( Chapter 15 ) we will examine Ebola and anthrax – two of the most accomplished killers of the human race – and see why we should be afraid, very afraid.

Excerpted from Immune by Catherine Carver. Copyright © 2017 by Catherine Carver. Excerpted by permission of Bloomsbury USA. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.