Your immune system’s war isn’t Saving Private Ryan — it’s Homeland

Before I read this book, I imagined the immune system as a defensive force, like the Germans on the beaches at Normandy on June 6 1944. When you’re young and vital, your immune system is the Germans in the early morning — scanning the horizon for movement, with plenty of ammunition in reserve. But life is a process of attrition; as you get older, you become like the Germans later that afternoon — your machine guns get jammed up, and then you use rifles, and pistols, and eventually bayonets, until the invaders finally destroy you — just like the first 20 minutes of Saving Private Ryan.

That’s what I used to think. Now I’ve read this book, I see things a bit differently. Of course, I was right in part — our bodies do have a border patrol, the mucosal immune system, which is responsible for more than 300 square metres of vulnerable territory. The mucosal immune system protects the soft, wet surfaces where our bodies come into contact with the outside world — mouth, lungs, eyes, guts. Idan Ben-Barak describes it as

a collection of frontline military units engaged in a never-ending low-intensity conflict at an open border, involving a complicated relationship with the civilian population, which may or may not contain hostile elements at any given point.

Here’s the thing: as soon as you begin to scrutinise it, you see that the the conflict between disease and immunity is not like a simple battle, with clearly defined goodies and baddies blasting away at each other. It’s much more like a modern cyber-conflict. It is, says Ben-Barak, about ‘intelligence, counterintelligence… misdirection, disguise, decoy, deceit, logistics and so on’. At the cellular level, a lot of your enemies dress up to look like civilians, and sometimes they manage to brainwash civilians, who then join the enemy forces.