It’s nighttime. You’re relaxing at home reading a book on Twitter’s invention.
You’re lying on your comfy bed while enjoying some Silicon Valley drama and getting ready to sleep. And then the most horribly annoying thing happens. As you try to turn the page, the sharp edge of the page brushes against your skin. You suddenly feel a sharp pain on the tip of your index finger. Alarmed you quickly look at it only to realize that it has happened again.
A papercut. How annoying! You grab a tissue to remove the tiny drop of blood from your finger. You briefly consider picking up a sticky plaster from your first aid kit at the back of your drawer. But it’s too far and you’re too lazy to get out of your cosy blankets. Besides, it’s a papercut, right? Who cares?
A bit irritated, you finally turn the page this time without injuring yourself and continue with your thrilling story.
While you were complaining about getting a papercut, your body had a very different experience. From the perspective of your skin cells, a huge dagger just fell from the sky ripping your outer layer of skin apart. Not only that but the hundreds of thousands of bacteria¹ that were chilling² on your skin are now trying to get into the wound and make your body their home.
This is not very good if you like being alive since most bacteria will try to take your resources and make an infinite amount of baby bacteria that take even more of your resources. This keeps happening until your whole body is full of bacteria. And then you die. You die from a papercut.
Oh! And besides that, your body is leaking blood through the papercut wound. This isn’t good either and if nothing is done about it you most likely will die from bleeding.
As you might know, if you are reading this, this usually doesn’t happen (although as we both know papercuts are quite annoying)³.
Why don’t you die from papercuts?
The short answer: your immune system.
The long answer: your immune system, but it’s a bit more complicated than that.
You should be really grateful that your Immune System functions correctly. In fact, the immune system is unfairly neglected of love by the general public considering the number of crucial functions it does for you: it protects you against bacteria, viruses, parasites and especially cancer⁴.
But anyway, back to the papercut scenario. As bacteria and the corpses of your poor dead cells start to pile up, something powerful and ancient wakes up: your Innate Immune System.
As its name suggests, you’re born with this part of your immune system prebuilt in your operating system. You can imagine it as a sort of multi-use tool to take care of any disease. It’s comprised of several cells such as neutrophils, monocytes and macrophages.
The first to respond to the catastrophic disaster are macrophages. If you were the size of a cell (which is 10 to 100 μm in diameter), macrophages would be like black rhinos that swallow bacteria and do all sorts of crazy stuff.
I said “swallow”, but it gets crazier than that. Macrophages engulf bacteria by surrounding them with their own cell wall. Basically, if you were a macrophage you would surround bacteria with your own skin in an attempt to bring them inside of you. This is called phagocytosis (in scientific language). Kind of like this:
So, as hordes of bacteria start to invade your body, macrophages start “eating bacteria” and temporarily stop the invasion.
But this is not the only important thing macrophages do. They also warn everyone else by releasing signals known as cytokines. This is basically the way they have of saying “Guys! There’s a big problem over here! Please come and help me!”.
And so other cells come and join the party: neutrophils. These are equally terrifying-looking cells if not more. They have granules inside them containing very dangerous stuff.
I won’t get into what it is, but just know that bacterias really don’t like it. Neither do your cells. Essentially, it kills bacteria and cells alike.
So, neutrophils rip themselves open to release all these potent chemicals that damage bacteria. Yeah. They literally open themselves up to kill bacteria. They die so you don’t die.
Here’s an insane fact: today 100 billion neutrophils in your body died this way to protect you (and 100 billion neutrophils were also produced).
But the worst is yet to come, as Natural Killer Cells arrive on the battlefield.
Natural Killer Cells
Jeez! What a name! It’s terrifying only to hear. And do exactly what their name describes: kill. They look for any indication of something not going right in cells. And when they see something not going right they mercilessly and ferociously tell infected cells to quietly kill themselves.
Yep. This is not a joke by the way (just in case you were wondering). They basically secrete some signals that make the cell kill itself trapping all the bacteria inside them.
Coincidently, this is also how they kill cancer cells. When a cell looks stressed Natural Killer Cells detect it and kill it. This isn’t always as easy though, since cancer cells have really tricky ways of hiding their stress.
Why you don’t die from papercuts
As you’ve seen, your Immune System is no joke. It protects you against pretty much everything out there that could harm you (except Godzilla obviously).
It is as essential to your long-term survival as your heart, lungs or any other major organ you think is important.
Oh! And also thanks to the immune system, when you get a paper cut you don’t die. So that’s pretty cool.
The final player
If all of this wasn’t enough, a very powerful cell is about to emerge on the battlefield: the dendritic cell (sorry if I’m overwhelming you with names, but I’m blaming immunologists on this one).
You might be asking, what the hell is that?! And you are right, if you didn’t know you could very confidently say that this is an alien. But this octopus-like cell performs a vital function. It activates something very powerful. Something that is prepared for every disease that has existed, exists and will ever exist. Something so well prepared that gives nightmares to bacteria.
Something that we’ll see in the next blog post.
This blog post was largely inspired by the book Immune by Philipp Dettmer. Make sure to read it if you are at all interested in the immune system.
For the footnotes and to see other cool stuff go to thegreencode.org
¹ That’s right! Whether you like it or not your whole body is covered in millions of bacteria 🙂
² Actually, they were not really chilling as your skin is a very hostile place to live if you are a microbe. Your skin is covered in a fine layer of acid (not harmful to you) called acid mantle. This is not harmful to you but keeps a lot of bacteria away.
³ Unfortunately, quite a lot of people suffer from Immune System related diseases. And are unable to take that for granted.
⁴ Without a functioning and healthy immune system, it’s very unlikely to live for long. Unfortunately, this is the case for some people who suffer from Severe combined immunodeficiency (SCID), you might know them as the bubble kids. They lack a fully functioning immune system and therefore have to be kept away in “bubbles” so they don’t catch any microbe whatsoever.
Last updated: January 26, 2022