Immunological System — the private army inside your body
Ever felt like you’re useless, cursed by every possible plague, with runny nose, aches everywhere and no desire to live whatsoever?
Do you feel like that right now? That’s actually good. Your body is now trying to make your life hell, so that the bacteria, fungi and viruses invading your system can feel pretty bad, too. How does it work? And why your cold takes 7 days regardless of the amounts of vitamin C you take?
Every day your body is under constant attack. Bacteria, fungi and viruses are viscously observing you all the time.
That’s why you need an immunological system. A complex and sophisticated defence barrier that keeps you from… well… dying. Let’s have a look at what types of defence are available:
No wonder you’re such a worthy target. You’re warm, moist, full of nutrients and minerals. Everything they need to live and thrive is readily available…
Imagine a normal day, when suddenly, you cut yourself
What a mess! You've just breached the first barrier of your defence. Your skin is no longer protecting you, and the bacteria are free to enter your system. They will be using up all the goodness of your blood… these yummy nutrients will help them grow and double in size approx. every 20 minutes.
Something’s not right. These little invaders are now changing the environment around, to suit them. What a poor manner! It’s time to kick’em outta here.
Macrophages
They are big, lumpy creatures who travel through your body in the search of something that’s simply not right. Just look how cute (and powerful) they are!
They will try to engulf the bacteria and trace them until they’re eaten up. They can catch and kill up to 100 bacteria each. Impressive stuff.
They can’t cope with it now. Let’s call some help
The immunological system has its own language and signalling. White blood cells will leave some proteins, called interleukins; they’re something like the smell of cake in cartoons (remember Tom&Jerry, with Tom flying by the smell of cake?), other cells will follow the smell, until they can find the battlefield.
Neutrophiles
Now, these are the bad guys. They have multiple detectors to spot the invaders, and quite a few weapons, too.
So, what they can do to fight off the intruders?
- lower the pH to around 3.5–4.0 (making your life hell, again)
- release toxic molecules (e.g. O2-, H2O2, OCl-, NO, etc.)
- throw defensins and catonic proteins (myeloperoxisase, lyzosomes, acid hydrolyses, to dissolve cell walls and digest bacteria)
- compete for food and block bacteria from getting it, thus starving them to death (yeah, take that, bac!)
They’re so aggressive that they’ll destroy everything in their sight.
Now, get that: they even fight so furiously, that they will commit suicide after 5 days, because they know that otherwise, they’ll hurt you. That’s a cute story, isn’t it? And, they make something super-cool at the end. They literally BURST and throw all nasty stuff from inside to the bacteria + they do that so intelligently that the intruders will be trapped by their corpses.
Natural Killer Cells
Pretty cool name, huh? These guys are a bit more intelligent. Whilst most of the first phase response is pretty much #Let’sDestroyEverything, and maybe #SomeOfItWillBeRight thing #YOLO, the NK cells have a way to recognise special ligands (MHC-I), and say
“Hey, you… yes, I’m talking to you. Show me your MHC-I! (NK connects to you), oh you HAVEN’T GOT one? Though luck. (NK injects deadly poison inside you) (you die)”
Classic history of my life.
NK cells will also order Macrophages to fight more passionately and not to stop. They will be on the battlefield, making speeches and motivating others to fight.
Fun fact: Some viruses can forge the MHC-I and appear as if they’re normal cell of the body… but that’s for another time.
Bacteria are growing faster. We need more help. Now!
Dendrite cells
The immune’s system pervert uncle. Yes, these are the cells with tentacles, walking around, touching everything, wobbling through capillaries, slapping and sampling. They then eat and look at all the random stuff they’ll find.
They’re pretty smart, too. Dendrite cells will learn from what they see, feel or eat, and they have very smart decision to make. Now, they've just received an SOS from the battlefield.
‘Well, our lads seem to have a bit of a struggle down there,’ they’ll say
‘What shall we do? Do we activate a virus response pathway or bacterial one? Do we look up a strategy from our memory or do we compose a new defence system? Perhaps we should engage these cells, and shut down those for the optimal response,” they wonder, before making a decision.
Now, take that: making a decision. These little guys will have to make intelligent guesses, take risk, command the cell armies and decide what strategy is best for you. Once they’ve taken one decision (e.g. to fight off the viruses), there’s little way back.
Imagine, how a little cell can take so much responsibility and get it right almost all the time? Their decision will make a difference between just an ordinary cold and a life-threatening situation.
Good. Let’s activate some antibacterial stuff. T-cells ready?
Lazy but educated
If we think of the neutrophiles as Rambo-like killing machines, who will simply massacre everything around them in a furious and deadly attack,
T-cells are silent and super precise snipers.
Before they could be where they are now, they needed to travel to T-cell’s university. It’s called thymus (near your heart). There, they have learned about bacteria, viruses, different types of defence and how to recognise the threat. They would then pass very strict exams (with pass rate of 5% for some). This will be in my next article, so stay calm for now.
The thing is, they have now been through all that education and exams, and they’d rather sit comfortably in the lymph nodes, showing their superiority and awesomeness, than go do the hard work
(Like the post if you know someone behaving like that, though!)
Dendrite cells will come to the lymph nodes and wake them up. They will then start multiplying and travelling to the battlefield, when they could finally kill some invaders.
T-cells will also take over the command of the battle, and send the NK cells off. They will then release massive stimuli to all other cells to fight their socks (or cytoplasms) off.
B-cells will also come to help. They will take orders from T-cells and be stimulated to push their abilities to the limit.
The battle nears its end
Finally, the B-cells will start produce antibodies. They will attach to the invaders and not only make them more visible, but also destabilise them and eventually kill the pathogens altogether.
Once this is done, most of the cells will have died from exhaustion or lack of signals to live. Some will commit suicide, not to waste any more of your resources.
Don’t worry about the damages — your body will get your cells back shortly. You’ll need some time to recover, but we can put you back on the go. Your fever and feeling of uselessness will go away, and you’ll feel much better.
Now, some of the cells will not die. They will save up the details of the invaders, so that next time, we know how to fight it off more efficiently. They will also serve as ‘encyclopaedia’ of pathogen, and cells will be free to consult it, if they want to learn more.
Pretty cool and sophisticated, huh?
Yes. This is overly simplified and has a lot of shortcuts, but you get the point, right? Next time, I’ll talk a bit more about the T-cells learning, how B-cells produce antigens and how to make the system more intelligent.
For now, I hope you enjoyed it and start to realise how much is going on right in your body, to protect you every day.
If you want to have a quick recap, why don’t you look through the Kurzgesagt video? They made it really nicely!
Thanks for reading and I look forward to your comments!
