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Immunological System — the private army inside your body

Ever felt like you’re useless piece of sheet, 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.


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.


Body is now activated and ready to work together on supporting immune system!

Fun fact: You might have heard doctors saying something about your “CRP” in your blood test results. Its higher than normal levels indicate infection, because that’s what liver makes to flag up the bacteria.


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!)

Oi, mate! I didn’t get me degree for nowt, did I? I ain’t going nowhere, right?


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.

Thanks for reading and I look forward to your comments!

Oh, and final Fun fact: Although there is some evidence that taking vitamin C before you’re ill can shorten your cold by a couple of hours, it won’t do you any good if you take loads of it whilst you’re actually sick. However, taking vitamins and healthy lifestyle can boost your immunity, so that you’re not sick at all.

Prevention better than cure!

Pictures from the beginning courtesy of Kurzgesagt: In a nutshell. Explore their awesome videos and graphics here.

About the author

Max Brzezicki

Max Brzezicki

Passionate about evidence-based medicine and science, likes slicing meat, crushing rat brains, criminal & public law, foreign languages, rhetoric, history, classical studies and political thought. FNS since 2015.

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34 thoughts on “Immunological System — the private army inside your body

    1. Some day… ST, MRCS, DrPhill and stuff, then we’ll think… 🙂 thanks for nice comment hope you liked the article

  1. I really liked it. Enjoyed the read. Isn’t it a little overestimation that these cells think? It’s a bit far-fetched to me.

    1. It’s awesome, isn’t it? They really do take these decisions and are quite smart, too. Read up on them, they do some cool stuff

  2. Got to tell you it’s really nicely written. But, you said the inteleukins are left by the macrophages, wheras in fact, they are made by many cells and sometimes by other organs, this is simply not true, maybe you should read something about it before trying to impress somebody?

    1. Yes , as with all articles here, we need to strike a balance between simplification and scientific accuracy. Although this premise implies something not entirely correct, I believe it doesn’t threat the integrity of the article. Thanks for spotting!

  3. Do you genuinely expect us to believe that these little thingies can make decisions? Really? You think that because you’re an Oxford-educated fella you can speak to us like we’re infinitely inferior to your intellect? No thanks

    1. They do just that, Brigitte, and quite frankly, the reason why you can come here and comment is because they do that all the time. Isn’t that just fascinating how elegant and smart the immunological system works? It is certainly for me. To put you mind at ease, dendritre cells don’t quite differ between Oxford graduates and any other healthy human being (although I sometimes question whether the former belong to the latter) .
      Thanks for you contribution. Any questions let me know.

  4. He’d make a terrible one your thinking he must of gotten a whole loads of knowledge and he gets his shitting us books and experiments? Get lost.

    1. Thanks, Hans! I love all commentators and their contributions regardless of their quality or relevance. I really do.

    1. Thanks Fredro! I LOVE Geeky Medics. It’s a wonderful website. Actually recommended to me by one of the GPs. Basic knowledge and skills all in one place.

    1. Thank you for your comment, Theckla. I would be thrilled to have discovered anything in immunology. However, I’ll have to leave it to you and other scientists at the moment. For the time being, I shall modestly assume the role of chronicle writer in the annals of immunology. I hope that’s all right with you.

  5. How come it’s such an idiotic title? Private army? Really? I can see how little soldiers are marching through my lymph nodes…. whoa. Do I have to pay them? Maybe when they’re attacked by viruses, these will pay them more, so that infection can spread? Where’s your brain???

    1. Hi Vlad, this publication is not a peer-reviewed paper. It’s just an article for every Tom, Dick and Harry to read, enjoy, and hopefully learn and understand the basics of immunology. I hope that’s all right with you, and I’m sorry if you wanted to read something more academically challenging. I can point you to some of more detailed papers, if you wish, just drop me a line.
      Thanks for reading!

  6. I, on the other hand, would say it’s a very nicely written paper. Quite a few shortcuts, granted, but overall, it’s a very neat start to understanding the immune system. I assume you know it’s way more complicated than that.

    1. Hi John, of course it’s more complicated than that. Waaay more complicated. I’ll try to cover some more details in the second part, but I’ll have to leave some of the nitty gritty of the gourmet immunology for us to enjoy 🙂 <3

  7. Very interesting entry. Next time You may write about something greater, for example how our body combats parasites 😉 Prevention better than cure! 😀

    1. You’d be surprised, but the parasite immunology is very similar to that of viruses and bacteria, as far as first principles are concerned. Eosinophiles are the white blood cells who predominantly deal with that, and there are special classes of B-cells / antibodies predisposed to fight off the parasites. However, due to variety of parasites and vast survival intelligence of these creatures, the exact process is more complicated (and, quite frankly, not well understood) and differs depending on the species.
      Very good question, though, I really appreciate your input and your extraordinary spellchecking skills. Well done, you’re a star!

  8. I’m surprised! 😮 I thought it was another way to get rid of the parasites from the organism. Thank you for your comprehensive statement 🙂

  9. I love how easy it’s explained here… I get it must be oversimplified, but I really love it. Without having a clue in immunology, I think I begin to like it cheers, man!

  10. Take my congrats, Max. That’s one good article there! Don’t worry about professorship now, you’ll find a career pathway just right for you. Keep posting and good luck. Come back to Oxford for a cup of tea sometime. You didn’t forget about chest medicine, did you?

  11. Me like. Very nice and clear view of everything I needed to know. I may need to learn more but it’s enough for now. Thank you Dr Max

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