It has lots of false positives and false negatives. It is actually a very simplistic system, if it was "smart enough" we wouldn't have diseases. In fact, a good number of diseases, especially chronic ones that millions or billions of people suffer from throughout their lives, are actually the immune system's fault. It is not a "smart" system. It is clever. Sometimes. Until it's not.
this post was submitted on 24 Feb 2026
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All cells are covered in little bumps called antigens. Your body contains antibodies that bind to antigens on foreign cells. Your white blood cells then only attack cells that have antibodies attached to them.
So it's not about good/bad, but really just about which cells are your own and which are foreign.
Usually, autoimmune diseases fuck it all up.
It's never lupus!
Oh man, that part of the immune system development is probably my favourite. Specifically how in the world the body is able to detect theoretically basically anything that can exist.
This is probably going too deep but you can read a bit on wikipedia if you are interested: https://en.wikipedia.org/wiki/V(D)J_recombination
And to pivot back what you asked, the part where the immune system can detect anything that exists would of course be bad if it detects your own body too, since it attacks what it can detect.
So theres like a training camp for immune cells where they are tested if they can detect your own body's cells. And if they can, they are killed off. Therefore anything that is left can distinguish between what is good (you) and what is bad (other stuff).
There's lots of other mechanisms around that though, otherwise allergies or intolerances wouldn't exist, of course.
Most explanations you read/see about how the immune system works do a lot of anthropomorphising unfortunately, usually because the actual processes are too complex to explain. White bloods cells don't do anything, they are just cells, they float around. They have no agency, they have no purpose, they have no directive.
I didn't appreciate how much of chemistry and biology is just geometry until reading about AlphaFold. AFAIK, antigens bind because they literally "fit". And if they don't fit, it just slips off until the body can produce a matching geometry.
As far as I know, white blood cells move independently, crawling like amoebas or "millipedes" along vessel walls to reach infection sites. They use special adhesive "legs" to move at high speeds, even swimming in liquid using molecular "paddles". WBCs actively exit blood vessels, following chemical signals to damaged tissue.
They don't go after everything foreign. They are produced with instructions by which they identify a threat.
It's their production source which provides the instructions and it's not that smart or we wouldn't have cases where the immune system attacks the body itself.
yes, in fact our moral reasoning comes from the function of white blood cells and their extreme xenophobia - it is an important lesson to learn that foreign = bad, white = good ... oh wait, hmmmmmmmmm
don't give them nazis more ideas plz. they already have [gereric rationalization for their shit].
lol, you're right - white blood cells justify bigotry is a much better argument than "my sky daddy said so!"
Not really. That's what common food allergies are. It's the body's inability to tell good from bad and going to war with something benign.
Despite all the caveats, red blood cells “discern bad from good” better than most government officials.
I thought it was that certain roaming immune cells are basically pretty interested in literally everything they encounter, but you're own cells have chemicals cues that signal they are ok. And as soon as a they doesn't get the ok signal, all hell breaks loose, signaling the home bade, calling for backup, etc.
But this can go wrong, with like bacteria or cancer trying to mimic the "ok" Signal.
If someone wants to add, please do, because although i'm a biologist i mostly remember that the immune system is way more complex than you'd think.
Nothing is perfect, no defense is 100%.
Allergies.
How do you explain autoimmune diseases then?
Being a foreigner doesn't automatically mean something is bad - just unfamiliar.
look at Mr. Rogers over here