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.

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.

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.

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.

Being a foreigner doesn’t automatically mean something is bad - just unfamiliar.

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

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.

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.

How do you explain autoimmune diseases then?

Despite all the caveats, red blood cells “discern bad from good” better than most government officials.

Allergies.

Nothing is perfect, no defense is 100%.

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.

Your own cells have protein signature directly dependent on the genetics. Everything that doesn’t match is attacked