Why does the human body have an immune system that sometimes attacks itself, like in autoimmune diseases?
In: Biology
Your immune system isn’t “smart”. Your genes don’t come with a list of things for your immune system to attack and things not to attack. Your immune system has to build that list on its own as your body first develops. Sometimes that list gets messed up or is missing parts that it shouldn’t be.
Your immune system is also the product of hundreds of millions of years of “war” against pathogens which are trying to evade your immune system. They do this by camouflaging themselves, either as something harmless or as part of *you*. Your cells can pass things back and forth like packages, with proteins attached as “tags” that signal for the cell to bring the “package” inside the cell. Viruses mimic these proteins so that your cells will bring the virus particle inside, where it can take over the cell.
Your immune system is kind of like a paranoid security guard. If it isn’t paranoid *enough* then pathogens can sneak into your body. Sometimes, though, your immune system becomes *too* paranoid and attacks something it shouldn’t. The mostly harmless version of this is allergies. Your immune system sees something harmless like pollen and reacts as if the pollen is a horribly deadly disease.
An autoimmune disease is your immune system becoming too paranoid and “forgetting” that the thing it sees is part of you and is safe. A lot of things can trigger this, but sometimes it’s because there was an infection by a pathogen mimicking your own body’s proteins. Your immune system figures out that there’s an infection and fights it off, but in the process it learns to notice the protein that looks like you. That’s what the invader looked like, so that’s what the immune system should attack. Except, of course, it *is* you and should not be attacked.
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