ELI5, how come when you get an organ transplant, there’s a chance your body will reject it and your immune system will kill it. But when you get infected by a new disease, it’s difficult for your immune system to kill the disease.
In: Biology
Your organs don’t try to hide their identity. They proclaim it loudly to anything that runs into them. There’s normally no reason for your organs to hide their identity.
All the cells in my liver have big, obvious ID badges that say “I AM /U/OPTRODE’S LIVER”. There is normally a good thing. If my liver (or part of it, more likely) got transplanted into another person, my liver cells are going to carry on loudly yelling “I AM /U/OPTRODE’S LIVER”, and that’s going to attract attention from the recipient’s immune system, because under 99.99999% of circumstances, something in one of your organs that isn’t part of you is a bad thing.
Viruses and bacteria, on the other hand, have evolved to be hard to detect. They don’t wear any obvious ID badges, since their whole business model involves being in places where if they get recognized they’ll be killed on sight.
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