Why does the body reject transplanted organs?



What is it about a transplanted organ that tells the body it’s foreign and doesn’t belong?

In: Biology

Every cell in your body is covered with “Human leukocyte antigens” which is a crazy random protein that is different for basically everyone alive. The immune system looks for all sorts of things, but if it finds cells and they don’t have the right HLA then it defaults to “kill this thing”.

Think bout it like this:

You live in a big house with like 10 other people who you know really well. One day, one of them starts behaving weird and you’re kinda worried about them but you don’t understand what’s going on with them. Then, suddenly that person becomes “normal” again, but you feel something about them is just off. And then later you notice that they’re not that person. It’s another person impersonating them. Obviously you will boot the imposter out of your home right?? But if they just don’t /can’t leave (because of a lease perhaps?) , you and the other housemates would do everything you can to not come in contact/cooperate with them.

Every cell as little things on it that makes sure other cells can recognise them. These things are unique to everyone, kinda like our fingerprints. When your body gets cells with a different “cellprint” it assumes this is something that can make you sick and will destroy it. This helps with bacteria, viruses and parasites that causes us to be sick, but causes a problem when you get blood or an organ from someone else.

This is why it’s so important to “match” with the donar. The more similar these cellprints, the higher the change it will be successful, with blood type being the most commonly known. Even with a successful transplantation it will get rejected, it may just take longer, you’ll also get medication which effects the immune system so it won’t attack the new organ