Why does our body reject other people’s donated organs and require immunosuppressants to be taken but getting someone else’s blood is ok?

Question

Why does our body reject other people’s donated organs and require immunosuppressants to be taken but getting someone else’s blood is ok?

In: 157

Answer 1

Before you are born, your body takes a sort of census of everything that is “you”. This is how your immune system knows how to identify what it is protecting, and what it is protecting you *from*. Based on that census, and a sort of index of all of the proteins your body knows how to synthesize, your immune systems creates specialized cells that go off and hunt for things that are “not you”.

Blood is pretty simple. While there are a lot of them, all your regular blood cells are pretty close to identical. Even so, while you can get blood from other people, they have to have a compatible Type and Rh factor, or your body absolutely will reject and attack it. It causes big clots to form, and it absolutely can be lethal if not treated, though it isn’t always. Even if you get a transfusion of the wrong blood type, the cells don’t live very long, and as a percentage of your blood volume, it’s not very much. Even if your body didn’t reject them, they’d be completely gone in a few weeks.

Organs are waaaay more complicated. Instead of only one kind of cell, it can have dozens, or hundreds that do specialized things. That’s a lot more chances that your immune system is going to decide that the new organ is “not you”, and decide to attack it.

Blood cells only live a couple of months, but your new organ has to work for the rest of your life. If all you transplanted blood gets killed, we’ll, meh. If all the cells in your new kidney get killed – that’s very bad.

Then there is how your immune system works. Once it decides that you’re new organ is the enemy, it goes back and teaches other immune cells how to make cells that are specifically made to attack those organ cells. As more and more of your immune cells encounter your organ cells, and learn to make cells to attack it, the number, and effectiveness of cells that target you organ increase. Without immune suppression, In not very long, your immune system will be destroying the organ cells faster than your new organ can replace them, or your body can clean up the mess made by killing them.