Why does our body reject other people’s donated organs and require immunosuppressants to be taken but getting someone else’s blood is ok?
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Trying to keep it at ELI5 level: there are two important parts to know about to understand this.
1. your immune system looks on cells for information/markers to say it belongs there, like an ID badge. Wrong ID badge means it’s killing time
Blood cells have very simple ID badges. There are only a small number of types of blood around, so it’s relatively simple to test recipient against donor blood to see if the recipients immune system would attack and kill it.
For matching organs, cells often have more information on them, think of “the id badge” being more elaborate. The chances of finding someone who has the exact matching “id badge” is small, but you might get someone who has a very similar “badge”. With the similar badge you get low level attack from the immune system. (If there wasn’t any matching the attack is aggressive and just won’t work for transplanting).
Add in the immunosuppressants and that attack falls even lower.
2. How long the blood or organ is going to last.
We are constantly replacing our blood. Red blood cells have a life span of around 120 days. When you give a transfusion, those cells are already old. They will die off and be replaced by your own new blood cells with time. So even if there was a very subtle mismatch with the donated blood that might result in slightly faster killing of the donor blood, it wouldn’t matter because the cells die off and get replaced anyway.
If you think about a heart transplant or another organ, that organ needs to last the rest of your life. So a very slightly mismatch, and very low level attack over time is far more important. Slow sustained attack from the immune system damages the organ and reduces the length of time it will work. So get the match as close as possible to start with and then suppress the immune attack more, and the transplant will last longer
The ideal situation for a transplant in most cases would be an identical twin. The ID badges match perfectly and no immunosuppressive would be needed.
Ask more questions because I’m not sure my ID badge idea works well
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