ie, if every cell is constantly replaced wouldn’t the organ eventually be replaced by your own cells that your isn’t trying to kill?
In: Biology
No it won’t, because the cell replacement happens locally, from stem cells specialised to that tissue – so for example the deep layers of your skin contain skin stem cells, that can duplicate and specialise into the different stem cells that make up your skin.
Almost all human cells have something called the major histocompatibility complex – a set of proteins on the surface of the cell that, like a sort of name tag or ID badge, tell your immune system to not attack your own body cells. This is determined by the DNA of the cell, and since a transplanted organ regenerates its cells from its own stem cells, it will continue to express the donor’s MHC, which, if it is too different from the host’s MHC, will cause the host’s immune system to attack the transplanted organ, leading to rejection.
The MHC proteins themselves are determined by multiple different genes, some of which exist in a few hundred different variations among the human population, so there is a huge number of different possible MHC configurations – that is why it is so difficult to find a matching partner for a transplant.
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