If most organ cells, like in the liver, are replaced every three years or so, why isn’t a transplant eventually accepted by the new body?

Question

If most organ cells, like in the liver, are replaced every three years or so, why isn’t a transplant eventually accepted by the new body?

In: 350

Answer 1

All cells that contain a nucleus have a Major Histocompatibilty Complex (MHC). This MHC is used to help your immune system recognize friendly cells (aka host cells) as well as a couple other things. When a transplant occurs, those donor cells contain the donor MHC as well. MHCs are more unique than fingerprints, so the odds of having an MHC similar enough to the host MHC so as not to trigger the immune system is… very unlikely.

There are mainly three possibilities with most transplants: hyper acute rejection, acute rejection, and chronic rejecting. The ideal transplant will be chronically rejected, meaning that the transplant will take years to no longer be accepted by the body. This can be done using immunosuppressive medicines to stop the body from rejecting it via the other two possibilities; this of course leaves the host with a weakened immune system and a life long prescription of immunosuppressants.

Source: made a B in Immunology