immune rejection
Immune rejection is what happens when your immune system spots transplanted cells, tissue, or an organ as 'not me' and attacks it. Your body runs a kind of identity check on every cell, like a bouncer reading ID badges at a door. Each person's cells carry their own molecular badges, and donor cells usually carry the wrong ones.
Immune cells patrol the body and read surface markers on every cell they meet. When they find foreign markers on a graft, they raise the alarm, multiply, and mount an attack — much as they would against a virus. The closer the donor's markers match the recipient's, the gentler this reaction; a poor match triggers a fast and fierce assault.
Rejection is the central obstacle of transplantation. It is why donors and recipients are carefully matched, and why most graft recipients must take immune-dampening drugs. Overcoming it without those drugs — true acceptance — is one of the field's biggest prizes.
The body treats a transplanted kidney a bit like a splinter it cannot ignore: an immune crew gathers around the 'foreign' tissue and works to remove it unless drugs hold them back.
The 'not me' alarm at the heart of transplantation.
Rejection is the main reason donor and recipient must be matched and why most graft recipients take immune-dampening drugs.