Illustration of an alligator giving blood


Organ donation requires a good match between donor and recipient

If a person needs an organ transplant, close relatives are potential donors. But the donor’s blood group and tissue type must be compatible with the recipient’s. Tissue type is determined by a set of genes that code for MHC (self) proteins.

Children inherit these genes from their parents, half from their mother and half from their father. Sometimes, the parents share some of the same genes, so the child may end up having a tissue type very like one or other parent, who may be a ‘perfect match’ for donation. Or the child may end up with a tissue type that is not really close to either parent. In this case, an unrelated donor may be a better match. Better matches reduce the chance of the recipient’s immune system rejecting the donated organ as non-self.

Family members are not always good matches, and for some organs, like hearts, the donation can come only from someone who has died. Organ shortages mean that animals have also been considered as donors.

In 1983, the surgeon Leonard Bailey transplanted a baboon heart into a newborn baby. ‘Baby Fae’ lived for only 20 days, as her immune system rejected the organ. However, since then, many children born with heart defects have received replacement heart valves from pigs or cows. Transplanting tissue from one species to another is called xenotransplantation. The tissues are chemically treated to mask the antigens that the immune system reacts to.

People who receive transplants may have to take immunosuppressive drugs for the rest of their lives, with the unfortunate side-effect that they become more susceptible to infections. Different drugs address different aspects of the immune system, and many transplant recipients take drugs that reduce the activity or growth of T cells.

Lead image:

Illustration © Glen McBeth


About this resource

This resource was first published in ‘Immune System’ in January 2015.

Physiology, Genetics and genomics, Immunology
Immune System
Education levels:
16–19, Continuing professional development