One of the critical problems doctors face when it comes to transplant surgery is convincing the body of the recipient to accept the new organ. Organ rejection is caused by the immune system of the recipient as it reacts to something in the body that did not originally grow there. Any foreign substance, whether a bacteria, virus, or transplanted organ, is seen by the immune system as a potential danger to the body. The natural response of the immune system is to attack the foreign object to destroy it before it can do damage.
What causes organ rejection?
The immune system uses cells called lymphocytes or white blood cells to locate cells that are recognized as not being part of the body, or “self”. Some white cells latch onto a cell that is “not self” to weaken and destroy it. When a donor organ is placed in the body, the white blood cells do not recognize the new tissue and attack it. Depending on the circumstances, this can happen soon after a transplant or it can happen weeks or months after the transplant is complete.
By studying human tissues, scientists have identified certain factors known as antigens that can cause a transplanted organ to be rejected. If the donor and the recipient have the same antigens, the white cells are less likely to notice that the organ is “not self” so the organ is less likely to be attacked. A more familiar example of this kind of matching is blood type. Doctors must be careful to match the type of blood, whether type O, A, B, or AB, before giving a blood transfusion because the wrong type of blood can make the recipient sick. In the same way, doctors must match the antigens between the donor and recipient to improve the odds that the organ will not be rejected.
Matching antigens to find a donor
Similar to blood transfusions, doctors must match the antigens between an organ donor and the recipient to improve the odds that the organ will not be rejected. As the number of matching antigens goes down, the odds of the organ being rejected goes up. Because there are many antigen combinations, it is difficult to find a perfect match aside from identical twins.