Transplant Rejection: Process & Prevention

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Most of the time it's beneficial for your body to attack foreign cells because these cells may harm you. But sometimes, like when you receive a transplant, you want these cells to be accepted, which your immune system has trouble doing.

Immune System Protection

Your body's immune system is built to keep out foreign invaders. Microscopic invaders are constantly attacking you, but if your immune system is doing its job then you don't even notice these attacks because it stops them before you get sick. Your immune system is so good that it can even tell the difference between your cells and someone else's! And this is important because your body needs to fight off foreign cells without attacking its own cells accidentally.

Your immune system does this through the recognition of proteins on a cell's surface. These proteins are like a fingerprint because they are unique to an individual. The main 'fingerprint' proteins that identify you from someone else are called major histocompatibility complex molecules, or MHC for short. There are hundreds of different alleles, or gene variations, for each MHC gene, so except for identical twins it is extremely unlikely that any two people would have exactly matching MHC protein sets.

Transplant Rejection

In rare cases, however, this defense may actually work against us. For example, if you were to receive a transplant, say a blood transfusion, or a new kidney, lung, or heart, this new tissue is made up of someone else's cells. Your immune system will not recognize the MHC fingerprint, and as it's programmed to do, it will attack. That's exactly what you DON'T want to happen to your new transplant! When the body doesn't accept the newly transplanted tissue or organ as its own we call this a transplant rejection, and there are three kinds.

Acute rejection occurs for everyone who receives a transplant, though the amount of rejection varies from person to person. It can occur any time between the first week and three months after transplantation. It can usually be treated if caught early, and this type of rejection is often limited by immunosuppression drugs that weaken the immune system (and therefore the attack on foreign cells in the body).

If episodes of rejection continue to occur and occur over long periods of time, then this is a chronic rejection. Over time, the barrage of attacks from the immune system weaken the new tissues or organ so much that it can lead to complete failure of the transplant.

Transfusing the wrong type of blood may lead to a hyperacute rejection
blood transfusion

In some cases, the body might even reject the new organ or tissue completely within the first few minutes after transplantation. This is called hyperacute rejection. When this happens, the transplant must be removed right away to prevent the recipient from dying.

What symptoms might you expect to experience if your body is rejecting a transplant? Well, it depends on what organ or tissue you received. For example, if you got a heart transplant then you might have symptoms related to heart failure, if you received a kidney transplant you might experience kidney failure. In general, you can expect to feel unwell because the organ or tissue is failing due to the rejection.

Preventing Transplant Rejection

One of the best ways to prevent a transplant from being rejected is to match the MHC fingerprints from the recipient and donor as closely as possible. The more closely matched they are the less the body will attack the new tissue. For example, hyperacute rejection most often occurs when the donor and recipient are not matched at all, as would be the case if a person with blood type A receives a kidney from a donor with blood type B.

Immunosuppressant drugs are commonly used to help keep the recipient's body from attacking the transplant. While this protects the new tissue or organ, it can leave the recipient open to infection and disease since their immune system is not at full strength.

3D printers may eventually be able to print new organs from a recipient
3d printer

Modern science is working to prevent rejection altogether by producing tissues and organs from the recipient's own cells. This has already been done to create 'artificial' skin for people like burn victims. Replacement tissue is grown from human fibroblasts, which are tissue-generating cells, and then those cells multiply and grow along a protein scaffolding that produces new 'skin' for the patient! Laboratory-produced bladders (grown from the recipient's own cells) have already been successfully transplanted in numerous patients.

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