The Eye and Immune Privilege

It is often said that the eyes are the window to the soul. But we might also think of the eye as a doorway to medical breakthroughs. This is because the eye is one of a few sites in the body with something called immune privilege. That special status makes the eye an ideal environment for researching certain therapies for treating vision loss.

Pros and Cons of an Immune System Response

The body’s immune system—made up of organs, tissues and cells—works to protect us from infection and disease. When a virus or other foreign substance is detected, the immune system kicks in. It makes molecules called antibodies to attack these invading substances known as antigens. This natural defense system is called an inflammatory response, and results in swelling of tissue and a higher-than-normal temperature.

While an inflammatory response can help fight off infection or disease, it can also cause problems. For example, if someone has a donated organ transplanted in their body, their immune system may recognize the organ as foreign tissue and mount an inflammatory response. This can cause the transplant to fail.

What is Immune Privilege?

Interestingly, certain areas of the body have something called immune privilege. This means that the body’s normal inflammatory immune response is limited here. Scientists think the purpose of immune privilege is to protect these important areas from damage that may occur with swelling and higher temperatures from the immune response. The eye is one of a few areas of the body with immune privilege. The eye limits its inflammatory immune response so that vision isn’t harmed by swelling and other tissue changes. Other sites with immune privilege include the brain, testes, placenta and fetus.

Because of this immune privilege, the eye offers an excellent location for certain kinds of research and therapy. For example, scientists can implant types of cells called stem cells in the eye to study their role in regrowing or repairing damaged tissue. Cells implanted in the immune-privileged eye are less likely to be rejected than they might be in other parts of the body. Studies of stem cell use in the eye have shown promise in treating vision loss.

Another reason the eye is a good place for researching new therapies? It is relatively easy to reach and see inside of the structure. That makes implanting cells in the eye much easier than other areas of the body.