The body has a natural response to foreign antigens that cause illnesses and diseases. This response is called an immune response, and every part of the body possesses this response to some degree. Sometimes there are parts of the body that do not have an immune response to foreign antigens. A lack of response such as this is called immune privilege. There are specific parts of the body that are common sites of privilege, which include the eyes, central nervous system, and the placenta and fetus.
Foreign antigens enter the body and are introduced to T cells that are made by the immune system. Normally, the T cells fight off the antigens and also remember the introduction of antigens. By remembering antigen exposure, when these antigens try to invade the body again, the immune system jumps into action with minimal effects. Unfortunately, immune privilege prevents this process from occurring. Each site of privilege reacts similarly but in a different area.
Typically, the eyes have their own immune cells just like other areas of the body. These cells can cause a complete full body immune response when the eye is exposed to antigens. When the eye is an immune privilege site, T cells develop a lack of response to self-antigens. The T cells and self-antigens are bound together, which causes the self-antigens to become inactive. With self-antigens inactive, an introduction of foreign antigens in the eye does not trigger an immune response as it should, which leaves the eye vulnerable.
Immune privilege in the central nervous system plays a large role in halting inflammatory immune responses. The central nervous system is separated from the systemic immune system by the blood-brain barrier. Research suggests that immune privilege often originates in the white matter of the central nervous system. Although research is ongoing, it is evident that foreign antigens that enter the lymph nodes do not trigger any response from the immune system.
During pregnancy, a mother’s immune system is normally able to protect her body against foreign antigen exposure without affecting the fetus or the placenta. In some cases, the placenta and fetus may be an area of immune privilege. Some research has shown that a woman’s immune system detects a fetus or the placenta as a foreign antigen and attacks. This instance may provide an explanation of miscarriages that occur without other medical causes.
If the body has an area of immune privilege and the immune system cannot defend this area, a wide array of diseases and illnesses can occur quite easily. A tissue graft is a common cause for a person to develop an area of privilege that did not previously exist. Organ transplants are either accepted or rejected by the body in most cases, but if privilege occurs as a result of transplantation, the organ can be attacked and damaged by foreign antigens.
Although privilege can be harmful to the body, it can also be beneficial. Due to how an area of immune privilege is cut off from the immune system, this can be helpful for tissue grafts and transplants as well. The immune system does not have as much of an opportunity to reject or attack the addition as a result.