Immune privilege

Immune privilege is a term that refers to certain sites of the body which are able to tolerate the introduction of antigens without eliciting an inflammatory immune response. These sites include the central nervous system, the eye, the pregnant uterus, and the testis.

Overview

The concept of immune privilege was first proposed by Peter Medawar in the 1940s when he noticed that skin grafts placed on the eye or the brain of the same species were not rejected, unlike skin grafts placed on other parts of the body. This led to the idea that certain parts of the body are "privileged" and can avoid the normal immune response.

Mechanisms

The mechanisms of immune privilege are complex and not fully understood. However, several factors have been identified that contribute to this phenomenon. These include:

• Physical barriers: Many immune privileged sites are physically separated from the rest of the body by barriers such as the blood-brain barrier or the blood-testis barrier.

• Local immunosuppression: Immune privileged sites often produce immunosuppressive molecules that inhibit the immune response. For example, the eye produces transforming growth factor-beta (TGF-β) and the brain produces cortisol.

• Lack of lymphatic drainage: Most immune privileged sites lack lymphatic drainage, which prevents antigens from being transported to lymph nodes where they could activate the immune response.

Clinical significance

Understanding immune privilege has important implications for transplantation, autoimmune diseases, and cancer. For example, the immune privilege of the eye is the reason why corneal transplants have a high success rate even without the need for immunosuppressive drugs. On the other hand, immune privilege can also allow cancer cells to evade the immune system and grow unchecked.

See also

• Immune tolerance
• Immune response
• Immunosuppression

References

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