Question

Which statement is not true regarding immune privilege? a. The phenomenon of immune privilege was initially described in the nineteenth century. b. Immune privilege is defined as a prolonged, sometimes indefinite, survival of organ or tissue grafts at special body/organ sites. c. Immune privilege is a dynamic process maintained by anatomic structures and immunoregulatory forces. d. Grafts placed in immune privileged sites remain sequestered from the immune environment. e. Both active and passive factors of immune privileged sites and tissues contribute to the privileged status.

Short answer

a. The phenomenon of immune privilege was initially described in the nineteenth century. b. Immune privilege is defined as a prolonged, sometimes indefinite, survival of organ or tissue grafts at special body/organ sites. c. Immune privilege is a dynamic process maintained by anatomic structures and immunoregulatory forces. d. Grafts placed in immune privileged sites remain sequestered from the immune environment. e. Both active and passive factors of immune privileged sites and tissues contribute to the privileged status. Answer: d. Grafts placed in immune privileged sites remain sequestered from the immune environment.

Step-by-step solution

Understanding Immune Privilege

Immune privilege refers to certain parts of the body at which the immune system either doesn't respond or has a reduced response, meaning that foreign grafts can survive for prolonged periods or indefinitely. This reduced immune response can be due to a combination of anatomical structures and immunoregulatory factors that actively suppress immune reactions.

Evaluating Statement a

a. "The phenomenon of immune privilege was initially described in the nineteenth century." This statement is true. The concept of immune privilege was first described by the French surgeon Paul Bert in the nineteenth century when he observed that foreign tissues could survive for prolonged periods when grafted into certain sites.

Evaluating Statement b

b. "Immune privilege is defined as a prolonged, sometimes indefinite, survival of organ or tissue grafts at special body/organ sites." This statement is true. Immune privilege refers to specific body sites where foreign grafts can survive longer than in other sites, primarily due to a reduced or suppressed immune response.

Evaluating Statement c

c. "Immune privilege is a dynamic process maintained by anatomic structures and immunoregulatory forces." This statement is true. Immune privilege results from a complex interplay of anatomical structures, such as the blood-brain barrier, and immunoregulatory factors that actively suppress immune reactions.

Evaluating Statement d

d. "Grafts placed in immune privileged sites remain sequestered from the immune environment." This statement is false. While it is true that grafts at immune privileged sites can survive for longer periods than grafts placed elsewhere, they are not completely sequestered from the immune environment. Instead, they benefit from a combination of anatomical and immunoregulatory factors that help reduce or suppress immune reactions.

Evaluating Statement e

e. "Both active and passive factors of immune privileged sites and tissues contribute to the privileged status." This statement is true. Immune privilege is maintained by both active factors, such as the production of immunosuppressive molecules, and passive factors, like anatomical barriers that prevent access of immune cells to the graft. In conclusion, the statement that is not true regarding immune privilege is statement d: "Grafts placed in immune privileged sites remain sequestered from the immune environment."

Key concepts

Organ Transplantation

Organ transplantation is a medical procedure where a damaged or missing organ is replaced with a healthy one from a donor. This procedure is often lifesaving or significantly improves quality of life. However, one major challenge in organ transplantation is the risk of rejection by the recipient's immune system.
The immune system typically recognizes the transplanted organ as foreign and may attack it, resulting in rejection.
This is where the concept of immune privilege becomes particularly important.
In areas of the body that are considered immune privileged, like the eyes and brain, transplanted tissues can sometimes last longer as they are less exposed to the host's immune response.

• This is due to special properties of immune privileged sites that naturally reduce immune activity.
• Thus, understanding immune privilege can potentially lead to better outcomes in transplantation by choosing optimal sites for grafting or developing treatments that mimic these privileged conditions.

Immunoregulation

Immunoregulation refers to the mechanisms by which the body controls and modulates the immune response. This complex system ensures that the immune system can efficiently respond to pathogens while avoiding damage to the body's own tissues.
In terms of immune privilege, immunoregulation plays a crucial role.
Several immunoregulatory mechanisms actively suppress the immune response in privileged sites.
Some of these mechanisms include:

• The secretion of anti-inflammatory cytokines that reduce immune activation.
• Presence of regulatory cells that help maintain a balanced immune response and prevent excessive attack on the transplanted tissue.

These immunoregulatory factors are critical in preventing rejection of grafts and maintaining tissue compatibility. Proper immunoregulation can thus be a key factor in the success of organ transplants, allowing the recipient to accept the new organ without adverse immune reactions.

Anatomical Structures

Anatomical structures play a pivotal role in maintaining immune privilege. These structures create physical and chemical barriers that help protect tissues from the immune system's attack.
For example, the blood-brain barrier is a well-known anatomical structure that contributes to the immune privilege of the brain. It is a selective barrier that prevents large molecules and immune cells from entering the brain's tissue, thereby reducing the possibility of an immune reaction.

• Similar barriers are found in the eyes, where the unique anatomical environment supports the immune privilege of ocular tissues.
• This environment is partly due to the absence of certain types of lymph vessels and the presence of cellular barriers.

Understanding these anatomical structures and their functions is crucial for developing strategies in organ transplantation and therapeutic approaches to maintain graft integrity and function.