By the end of this lesson, students should be able to describe immune privilege, identify immune-privileged organs, and explain the clinical implications for immune responses and transplantation at these sites.
Immune privilege refers to the ability of certain organs and tissues to tolerate the introduction of antigens without eliciting an inflammatory immune response.
This mechanism prevents tissue damage that could occur from immune-mediated inflammation in functionally vital or delicate structures.
Immune-Privileged Sites
| Site | Rationale / Mechanism |
|---|---|
| Eye | Tight junctions (blood–ocular barrier), immunosuppressive cytokines (e.g., TGF-β) prevent inflammation that could impair vision |
| Brain | Blood–brain barrier limits immune cell entry; CNS has limited MHC expression |
| Placenta | Physical separation of maternal and fetal blood; local immune tolerance protects the fetus |
| Testes | Blood–testis barrier and immunosuppressive Sertoli cells prevent immune attack on sperm antigens |
Mechanisms Maintaining Immune Privilege
| Type | Example / Function |
|---|---|
| Physical barriers | Blood–tissue barriers (e.g., tight junctions) |
| Anti-inflammatory cytokines | TGF-β, IL-10 |
| FasL expression | Induces apoptosis in infiltrating immune cells |
| Low MHC expression | Reduces antigen presentation |
Clinical Correlation
- Allograft transplantation at immune-privileged sites (e.g., corneal transplant) has lower rejection risk due to local immunosuppression.
- Loss of immune privilege (e.g., after trauma or infection) can trigger autoimmune disease, such as:
- Sympathetic ophthalmia – bilateral uveitis following trauma to one eye, exposing sequestered antigens.
Key Points
- Immune privilege prevents immune-mediated tissue injury in sensitive organs.
- Maintained by barriers, cytokines, and local immune suppression.
- Clinically relevant for transplantation success and autoimmune complications
