Q.Cornea transplant in humans is almost never rejected. State the reason.

Immune Privilege of the Cornea

Organ transplants usually fail unless the donor and recipient are carefully matched and the patient takes immunosuppressive drugs — the immune system attacks "foreign" tissue. Yet corneal transplants (grafts) succeed remarkably often even without matching. Understanding why reveals a beautiful piece of physiology called immune privilege.

What immune privilege means

An immunologically privileged site is a part of the body where foreign tissue (like a graft) can be placed without triggering the usual immune rejection. The cornea — the clear front window of the eye — is a classic example. So are certain other sites such as the brain and the interior of the eye.

Why the cornea is privileged — the key reason

The central reason is that the cornea is avascular — it has no blood vessels. Blood vessels are the highways along which immune cells travel to inspect tissue and mount an attack. Because the cornea gets its oxygen and nutrients from tears and the fluid behind it rather than from blood, immune cells simply do not routinely patrol it. With no blood supply carrying immune surveillance to the transplanted tissue, a corneal graft largely escapes detection, and rejection is rare.

Additional factors reinforce this: the eye maintains a local environment that actively dampens immune responses, further protecting the graft.

Why this matters medically …