Unlike other parts of the body, the eye will tolerate the presence
of foreign tissue in certain areas, such as the anterior chamber
between the iris and the cornea, or the space underneath the retina.
The same tissue placed elsewhere in the body (on the skin, for example)
would trigger an immune reaction and be rejected.
School of Medicine researchers have studied this unique ability
of the eye to develop methods of inhibiting rejection by selectively
enhancing immunological unresponsiveness or “tolerance.”
Yijun Xu and Judith Kapp of the departments of ophthalmology, pathology
and the Winship Cancer Institute, reported the results of their
work in the November issue of Investigative Ophthalmology and Visual
The major problem with any organ or tissue transplantation is that
the recipient usually rejects cells from another person (unless
they are twins). The recipient’s immune system does not distinguish
between a transplanted retinal cell, for example, or invading microorganisms
such as bacteria and viruses.
Inflammation is the body’s way of fighting infection, as the
white blood cells (called lymphocytes) and antibodies attack and
destroy antigens carried by the “invader.” In the eye,
inflammation may result in excessive tissue damage that could lead
Xu and Kapp are studying how a phenomenon called Anterior Chamber-Associated
Immune Deviation (ACAID) combats inflammation. ACAID occurs when
the hypersensitivity of the eye against an invader is reduced with
administration of an antigen, thereby decreasing the risk of sight-threatening
Studies with mice have shown that by delivering a certain antigen,
the white blood cells can be neutralized and their ability to produce
antibodies reduced. Delivery of a soluble form of antigen into the
anterior chamber of the eye of anesthetized mice triggered the ACAID
phenomenon, decreasing the hypersensitivity in the eye and throughout
The technique requires certain specific white blood cells, called
gamma delta T cells, Xu and Kapp learned. In otherwise normal mice,
which did not have a sufficient quantity of T cells, the immune
response could not be inhibited. This led the Emory scientists to
conclude that ocular tolerance depends upon the participation of
these special lymphocytes.
Understanding how T cells affect tolerance may one day be used to
prevent graft rejection and to provide novel treatments for patients
with autoimmune diseases.