Eye Center Researchers Identify Lymphocytes Required for Ocular Tolerance
ATLANTA -- 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 immunereaction and be rejected.
Researchers at the Emory
University School of Medicine have studied this unique ability of the
eye to develop methods to inhibit rejection by selectively enhancing
immunological unresponsiveness, or "tolerance." Yijun Xu, PhD, and Judith
A. Kapp, PhD, of the departments of Ophthalmology, Pathology and Winship
Cancer Center, report the results of their work in the November issue
of Investigative Ophthalmology and Visual Science.
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 an invading microorganism, 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 to blindness.
Drs. Xu and Kapp are studying
how a phenomenon called Anterior Chamber-Associated Immune Deviation
or ACAID by its initials, 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 inflammation.
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 body.
The technique requires certain
specific white blood cells, called (gamma delta) T cells, as Drs. 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.
Contact: Judith A. Kapp,
PhD, Department of Ophthalmology, Emory University School of Medicine,
Building. B, Room 2602, 1635 Clifton Road, NE, Atlanta, GA 30322 (tel:
404-778-4754; fax: 404-778-2109; e-mail: email@example.com)