The survival and rejection of epithelium in experimental corneal ...

174 Khodadoust and Silverstein 1nve.it'.igatioe Ophthalmology
April 1969
For this purpose, the epithelium of the prospective
donor was intensively labeled with tritiated
thymidine prior to transplantation. This was accomplished
by first scraping the donor cornea centrally
over an area of about 10 mm. in diameter.
Several drops of a solution of tritiated thymidine
(100 MC per milliliter) were applied topically
twice a day for 2 weeks, during the process of
epithelial regeneration. Corneal transplantation was
performed 3 days after discontinuation of the
drops, and the grafts were removed 10 to 14 days
after operation. The eyes were fixed, embedded,
sectioned, and radioautographs prepared according
to well-established procedures 2 for the localization
of isotopically labeled cells. These radioautographs
(Fig. 3) clearly demonstrate that not only does
donor epithelium heal and survive during this 2
week period, but also that it shares in epithelial
wound healing. Even after 2 weeks, one half of
the graft scar is covered by donor epithelium and
the other half by host cells which show no tendency
to invade the graft and replace the donor
epithelium during this period.
Control experiment. In a parallel experiment,
the cornea of the recipient was labeled by scraping
its epithelium over a wide area, followed by
topical application of tritiated thymidine as described.
Two weeks later, an 8 mm. lamellar graft
with nonlabeled epithelium was placed centrally
upon this cornea. The grafted corneas were removed
10 days to 2 weeks after transplantation,
and radioautographs prepared as described previously.
In this instance, labeled epithelium could
be seen covering only the host stroma and a
portion of the adjacent graft scar. During this 2
week period, there was no tendency on the part
of labeled recipient epithelial cells to invade the
surface of the donor button.
Observations of epithelium in vascularized
corneal allografts. In studies to be reported elsewhere
7 ' s it was observed that the epithelium
covering a donor allograft is apparently able to
participate in a specific manner in the rejection
process. To recapitulate these observations briefly,
epithelial rejection induced during the early period
after transplantation presents as a linear defect,
stainable by methylene blue, which slowly proceeds
across the surface of the donor graft, until
the entire donor surface has been traversed. The
"epithelial rejection line" invariably starts precisely
at the donor-recipient graft junction, and always
in close approximation to the blood vessels which
Fig. 4. Methylene blue staining of the epithelial rejection line on an eccentrically placed
lamellar allograft. Vascularization of the superior quadrant has stimulated graft rejection which
is manifested by an arcuate epithelial defect extending from one margin of the graft to the
other. During the course of the rejection process, this defect is seen to traverse the entire
donor corneal surface, starting always in the zone adjacent to the invading capillaries.