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Jonathan D. Wirtschafter, Jeffrey M. Ketcham, Robert J. Weinstock, Tara Tabesh, Linda K. McLoon; Mucocutaneous Junction As the Major Source of Replacement Palpebral Conjunctival Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 1999;40(13):3138-3146.
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purpose. The conjunctival epithelium performs an important role in the
homeostasis and integrity of the eye. To protect the integrity of the
ocular surface, these cells must be replaced from locally concentrated
or randomly distributed foci of stem cells. These slow-cycling stem
cells produce transient amplifying cells that undergo further divisions
before becoming mature conjunctival epithelial cells. In the current
study, the source of palpebral conjunctival cells was determined.
methods. Adult rabbits were injected intraperitoneally with bromodeoxyuridine
(BrdU) at a dose of 50 mg/kg body weight and killed after 1, 3, 5, and
7 days and 2 months. The orbital contents and eyelids were exenterated
en bloc, frozen to maintain the orientation between the eyelids and
globe, and sectioned in a parasagittal plane. Random midglobe sections
were stained for the presence of proliferating cell nuclear antigen
(PCNA). Additional sections were immunostained to detect BrdU-labeled
conjunctival epithelial cells. BrdU-positive cells were counted in a
series of 0.4-mm zones from the mucocutaneous junction of the eyelid,
through the fornix and bulbar conjunctiva. A second set of rabbits
received daily injections of BrdU for 2 or 4 weeks followed by a
2-month BrdU-free period before death and processing.
results. In all eyelid sections examined, there was a focus of
PCNA-positive cells in the mucocutaneous junction and a few scattered
PCNA-positive cells along the length of the palpebral conjunctiva
toward the fornix. In both the upper and lower eyelids, the peak
concentration of BrdU-labeled cells/0.4-mm zone was located at
progressively greater distances from the mucocutaneous junction in the
animals killed at 1, 3, and 5 days respectively and was unidentifiable
by 7 days. A focus of BrdU-labeled conjunctival cells remained within 1
to 2 mm of the mucocutaneous junction at all postinjection intervals.
These were always found within one cell height of the basement membrane
in the basal layer of the epithelium. In the long-term studies,
BrdU-labeled nuclei were retained at the mucocutaneous junction.
conclusions. The mucocutaneous junction of the conjunctival epithelium is a
source of actively dividing transient amplifying cells that migrate
toward the fornix at a rate of approximately 1.7 mm/d with a transit
time of approximately 6 days. Long-term retention of label at the
mucocutaneous junction indicates that slow-cycling stem cells are
present at this location. It appears that most palpebral conjunctival
epithelial stem cells are located near the mucocutaneous junction.
These results are not necessarily at variance with previous studies,
but they diminish the relative importance of the forniceal region in
palpebral conjunctival homeostasis. The mucocutaneous junction may
provide a therapeutically significant source of replacement
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