PALPEBRAL CONJUNCTIVAL TRANSIENT AMPLIFYING CELLS ORIGINATE AT THE MUCOCUTANEOUS JUNCTION AND THEIR PROGENY MIGRATE TOWARD THE FORNIX*

Purpose: The conjunctival epithelium performs an important role in the homeostasis and integrity of the eye. These cells need to be replaced in order to protect the integrity of the ocular surface. Epithelial cells are replaced from slow cycling stem cells which in turn produce transient amplifying cells that undergo further divisions before becoming mature conjunctival epithelial cells. The natural history of the bulbar palpebral conjunctival cells has not been previously described. Methods: A single injection of bromodeoxyuridine (brdU), a thymidine analogue, was administered intraperitoneally to adult rabbits at a concen-tration of50 mg/kg body weight. The rabbits were sacrificed at 1, 3, 5, and 7 days following the injections. The orbital contents including the eyelids were exenerated en bloc, frozen in a manner that maintained the orienta-tion and continuity between the eyelids and globe and sectioned in a parasagittal plane. The tissue was stained immunohistochemically to detect brdU labeled conjunctival epithelial cells. The brdU-positive epithelial cells were counted in a series of 0.4 mm zones starting at the mucocutaneous junction of the eyelid and progressing through the fornix and bulbar conjunctiva. Rabbit eyelids and human eyelid surgical speci-mens were stained for cyclin Dl, a marker for cells that are in the GC phase of the cell cycle. Results: In both the upper and lower eyelids, the peak number of brdU labeled cells/0.4 mm zone was located at progressively greater distance