LABEL-RETAINING CELLS ARE PREFERENTIALLY LOCATED IN FORNICAL EPITHELIUM - IMPLICATIONS ON CONJUNCTIVAL EPITHELIAL HOMEOSTASIS

Purpose. To deter-mine the cell kinetic properties of epithelial cells from various zones of the conjunctiva. Methods. The morphology and ce ll kinetics of bulbar, fornical, and palpebral conjunctival epithelium were studied in neonatal and adult SENCAR mice. To examine the prolif erative rate of the conjunctival epithelium, a single administration o f tritiated thymidine (H-3-TdR) was used to detect cells in ''S'' phas e. Proliferative rates were also assessed by determining mitotic activ ity after an intraperitoneal injection of colchicine to arrest cells i n mitosis. To detect slow-cycling cells, mice received H-3-TdR continu ously for 1 week. After a 4-week chase, animals were sacrificed and ey es were surgically removed. All tissues were immediately fixed in form alin and processed for histology and autoradiography. Results. Slow-cy cling cells, detected as label-retaining cells (LRCs), were identified in bulbar, fornical, and palpebral epithelia, as well as in limbal ep ithelium. The greatest number of LRCs was found in fornical epithelium . In addition, we found a number of label-retaining goblet cells. This cell population was shown to incorporate H-3-TdR after a single pulse administration, and mitotic figures were seen in goblet cells after c olchicine treatment, indicating that conjunctival goblet cells have pr oliferative capabilities. Conclusions. These findings are consistent w ith earlier in vitro data that the fornical epithelium may be a zone e nriched in conjunctival epithelial stem cells. This has important impl ications in conjunctival epithelial development and is relevant in wou nd repair. Furthermore, the concept that goblet cells are slow-cycling cells with proliferative capabilities provides new insights into the area of conjunctival homeostasis.