Clusters of corneal epithelial cells reside ectopically in human conjunctival epithelium

PURPOSE. The ocular surface is covered by two biologically distinct epithelia: corneal and conjunctival. The expression of keratin12 (K12) is currently considered a hallmark of cornea-type differentiation. In the current study, the biological features of K12-positive cells in human bulbar conjunctival epithelium were examined. METHODS. Human conjunctival tissues were subjected to investigate the K12-positive cells in Conjunctiva by immunostaining, in situ hybridization, Western blot analysis, reverse transcriptase-polymerase chain reaction (RT-PCR), and fluorescence-activated cell sorting (FACS). Gene expression profiling of these cells was performed with introduced amplified-fragment length polymorphism (iAFLP). To determine the presence of stem- or progenitor cells, immunostaining and colony-forming assays were performed. RESULTS. Western blot analysis, RT-PCR revealed that K12 was expressed in conjunctival epithelium. Immunostaining analysis showed that K12-positive cells reside mainly in clusters in conjunctival epithelium. FACS analysis showed that 0.2% to 1.7% of conjunctival epithelial cells collected from the inferior bulbar conjunctiva were K12 positive. iAFLP analysis revealed that the gene expression patterns of these cells were highly similar to that of corneal epithelial cells. p63 and ABCG2 were expressed beneath the K12-positive cells. Some colony-forming cells expressed K12. CONCLUSIONS. The K12-positive cells appear to be ectopically residing, self-maintaining corneal epithelial cells in the conjunctival epithelium.