Topographical distribution and characterization of epithelial cells and intraepithelial lymphocytes in the human ocular mucosa

The conjunctiva plays a key role in the protection of the ocular surface by initiating and regulating immune responses. In this study, we analyze the relative proportion of intraepithelial lymphocytes (IELs), apoptotic cells, and proliferative state in three different topographical regions of the normal human conjunctiva. Superior tarsal, superior bulbar, and inferior tarsal-bulbar-fornical conjunctival cells were collected by brush cytology from 63 healthy donors. Flow cytometry analysis showed higher levels of CD3(+) and CD8(+) IELs in both upper tarsal and bulbar conjunctiva than in the inferior tarsal-bulbar-fornix, where the CD19(+) B cells were increased. For all zones two different cell populations (by cell size and complexity) were present in the apoptosis assay. The more complex cells were reduced within the inferior tarsal-bulbar-fornix when compared with the superior bulbar and tarsal areas. Less complex cells were more predominant in the inferior conjunctiva and were mainly alive. The mean proliferation index of the conjunctival epithelium was significantly lower in the superior bulbar conjunctiva than in superior tarsal and inferior fornical conjunctivas. These findings suggest that each topographical zone from normal human conjunctiva has a unique profile of immunophenotype, viability, and proliferative state that could be related to a differentiated regional functionality.