Kinetics of immune cell migration at the human ocular surface

Aim: The conjunctiva has a resident population of intraepithelial and stromal immune cells. These cells play an active part in ocular surface defence and disease. Our aim was to study the migration of immune cells in the human conjunctiva, across the basement membrane and to characterize their phenotypes. Methods: Organ cultures of human conjunctival samples, denuded of the epithelium, were maintained for varying time periods. Cells migrating on to the surface were harvested and analysed by flow cytometry. Conjunctival samples were also studied by immunohistology and electron microscopy. Results: A preferential unidirectional migration of immune cells from the stroma, through pores in the basement membrane, towards the surface was noted. Cells migrated through intrastromal channels, communicating with the surface basement membrane pores. CD3+ T cells (76.18%) were the predominant migrating phenotype. The ratio of CD4:CD8 T cells was approximately 4:1 as compared with the control conjunctiva where the ratio was approximately 2:1. Various other phenotypes including NK, NKT and B cells were also detected. Only 8.41% of the migrating population expressed the Human mucosal lymphocyte-1marker of intraepithelial lymphocytes. Conclusions: Immune cells migration at the ocular surface is an active process involving the formation of intrastromal channels, and cell egression through intact basement membrane pores. The preferential migration of CD4 T cells indicates that this is a specific response of conjunctival lymphoid tissue and not a passive movement of cells. A wide range of immune cell phenotypes exist at the ocular surface. This model can serve to test in vitro the effects of injurious agents on the ocular surface.