DISTRIBUTION OF A PUTATIVE ENDOTHELIAL BARRIER ANTIGEN IN THE OCULAR AND ORBITAL TISSUES OF THE RAT

Background-A rat endothelial barrier antigen (EBA) recognised by a mon oclonal antibody has been shown to be expressed strongly by endothelia l cells of brain capillaries possessing a blood-brain barrier and only weakly expressed by fenestrated brain vessels. Methods-In this study immunocytochemical methods for light and electron microscopy were used to study EBA distribution in the eye and orbital tissues of the rat. Results-Blood-ocular barrier vessels in the optic nerve, retina, iris, and some vessels in the choroid and ciliary body were immunopositive for EBA. By preembedding immunocytochemistry for electron microscopy t he antigen was observed on the luminal endothelial cell surface. Concl usion-Surprisingly, some nonbarrier vessels in the ciliary body and ch oroid expressed EBA suggesting that it may play a broader role in endo thelial properties than previously recognised. The functional signific ance of EBA remains to be elucidated.