ANTIGEN PRESENTATION BY RAT-BRAIN AND RETINAL ENDOTHELIAL-CELLS

Brain and retinal endothelial cells (EC) form the blood-brain and vasc ular blood-retinal barriers, respectively, and are believed to play a role in mediating T cell responses in the central nervous system. In t his study, Lewis rat retinal and brain EC grown in vitro were capable of expressing MHC class II I-A but not I-E molecules following treatme nt with interferon-gamma. In the presence of their antigen, CD4(+) ant igen-specific T cells were able to mediate lysis of retinal EC monolay ers to a similar extent as brain EC. T cell proliferation was poorly s upported by confluent retinal or brain EC monolayers, but subconfluent EC monolayers supported proliferation in a MHC class II (I-A)-restric ted manner (P < 0.001). Exposure of T cells to confluent retinal EC mo nolayers resulted in them becoming less responsive to subsequent antig en presentation by thymocytes. Conversely, pre-exposure with subconflu ent EC had no such effect. These results suggest that a non-proliferat ing EC monolayer is able to downregulate T cell responsiveness which m ay have important implications during lymphocyte traffic across the bl ood-tissue barriers of the central nervous system.