Role of LFA‐1, ICAM‐1, VLA‐4 and VCAM‐1 in lymphocyte migration across retinal pigment epithelial monolayers in vitro

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Abstract
The blood-retinal barrier (BRB), which is composed of the retinal pigment epithelium (RPE) and retinal vascular endothelium, normally restricts the traffic of lymphocytes into the retina. During ocular inflammatory conditions such as posterior uveitis there is a large increase in lymphocyte migration across the BRB. The differential role played by the two barrier sites, however, remains unclear. To evaluate the role of the posterior BRB, the migration of CD4+ antigen-specific T-cell line through rat RPE cell monolayers was investigated in vitro using time-lapse videomicroscopy. The adhesion molecules involved in controlling transepithelial migration across normal and interferon-gamma (IFN-gamma)-activated RPE was assessed with monoclonal antibodies directed against cell adhesion molecules. Lymphocytes were treated with antibodies specific for CD11a (alpha L subunit of LFA-1), CD18 (beta 2 subnit of the leucam family) and CD49 d (alpha 4 subnit of very late activation antigen-4, VLA-4), and the RPE with antibodies specific for CD54 (intracellular adhesion molecule-1, ICAM-1) and CD 106 (vascular cell adhesion molecule-1, VCAM-1). Migration across unstimulated RPE was inhibited by antibodies to ICAM-1 (48.6 +/- 3.5% reduction), leucocyte functional antigen-1 (LFA-1) alpha (61 +/- 5.2%) and LFA-1 beta (63.2 +/- 4.7%), but not by antibodies to VLA-4. VCAM-1 was not expressed on untreated RPE. Following activation of the RPE monolayers for 72 hr with IFN-gamma, antibodies to LFA-1 alpha, LFA-1 beta and ICAM-1 inhibited migration by 49.9 +/- 9.4%, 63.6 +/- 5.5% and 47.7 +/- 4.2% respectively. Antibodies to VLA-4 and VCAM-1 blocked migration by 21.5 +/- 8.4% and 32.3 +/- 6.2%, respectively, which correlated with the induction of VCAM-1 expression on RPE and increased migration. Under these conditions blocking both VCAM-1 and ICAM-1 reduced migration by 70.9 +/- 2.3%, which was greater than the effect of blocking either of these molecules alone. These results demonstrate that the posterior barrier of the BRB utilizes the same principle receptor-ligand pairings in controlling lymphocyte traffic into the retina as the vascular endothelium of the anterior BRB.