Analysis of the secretion pattern of monocyte chemotactic protein-1 (MCP-1) and transforming growth factor-beta 2 (TGF-β2) by human retinal pigment epithelial cells

Abstract

Retinal pigment epithelial (RPE) cells, situated between the neurosensory retina and the vascularized choroid, form part of the blood–eye barrier and are important for homeostasis of the outer retina. These cells are able to produce a variety of cytokines which may play a role in the maintenance of the immunosuppressive milieu inside the eye and in intraocular inflammatory responses. In the present study, we investigated whether RPE cells secreted the anti-inflammatory cytokine TGF-β2 and the proinflammatory cytokine MCP-1 in a polarized manner. Monolayers of human donor RPE cells were cultured on transwell filters. Secretion of TGF-β2 and MCP-1 at either the apical or basal side of the RPE cell monolayers, that were not treated or stimulated with IL-1β (200 U/ml), was analysed by ELISA. All three cell lines examined had a different TGF-β2 secretion pattern. In two of the three donor RPE cell lines tested, TGF-β2 secretion was polarized, but not in the same direction. TGF-β2 secretion was not up-regulated by stimulation with IL-1β. In contrast, IL-1β strongly induced MCP-1 secretion preferentially into the basal compartment of all RPE monolayers tested. These data indicate that human RPE cells are able to secrete TGF-β2 and MCP-1 in a polarized fashion. Our results suggest that MCP-1 can be secreted by RPE cells in the direction of choroidal vessels during inflammatory responses in the posterior part of the eye, which may limit damage to the neurosensory retina.