Transportation of Formed Elements Across the Retinal Pigment Epithelium

Abstract

Abstract: : Purpose: Only a fraction of transplanted retinal pigment epithelium in the subretinal space of domestic pigs is histologically identifiable post transplantation. . In order to investigate the fate of these grafts we transplanted RPE cells preloaded with rhodamine labelled microbeads. The fate of the beads was traced by immunofluorescence microscopy. Methods: 35 Danish Landrace pigs weighing approx. 30 kg were used. All pigs were treated according to guidelines set by the Danish animal experiments inspectorate and the ARVO resolution for use of animals in ophthalmic and vision research. 12 pigs were grafted with sheets of porcine RPE preloaded in vitro with Rhodamine labelled microbeads. The Rhodamine labelled microbeads (molecular probes 0,5–2,0 microns) only were injected in 23 pigs. Observation period varied between 3 hours and 35 days. In most eyes fundus photography and angiography were obtained before the eyes were enucleated. Paraffin sections were prepared from 16 eyes and cryo section from 19 eyes. Results: RPE phagocytized microbeads up to the size of 2,0 microns both in vitro and in vivo. Microbeads remained within the RPE cells during growth in vitro. In vivo the injected microbeads were transported from the subretinal space across the RPE to the episcleral space within a period of hours to days. Transplanted sheets of RPE containing microbeads were identified, but microbeads were also observed in the host neuroretina and the RPE. Conclusions: Host RPE cells are able to clear the subretinal space of formed elements up to a size of 2,0 microns within days. Latex microbeads are transported across the epithelium into the episcleral space without any visible damage to the RPE. The phagocytic properties of the host RPE may limit the number of usable tracers in RPE transplantation experiments.

Keywords: retinal pigment epithelium • transplantation • Bruch's membrane