97th DOG Annual Meeting 1999



S. Loebel, L. Kohen, V. Enzmann, P. Wiedemann

Purpose: IPE and retinal pigment epithelial (RPE) cells have continuos characteristics possessing the same embryological origin. IPE cells are potential candidates as autologuos transplant into the subretinal space to treat RPE defects in ARMD. A crucial function of the transplant is the phagocytosis of photoreceptor outer segments (POS) to rescue photoreceptors. We studied the involvement of the vitronectin receptor, the mannose receptor and the scavenger receptor CD36 in IPE phagocytosis that were characterized as potential phagocytosis pathways in RPE cells.

Method: Porcine IPE cells were fed with fluorescein isothiocyanate (FITC)-stained porcine POS for four hours. The POS uptake was measured by flow cytometry. The influence of vitronectin and mannose receptors were tested by stimulation with vitronectin and mannose in different concentrations. The involvement of the mannose receptor was also tested as the CD36 receptor indirectly by blocking with horseradish peroxidase for the mannose receptor and the phospholipids phosphatidylinositol and posphatidylserin for the CD36 receptor in different concentrations.

Results: Vitronectin and mannose had dose-dependant positive effects on phagocytotic capacity of IPE cells. High concentrations of horseradish peroxidase blocked the phagocytosis of IPE cells incomplete. Both phospholipids had no significant effect of phagocytosis on the IPE cells.

Conclusions: Vitronectin, horseradish peroxidase and mannose could modulate the uptake of POS by IPE cells. While vitronectin and mannose stimulated the POS uptake, horseradish peroxidase blocked in part the phagocytosis capacity of the IPE cells. These incomplete inhibition by horseradish peroxidase indicates that POS ingestion is mediated by a co-receptor mechanism. The investigation of the three potential POS phagocytosis pathways of the RPE lets us hypothesize that IPE cells use the vitronectin receptor and the mannose receptor mediated phagocytosis similar to the RPE cells.

Department of Ophthalmology, University of Leipzig, Liebigstr. 10-14, D-04103 Leipzig