Porcine iris pigment epithelial cells can take up retinal outer segments

This study investigates the ability of iris epithelial cells (IPE) to ingest rod outer segments (ROS) and compares the amount of phagocytosis of porcine RPE and IPE cells by the use of a pH sensitive fluorescent dye (carboxy SNAFL) at the light microscopic level. The dye allowed investigation of ingestion separately from binding of rod outer segments. In a second set of experiments, after exposing ferritin-labeled ROS to the cultured cells, phagosomes were also counted in electron microscopic sections. Additionally immunocytochemical staining was performed with IPE and RPE cells. Both cell types stained positive with polyclonal NaK-ATPase antibodies against the alpha 1 subunit from rat brain and kidney. The epithelial nature of the cultured cells was determined by monoclonal anti-human-cytokeratin antibodies. Moreover, the ultrastructure of the cells revealed high amounts of phagosomes smaller than 1 mu m in diameter present in both RPE and IPE cells. The iron label of the phagosomes was determined by EELS spectra taken from individual phagosomes. Electron and light microscopic quantification shows that cultured IPE cells have 64% of the phagocytic capacity of the RPE with respect to phagosomes larger than 1 mu m in diameter. (C) 1997 Academic Press Limited.