Advanced Analysis of Photoreceptor Outer Segment Phagocytosis by RPE Cells in Culture

Retinal pigment epithelial (RPE) cells are among the most actively phagocytic cells in nature. Primary RPE and stable RPE cell lines provide experimental model systems that possess the same phagocytic machinery as RPE in situ. Upon experimental challenge with isolated photoreceptor outer segment fragments (POS), these cells promptly and efficiently recognize, bind, internalize, and digest POS. Here, we describe experimental procedures to isolate POS from porcine eyes and to feed POS to RPE cells in culture. Furthermore, we provide experimental protocols to synchronize the POS binding and engulfment steps of phagocytosis. Finally, we describe three different and complementary methods to quantify total POS uptake by RPE cells and to discriminate surface-bound from engulfed POS.