Abstract
The phagocytosis of photoreceptor outer segments (POSs) by the retinal pigment epithelium (RPE) is essential for retinal homeostasis. Defects in this process can be caused by mutations in the photoreceptor cells, the RPE cells, or both cell types. This function can be experimentally investigated by performing an in vitro phagocytosis assay, in which cultured RPE cells are challenged with isolated POSs, and subsequently tested for their ability to degrade the POSs. A significant advantage of this approach is that mutant phenotypes can be attributed either to the photoreceptor or the RPE cells, by experimenting with different permutations of mutant and control photoreceptor and RPE cells. In this chapter, we detail the method for a double-immunofluorescence assay for analysis of the binding, ingestion, and subsequent degradation of isolated mouse POSs by cultured mouse primary RPE cells.