Resident Microglia and Bone Marrow Immigrants Remove Dead Photoreceptors in Retinal Lesions

Phagocytosis is essential for the removal of photore-ceptor debris following retinal injury. We used twomouse models, mice injected with green fluorescentprotein-labeled bone marrow cells or green fluores-cent protein-labeled microglia, to study the originand activation patterns of phagocytic cells after acuteblue light-induced retinal lesions. We show that fol-lowing injury, blood-borne macrophages enter theeye via the optic nerve and ciliary body and soonmigrate into the injured retinal area. Resident micro-glia are also activated rapidly throughout the entireretina and adopt macrophage characteristics only inthe injured region. Both blood-borne- and microglia-derived macrophages were involved in the phagocyto-sis of dead photoreceptors. No obvious breakdown ofthe blood-retinal barrier was observed.