Figure 4. Microglial phagocytosis of photoreceptors in alternative mouse models of retinitis pigmentosa (RP) and in human histopathological specimens.

• A–C Evidence of microglial phagocytosis of photoreceptors in other mouse models of RP. Histological analysis of a rd1 mouse retina (A) demonstrates microglial phagocytosis of photoreceptor nuclei in vibratome sections (left) and in flat-mounted retina (right). Phagocytosed nuclei were predominantly negative for TUNEL staining (arrows). Similar findings were found in the retinas of the rd16 mouse (loss-of-function mutation in the photoreceptor-expressed CEP290 gene, 1 month old) (B) and the RPGRIP-deficient mouse (6 months old) (C). Scale bar, 20 μm.
• D–G Evidence of microglial phagocytosis of photoreceptors in other human histopathological specimens of RP. (D) Retinal section from a 30-year-old male donor with autosomal recessive RP (AR RP) showing extensive microglial infiltration of the ONL; expanded inset (right) shows multiple photoreceptor nuclei in phagosomes that were predominantly negative for TUNEL staining. (E, F) Retinal sections from two separate donors with autosomal dominant RP (AD RP₁ = 68-year-old man, T17M rhodopsin mutation, AD RP₁ = 50-year-old woman, Q-64-ter rhodopsin mutation) showing similar evidence of microglial phagocytosis. (G) Retinal section from a 46-year-old male donor with X-linked RP. Arrowheads indicate phagocytosed photoreceptor nuclei. Scale bars, 20 μm.