Abstract
Purpose: :
The local immune system in the retina plays an important role in the aging eye and in AMD pathogenesis. We sought to investigate the presence, quantity and distribution of local microglia in a dystrophic retinal model and to compare this against normal aged retinas.
Methods: :
The Royal College Surgeon (RCS) rat is an appropriate animal model for retinal degeneration since it presents features similar to AMD, including neovascularization and atrophy. Following standard procedures, eyes from age-matched (3, 6 and 24 months) dystrophic (n=6) and non-dystrophic RCS control animals (n=6), were harvested. Using immunohistochemical procedures macrophages/microglia were visualised using ED1 (CD68, macrophages/microglia) ED2 (CD163 for peripheral/recruited macrophages), OX42 (CD11b, microglia) and Phosphotyrosine (for phosphorylated cells, largely microglia in the retina). The morphology of the cells was imaged on all retinal sections, and cells were counted separately in the inner and outer retina. Results were subject to statistical analysis.
Results: :
No staining with ED1/ED2 was observed in any of the retinas. An increasing trend in phosphotyrosine-positive cell numbers was observed from 3 to 24 month in dystrophic retinas. Changes in cell morphology were observed using OX42, showing an ‘activated’ amoeboid appearance in areas where degeneration or remodelling was occurring. A similar increasing statistically significant trend (p<0.05) was found when comparing non-dystrophic sections to dystrophic ones.
Conclusions: :
Cell numbers and distribution indicate a positive correlation between the early onset of dystrophy in specific retinal layers and the presence of ‘activated’ microglia, which are believed to migrate from the inner retina to areas of increased degeneration, initially in the photoreceptor layer, and later back to the inner retina. Imaging showed evidence of active phagocytosis by microglia in dystrophic retinas and also their activation in aged normal retinas.
Keywords: age-related macular degeneration • immunohistochemistry • microglia