Purpose: To compare the activation of microglia in response to retinal detachment in four species.
Methods: Experimental detachments were created in cats, rabbits, and ground squirrels and the retinas harvested 1, 3, 7, or 28 days later. Retinal reattachments of 28 days in duration were also performed in cats following a 3-day detachment. Human tissue was obtained during reattachment surgery. Microglia and macrophages were labeled with the lectins Griffonia simplicifolia and Ricinus communis and the antibody CD11b. Müller cell and photoreceptor responses were followed immunocytochemically on the same tissue sections labeled with microglial markers. Images were collected by laser scanning confocal microscopy.
Results: Lightly labeled microglia were observed primarily in the inner retina of control tissue. In the cat and rabbit, a progressive increase in the number of labeled cells occurred in the outer retina beginning at 1 day of detachment. In both long term human and cat detachments numbers of microglia were elevated throughout the retina. This is in contrast to the rabbit and ground squirrel retinas where microglial activation was dramatically diminished in longer term detachments. Presumptive macrophages (anti-CD11b labeled cells) occurred only in the subretinal space. Retinal reattachment in cats significantly attenuated the response except in areas of poor outer segment regeneration.
Conclusions: The robust microglial response to retinal detachment is an indicator of the importance of this cell type in the overall response of the retina. Our data suggest that the feline retina is a particularly appropriate model system for understanding this response in humans. Inhibiting the microglial response in that species should help us understand more precisely its potential role in photoreceptor survival in human pathology.