Abstract
Abstract: :
Purpose: To characterize the distribution of the complement system in normal human retina as a baseline for future studies. Methods: Posterior globes of five individuals (ages 47, 50, 63, 78, and 85 years) without known ocular disease and lacking grossly visible inner retinal edema were obtained from the UAB Age Related Maculopathy Histopathology Laboratory. Two blocks of tissue, the first extending from the optic nerve to the temporal parafoveal region and the second consisting of temporal retinal periphery, were excised, cryoprotected, embedded in OCT, and sectioned at 10 µm. Sections from each eye were reacted with antibodies against the C3a receptor (C3aR), C3, C5a receptor (C5aR), complement receptor 1 (CR1 or CD35), membrane cofactor protein (MCP or CD46), decay accelerating factor (CD55), and membrane inhibitor of reactive lysis (MIRL or CD59) and viewed with either bright–field or epi–fluorescence microscopy. Results: The C3aR was identified in a dentate–patterned band along the inner aspect of the nerve fiber layer. Vimentin, a M|*159*|ller cell marker, stained a similar pattern in the same area. C3 was detected within retinal and choroidal vasculature only. The C5aR was identified on scattered individual cells in the inner plexiform layer. CD46 was present in a continuous band along the basolateral surface of the RPE. CD55 was distributed throughout the neural retina but was most prominent in the nerve fiber layer. Neither CD35 nor CD59 were detected in the retina. Positive and negative controls stained appropriately for all antibodies. Staining patterns were consistent across all five eyes. Conclusions: Increasing evidence implicates the complement system in ocular diseases including uveitis and age–related macular degeneration. Understanding the normal expression and distribution of complement system components is prerequisite to understanding the role of complement in these conditions. Complement regulatory proteins and receptors are expressed in consistent patterns in the adult human retina. The location of the components suggests that in the neural retina, complement is tightly regulated. The presence of the C3aR adjacent to the vitreous cavity suggests that M|*159*|ller cells may sample the intraocular environment to monitor the status of complement activation. The presence of CD46 on the basolateral RPE suggests that control of complement activation may be important in preventing damage to the photoreceptors by agents delivered via the choroidal circulation. These findings provide a baseline to which studies of pathologic tissue samples can be compared.
Keywords: immunomodulation/immunoregulation • microscopy: light/fluorescence/immunohistochemistry • retina