Macular and peripheral distribution of ICAM-1 in the human choriocapillaris and retina.

Purpose: In order to understand the extent of choriocapillary endothelial cell activation in different topographic regions of the eye, we sought to compare the localization of intercellular adhesion molecule-1 (ICAM-1) in macular and peripheral regions of human eyes.
Methods: Sections of sucrose-embedded human donor eyes that included the macula and ora serrata were evaluated for ICAM-1 and ICAM-2 immunoreactivity with monoclonal and polyclonal antibodies. Patterns of ICAM-1 labeling in peripheral and macular regions were examined in 20 eyes. Morphometric analyses of anti-ICAM-1 labeling intensity in the choriocapillaris were performed using ImageJ software on a series of macular and extramacular punches from nine eyes. Quantitative PCR analysis for ICAM-1 mRNA was performed on the RPE-choroid from the same regions from six of the same eyes, and Western blots of samples treated or untreated with N-glycosidase were performed to compare retinal and choroidal ICAM-1.
Results: ICAM-1 labeling of the choriocapillaris was typically more intense in the macula than in the peripheral choroid in human donor eyes (14/20). ICAM-2 was also detected in the choriocapillaris and retinal vessels. Morphometric measurements confirmed a significant macular-extramacular difference in ICAM-1 in six of nine eyes (p<0.05), with 1 of 9 eyes showing the opposite pattern. This pattern was not noted for endogenous alkaline phosphatase or ICAM-2. The opposite pattern was noted in the external limiting membrane (ELM), which exhibited more intense ICAM-1 labeling in the far periphery than in the macula. On Western blots, choroidal ICAM-1 exhibited a greater molecular weight than the retinal form, with most of the apparent weight difference due to N-linked carbohydrate chains.
Conclusions: The regional differences in ICAM-1 distribution in the choriocapillaris may indicate that this region is subject to increased leukocyte trafficking. In view of the role of inflammatory processes in age-related macular degeneration (AMD), we propose that the higher level of ICAM-1 protein in the macular choriocapillaris may impart greater susceptibility of the macula to immune cell-mediated damage in AMD.