Figure 2.

Confocal microscopic localization of the membrane attack complex (C5b-9) in drusen (Dr) and in compromised retinal pigment epithelium (RPE) cells. A, Anti-C5b-9 labeling pattern at low magnification. Labeling in the choroid (Chor) (blue channel) is unremarkable except for staining in the Bruch membrane (BM) and around the choriocapillaris. Two RPE cells that may be the targets of complement attack are labeled (arrows). A nucleic acid-binding dye (YO-PRO; Invitrogen, Carlsbad, California) that also binds to the elastic layer of BM is used to visualize cell bodies on the green channel. No nucleic acid staining is evident in the anti-C5b-9–labeled RPE cells. B, Anti-C5b-9 labeling of Dr (blue channel). A condensed clump of lipofuscin granules (arrow) may have been expelled from the adjacent RPE cell. C, High magnification of a cell on the BM with anti-C5b-9 immunoreactivity on the basal surface. The only indication of its identity is the presence of a single red autofluorescent granule (arrow). Tightly packed vesicles in the cytoplasm are stained by the YO-PRO dye (green channel). D, C5b-9 immunoreactivity is present in the sub-RPE nodules that flank the Dr (blue channel). In this example, the nodule may have coalesced with the adjacent Dr. Reproduced with permission from Anderson et al.⁵