(A) Comparison of protein levels of ICAM1, ITGB2 and CD45 in RPE/choroid of young (Y, n = 3) and old (O, n = 3) mice by immunoblot. ICAM1, ITGB2 and CD45 are all increased in RPE/choroids from old animals. β-actin was used as a loading control. (B–I) Localization of leukocytes in young and old RPE/choroid. Leukocytes are labeled with leukocyte common antigen, CD45 (red). (B) In the young RPE/choroid, there are no leukocytes attached to Bruch's membrane or in the RPE layer. (C–I) Leukocytes in the old RPE/choroid. There are many leukocytes attached to Bruch's membrane in the RPE/choroid in old animals (C–E, arrows). Note the leukocyte that is attaching to the endothelial surface of the choroidal capillary (F, arrow heads), the leukocyte that migrated from the vessel to the local tissue (G, arrow heads), and the leukocyte passing through Bruch's membrane (H, arrow heads). The leukocyte attaching to Bruch's membrane has a lobated nucleus, indicating a polymorphonuclear leukocyte (I, arrow heads). OS, outer segment; RPE, retinal pigment epithelium; CC, choroidal capillaries; BM, Bruch's membrane. Scale bar = 20 µm.