Immunology of the eye
Retinal Pigment Epithelium (RPE) produce the neuropeptide alpha-melanocytes stimulating hormone (α-MSH) that regulates the phagocytic pathway in monocytes. This regulation has the potential to alter antigen processing and presentation that would activate effector T cells. The expression of α-MSH is greatly diminished during Experimental Autoimmune Uveitis (EAU). This suggests the possibility that RPE regulation of the phagocytic pathways in antigen presenting cells (APC) is diminished in EAU permitting the activation of effector T cells. We assayed for changes in RPE regulation of the phagocytic pathway by collecting the conditioned-media of cultured RPE-eyecups from eyes of healthy and EAU mice. Resting macrophages (RAW 264.7 cells) were treated with conditioned-media and fed opsonized-Ovalbumin (OVA)-coated magnetic beads for 24 hours. The magnetic bead containing intracellular vesicles were isolated, and assayed by immunoblotting for Rab5 and Lamp1. APC activity was assayed by feeding resting peritoneal macrophages with opsonized-OVA-antigen while treated with conditioned-media overnight, washed, OVA-specific T cells were added, and proliferation was measured 72 hours later. The isolated phagosomes from EAU conditioned-media treated macrophages matured showing a significantly higher ratio of Lamp1 to Rab5 (1.2±0.13) than the healthy conditioned-media treated macrophages (0.8±0.23). The EAU conditioned-media treated OVA presenting APC were not suppressed in their ability to stimulate OVA-specific T cell proliferation (0.9±0.04%) in contrast to the suppressed stimulation of proliferation (0.45±0.06%) by APC treated with healthy conditioned-media. The results demonstrate that EAU RPE cannot suppress phagosome maturation in potential retinal APC, and may contribute to uveitis by permitting antigen presentation to effector T cells.