Reduced Phagocytosis as a novel pathogenic mechanism in AMD pathogenesis

Abstract

Purpose : Age related macular degeneration (AMD) is characterized by the accumulation of debris in the retinal/retinal pigment epithelium/Bruch’s membrane complex, yet the exact cause of this accumulation is not known. Our aim was to determine whether the phagocytic ability of peripheral blood monocytes (PBMC) in participants with a range of the AMD phenotypes is reduced when compared with age-matched controls.

Methods : Eligible participants from the Centre for Eye Research Australia were aged 50 or over and had either intermediate AMD, geographic atrophy, choroidal neovascularisation or were healthy controls (HC). Participants were fully phenotyped using multi-modal imaging and were graded per the Beckman classification. Peripheral blood was collected from participants and mononuclear cells were isolated and labelled with surface phenotype markers. Phagocytosis of yellow-orange fluorescent latex beads (YO beads) by monocytes was measured using a real-time tri-colour flow cytometry method. Phagocytosis ability was calculated as the area under the bead uptake curve. The phagocytic ability was correlated with the level of AMD disease. Glatiramer acetate [Copaxone ®] (CPX), a drug used to augment phagocytosis, was used to treat the cells prior to the addition of beads. A derived CPX stimulated phagocytic index was calculated as the phagocytosis ability of CPX treated cells minus that of the untreated cells.

Results : 70 cases of AMD and 36 aged matched healthy controls were recruited. The average basal phagocytic ability of classic monocytes in HC was significantly higher than that in AMD cases (106117±35734 vs. 88473±21945, p<0.002). Similar significance was found in other monocyte subsets. After the cells were incubated with CPX, the CPX stimulated index was significantly higher in the AMD cases compared with the controls (p<0.04), which subsequently restored the lower basal phagocytic ability in AMD cases to a similar level as HC.

Conclusions : This pilot study confirmed that PBMC of people with AMD have a reduced phagocytic ability when challenged with beads in a laboratory setting. Copaxone® appears to augment the phagocytic ability of monocytes from AMD participants. These results suggest a novel pathogenic mechanism for AMD, as well as a potential treatment target.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.