Choroidal macrophages in homeostasis, aging and age-related macular degeneration

With increasing age, the optimal functioning of the choroid is essential for efficient removal of waste products formed from photoreceptor renewal. A decline in regulatory elements of the immune system, termed immunosenescence, and the failure of para-inflammation to restore tissue homeostasis can result in the progression of healthy aging to sight-threatening inflammation of the choroid. Macrophages are uniquely situated between the innate and adaptive immune systems, with a high capacity for phagocytosis, recognition of complement components, as well as antigen presentation. In this review, we provide an overview of macrophages and their properties in the healthy choroid and cover the impact of aging, immunosenescence and inflammaging on the function of choroidal macrophages. We will discuss the impact of age on macrophage phenotype and behaviour in the pathophysiology of age-related macular degeneration.