From EurekAlert!: "age is key in determining whether damaging blood vessels will form beneath the retina and contribute to vision loss. The scientists discovered that specific immune cells called macrophages play a role in the disease process in older mice by failing to block the development of abnormal, leaky blood vessels behind the retina. But in younger mice, macrophages typically prevent abnormal blood vessel formation. The scientists believe better understanding of how macrophages work may provide potential targets for therapies to slow or even reverse vision loss. There are two basic types of macrophages - known as M1 and M2 - and in the older mice, there was a preponderance of cells with the M2 signature. These M2 cells promoted abnormal blood vessel growth in the eyes of older mice. In younger mice, most macrophages had the M1 signature, and those cells inhibited the development of defective blood vessels ... it appears the population of macrophages drifts from the M1 type to M2 cells because of an increase in the levels of an immune system molecule called interleukin-10 (IL-10) in the eye as the mice get older."