PEDF can improve retinal diseases, such as age-related macular degeneration, by effectively downregulating the mRNA expression of pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, inducible nitric oxide synthase (iNOS), and IL-17a (Wang et al., 2013). The gene discussed is NOS2; the disease is age-related macular degeneration.