However, when microglia are activated by injury and infection, they produce various pro-inflammatory mediators (free radicals), including nitric oxide (NO), reactive oxygen species (ROS), and cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α (Kreutzberg 1996; Hanisch 2002). The gene discussed is TNF; the disease is infection.