NOS2 and infection: Infection of pathogenic microorganisms or tissue damage activates innate immune system, which recruits granulocytes including macrophages to clear microbial pathogens and injured tissue, releases inflammatory mediators such as pro-inflammatory cytokines TNF-α, IL-1β, and IL-6, reactive oxygen species (ROS), nitric oxide (NO), prostaglandins (PGs), and inflammatory enzymes including inducible NO synthase (iNOS) and cyclooxygenase (COX)-2, and arouses cellular inflammatory response to pathogens or tissue damage [8–10].