Neutrophils and other phagocytes manufacture O₂⁻ (superoxide) by the one-electron reduction of oxygen at the expense of NADPH. Most of the O₂⁻ reacts with itself to form H₂O₂ (hydrogen peroxide). From these agents a large number of highly reactive microbicidal oxidants are formed, including HOCl (hypochlorous acid), which is produced by the myeloperoxidase-catalyzed oxidation of Cl⁻ by H₂O₂; OH^· (hydroxyl radical), produced by the reduction of H₂O₂ by Fe⁺⁺ or Cu⁺; ONOO⁻ (peroxynitrite), formed by the reaction between O₂⁻ and NO^·; and many others. These reactive oxidants are manufactured for the purpose of killing invading microorganisms, but they also inflict damage on nearby tissues, and are thought to be of pathogenic significance in a large number of diseases. Included among these are emphysema, acute respiratory distress syndrome, atherosclerosis, reperfusion injury, malignancy and rheumatoid arthritis.