Reactive oxygen species in normal physiology, cell injury and phagocytosis.

Formation of free radicals and other ROS is a continuous aspect of life. Examples include the free radical intermediates which are formed by the nonenzymatic peroxidation of polyunsaturated fatty acids of membrane lipids in a destructive process and which are also formed by the enzymatic peroxidation of arachidonic acid in the biosynthesis of potent chemoattractants. Organisms cope with these reactive species by a variety of strategies that limit formation of ROS or remove cytotoxic products. Oxidative burst reactions that yield ROS provide an effective, vital process for killing invading organisms. Research on why ROS formation is impaired in phagocytic cells of people with chronic granulomatous disease has provided new insights into the complexity of the factors that prevent inadvertent activation of this destructive force.