Determinants of the production of active oxygen species by granulocytes and macrophages

Under certain conditions, phagocytic leukocytes generate considerable quantities of superoxide and hydrogen peroxide, as well as small quantities of hydroxyl radical and singlet oxygen. These activated forms of oxygen are involved in the antibacterial, antiparasitic and antitumour functions of the cells. Important factors in the production of the different oxygen species are the nature of the stimulant and the animal species from which the cells are derived; in addition, macrophages exist in various metabolically modulated states within the organism. The oxidases involved in this process are localized in the leukocyte plasmalemma, where they catalyse the oxidation of reduced pyridine nucleotides; a cytochrome may also be involved in the electron transport. Other oxidases are also present in certain species; for example, guinea pig cells contain aldehyde oxidase. Active forms of oxygen can attack bacteria and other foreign bodies inside the phagocytic vacuole or outside the cell. Peroxidase may play a critical role, chiefly in granulocytes. In this kind of multienzyme system, it is self evident that different genetic defects can lead to the same phenotypic end results, e.g. Chronic Granulomatous Disease in children, and other biochemical disorders.