Abstract
When normal leukocytes, especially neutrophils, are stimulated by various stimuli, such as opsonized zymosan, opsonized bacteria and phorbol myristate acetate etc, they produce O-⋅2 (superoxide) from O2 by the catalytic action of NADPH oxidase systems present in their plasma membrane. Superoxide is not a powerful oxidant and easily converted to H2O2 by the dismutation of 2O-⋅2. Hydrogen peroxide itself is not a oxidant in aqueous media, but can be converted to powerful oxidants, one for ⋅OH and another for HOCl in neutrophils. The most plausible way for the generation of ⋅OH in the leukocytes is the reaction of H2O2 with Fe2+ (Fenton's reaction) . Ferrous ion could be supplied by the redution of Fe3+ by O-⋅2 (probably also by ascorbate) . Such ⋅OH generating system is extensively important for killing bacteria in myeloperoxidase-deficient leukocytes. The generation of HOCI from H2O2 is catalyzed by myeloperoxidase in neutrophils in the presence of CI-. Bacterial membrane and energy-producing system are strongly damaged by HOCI (probably also by ⋅OH) . Of the active oxygen species, 1O2 may also be produced during dismutation of O-⋅2 and by the reaction of H2O2 with -OCI at neutral pH, but in a very small quantity. Judging from very short lifetime and very selective reactivity of 1O2 to organic compounds, it seems unlikely that 1O2 is an active species for killing bacteria. The mechanism of luminol-dependent chemiluminescence produced by activated leukocytes is also discussed in this review.
