Stimulation of the bactericidal activity of polymorphonuclear leukocytes by manganese

An antioxidant effect of manganese (Mn) complexes due to the scavenging of the superoxide anion (Of) or to the decomposition of hydrogen peroxide (H2O2) has been described. We report here that Mn also can exert a prooxidant effect under certain experimental conditions. Thus Mn2+ in phosphate buffer increased the bactericidal effect of phorbol myristate acetate-stimulated polymorphonuclear leukocytes (PMNs) on extracellular Escherichia coli. This effect was inhibited by azide, catalase, and a decrease in chloride concentration and was not observed when normal PMNs were replaced by those of patients with chronic granulomatous disease or myeloperoxidase (MPO) deficiency. Mn2+ could be replaced by Mn3+ or by superoxide dismutase (SOD). These findings suggest that Mn (or SOD), by increasing the conversion of Of to H2O2, can increase the activity of the MPO-H2O2-chloride antimicrobial system released by stimulated PMNs. J. Leukoc. Biol. 53: 666–672; 1993.