Expression of antioxidant enzymes in human inflammatory cells

Because antioxidant enzymes may have an important role in the oxidant resis tance of inflammatory cells, we investigated the mRNA levels and specific a ctivities of manganese and copper-zinc superoxide dismutases (Mn SOD and Cu ,Zn SOD), catalase (Cat), and glutathione peroxidase, as well as the concen trations of glutathione (GSH) in human neutrophils, monocytes, monocyte-der ived macrophages, and alveolar macrophages. Levels of GSH and glutathione p eroxidase activity in monocytes were three times higher than in neutrophils , whereas the mRNA of Cat was 50-fold and its specific activity 4-fold high er in neutrophils. Although Mn SOD mRNA levels were higher in neutrophils, enzyme activities, as well as those of Cu,Zn SOD, were similar in all phago cytic cells. Neutrophils lost their viability, assessed by adenine nucleoti de depletion, within 24 h ex vivo and more rapidly if GSH was depleted. How ever, neutrophils were the most resistant cell type to exogenous H2O2. In c onclusion, high Cat activity of neutrophils appears to explain their high r esistance against exogenous H2O2, whereas low GSH content and GSH-related e nzymes seem to account for the poor survival of human neutrophils.