Expression of antioxidant enzymes in human inflammatory cells

Because antioxidant enzymesmay have an important role in the oxidant resistance ofinflammatory cells, we investigated the mRNA levels and specificactivities of manganese and copper-zinc superoxide dismutases (Mn SODand Cu,Zn SOD), catalase (Cat), and glutathione peroxidase, as well asthe concentrations of glutathione (GSH) in human neutrophils,monocytes, monocyte-derived macrophages, and alveolar macrophages.Levels of GSH and glutathione peroxidase activity in monocytes werethree times higher than in neutrophils, whereas the mRNA of Cat was50-fold and its specific activity 4-fold higher in neutrophils.Although Mn SOD mRNA levels were higher in neutrophils, enzymeactivities, as well as those of Cu,Zn SOD, were similar in allphagocytic cells. Neutrophils lost their viability, assessed by adeninenucleotide depletion, within 24 h ex vivo and more rapidly if GSH wasdepleted. However, neutrophils were the most resistant cell type toexogenousH₂O₂.In conclusion, high Cat activity of neutrophils appears to explaintheir high resistance against exogenousH₂O₂,whereas low GSH content and GSH-related enzymes seem to account for thepoor survival of human neutrophils.