Phagocyte-derived free radicals stimulated by ingestion of iron-rich Staphylococcus aureus: a spin-trapping study

Phagocytic cells generate superoxide (O2-) and hydrogen peroxide (H2O2), creating the substrates for hydroxyl radical (HO.) in the presence of redox active metals. Previously it was shown that HO. is not a physiologic product of human neutrophils or monocytes but can be generated in the presence of high concentrations of iron. This study was undertaken to determine whether bacterial iron could be used for the generation of HO. The growth of Staphylococcus aureus under iron-rich conditions increased bacterial iron concentration and phagocytosis of iron-rich bacteria allowed neutrophils to accumulate threefold more iron than ingestion of iron-starved organisms. Neither neutrophils nor monocytes ingesting iron-rich S. aureus generated iron-catalyzed HO. at levels detectable by spin-trapping techniques. No differences in the killing of iron-rich organisms by neutrophils was noted. The results suggest that HO. does not play a role in the killing of S. aureus by human neutrophils, regardless of their ability to deliver iron to the cell.