The most important mechanism by which neutrophils inactivate bacteria was thought to be mediated by reactive oxygen species and myeloperoxidase-catalysed halogenation. But in March 21 Nature, Emer Reeves and colleagues from University College London show that the killing activity of neutrophils works through activation of proteases by potassium ions (Nature 2002, 416:291-297).

Reeves et al. found that mice made deficient in neutrophil-granule proteases but with normal superoxide production and iodinating capacity, cannot fight staphylococcal and candida infections. Bacterial ingestion by neutrophils increased the concentration of reactive oxygen species in the endocytic vacuole and the resulting accumulation of anionic charge was compensated for by a surge of potassium. This determined the release of cationic granule proteins, including elastase and cathepsin G, from the anionic sulphated proteoglycan matrix. The authors suggest that "early theories implicating oxygen radicals in tissue damage [...] will need to be reassessed in the...

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