Peritoneal polymorphonuclear neutrophils (PMN) from mice were tested for their ability to kill the yeast form of (Bd) and for their fungicidal mechanisms. PMN elicited from immune mice by the intraperitoneal injection of non-viable Bd (referred to as immunologically activated PMN or ActPMN) showed significantly enhanced fungicidal activity in comparison with PMN elicited with thioglycollate medium (ThioPMN) [means=44·7% (SD 12·8%) and 16·4% (SD 9·2%) killed; n= 14; p < 0·001]. Production of superoxide anion (0 ) by ActPMN after stimulation with phorbol myristate acetate was enhanced in comparison with production by ThioPMN. Superoxide dismutase, which removes O , inhibited ActPMN killing by 75% (p < 0·001) when added to cultures immediately before challenge with Bd (optimal concentration: 6000 U/ml). Sodium azide, which inhibits myeloperoxidase and scavenges singlet oxygen (O), and catalase, which breaks down hydrogen peroxide (HO), inhibited ActPMN killing by 64% (p < 0·001) and 52% (p < 0·001), with optimal concentrations of 1 mM and 10 000 U/ml, respectively. Two agents that both scavenge O and antagonise hypochlorous acid (HOCl), histidine and tryptophan, were also powerful inhibitors of ActPMN killing. Quenchers of hydroxyl radical (·OH), dimethylsulfoxide and sodium benzoate, had less effect, and required higher concentrations. These data suggest that the enhanced killing of Bd by ActPMN involves one or more oxidative mechanisms, and that there is a prominent role for 0 , either directly or as a precursor of other active oxygen species, a probable role for HO, and possible roles for O, HOCl. and · OH.


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