Mechanisms and target sites of damage in killing of Candida albicans hyphae by human polymorphonuclear neutrophils

Abstract

Target sites of fungal cell damage were studied to define mechanisms of neutrophil-mediated killing of Candida albicans hyphae. Neutrophils induced hyphal cell wall damage, as evidenced by release of cell wall glycoproteins and confocal microscopic changes. Damage occurred in the presence of neutrophil granule extracts and did not require oxidants. However, oxidation of hyphal surface glycoproteins correlated strongly with parallel increments in fungicidal activity, suggesting that oxidants did contribute to maximal cell wall damage. Neutrophil oxidants also induced hyphal DNA fragmentation, primarily single-strand breakage, as shown by increased electrophoretic migration after nuclease-S1 DNA digestion at single-strand break sites. The onset of damage to hyphal cell walls and DNA preceded detectable neutrophil-mediated fungicidal effects. Likewise, hyphal amino acid and nucleotide turnover as well as ATP initially rose, then declined as lethal effects became detectable. Thus, preceding detectable fungal cell death, neutrophil oxidative and oxygen-independent mechanisms damaged defined targets.