Fig. 5. Contribution of oxidative mechanisms to neutrophil-mediated toxicity.

(A) To determine the inherent sensitivity of each species to oxidative stress, all strains were incubated in the presence of 1 mM H₂O₂, followed by XTT assay. Data are expressed as the percentage of XTT activity of yeast of the same strain incubated in the absence of H₂O₂. Error bars represent standard deviation. C. parapsilosis strains were significantly more sensitive to H₂O₂ than C. albicans (p < 0.01 for all strains). (B) Toxicity assays were conducted as described in Fig. 4 in the presence of varied concentrations of the ROS scavenger, N-acetylcysteine. Data are expressed as the percentage of XTT activity of yeast of the same strain incubated in the absence of neutrophils. Data are from 5 individual donors in a minimum of 4 individual experiments, and each was performed in triplicate. Error bars represent standard deviation. This agent led to a dose-dependent inhibition of toxicity, and statistical significance was achieved for C. albicans strain Ca3153A and C. parapsilosis strain Ro75 (* p = 0.009; ** p = 0.02). Because the quantity of neutrophils that could be obtained from an individual donor was limited, only two strains of each species were tested.