Heterogeneity of human neutrophil phagolysosomes: functional consequences for candidacidal activity

Opsonized yeast phase Candida albicans, incubated with human neutrophils, are internalized into two classes of phagosomes. One class, termed “unsealed vacuoles,” comprises approximately 40% of the total and maintains functional communication to the cell's exterior that is sufficient to permit ingress of dyes, such as trypan or methylene blue. The remaining cell-associated yeasts are contained in “sealed vacuoles,” completely sequestered from the external milieu. Approximately 71.8% of C albicans within sealed vacuoles are rendered nonviable within 60 minutes, whereas only 14.5% of organisms within unsealed vacuoles are killed during this time. We conclude that vacuolar sealing mechanisms are imperfectly developed in normal human neutrophils and that incompletely sealed vacuoles support antimicrobial processes substantially less well than do completely sealed ones.