Effects of neutrophils and in vitro oxidants on survival and phenotypic switching of Candida albicans WO-1.

The relationship to pathogenesis of the spontaneous phenotypic switching of Candida albicans is uncertain. Since neutrophils are critical in containment of disseminated candidiasis, we used these cells and some of their potentially microbicidal oxidative products to define effects on a C. albicans strain (WO-1) that exhibits characteristic, easily recognized switching between the white and opaque phenotypes. Blastoconidia of the opaque phenotypes were more susceptible than those of the white to killing by either intact neutrophils or cell-free oxidants, including reagent hydrogen peroxide or the myeloperoxidase-H2O2-Cl- system. Paralleling these findings, opaque blastoconidia were 2.8- to 3.6-fold more potent stimuli of neutrophil superoxide generation than were the white cells. In addition, both neutrophils and oxidants (reagent H2O2 or hypochlorous acid as well as the myeloperoxidase-H2O2-Cl- system) induced unidirectional increases in spontaneous rates of switching from white to opaque phenotypes. Differences in expression of C. albicans phenotypes therefore may determine relative susceptibility to neutrophil fungicidal mechanisms, and neutrophils themselves appear to be capable of selectively augmenting the switching process.