Killing of Yeast, Germ-tube and Mycelial Forms of Candida albicans by Murine Effectors as Measured by a Radiolabel Release Microassay

Abstract

C. albicans undergoes yeast to mycelial conversion under both in vivo and in vitro conditions but the relative pathogenicity of the 2 forms of growth is still unknown. A recently developed 51Cr radiolabel release assay was adapted to quantify the killing ability of different murine effector cell populations for the hyphal form of C. albicans. Up to 50% of specific 51Cr release from the mycelial form could be detected after incubation for only 1 h, with no requirement for opsonization, provided that appropriate effector:target cell ratios were used. The specific 51Cr release correlated well with viability, as assessed by dye exclusion tests, and with pathogenicity potential in cyclophosphamide-immunodepressed mice. Comparison of the activity of different murine effectors against yeast and hyphal forms showed that hyphal forms were killed by murine effectors to a similar, if not greater, extent than yeast forms. In particular, thioglycollate-induced murine polymorphonuclear neutrophils were able to kill hyphal cells extracellularly and without an opsonic requirement.