Phenotypic switching and its implications for the pathogenesis of Cryptococcus neoformans.

Phenotypic switching has been described in several strains of Cryptococcus neoformans. It occurs in vivo during chronic infection and is associated with differential gene expression and changes in virulence. The switch involves changes in the polysaccharide capsule and cell wall that affect the yeast's ability to resist phagocytosis. In addition, the phenotypic switch variants elicit qualitatively different inflammatory responses in the host. The host's immune response ultimately affects selection of the switch variants in animal models of chronic cryptococcosis. The biological relevance of phenotypic switching is demonstrated in several murine infection models and further underlines the importance of phenotypic switching in the setting of human disease. This includes the association of switching and poor outcome in chronic infection, the ability of the mucoid variant of strain RC-2 (RC-2 MC) but not the smooth variant (RC-2 SM) to promote increased intracranial pressure in a rat model, and lastly the observation that antifungal interventions can promote the selection of more virulent switch variants during chronic murine infection.