Immunoregulation by capsular components of Cryptococcus neoformans

Cryptococcus neoformans is an encapsulated yeast that is pathogenic for hum ans. The capsule is a major virulence factor composed mainly of glucuronoxy lomannan (GXM) and two minor constituents, galactoxylomannan, and mannoprot ein (MP). A hallmark of disseminated cryptococcosis is the presence of high concentrations of GXM in body fluids of infected hosts. GXM provides a cri tical negative signal for T cell activation and neutrophil migration at the site of the inflammatory process. There is also strong evidence that MP pr omotes critical events associated with protective responses such as delayed type hypersensitivity and presumably a T helper type 1 response. The contr asting roles of GXM and MP in regulation of the immune response to C. neofo rmans offer a promising template for a successful approach to intervention, by scavenging GXM to attenuate its negative signals, while preserving the positive effects of MP.