Cryptococcus neoformans melanin and virulence: Mechanism of action

Y. Wang, P. Aisen, A. Casadevall

Research output: Contribution to journalArticle

Abstract

Black melanin-like pigments are produced by several neurotropic fungi, including Cryptococcus neoformans. Pigment production is associated with virulence. In media containing phenolic substrates such as L-dopa, C. neoformans cells become black as a result of pigment accumulation. Pigmented and nonpigmented C. neoformans cells were studied with transmission electron microscopy and electron spin resonance (ESR) spectroscopy. Transmission electron microscopy showed electron-dense cell walls, and ESR spectroscopy revealed a stable free-radical population in pigmented cells. The ESR signals of pigmented cells were increased by light, alkaline pH, and Zn2+ and decreased by acid pH, indicating that the black pigment was a type of melanin. A mutant deficient in melanin synthesis (mel) generated by UV radiation lacked ESR-detectable radicals, was less virulent for mice, was more susceptible to killing by nitrogen- and oxygen-derived radicals, and had 100-fold-less phenoloxidase activity than the parent strain. The interaction of melanized C. neoformans, nonmelanized C. neoformans, and the hypomelanotic mel mutant with J774.16 murine macrophage-like cells was studied. Melanized cells were more resistant to antibody-mediated phagocytosis and the antifungal effects of murine macrophages than nonmelanized cells. Small increases in the intensity of the ESR signals of melanized cells in solutions containing chemically generated oxygen- and nitrogen-derived radicals indicated electron transfer to or from melanin. Melanin appears to contribute to virulence by protecting fungal cells against attack by immune effector cells.

Original languageEnglish (US)
Pages (from-to)3131-3136
Number of pages6
JournalInfection and immunity
Volume63
Issue number8
StatePublished - Jan 1 1995
Externally publishedYes

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ASJC Scopus subject areas

  • Parasitology
  • Microbiology
  • Immunology
  • Infectious Diseases

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