Effect of melanin and carotenoids of Exophiala (Wangiella) dermatitidis onphagocytosis, oxidative burst, and killing by human neutrophils

The black yeast Exophiala (Wangiella) dermatitidis is an increasingly recog nized pathogen and a leading cause of severe pheohyphomycosis. Melanin is t hought to contribute to the virulence of E. dermatitidis. Whereas the synth esis and the redox properties of melanin have been studied intensively, the influence of melanin and carotenoids on the phagocytosis, the oxidative bu rst, and the killing off. dermatitidis by human neutrophils has not been st udied. To study their effects on these phenomena,,ve applied a combination of flow cytometry and a colony-count-dependent method. Using E. dermatitidi s wild-type strain 8565 and several melanin-deficient mutants that have bee n described previously, we demonstrate that melanin prevents this pathogen from being killed in the phagolysosome of the neutrophils. Melanin did not influence the phagocytosis or the oxidative burst of the neutrophils involv ed. The carotenoids torulene and torularhodine were not found to contribute to the prevention of killing. The ability of E. dermatitidis to block the effects of the neutrophil oxidative burst may critically impair the potenti al of the host to sufficiently eliminate this fungal pathogen and thus may play an important role in the pathogenesis of phaeohyphomycosis.