Melanin fromFonsecaea pedrosoiInduces Production of Human Antifungal Antibodies and Enhances the Antimicrobial Efficacy of Phagocytes

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Abstract
Fonsecaea pedrosoiis a fungal pathogen that produces melanin. The functions of melanin and its possible influence in the protective immunological response during infection byF. pedrosoiare not known. In this work, treatment ofF. pedrosoimycelia with proteases and glycosidases followed by a denaturing agent and hot concentrated acid left a black residue. Scanning electron microscopy demonstrated that this processed melanized residue resembled very closely the intact mycelium in shape and size. Melanin particles were also isolated from culture fluids of conidia or sclerotic forms ofF. pedrosoi. Secreted melanins were reactive with sera from infected human patients, suggesting thatF. pedrosoisynthesizes melanin in vivo. The antibodies against melanin were purified from patients’ sera and analyzed by indirect immunofluorescence. They reacted with sclerotic cells from patients’ lesions as well as with sclerotic bodies cultivated in vitro, conidia, mycelia, and digested residues. Treatment ofF. pedrosoiwith purified antibodies against melanin inhibited fungal growth in vitro. The interaction ofF. pedrosoiwith phagocytes in the presence of melanin resulted in higher levels of fungal internalization and destruction by host cells, which was accompanied by greater degrees of oxidative burst. Taken together, these results indicate that melanin fromF. pedrosoiis an immunologically active fungal structure that activates humoral and cellular responses that could help the control of chromoblastomycosis by host defenses.