AUTHOR=Thywißen Andreas , Heinekamp Thorsten , Dahse Hans-Martin , Schmaler-Ripcke Jeannette , Nietsche Sandor , Zipfel Peter F., Brakhage Axel A.

TITLE=Conidial Dihydroxynaphthalene Melanin of the Human Pathogenic Fungus Aspergillus fumigatus Interferes with the Host Endocytosis Pathway

JOURNAL=Frontiers in Microbiology

VOLUME=2

YEAR=2011

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2011.00096

DOI=10.3389/fmicb.2011.00096

ISSN=1664-302X

ABSTRACT=<p><italic>Aspergillus fumigatus</italic> is the most important air-borne fungal pathogen of humans. The interaction of the pathogen with the host's immune system represents a key process to understand pathogenicity. For elimination of invading microorganisms, they need to be efficiently phagocytosed and located in acidified phagolysosomes. However, as shown previously, <italic>A. fumigatus</italic> is able to manipulate the formation of functional phagolysosomes. Here, we demonstrate that in contrast to pigmentless <italic>pksP</italic> mutant conidia of <italic>A. fumigatus</italic>, the gray-green wild-type conidia inhibit the acidification of phagolysosomes of alveolar macrophages, monocyte-derived macrophages, and human neutrophil granulocytes. Therefore, this inhibition is independent of the cell type and applies to the major immune effector cells required for defense against <italic>A. fumigatus</italic>. Studies with melanin ghosts indicate that the inhibitory effect of wild-type conidia is due to their dihydroxynaphthalene (DHN)-melanin covering the conidia, whereas the hydrophobin RodA rodlet layer plays no role in this process. This is also supported by the observation that <italic>pksP</italic> conidia still exhibit the RodA hydrophobin layer, as shown by scanning electron microscopy. Mutants defective in different steps of the DHN-melanin biosynthesis showed stronger inhibition than <italic>pksP</italic> mutant conidia but lower inhibition than wild-type conidia. Moreover, <italic>A. fumigatus</italic> and <italic>A. flavus</italic> led to a stronger inhibition of phagolysosomal acidification than <italic>A. nidulans</italic> and <italic>A. terreus</italic>. These data indicate that a certain type of DHN-melanin that is different in the various <italic>Aspergillus</italic> species, is required for maximal inhibition of phagolysosomal acidification. Finally, we identified the vacuolar ATPase (vATPase) as potential target for <italic>A. fumigatus</italic> based on the finding that addition of bafilomycin which inhibits vATPase, led to complete inhibition of the acidification whereas the fusion of phagosomes containing wild-type conidia and lysosomes was not affected.</p>