Melanin-dependent modification of phagolysosomal processing of conidia of the human pathogenic fungus Aspergillus fumigatus in macrophages

The human pathogenic fungus Aspergillus fumigatus represents one of the major threats to human health. This ubiquitous saprophyte has evolved versatile strategies to avoid attacks by the immune system and establish an infection in the immunocompromised host. Infection is initiated after inhalation of the airborne asexual spores (conidia) that settle in the lung alveoli and start to germinate. The formation of hyphae allows for penetration of the lung epithelia and dissemination of the infection. In the lung, conidia encounter resident alveolar macrophages that recognize, phagocytose, and eliminate the conidia by forming a fungicidal phagolysosome. However, pigmentation with 1,8-dihydroxynaphthalene (DHN)-melanin protects the conidia from degradation inside the phagolysosome by blocking the acidification of the lumen. This project aimed to describe the interference of A. fumigatus conidia with the host phagolysosomal maturation to provide insights into the DHN-melanin-dependent fungal immune evasion mechanisms. A new protocol to purify conidia-containing phagolysosomes was developed, allowing for enrichment of the phagolysosomal fraction. The dual proteome of host and pathogen in the purified phagolysosomal fraction was determined by LC-MS/MS. Abundance of identified proteins was quantified with a label-free method and the wild-type conidia-containing phagolysosomal proteome was compared against the proteome of pigmentless pksP mutant conidia-containing phagolysosomes. Differentially abundant proteins were compiled in a host regulatory module that reflects regulated processes in the phagolysosome.