Inflammatory risk of xerophilic Aspergillus fungal spores as studied in human leucocytes in vitro

Inhalation of fungal spores in indoor environments is an occupational hazard, especially in work environments with persistent exposure. Xerophilic/xerotolerant fungal growth (hereafter, xerophilic) in heritage sites (historical buildings, museums, and libraries) is documented, and represents a potential source of respiratory exposure. The health impact of xerophilic fungal spores remain unclear, specifically in the context of occupational risk assessment. This study assesses the potential of xerophilic Aspergillus species to induce production of reactive oxygen species (ROS) in a human cell line as a proxy to early immune cell responses to exposure. Museum-derived isolates of A. pseudogracilis , 17 different xerophilic Aspergillus species from a fungal collection, and A. fumigatus (positive reference) were put into a standardized, single spore suspension. Granulocyte-like cells (HL-60) were exposed to these spore suspensions, and ROS production was monitored for 3 hours. Cytotoxicity and inflammatory cytokine expression were also determined after exposure to selected fungal species. For the highest exposure concentration, the museum isolates and 16 of 17 species induced a significant ROS production with different responses between species. Aspergillus domesticus induced the highest response (3.5x higher than A. fumigatus ). Of eight tested xerophilic species, all caused increased expression of the cytokines TNFα, CXCL8, IL-1β, and CCL2. Exposure to seven of the eight species decreased HL-60 cell viability significantly. Overall, this systematic comparison of xerophilic species suggests that they have the potential to initiate a diverse inflammatory response in human leukocytes, and highlights the need to account for species-specific variability when determining exposure risk.