Aspergillus fumigatus is the major cause of human aspergilloses accounting for >90% of all cases of disease. Inhaled conidia interact with lung epithelial cells, and germinate into hyphae that penetrate and damage underlying tissues. It has been shown that epithelial cells respond actively to the inhaled fungus in addition to posing an anatomical barrier but the exact mechanism of response, and whether or not these mechanisms are protective or detrimental to the host is largely unknown. The aim of this study is to generate a global map of epithelial responses to A. fumigatus over time and characterise the role of these mechanisms in eventual epithelial cell destruction.
A549 epithelial cell line was co-incubated with live A. fumigatus and culture filtrate and induction of the following mechanisms in the epithelial cells over time were assayed (i) activation of signalling pathways using the Luminex multiplex assay, (ii) transcriptional responses using the TransAM ELISA assay for DNA binding activity and (iii) profile of cytokine expression using human XL cytokine profiler and Luminex method. The amount of damage induced by both live fungi and secreted products independently in A549 monolayer was measured using the LDH assay.
Live A. fumigatus induced epithelial cell damage as measured by LDH after 12 h of infection, whereas CF induced cell detachment in addition to damage as early as 30 min post exposure. Live A. fumigatus induced early and sustained NF-κB activation and late JNK activation, whereas CF activated JNK, p38 and ERK1/2 at 30 min post exposure. Live A. fumigatus increased the DNA binding activity of the transcription factors c-Fos and members of the canonical NF-κB pathway (p50 and p65), while decreasing MEF-2, Jun D and Rel B activities. On the other hand, CF exposure increased the DNA binding activity of the non-canonical NF-κB pathway (Rel B and p52), while decreasing the binding activity of MEF-2 and c-Myc. Live A. fumigatus induced significant production of GM-CSF and IL-8 but not IL-6 and G-CSF, while CF significantly reduced the levels of IL-8, IL-6 and G-CSF.
Together, this data suggests that A549 cells recognize and respond differently to live A. fumigatus and its secreted products. Current studies focus on elucidating the specific host and fungal properties driving these responses.