Objectives: Sensitization to fungi can lead to the exacerbation and complication of respiratory conditions such as asthma in predisposed patients. Extracellular proteases and toxins from A. fumigatus are involved in host cells activation leading to cell cytotoxicity, generation of cytokines and facilitation of allergic sensitization. However, little is known about the normal response to epithelial cells and macrophages to purified fungal allergens. The aim of this study was to describe which specific A. fumigatus allergens are able to induce inflammatory responses in epithelial cells and macrophages. 

Methods: 16HBE bronchial epithelial cells and monocyte-derived macrophages (THP-1) were exposed to A. fumigatus conidia, crude protein extracts and the recombinant purified allergens Asp f 1, Asp f 5, DppV and AfuS28 for 24 hours. Cell damage measured by lactate dehydrogenase release (LDH) and epithelial cells desquamation were determined. Cell response was evaluated by measurement of pro-inflammatory cytokines (IL-6, IL-8, IL1 and TNF) in cell culture supernatants. GraphPad Prism was used to interpret data and p values were calculated through One-way ANOVA test. 

Results: Aspergillus fumigatus hyphae and the purified allergens Asp f 1 and Asp f 5 significantly induced cell damage in bronchial epithelial cells and macrophages measured respectively by epithelial cells desquamation and LDH release (P < 0.01). Asp f 5 caused a higher percentage of epithelial detachment (70,3%) compared to Asp f 1 (17,63%) and A. fumigatus hyphae (19.6%). No differences between fungal protease-derived cytotoxicity in macrophages were observed. THP-1 macrophages secreted up to 4-fold more IL1, TNF and IL-6 than unchallenged controls in response A. fumigatus spores, Asp f 1 and Asp f 5 (P < 0.01). 16HBE bronchial epithelial cells released 2-fold more IL-6 and IL-8 in response to the purified A. fumigatus allergens DppV and Asp f 5 than unchallenged controls (P < 0.001).  The fungal allergen AfuS28 was unable to induce inflammatory responses bronchial epithelial cells and macrophages in our model.

Conclusions: (i) The mechanisms of epithelial cell and macrophage activation by fungal allergens is protein-dependant.  (ii) Asp f 5 can activate both epithelial cells and macrophages while Asp f 1 predominantly activates macrophages and DppV epithelial cells. (iii) Further research is needed to investigate the role of these fungal allergens in modulating the response of the bronchial epithelium and macrophages in patients with fungal allergy.

7 / Differential response of the bronchial epithelium and macrophages to Aspergillus fumigatus allergens