Objectives: Fungal colonisation of the airway epithelium is linked to poorly controlled asthma in patients with allergic bronchopulmonary aspergillosis (ABPA) and severe asthma with fungal sensitization (SAFS). Impaired mucociliary function in patients with asthma has been associated with increased fungal growth and colonisation of the respiratory airways. However, not all asthmatics develop fungal asthma and host genetic factors might be important. The aim of this study was to characterise the role of the human genes IL17RA and CARD10 in controlling fungal colonisation of the respiratory airways. 

Methods: Genetic variability in the IL17RA and CARD10 genes is very high in patients with ABPA, suggesting and altered function of those genes. 16HBE bronchial epithelial cells deficient in IL17RA (16HBEIL17RA) and CARD10 (16HBECARD10) were generated by CRISPR/Cas9 and used in Aspergillus fumigatus challenge experiments. Differences in cell damage induced by the fungal allergen Asp f 5 and A. fumigatus (A1163) spores were evaluated by determining cell desquamation and IL-8 release in 16HBE, 16HBEIL17RA  and 16HBECARD10 after 24 h exposure. Fluctuations in the fungal burdens were determined by qPCR. GraphPad Prism was used to interpret data and p values were calculated through Two-way ANOVA test. 

Results: A. fumigatus A1163 and the purified allergen Asp f 5 were able to cause epithelial cell desquamation in both, 16HBE and 16HBEIL17RA (P < 0.0001). However, 16HBECARD10 desquamation was only induced by A. fumigatus hyphae. Epithelial cell detachment produced by A. fumigatus hyphae was 20% higher in 16HBEIL17RA than in 16HBE cells (P < 0.0001). These observations correlated with 5-times higher fungal burdens in 16HBEIL17RA exposed to A. fumigatus than in 16HBE cells (P < 0.05). IL-8 release by 16HBEIL17RA exposed to Asp f 5 and hyphae doubled that produced by 16HBE cells (P < 0.0001). No IL-8 response was observed in 16HBECARD10 exposed to Asp f 5 and A. fumigatus hyphae. 

Conclusions:  Our results indicate that exposure of bronchial epithelial cells deficient in IL17RA to Aspergillus fumigatus leads to epithelial cell desquamation, high fungal loads and a strong IL-8 function. Furthermore, the response of CARD10 deficient bronchial epithelial cells is limited.

6 / The IL17RA and CARD10 genes are important in controlling Aspergillus fumigatus colonisation of the lung in allergic bronchopulmonary aspergillosis