The human cathelicidin antimicrobial peptide LL-37 promotes the growth of the pulmonary pathogen Aspergillus fumigatus.

Aspergillus fumigatus contributes to invasive and allergic pulmonary disease in immunocompromised individuals. The pulmonary mucus of cystic fibrosis (CF) patients displays elevated levels of the pleiotropic cathelicidin antimicrobial peptide LL-37 and the aim of this work was to assess the effect of LL-37 on the growth A. fumigatus. Exposure of A. fumigatus conidia to high concentrations of intact LL-37 (100 μg/ml) for 24 hours had a positive effect on growth (277.45 ± 22.59% (p < 0.01)) whereas scrambled LL-37 (76.45 ± 7.46%) did not. Exposure of 24 hour pre-formed mycelium to 5 μg/ml LL-37 for 48 hours increased hyphal wet weight significantly (4.37 ± 0.23 g, p < 0.001) compared to the control (2.67 ± 0.05 g). Amino acid leakage from mycelium was observed in the presence of LL-37 and gliotoxin secretion was increased at 24 hours from LL-37 exposed hyphae (169.1 ± 6.36 ng/mg hyphae, p < 0.05) compared to the control (102 ± 18.81 ng/mg hyphae). Quantitative proteomic analysis of 24 hour LL-37 treated hyphae revealed an increase in the abundance of proteins associated with growth (eIF-5A (16.3 fold increased), tissue degradation (aspartic endopeptidase (4.7 fold increased)) and allergic reactions (Asp F13 (10 fold increased)). By 48 hours there was an increase in proteins indicative of cellular stress (glutathione peroxidase (9 fold increased)), growth (eIF-5A (6 fold increased), and virulence (ribonuclease mitogillin (3.7 fold increased). These results indicate that LL-37 stimulates A. fumigatus growth and this may result in increased fungal growth and secretion of toxins in the lungs of CF patients.