Aspergillus fumigatus is an opportunistic fungal pathogen that typically infects the lungs of immunocompromised patients leading to a high mortality. H-ficolin, an innate immune opsonin, is produced by type II alveolar epithelial cells and could participate in lung defences against infections. Here, we utilised the human type II alveolar epithelial cell line, A549, to determine the involvement of H-ficolin in fungal defence. Additionally, we investigated the presence of H-ficolin in bronchoalveolar lavage fluid (BAL) from transplant patients during pneumonia. H-ficolin exhibited demonstrable binding to A. fumigatus conidia via L-fucose, D-mannose and N-acetylglucosamine residues in a calcium- and pH-dependent manner. Moreover, recognition led to lectin complement pathway activation and enhanced fungal association with A549 cells. Following recognition, H-ficolin opsonization manifested an increase in IL-8 production from A549 cells which involved activation of the intracellular signalling pathways MEK 1/2, p38 MAPK and JNK. Finally, H-ficolin concentrations were significantly higher in BAL of patients with lung infections compared to control subjects (n=16; p=0.00726). ROC curve analysis further highlighted the potential of H-ficolin as a diagnostic marker for lung infection (AUC=0.77; p<0.0001). Thus, H-ficolin participates in A. fumigatus defence via activation of the lectin complement pathway, enhanced fungal-host interactions and modulated immune responses. This article is protected by copyright. All rights reserved.