Analysis of chronic host-aspergilloma interactions using a novel mouse model

An aspergilloma is a fungus ball caused by chronic infection of Aspergillus species in a pre- existing cavity, such as a destroyed lung or the sinuses. Patients with pulmonary aspergilloma are at risk of sudden life-threatening hemoptysis. Antifungal therapy is administered to aspergilloma patients who are ineligible for surgery, but its efficacy is limited. Understanding the pathophysiology of aspergilloma is crucial for developing further treatment strategies. The mechanism behind the long-term host response to aspergilloma is poorly understood. We created a novel mouse model to analyze the host response to aspergilloma by implanting a fungus ball of Aspergillus fumigatus into an air-filled subcutaneous cavity. Our findings indicate that a live fungus ball led to tissue invasion, even in immunized mice. When a fungus ball consisting of dead hyphae was implanted, it persisted for over three months and induced pathological findings simulating human aspergilloma, including an inflammatory cell infiltration into the fungus ball and angiogenesis in the cavity wall. Dead fungus ball induced Th1 and Th17 inflammatory cytokines and vascular endothelial growth factor. Neutrophils infiltrated the inside of the fungus ball immediately after implantation, and macrophages surrounded it after a one-week delay. The macrophages around the fungus ball were swollen with phagocytosed fragments of dead hyphae and transformed into foam cells containing fat droplets. We also confirmed in vitro that macrophages were damaged and transformed into foam cells by direct contact with dead hyphae. This model holds promise to provide new insights into the fungal-host interaction during aspergillomas. NOTATION OF PRIOR ABSTRACT PUBLICATION/PRESENTATIONNone IMPORTANCEChronic aspergillosis, which affects over 3 million people worldwide with a 5-year survival rate of 50%, is understudied compared to other forms. Our study focuses on aspergilloma, a key aspect of chronic aspergillosis, using a groundbreaking mouse model that mirrors clinical features over three months. By studying host-fungal interactions within aspergillomas, we discovered Th1 and Th17 inflammatory responses to dead fungal hyphae. Initially, neutrophils dominate, later giving way to macrophages with a lipid-accumulating foamy phenotype. This transition may impede aspergilloma clearance. In addition, even dead hyphae induce vascular endothelial growth factor and promote angiogenesis. Our findings, which are critical for the prevention of fatal hemoptysis, highlight the need for innovative treatments that target fungal clearance and challenge the limited efficacy of antifungal agents against dead fungal bodies. This research represents a significant step forward in the understanding of chronic aspergillosis.