Experimental infection of alveolar macrophages from domestic ferrets (Mustela putorius furo) with Cryptococcus neoformans

Cryptococcus neoformans is afungal pathogen of humans and animals. Tissue-resident alveolar macrophages (AMs) are important for pulmonary immune surveillance and act as first-responders to inhaled pathogens. AMs are the first targets during natural cryptococcal infection and play a key role in the innate immune response via pathogen recognition and antigen presentation. Prior studies suggest that alterations in AM populations impact host susceptibility to cryptococcal infection. Nonetheless, few models for cryptococcal infection of AMs exist. Here, we studied C. neoformans infection of AMs collected via post-mortem bronchoalveolar lavage from the domestic ferret (Mustela putorius furo). We selected the ferret as the donor species given its natural susceptibility to cryptococcosis, established use as a model for other respiratory pathologies, and larger body size than laboratory rodents allowing for greater AM yield. We used real-time live-cell imaging to analyze C. neoformans-AM interactions and identified events consistent with cryptococcal infection, including phagocytosis, non-lytic exocytosis (vomocytosis), cell-to-cell lateral transfer (dragotcytosis), and intracellular and extracellular replication of cryptococcal cells. Unlike murine AMs but consistent with findings in human AMs, activation of ferret AMs with interferon-gamma and lipopolysaccharide did not affect phagocytic activity upon exposure to C. neoformans. Our results indicate that ferret AMs are susceptible to experimental infection with C. neoformans, consistent with the notion that the natural susceptibility of this species reflects an inability of lung macrophages to control fungal burden.