The influenza A virus promotes fungal growth of Aspergillus fumigatus via direct interaction in vitro.

Seasonal influenza A virus (IAV) infections still pose a major burden for public health worldwide. Severe disease progression or even death is often related to superinfections of the virus and a secondary bacterial pathogen. However, fungi, especially Aspergillus fumigatus, are also frequently diagnosed during IAV infection. Although, clinical studies have reported the severity of influenza-associated pulmonary aspergillosis, the molecular mechanisms underlying this type of disease are poorly understood. Here, a new in vitro model is introduced that allows the investigation of complex pathogen-host and pathogen-pathogen interactions during coinfection of lung epithelial cells with IAV and A. fumigatus. Our data reveal a reduced IAV load and IAV-induced cytokine and chemokine expression in the presence of A. fumigatus. At the same time, IAV infection promotes the growth of A. fumigatus. Even in the absence of the human host cell, purified IAV particles are able to induce hyphal growth, due to a direct interaction of the virus particles with the fungal surface. Thus, our study gives first insights into the complex interplay between IAV, A. fumigatus and the host cell as well as the two pathogens alone.