LSC Abstract – A systems biology approach to aid identification of the mechanisms employed by BPIFA1/SPLUNC1 to restrict influenza A virus infection in the lung

Defence proteins produced by epithelial cells are a critical component of the host response to respiratory infection. BPIFA1/SPLUNC1 is a member of the bactericidal/permeability-increasing (BPI) fold-containing (BPIF) protein family and is secreted in the mammalian respiratory tract. While it has been implicated in airway host defence its function is yet unresolved. The objective of this study was to use system biology tools to assess SPLUNC1 function in the respiratory tract in response to Influenza A virus (IAV) infection. We have established an in vivo model for studying SPLUNC1 function using knockout mice. As early as day 1 post infection, there is a 1 log increase in IAV titre and a more rapid spread of virus. Analyses of both label-free quantitative proteomics and transcriptomics data sets show an increased infiltration of inflammatory cells in the lungs of infected SPLUNC1 KO compared with wild-type controls. This has been complemented by histopathology as well as flow cytometric analysis, which shows a 3-fold increase in neutrophils in the lungs and BAL. Pathway analyses also reveals a modulation in cell movement and humoral immune responses in the KO mice. Gene set enrichment analysis of RNAseq output shows a significantly reduced enrichment in the expression of B and T lymphocyte surface markers in KO mice compared to wild-type mice, hence identifying molecular signatures associated with SPLUNC1 action. Our data indicate that SPLUNC1 is a crucial component of the mucosal host defence against Influenza A virus and provide further support for its function in influencing inflammation and adaptive immunity.