In vitro approaches to identify an antiviral role for BPIFB1 in the airway epithelium

It has been assumed that BPIFB1, a secretory protein produced by the respiratory tract, functions in host defence, based on analogy to other members of the wider BPI-fold contain family. Studies have been hampered by the fact that the gene is only expressed in differentiated primary airway cells grown at the air liquid interface (ALI). Our previous studies have shown that BPIFB1 is found in a subpopulation of “goblet cells” in the airway, and IL-13 induces bpifb1. Influenza A virus (IAV) is a significant respiratory pathogen and our preliminary data demonstrated that bpifb1 is reduced in lungs following X31 strain IAV infection. We hypothesised that BFIFB1 contributes to the defence against IAV infections and this can be studied in vitro. Analysis of primary mouse tracheal epithelial cells (mTECs) showed that bpifb1 increases during 14 days of ALI differentiation, and western blotting confirmed production of BPIFB1 as an N-glycosylated protein. A series of FLAG-tagged expression constructs were shown to produce recombinant murine BPIFB1 proteins. We developed an IAV infection assay in mTECs that can be used with these proteins to identify regions of BPIFB1 that modulate viral infection. In parallel to mTEC studies, we are utilising HBEC3-KT cells, a human immortalized cell line that expresses BPIFB1 as it undergoes mucociliary differentiation. We generated a CRISPR based a BPIFB1 knock out cell line, and studies using recombinant BPIFB1 protein and PR8 IAV infection revealed a protective effect against viral susceptibility. Taken together, our study has established mTECs and HBEC3-KT cells as suitable model systems to investigate the protective role of BPIFB1 in viral IAV infection.