BPIFA1 and susceptibility to pneumonia measurement: Furthermore, when we re-examined tissues from our earlier infection experiment (Dietert et al. 2014) in terms of altered expression of BPIFA1 in Clca1−/− mice, we were able to confirm the effect seen ex vivo to be true for the in vivo scenario of S. aureus-induced pneumonia in that Bpifa1 mRNA was less reduced in Clca1−/− mice at 24 h post-infection in the trachea (Fig. 6).