BPIFA1 and infection: Both pre-existing serous cells of steady-state airways and expanding populations of serous cells observed during the early injury/inflammatory phase following PR8 infection were unique among distal lung epithelial cell types in their expression of genes such as Ifitm1, Ifitm3, Bpifa1, and Ltf, that were associated with anti-microbial host defense (Fig. 1F; Supplementary Figs. 1D, 2A).