Importantly, the ratio of cholesterol to total phospholipids in surfactant was already elevated 3-fold in Csf2−/− mice at 6 weeks compared to WT, and remained elevated but did not increase further at 12, 24, and 36 weeks (Fig. 2g), whereas PAP lung disease severity increased steadily (Fig. 2a). This evidence concerns the gene CSF2 and lung disorder.