Studies in humans and CF cell lines indicate that pH of ASL is reduced in the absence of CFTR function (Smith and Welsh, 1992; Coakley et al., 2003; Abou Alaiwa et al., 2014a), and the more acidic pH diminished the effect of ASL antimicrobials including LL-37 and β-defensin-3 (Abou Alaiwa et al., 2014b). Here, CFTR is linked to cystic fibrosis.