However, in CF, mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene leads to reduced HCO3− secretion and produces an abnormally acidic pH in ASL [177,178], which studies on humans and animal models have suggested can negatively affect the efficacy of ASL antimicrobial molecules and predispose CF airways to microbial infection (Figure 3) [165,179]. Here, CFTR is linked to cystic fibrosis.