The mucus on mucosal barriers traps particles and pathogens and eliminates them through mucociliary clearance. In Nature, Evans and colleagues show that in mice, the mucin MUC5B is required for mucociliary clearance, homeostasis of the immune system and control of infection in the airways. MUC5A-deficient mice have upper airway obstruction with defective breathing and develop spontaneous and fatal infection with Staphylococcus aureus. Macrophages showing phagocytic exhaustion and signs of apoptosis accumulate in the lungs of MUC5A-deficient mice. However, activation of macrophages and elimination of S. aureus are enhanced in mice with transgenic expression of Muc5b. MUC6 is known to inhibit Helicobacter pylori, whereas MUC5AC inhibits Trichuris muris, but neither inhibits S. aureus growth, which suggests specificity in mucin-mediated defenses. Human MUC5B is highly polymorphic and promoter variants with higher expression are also known, which suggests that MUC5B variants may regulate airway homeostasis in humans.

Nature (8 December 2013) doi:10.1038/nature12807