MUC5AC and idiopathic pulmonary fibrosis: For example, the rs5743890 polymorphism in the TOLLIP gene is associated with increased susceptibility to IPF, increased mortality and reduced expression of this protein, which normally functions as a negative regulator of TLR signalling.30 Similarly, the gain‐of‐function mutation in the mucin MUC5B gene promoter (rs35705950) leads to overexpression of mucin in the lung and accumulation in terminal bronchioles.31 Mucin is believed to play an important host defence function by trapping inhaled particles and pathogens to allow for mucociliary clearance.