Idiopathic pulmonary fibrosis (IPF), the most common of the idiopathic interstitial pneumonias remains a disabling, progressive lung disease with extremely poor prognosis, in which no pharmacological intervention significantly alters outcome.1 A relatively poor understanding of the complex pathophysiology of IPF continues to hinder the identification of effective therapies, and of patients most likely to benefit from existing treatments.

Usual interstitial pneumonia is the histological hallmark of IPF, characterised by temporospatial heterogeneity in which normal lung is interspersed with areas of subpleural interstitial fibrosis, loss of normal alveolar architecture and the presence of fibroblastic foci.2 Histological sections may also show ‘bronchiolisation’ of the distal airway with alveolar structures replaced by enlarged airspaces (forming characteristic honeycomb cysts) lined by epithelial cells more akin to proximal airway epithelium, often ciliated and mucus producing.3 ,4 The potential importance of mucus production in the pathogenesis of IPF has been highlighted by a landmark study demonstrating that a common variant within the putative promoter region of MUC5B (an airway mucin gene) is strongly associated with familial interstitial pneumonia and IPF.5 Moreover, subjects with IPF had significantly higher expression of MUC5B protein levels compared with controls, and this was localised to areas of lung fibrosis. It has been hypothesised that excessive MUC5B may impair the host response to alveolar injury through excess mucus plugging and impaired clearance of inhaled substances and micro-organisms. Alternative theories propose that MUC5B may interfere directly with alveolar repair mechanisms, either through disruption of interactions between type II alveolar epithelial cells and extracellular matrix, or …