MUC5B and pulmonary fibrosis: Certain patients with familial IPF have mutations in SpA and SpC genes, and accumulation of misfolded proteins in alveolar epithelial cells has been shown to contribute to endoplasmic reticulum stress [4] and enhanced susceptibility to bleomycin-induced injury [5] and fibrosis [6].The mucin gene, mucin 5B (Muc5b) expressed in distal airways, also has been strongly linked to pulmonary fibrosis [7].