MUC5AC and inflammatory bowel disease: ER stress in mucin‐producing goblet cells has been demonstrated in a mouse model, in which aberrant mucin biosynthesis due to a protein misfolding mutation in the MUC2 mucin cells leads to goblet cell ER stress and an inflammatory bowel disease‐like phenotype.38, 39 Mediators that can induce ER stress in the gut and airway epithelial cells include oxidative stress and pro‐inflammatory cytokines.