MUC5B and cystic fibrosis: Mucus taken from the endotracheal tubes (ETT) of patients with no lung disease actually produced proportions of mucin similar to those found in the sputum of patients experiencing CF exacerbations (12% more MUC5AC in CF exacerbation vs. ETT, 4% less MUC5B in CF exacerbation vs. ETT) [55].