MUC5B and chronic obstructive pulmonary disease: The composition of mucus in asthma and COPD is generally altered, with higher expression of the low charge isoform MUC5B, particularly in COPD, and with the expression of small amounts of the insoluble MUC2; in COPD the ratio of mucus cells to serous cells in the submucosal glands is also increased [69].