MUC5B and pulmonary fibrosis: Furthermore, we report an increase in secreted mucins vs. decreased or no change in membrane-bound mucin expression levels in lung tissue of TIMPKO mice as compared to the WT-SHAM mice indicating that the secreted mucins MUC5AC and MUC5B may be more critical to airway defense and asthma disease progression compared to the membrane-bound mucins that may play a significant role in lung fibrosis and tumor progression.