MUC5AC and cystic fibrosis: Further supporting these observations, studies of bronchoalveolar lavage fluids performed on CF preschoolers have shown that the incipient mucus material harvested from CF lungs consisted of abundant and irregular/rough MUC5B/MUC5AC mucus flakes, indicating disturbance of mucus homeostasis in the distal airways in CF lung disease (see mucin distribution and effects on mucin network below) [19].