MUC5AC and asthma: These mucous cells produce the mucin glycoprotein (MUC), the predominant form in the airways being MUC5AC; and the submucosal glands mainly produce MUC5B, with MUC5B being predominant under normal conditions and MUC5AC over-regulated in asthma (Evans et al., 1999; Kirkham et al., 2002; Rose and Voynow, 2006).