Expression of respiratory mucins in fatal status asthmaticus and mild asthma

The airways of patients with asthma are characterized by chronic inflammatory changes comprising mainly T-cells and eosinophils, and airway remodelling with goblet cell metaplasia and submucosal gland hyperplasia. Mucus hypersecretion is often a marked feature, particularly in status asthmaticus. The matrix of airway sputum consists of high molecular glycoproteins and mucins. In this study, the expression and distribution of the major gel-forming mucins MUC5AC and MUC5B were studied in fatal status asthmaticus tissues and bronchial biopsies of mild asthmatic patients. The effect of inhaled corticosteroids on the expression of these mucins was also investigated.

Polyclonal antibodies specific for MUC5AC and MUC5B, and a monoclonal antibody for MUC5B were used to stain lung tissues and airway mucosal biopsies obtained from patients who died of status asthmaticus (n=5) and from mild asthmatics (n=4), respectively. Immunohistochemistry for MUC5AC revealed abundant staining of goblet cells situated in the epithelial surface lining and glandular ducts of tissues from patients with fatal asthma. MUC5B immunoreactivity was restricted to mucous cells of submucosal glands and to epithelial cells. In mild asthmatics, large amounts of MUC5B, but not MUC5AC, positive extracellular mucus was found in the airway lumen as plugs, adjacent to the epithelial lining and in the necks of glandular secretory ducts of mild asthmatics. The distribution of MUC5AC and MUC5B in bronchial biopsies of mild asthmatics was similar before and after inhaled steroid treatment.

The expression of MUC5AC and MUC5B shares a similar distribution to normal airways in different states of asthma. The distribution is not affected by topical corticosteroid therapy.