Structural alterations and inflammation of bronchi in asthma.

The structural and inflammatory changes occurring in the bronchi of asthmatics have been examined in specimens from subjects dying in status asthmaticus and from bronchial biopsies of subjects with mild asthma. Histological changes in the bronchi of asthmatics include shedding and damage of the airway surface epithelium and thickening of the reticular basement membrane. Exposure of an asthmatic subject to an allergen results in an immediate allergic response characterised by mast cell degranulation. This may be followed by a late-phase response involving eosinophil degranulation and differentiation of a myofibroblast phenotype which may be the precursor of increased amounts of bronchial smooth muscle present in chronic severe asthma. These changes are accompanied by vasodilatation, vascular congestion and consequent oedema, and result in thickening of the airway wall and reduction of the airway lumen. Mucus secretion further increases airflow resistance and, in conjunction with an inflammatory exudate, forms tenacious airway plugs which are characteristic of severe life-threatening attacks.