The role of the mast cell in asthma: a reassessment

Interest in the role of the mast cell in bronchial asthma has waxed and waned over several decades, but there is now compelling evidence that mast cells make an important contribution to the pathophysiology of this disease. This review will discuss current advances in this field.

Mast cells, but not T cells or eosinophils, localize within the bronchial smooth muscle bundles in patients with asthma but not in normal individuals or those with eosinophilic bronchitis. Smooth muscle mast cell density correlates significantly with indices of bronchial hyperresponsiveness, and is likely to be an important factor determining the asthmatic phenotype. Tryptase induces proliferation in human airway smooth muscle, and the recently identified transmembrane form induces the development of bronchial hyperresponsiveness in mice. IL-4 and IL-13, known mast cell products, also induce bronchial hyperresponsiveness in the mouse, in the absence of an inflammatory response. There are therefore several pathways by which the close approximation of mast cells with airway smooth muscle cells might lead to disordered smooth muscle function. Mast cells also infiltrate the airway mucous glands in patients with asthma, showing features of degranulation, and a positive correlate with the amount of mucus obstructing the airway lumen. Taken together these observations suggest that mast cells also play an important role in regulating mucous gland secretion.

The development of potent and specific inhibitors of mast cell secretion, which remain active when administered long term to asthmatic airways, should offer a novel approach to the treatment of asthma.