Our changing understanding of asthma.

It is now becoming clear that asthma is a chronic inflammatory disease, involving many interacting cells. These cells release a wide variety of inflammatory mediators that activate several target cells in the airway, resulting in bronchoconstriction, microvascular leakage and oedema, mucus hypersecretion and stimulation of neural reflexes. Recent evidence suggests that mast cells do not have a key role in either the late response or in bronchial hyper-responsiveness, though they may be involved in immediate responses to allergens. The possible role of other inflammatory cells and the many different mediators which have been implicated in asthma are discussed. Microvascular leakage and the role of neural mechanisms are also examined. It seems probable that there are several different types of asthma, involving different mechanisms, which may respond to different forms of therapy, but more research is needed.