Eosinophils and allergy in asthma.

Eosinophils are recruited to the site of IgE-mediated allergic reaction in the airway in asthma. Major eosinophil-chemotactic factors released from mast cells are platelet activating factor and Leukotriene B4. In addition, T cells and bronchial epithelial cells produce eosinophil chemotactic cytokines. Cytokines including IL-5, IL-3, and GM-CSF, which are released mainly from CD4+ T cells and possibly Th2, activates eosinophils for migration, tissue damage, and survival. Adhesion molecules on eosinophils and constituent structures of the airway participate in the process of eosinophil migration. Among a variety of adhesion molecules, VLA-4 and VCAM-1 are unique to the interaction between eosinophils and endothelial cells. A major role of recruited eosinophils in the airway in asthma is considered to be damage to the bronchial epithelium caused by eosinophil specific granules proteins, in addition to production of lipid mediators, production of cytokines, antigen-presenting cell function, and possible induction of basement membrane thickening in the airway.