ABSTRACT
Mast cells and basophils are generally recognized as the principal cell types to initiate IgE-dependent immediate hypersensitivity reactions (type I), and more recently as cells that also contribute to innate and acquired immunity and to tissue remodeling (Fig. 1). Experimental challenge of an IgEsensitized host with allergen reveals two phases to the subsequent immediate hypersensitivity reaction. The early phase of the IgE-dependent reactions (5-30 min postchallenge), depending on the target tissue and distribution of allergen, involves local edema, smooth muscle contraction, vasodilation, and increased permeability of postcapillary venules. The late phase of an immediate hypersensitivity reaction (4-12h postchallenge) involves the recruitment and activation of basophils, eosinophils, and other cell types. These late reactions can persist for at least 2 days in the challenged lower airway, but eventually appear to resolve completely. In contrast, chronic allergic intlammation results from prolonged allergen exposure, and may provoke changes in the target tissue that resolve much more slowly, if at all.
