Immunologic basis of chronic allergic diseases: clinical messages from the laboratory bench.

During the past decade there have been significant advances in our understanding of the mechanisms underlying allergic responses. Immediate hypersensitivity reactions are mediated primarily by mast cells in an IgE-dependent manner. After the local release of various mediators, proinflammatory cytokines, and chemokines, there is a cell-mediated response that is dominated by eosinophils and T lymphocytes. The majority of T cells in early allergic reactions are memory T cells secreting helper type 2 (TH2)-like cytokines, i.e. IL-4, IL-5, and IL-13, but not interferon-gamma. These cytokines regulate IgE synthesis and promote eosinophil differentiation and cell survival, thus contributing to allergic inflammatory responses. Failure to control immune activation early in the course of allergic inflammation may blunt the response to glucocorticoid therapy and contribute to long-term morbidity of disease. The identification of key cells and cytokines involved in the initiation and maintenance of allergic inflammation is likely to become an important therapeutic target in the future management of this important group of diseases.