[Pathophysiology of the IgE-dependent reaction in respiratory allergy]

The IgE-dependent reaction is a specific type of inflammatory reaction occurring in allergic persons responding to an allergen. When the allergen penetrates the airways, it is captured by the antigen presenting cells and presented to CD4+ T cells. The most important conditions of antigenic presentation are the presence of IL-4 and not IL-12 at the presentation site and the implication of certain coreceptors determining T-cell differentiation to Th2 cells, which produce IL-4, IL-3, and IL-5. Il-4 and IL-3 induce IgE production by plasmocytes and IL-5 activates eosinophils. The specific IgEs of the allergens then bid to their high-affinity receptor on the surface of mast cells (sensitivization phase). If the allergens are still present or if there is an new exposure, coaggregation of high-affinity receptors via specific IgEs induces mast cell degranulation and release of vaso- and broncho-active mediators which lead to the acute signs of rhinitis or asthma (early phase of the immediate reaction). At the same time, activated eosinophils, attracted by IL-5 as well as chemokines, infiltrate the mucosa, producing basic proteins toxic for the epithelium. These cells are responsible for the late phase of the immediate allergic reaction, and during repeated or continuous exposure, are the cause of the chronic allergic disease.