Mechanisms of immediate-type allergic reactions: indispensable facts

Immediate-type hypersensitivity includes that group of allergic reactions that occur in genetically predisposed individuals, i.e., those who are atopic. In such individuals, repeated exposure to environmental antigens (allergens) leads to increased IgE antibody production. IgE-dependent activation of sensitised mast cells by allergen induces rapid release of vasoactive mediators as well as agents active on smooth muscle, resulting in an acute (immediate) reaction. The target organs and tissues of the immediate reaction are also the site of an inflammatory reaction (late phase), maintained and amplified by exposure to environmental allergens. This inflammation is responsible, directly or indirectly, for increased reactivity (hyper-reactivitity) of the target organs and tissues (skin and nasal, bronchial and gut mucosa) to stimulation induced by the allergens and by non-specific environmental factors (irritants, cold dry air, exercise etc.). Therefore, treatment involves counteraction of this inflammatory response by avoidance of the responsible allergens, carried out as forcefully as possible, and with anti-inflammatory drugs and eventually, allergen-specific immunotherapy. (C) 2003 Editions scientifiques et medicales Elsevier SAS. Tous droits reserves.