Dictionary of Allergies .. Atopic allergy

Atopic allergy is a hypersensitive immunologic condition mediated by a distinct class of serum antibodies called reagins, which were identified in the mid-1960s to be immunoglobulin E (IgE). Atopic allergy is associated with an imbalance between various types of T cells and, as a consequence of this, an increased synthesis of IgE. In all important types of childhood atopic diseases, such as bronchial asthma and hay fever, urticaria, anaphylactic shock, as well as atopic dermatitis there is a T-cell imbalance. Human T helper type 1 (Th1) cells are characterized by their ability to produce among others, the cytokine IFN-γ. The Th2 cells produce other cytokines, particularly IL-4, IL-5, and IL-13. The common term Th1/Th2 cell balance is somewhat misleading, and it may be preferable to talk about a balance between type 1 and 2 cytokines.

Atopic diseases are characterized by an imbalance between these two types of cytokines, so that type 2 cytokines are formed in abnormally high concentrations relative to the type 1 cytokines. An imbalance between Il-4 and IFN-γ may lead to an abnormally high production of IgE and of the various mediators that give rise to allergic symptoms. Immunocompetent B lymphocytes, when stimulated by a specific allergen, produce IgE antibodies by a specific allergen. IgE antibody binds via its Fc portion to receptors on the surface of mast cells and basophilic leukocytes. Subsequent binding of allergen to cell-bound specific IgE triggers cell degranulation and the release of vasoactive amines, causing smooth muscle contraction, itch, swelling, and transmucosal leakage of extracellular fluids. The assessment of a patient's IgE level for various allergens is valuable in the diagnosis and treatment of atopic allergy.

References

1. Romagnani S.  et al: An update on human Th1 and Th2 cells. Int Arch Allergy Immunolol 1997;113:153-156

2. Strannegård, Ö.,. Strannegård I–L.: The causes of the increasing prevalence of allergy: is atopy a microbial deprivation disorder? Allergy 2001:56:91-102