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e-Journal

 

ABC's Of Allergies
(Released August 2006)

 
  by Sujata Suri  

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The Immunology of Allergies

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The immune system protects our body against pathogens and other foreign substances by producing a kind of glycoprotein known as immunoglobulin (Ig) or antibodies from plasma cells or B-cells (a type of lymphocyte). Antibodies are mainly of five types, each one having a different function; the type involved in allergy is immunoglobulin E (IgE).

Immunoglobulin E (IgE) is overproduced during an allergic response. On the very first exposure to an allergen, an allergic person becomes sensitized by producing allergen-specific IgE that binds with IgE receptors on mast cells (in tissues) and basophils (in circulation).
chart showing the sequence that leads to an allergic reaction
 If the sensitized person has another exposure to this specific allergen, then this allergen will bind to the antigenic determinant site (Fab) of IgE attached to the mast cells and basophils. Binding of two or more IgE molecules to mast cells (crosslinking) is required to activate the mast cells. These activated cells result in the release of certain chemicals, such as histamine, serotonin, proteoglycans, serine protease, leukotriene C4 and heparin, that will further bind with their receptors present in other cells (e.g., histamine receptors of blood vessels) and lead to inflammation, irritation, redness and other allergic symptoms.

The primary function of our immune system is to defend against infection; however, during an allergic reaction the immune system responds against a substance that is harmless to most people. There are two subpopulations of T helper cells, Th1 and Th2. Th1 cells are helpful in protecting against invading microbes and other particles by producing interferons and some cytokines. Th2 cells are responsible for triggering allergies by the overproduction of IgE, and are also involved in the struggle against parasitic worms. Th2 cells produce cytokines like interleukins (such as IL-5) that enhance the production of specific IgE antibodies by B cells and result in hypersensitivity, eosinophil activation, mucus production and IgE secretion (Drouin et al. 2001).

chart showing development of immune system cells & how it leads to allergies

Go To Reducing the Risk of Developing Allergic Diseases

Special thanks to Deborah Whitman for her invaluable help with this Discovery Guide

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