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Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001.

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Immunobiology: The Immune System in Health and Disease. 5th edition.

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Chapter 12Allergy and Hypersensitivity

Allergic reactions occur when an individual who has produced IgE antibody in response to an innocuous antigen, or allergen, subsequently encounters the same allergen. The allergen triggers the activation of IgE-binding mast cells in the exposed tissue, leading to a series of responses that are characteristic of allergy. As we learned in Chapter 9, there are circumstances in which IgE is involved in protective immunity, especially in response to parasitic worms, which are prevalent in less developed countries. In the industrialized countries, however, IgE responses to innocuous antigens predominate and allergy is an important cause of disease (Fig. 12.1). Almost half the populations of North America and Europe have allergies to one or more common environmental antigens and, although rarely life-threatening, these cause much distress and lost time from school and work. Because of the medical importance of allergy in industrialized societies, much more is known about the pathophysiology of IgE-mediated responses than about the normal physiological role of IgE.

Figure 12.1. IgE-mediated reactions to extrinsic antigens.

Figure 12.1

IgE-mediated reactions to extrinsic antigens. All IgE-mediated responses involve mast-cell degranulation, but the symptoms experienced by the patient can be very different depending on whether the allergen is injected, inhaled, or eaten, and depending (more...)

The term allergy was originally defined by Clemens Von Pirquet as “an altered capacity of the body to react to a foreign substance,” which was an extremely broad definition that included all immunological reactions. Allergy is now defined in a much more restricted manner as “disease following a response by the immune system to an otherwise innocuous antigen.” Allergy is one of a class of immune system responses that are termed hypersensitivity reactions. These are harmful immune responses that produce tissue injury and may cause serious disease. Hypersensitivity reactions were classified into four types by Coombs and Gell (Fig. 12.2). Allergy is often equated with type I hypersensitivity (immediate-type hypersensitivity reactions mediated by IgE), and will be used in this sense here.

Figure 12.2. There are four types of hypersensitivity reaction mediated by immunological mechanisms that cause tissue damage.

Figure 12.2

There are four types of hypersensitivity reaction mediated by immunological mechanisms that cause tissue damage. Types I–III are antibody-mediated and are distinguished by the different types of antigens recognized and the different classes of (more...)

In this chapter we will first consider the mechanisms that favor the production of IgE. We then describe the pathophysiological consequences of the interaction between antigen and IgE that is bound by the high-affinity Fcε receptor (FcεRI) on mast cells. Finally, we will consider the causes and consequences of other types of immunological hypersensitivity reactions.

Contents

The production of IgE

Effector mechanisms in allergic reactions

Hypersensitivity diseases

Summary to Chapter 12

General references

Section references

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2001, Garland Science.
Bookshelf ID: NBK10756

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