Immunoglobulin E IgE

The potent biological activity of IgE allowed it to be identified in serum despite its extremely low average serum concentration (0.3 ^g/ml). IgE antibodies mediate the immediate hypersensitivity reactions that are responsible for the symptoms of hay fever, asthma, hives, and anaphylactic shock. The presence of a serum component responsible for allergic reactions was first demonstrated in 1921 by K. Prausnitz and H. Kustner, who injected serum from an allergic person intra-dermally into a nonallergic individual. When the appropriate antigen was later injected at the same site, a wheal and flare reaction (analogous to hives) developed there. This reaction, called the P-K reaction (named for its originators, Prausnitz and Kustner), was the basis for the first biological assay for IgE activity.

Actual identification of IgE was accomplished by K. and T. Ishizaka in 1966. They obtained serum from an allergic in

(a) Structure of secretory IgA

(a) Structure of secretory IgA

Secretory Iga Images
Secretory component

(b) Formation of secretory IgA

(b) Formation of secretory IgA

Componente Secretor Iga

Lumen

Secretory IgA

Structure and formation of secretory IgA. (a) Secretory IgA consists of at least two IgA molecules, which are covalently linked to each other through a J chain and are also covalently linked with the secretory component. The secretory component contains five Ig-like domains and is linked to dimeric IgA by a disulfide bond between its fifth domain and one of the IgA heavy chains. (b) Secre

Lumen

Secretory IgA

FIGURE 4-15

Structure and formation of secretory IgA. (a) Secretory IgA consists of at least two IgA molecules, which are covalently linked to each other through a J chain and are also covalently linked with the secretory component. The secretory component contains five Ig-like domains and is linked to dimeric IgA by a disulfide bond between its fifth domain and one of the IgA heavy chains. (b) Secre tory IgA is formed during transport through mucous membrane epithelial cells. Dimeric IgA binds to a poly-Ig receptor on the baso-lateral membrane of an epithelial cell and is internalized by receptor-mediated endocytosis. After transport of the receptor-IgA complex to the luminal surface, the poly-Ig receptor is enzymatically cleaved, releasing the secretory component bound to the dimeric IgA.

dividual and immunized rabbits with it to prepare anti-isotype antiserum. The rabbit antiserum was then allowed to react with each class of human antibody known at that time (i.e., IgG, IgA, IgM, and IgD). In this way, each of the known anti-isotype antibodies was precipitated and removed from the rabbit anti-serum. What remained was an anti-isotype antibody specific for an unidentified class of antibody. This antibody turned out to completely block the P-K reaction. The new antibody was called IgE (in reference to the E antigen of ragweed pollen, which is a potent inducer of this class of antibody).

IgE binds to Fc receptors on the membranes of blood ba-sophils and tissue mast cells. Cross-linkage of receptor-bound IgE molecules by antigen (allergen) induces basophils and mast cells to translocate their granules to the plasma membrane and release their contents to the extracellular environment, a process known as degranulation. As a result, a variety of pharmacologically active mediators are released and give rise to allergic manifestations (Figure 4-16). Localized mast-cell degranulation induced by IgE also may release mediators that facilitate a buildup of various cells necessary for antiparasitic defense (see Chapter 15).

Immune benefits of breast milk

Antibodies of secretory IgA class

B12 binding protein

Bifidus factor

Fatty acids Fibronectin

Hormones and growth factors

Interferon (IFN-7)

Lactoferrin

Lysozyme Mucins

Oligosaccharides SOURCE: Adapted from J

Bind to microbes in baby's digestive tract and thereby prevent their attachment to the walls of the gut and their subsequent passage into the body's tissues.

Reduces amount of vitamin B12, which bacteria need in order to grow.

Promotes growth of Lactobacillus bifidus, a harmless bacterium, in baby's gut. Growth of such nonpathogenic bacteria helps to crowd out dangerous varieties.

Disrupt membranes surrounding certain viruses and destroy them.

Increases antimicrobial activity of macrophages; helps to repair tissues that have been damaged by immune reactions in baby's gut.

Stimulate baby's digestive tract to mature more quickly. Once the initially "leaky" membranes lining the gut mature, infants become less vulnerable to microorganisms.

Enhances antimicrobial activity of immune cells.

Binds to iron, a mineral many bacteria need to survive. By reducing the available amount of iron, lactoferrin thwarts growth of pathogenic bacteria.

Kills bacteria by disrupting their cell walls.

Adhere to bacteria and viruses, thus keeping such microorganisms from attaching to mucosal surfaces.

Bind to microorganisms and bar them from attaching to mucosal surfaces.

Newman, 1995, How breast milk protects newborns, Sci. Am. 273(6):76.

Allergen

Granule

Allergen

Granule

Immunoglobulin

Fc receptor specific for IgE

Mast cell

Fc receptor specific for IgE

Mast cell

Degranulation and release of granule contents

Histamine and other substances that mediate allergic reactions

Immunoglobulin Allergic
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