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Immunoglobulin (Ig)


Fundamental role: allergic reactions, parasitic infections, and hypersensitivity reactions.

Not fundamental in: agglutination or complement activation.

Where found: widely found in the lungs, skin, and mucous membranes.

Presence in serum: the least common serum immunoglobulin.

Presence in the cell: predominantly cell bound.

Activity when bound by allergen: release of vasoactive amines into surrounding tissue, like histamine, heparin and leukotrienes.

The role of IgE in the allergic response

The heavy chain of IgE contains an extra domain, by which it attaches with high affinity to Fc epsilon Receptor I (FcεRI) found primarily on eosinophils, mast cells and basophils. When antigens such as pollen, venoms, fungus, spores, dust mites or pet dander bind with the Fab portion of the IgE attached to the cells, the cells degranulate and release factors like heparin, histamine, proteolytic enzymes, leukotrienes and cytokines. Vasodilatation and increased small vessel permeability is a consequence, causing fluid to escape from capillaries into the tissues, leading to the characteristic symptoms of an allergic reaction. Most of these typical allergic reactions like mucus secretion, sneezing, coughing or tear production are considered beneficial to expel remaining allergens from the body.

Studies have shown that conditions such as asthma, rhinitis, eczema, urticaria, dermatitis, and some parasitic infections (e.g. helminths and tapeworms) lead to increased IgE levels. Binding of eosinophils with Fc receptors to IgE-coated parasitic helminth worms results in killing of the parasite. Low levels of IgE can occur in a rare inherited disease that affects muscle coordination (ataxia-telangiectasia).

Mouse studies are an important mode of research regarding the mechanisms and treatment of allergic responses, and quantification of IgE levels is an important testing parameter.