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Immunoglobulin E (IgE) is a kind of antibody (or immunoglobulin (Ig) "isotype") that has only been found in mammals. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the ε chain containing 4 Ig-like constant domains (Cε1-Cε4). IgE's main function is immunity to parasites such as helminths like ''Schistosoma mansoni'', ''Trichinella spiralis'', and ''Fasciola hepatica''. IgE is utilized during immune defense against certain protozoan parasites such as ''Plasmodium falciparum''. IgE also has an essential role in type I hypersensitivity, which manifests various allergic diseases, such as allergic asthma, most types of sinusitis, allergic rhinitis, food allergies, and specific types of chronic urticaria and atopic dermatitis. IgE also plays a pivotal role in responses to allergens, such as: anaphylactic drugs, bee stings, and antigen preparations used in desensitization immunotherapy. Although IgE is typically the least abundant isotype—blood serum IgE levels in a normal ("non-atopic") individual are only 0.05% of the Ig concentration, compared to 75% for the IgGs at 10 mg/ml, which are the isotypes responsible for most of the classical adaptive immune response—it is capable of triggering the most powerful inflammatory reactions. IgE was simultaneously discovered in 1966 by two groups: Dr. Lawrence Lichtenstein and Dr. Philip Norman in the Johns Hopkins Department of Medicine's Division of Allergy and Infectious Diseases, as well as Dr. Kimishige Ishizaka and Dr. Margaret M. Hornbrook in the Children's Asthma Research Institute and Hospital in Denver, CO. == Receptors == IgE primes the IgE-mediated allergic response by binding to Fc receptors found on the surface of mast cells and basophils. Fc receptors are also found on eosinophils, monocytes, macrophages and platelets in humans. There are two types of Fcε receptors: *FcεRI (type I Fcε receptor), the high-affinity IgE receptor *FcεRII (type II Fcε receptor), also known as CD23, the low-affinity IgE receptor IgE can upregulate the expression of both types of Fcε receptors. FcεRI is expressed on mast cells, basophils, and the antigen-presenting dendritic cells in both mice and humans. Binding of antigens to IgE already bound by the FcεRI on mast cells causes cross-linking of the bound IgE and the aggregation of the underlying FcεRI, leading to the degranulation and the release of mediators from the cells. Basophils, upon the cross-linking of their surface IgE by antigens, release type 2 cytokines like interleukin-4 (IL-4) and interleukin-13 (IL-13) and other inflammatory mediators. The low-affinity receptor (FcεRII) is always expressed on B cells; but IL-4 can induce its expression on the surfaces of macrophages, eosinophils, platelets, and some T cells . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Immunoglobulin E」の詳細全文を読む スポンサード リンク
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