Immunoglobulin E (IgE) is a class of antibody (or immunoglobulin (Ig) "isotype") that has been found only in mammals. IgE exists as monomers consisting 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 parasitic worms like Schistosoma mansoni, Trichinella spiralis, and Fasciola hepatica. IgE may also be important during immune defense against certain protozoan parasites such as Plasmodium falciparum.
IgE also plays an essential role in type I hypersensitivity, which manifests various allergic diseases, such as allergic asthma, allergic rhinitis, food allergy, and some types of chronic urticaria and atopic dermatitis. IgE also plays a pivotal role in allergic conditions, such as anaphylactic reactions to certain drugs, bee stings, and antigen preparations used in specific 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 10 mg/ml for the IgGs (the isotypes responsible for most of the classical adaptive immune response) - it is capable of triggering the most powerful inflammation reactions.
IgE was discovered in 1966 by the Japanese scientist couple Teruko and Kimishige Ishizaka.
Read more about Immunoglobulin E: Receptors, Physiology, Role in Disease, Drugs Targeting The IgE Pathway