A class of antibody normally present in very low levels in humans but found in larger quantities in people with allergies and certain infections. It is the primary antibody responsible for the classic allergic reaction.
In biology, Immunoglobulin E (IgE) is an antibody subclass (known as "isotypes"), found only in mammals. Although IgE is typically the least abundant isotype - blood serum IgE levels in a normal ("non-atopic") individual are ~150 ng/ml, 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 immune reactions. Most of our knowledge of IgE has come from research into the mechanism of a form of allergy known as type 1 hypersensitivityAnnual Review of Immunology 2003 Apr 21;579-628..