IgE

IgE, or immunoglobulin E, is one of the five major classes of antibodies in humans. Like other antibodies, an IgE molecule contains two heavy chains and two light chains. Its heavy chains are the epsilon type, which gives IgE its characteristic structure and determines its interactions with IgE-specific receptors. The variable regions of the antibody form binding sites that recognize particular antigens .^1,2

A major feature of IgE biology is its high-affinity binding to the IgE receptor FcεRI, which is found particularly on mast cells and basophils. IgE can remain attached to FcεRI while its antigen-binding regions remain available to recognize antigen. If an antigen cross-links neighboring FcεRI-bound IgE molecules, receptor signaling can activate the cell and trigger the release of inflammatory mediators .^1,2

This mechanism is central to immediate allergic reactions. In an allergic person, IgE directed against a particular allergen can sensitize mast cells and basophils to that substance. Later exposure to the allergen can activate these cells and promote release of mediators such as histamine, contributing to allergic inflammation and, in some circumstances, anaphylaxis. IgE also participates in type 2 immune responses associated with defense against helminth parasites and animal venoms .^1,2

IgE itself is therefore not synonymous with allergy. It is a normal antibody class with immune functions, whereas IgE-mediated allergy occurs when IgE recognizing an allergen contributes to an inappropriate hypersensitivity response. IgE also interacts with another receptor, CD23, which participates in regulating IgE responses and antigen handling .^1,2