Immunoglobulin E (κ); Plasma

Immunoglobulin E (IgE) is the least common serum immunoglobulin, as it binds to Fc receptors on basophils and mast cells, thereby minimizing the amount of IgE that is released into circulation. Structurally, IgE exists as a monomer, but has an extra domain in the constant region not found in other immunoglobulins.

As a result of binding to basophils and mast cells, IgE is involved in the immune system's response to allergens. An allergen that binds to an IgE molecule attached to a basophil or mast cell stimulates the release of various pharmacological factors that result in the development of allergic symptoms.

IgE is also involved in response to various helminth parasites. The binding of eosinophils to an IgE-coated helminth, via the Fc region of the IgE, results in the eradication of the parasite. As such, serum levels of IgE rise in certain parasitic diseases.

Increases in IgE may be found in hay fever, asthma, anaphylactic shock, IgE-myeloma, and atopic skin diseases, such as eczema. Low levels of IgE have been noted in congenital agammaglobulinemia and hypogammaglobulinemia.