Immunoglobulin E (IgE) is an antibody isotype, found only in mammals. Although IgE is typically the least abundant isotype – blood serum IgE levels in a normal (“non-atopic”) individual are ~150ng/mL, compared to 10mg/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 an allergy known as type 1 hypersensitivity. IgE plays an important role in allergy and in the immune system’s recognition of cancer. People who suffer from true IgE-mediated allergies can have up to 10 times the normal level of IgE in their blood (as do sufferers of hyper-IgE syndrome).
The IgE molecules (MW 200,000) bind to the surface of mast cells and basophilic granulocytes. Subsequently the binding of allergen to cell-bound IgE causes these cells to release histamines and other vasoactive substances. The release of histamines in the body initiates what is commonly known as an allergic reaction. IgE levels show a slow increase during childhood, reaching adult levels in the second decade of life. In general, the total IgE levels increase with the allergies a person has and the number of times of exposure to the relevant allergens. Significant elevations may be seen in the sensitised individuals, but also in cases of myeloma, pulmonary aspergillosi and during the active stages of parasitic infections.
The measurement of immunoglobulin E (IgE) in serum is widely used in the diagnosis of allergic reactions and parasitic infections. Before making any therapeutic determination it is important, however, to know whether the allergic reaction is IgE mediated or non-IgE mediated. Measurement of total IgE in serum sample, along with other supporting diagnostic information, can help to make that determination.