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Nov 11, 2023

What Is Immunoglobulin E (IgE)?

An Important Antibody Involved in the Allergic Response Farah Khan, MD, is a

An Important Antibody Involved in the Allergic Response

Farah Khan, MD, is a board-certified allergist/immunologist who treats pediatric patients at Nationwide Children's Hospital in Columbus, Ohio.

Immunoglobulin E (IgE) is an antibody—a protein produced by the immune system in response to a possible invader. It is primarily involved in the allergic response but also fights infections from parasites.

Increased blood levels of IgE are associated with allergies (including atopic dermatitis), parasitic and certain viral infections, some types of immunodeficiency, inflammation, asthma, and some cancers, including Hodgkin's and non-Hodgkin's lymphoma. Blood tests for IgE can be used to diagnose allergies.

This article will include a simple overview of the structural makeup and production of IgE, the function of IgE, its significance in certain conditions/diseases, the role of serum IgE testing, and medications that affect IgE.

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Immunoglobulin E is made by B cells (a type of immune system blood cell) after exposure and sensitization to a substance the immune system recognizes as foreign and potentially harmful.

In the case of allergens, the substance typically is not harmful to most people. But people who generate IgE to allergens can be negatively affected once they develop a sensitization. This process takes place in lymphoid tissues such as the tonsils, adenoids, and bone marrow.

IgE then diffuses through the tissues and into the bloodstream. Local synthesis (production) of IgE can occur in the bronchial and nasal mucosa.

IgE is a Y-shaped protein, made of two light chains and two heavy chains of peptides (building blocks of protein). The heavy chains form the body and arms of the Y shape, and the light chains attach just to the arms of the Y shape.

A defining characteristic of IgE is the heavy chains, called epsilon. IgE has four constant regions, which makes the molecule heavier. Both the light chains and the heavy chains have a variable region at the end of the Y arms, which binds to specific antigens.

IgE binds to two types of receptors—high-affinity receptors and low-affinity receptors. High-affinity receptors (where IgE binds more tightly) are located mostly on basophils and mast cells. These are immune system blood cells that have granules containing chemicals that are involved in allergic reactions.

IgE binds to these cells in the presence of specific antigens (substances such as allergens that provoke an immune response). The binding sets off a chain reaction that causes the cells to release chemical immune mediators (such as histamine), which are responsible for the symptoms of an allergic reaction.

Low-affinity receptors (where IgE binds less avidly) are located on several types of cells, including B cells, T cells, dendritic cells, monocytes, macrophages, neutrophils, eosinophils, and platelets.

IgE binding triggers different effects in cells. For example, when IgE binds to a specific marker on B cells, it inhibits (stops the growth of) the synthesis of more IgE. This is called negative feedback and is how the immune system regulates itself.

IgE is associated with these conditions:

Serum IgE testing may be used to diagnose allergies. The total amount of IgE in your blood can be measured. Another type of test, called a specific IgE test, can also be used. A specific IgE test measures how much IgE your body makes to a specific allergen.

However, specific IgE tests may have false positives, showing you are allergic to an allergen when you are not. For example, you don't have any allergic symptoms when you eat peanuts, but the test shows an elevation in peanut-specific IgE. This is called sensitization and healthcare providers use this test result to confirm what the patient has reported in their clinical history.

Other types of allergy tests may be used, such as skin tests. Serum IgE may also be used to screen for parasitic infections or aid in diagnosing other illnesses.

Xolair (omalizumab) is a medication that specifically targets IgE by reducing the number of receptors available for IgE to bind to. Xolair is typically used as add-on therapy for people who have allergic asthma, chronic hives, or nasal polyps and haven't responded to traditional therapies such as antihistamines or corticosteroids. This medication can also be used off-label to treat other conditions.

Other medications that may be used to treat IgE-associated conditions, such as steroids, target the immune response more broadly and are not as specific to IgE.

Immunoglobulin E (IgE) is a complex antibody with several functions but is best known for its role in the allergic response. It is an important antibody in fighting off parasites. Extremely high or undetectable levels of IgE are linked to various health problems. Research regarding the role of IgE in cancer is ongoing.

An estimated 50 million people in the United States have an allergy, and allergies are a leading cause of chronic illness. While research continues, a better understanding of the function of IgE has led to the development of important medications that can improve the lives of individuals with IgE-associated illnesses.

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Asthma and Allergy Foundation of America. Allergens and allergic asthma.

Immune Deficiency Foundation. Hyper IgE syndrome.

Lawrence MG, Palacios-Kibler TV, Workman LJ, et al. Low serum IgE is a sensitive and specific marker for common variable immunodeficiency (CVID). J Clin Immunol. 2018;38(3):225-233. doi:10.1007/s10875-018-0476-0

McCraw AJ, Chauhan J, Bax HJ, et al. Insights from IgE immune surveillance in allergy and cancer for anti-tumour IgE treatments. Cancers. 2021;13(17):4460. doi:10.3390/cancers13174460

MedlinePlus. Allergy blood test.

Xolair (omalizumab). Prescribing information.

Asthma and Allergy Foundation of America. Allergy facts and figures.

By Kristin Hayes, RNKristin Hayes, RN, is a registered nurse specializing in ear, nose, and throat disorders for both adults and children.