Immunoglobulin E (IgE)

Immunoglobulin E (IgE) is a type of antibody that your body makes to help you fight off infections. They’re especially important in helping to fight off parasitic infections. They can also cause allergic reactions, so healthcare providers often measure them to diagnose allergies. “Ig” is short for immunoglobulin, another name for antibody.

Antibodies are proteins with a unique shape that fit onto an antigen like a key that fits a single lock. Antigens are proteins or other markers that identify cells or organisms as part of your own body (“self”) or foreign (“non-self”) and potentially harmful. When an antibody comes across an antigen that it fits — like on the surface of a virus or bacterium — it alerts the rest of your immune system that it’s found something harmful. Your immune system can then destroy or try to flush out the harmful substance (pathogen).

IgE are supposed to help identify intruders, but they can mistake non-harmful substances, like food proteins or pollen, for harmful ones. This can cause severe allergic reactions, including anaphylaxis.

What is an IgE test used for?

Healthcare providers use IgE blood tests to help diagnose allergies, autoimmune conditions, infections and other illnesses. Types of IgE tests include:

• Total IgE test: For this test, a lab looks at your blood sample and counts the total number of IgE. This can help diagnose or treat conditions like asthma or atopic dermatitis.
• Specific IgE test: For this test, a lab determines whether you have antibodies to specific allergens individually. This can help diagnose food, pet, pollen and other allergies.

Where are IgE antibodies in the body?

Most immunoglobulin E is found on the surface of immune cells, like mast cells, basophils and eosinophils. These immune cells are most common in your skin and the mucous membranes of your:

• Respiratory tract (your nose, mouth, throat and lungs)
• Gastrointestinal tract (your stomach and intestines)
• Urinary tract (your kidneys, ureters, bladder and urethra)

Only low amounts of IgE are normally found in your blood.

What is the main function of IgE?

IgE antibodies sit on the surface of immune cells. They wait for antigens they recognize to come by. When they do, they can:

• Cause an allergic reaction: IgE sometimes mistakenly think harmless substances, like pollen or certain foods, are harmful. When IgE antibodies attached to the surface of an immune cell recognize an antigen, they can cause the immune cell to release chemicals like histamines that cause an allergic reaction. Sometimes, this can be so severe that it causes anaphylaxis, life-threatening swelling in your body.
• Alert other immune cells to destroy a pathogen: IgE receptors can attach to pathogens and label them as harmful. This lets other immune cells know to destroy them.

What’s the structure of IgE?

Immunoglobulins are made up of chains of proteins that form a “Y” shape. The straight end, called the Fc or constant region, is the same on all antibodies of the same type (IgA, IgD, IgE, IgG and IgM). The Fc region attaches to immune cells.

The forked end, called the receptor, or Fab region, is different for each antibody. The receptor has a unique shape that recognizes the antigen on the surface of viruses, bacteria or other potentially harmful intruders. IgE receptors recognize parasitic worms and allergens.

What is a normal IgE level?

Total IgE levels are usually between 1.5 and 150 kilounits per liter (kU/L) of blood. The “normal” amount depends on your age and other factors. Levels of IgE antibodies to a specific allergen should be fewer than 0.35 kU/L (or fewer than 0.10 kU/L for allergens that are more likely to cause severe reactions, like peanuts). Elevated IgE levels for a specific substance means you’re likely allergic to it.

What conditions have high IgE levels?

High IgE levels are associated with allergic conditions, including:

• Allergic rhinitis (hay fever)
• Asthma
• Food allergies
• Hives
• Hyper IgE syndrome

Hyper IgE syndrome is a genetic condition that causes your body to make too many IgE antibodies. It can cause symptoms similar to allergies and make you more likely to get infections.

Is IgE related to autoimmune disease?

If you have an autoimmune diseases, you might have IgE antibodies that attack proteins made by your own body (autoantibodies). IgE autoantibodies are often (but not always) higher in people with:

• Lupus
• Rheumatoid arthritis
• Bullous pemphigoid
• Atopic dermatitis
• Chronic urticaria

What are the symptoms of high IgE?

If you have a high level of IgE, you might have skin conditions like eczema and get frequent infections, including:

• Skin infections
• Yeast infections
• Pneumonia
• Lung abscesses

Are there any treatments for high IgE?

Healthcare providers sometimes use omalizumab (Xolair®) to treat allergic asthma, chronic urticaria, food allergies and nasal polyps. Omalizumab is a monoclonal antibody treatment that blocks IgEs, reducing allergy and asthma symptoms. Providers inject it under your skin every two to four weeks. Researchers are studying whether omalizumab could treat some autoimmune conditions, as well.