Immunoglobulin E is a specific type of antibodies produced by the immune system which is involved in hypersensitivity/allergic reactions. It was estimated that about 20% of the world’s population have some allergic condition.
Hypersenstitivity, allergy and atopy
The immune system protects human body against bacteria, viruses, parasites and fungi, furthermore, it reacts against any foreign particle and toxin. However, in some cases the responses of immunity are excessive and inappropriate and may be even harmful and life-threatening for the human-being. This kind of exaggerated responses is referred to as hypersensitivity reactions. Additionally, the conditions in which specific immunoglobulins E (IgE) or sensitized T lymphocytes play role in response to allergens are known as allergy. When person’s Th2 lymphocytes tend to produce abnormal amounts of IgE antibodies in response to exposure to common allergens, this state of the body is called atopy.
Role of IgE in allergic reactions
Immunoglobulins E are the antibodies which firmly bind to mast cells via binding sites on its Fc region so that only trace amounts of these antibodies are found in the serum. The process in which IgE attaches to mast cells and basophils is termed as sensitization. It is worth noting, that the specific IgE are produced in the body only after the first exposure to antigen and, respectively, the pure allergic reaction develops only on subsequent exposures.
When an allergen (most common allergens include pollens, animal danders and house dust mites) cross-links with two particles of immunoglobulin E on the surface of mast cells, the last ones are stimulated and release histamine and other substances (like heparin, proteases, cytokines) which influence the vascular tonus, smooth muscle contraction and permeability. This reaction (also referred to as “wheal and flare” response) occurs within minutes (5-10 minutes usually) after the second exposure to an allergen.
Immunoglobulin E-mediated disorders
IgE-mediated hypersensitivity reactions usually involve the upper and lower airways and gastrointestinal tract, causing nasal itching, sneezing and rhinorrhoea (runny nose), conjunctivitis, wheezing, breathlessness and cough.
The following conditions are considered to be IgE-mediated:
• Hay fever;
• Chronic allergic rhinitis;
• Urticaria and angioedema;
• Atopic eczema;
• Food allergies;
Immunoglobulin E: Job’s syndrome
Hyperimmunoglobulin E syndrome, also known as the Job’s syndrome, is an autosomal dominant disorder characterized by elevated serum IgE levels, increased number of eosinophils in the blood, eczema and recurrent skin and lung infections.
Immunoglobulin E: IgE detection in the serum
• Allergy test is performed to check whether the IgE levels are of normal values or increased (normal value for adults – less than 81 kU/L). The total amount of IgE in the serum is increased in allergic disorders, although parasitic infections may also raise the IgE values.
• The specific IgE (RAST) test should be performed in order to verify the exact allergen, avoid exposure to this substance and start specific therapy.
Immunoglobulin E: Another tests used to verify allergy
Skin testing may be performed via percutaneous and intradermal route.
• In percutaneous prick test allergen-containing solutions are placed on the skin, later the skin is pricked and the allergen enters the skin. Another way is to scratch the skin, allowing the allergen to contact with mast cells.
• In intradermal testing allergen is injected into the skin.
A red spot occurs on the site where the allergen to which a person is sensitized was introduced. Allergic response is confirmed by the presence of redness or swelling, more than 5 mm in diameter.