Immunoglobulin E
Overview
Immunoglobulin E (IgE) is a type of antibody that has only been found in mammals. It plays an essential role in the body's immune system against parasitic infections. However, it is also responsible for the allergic reaction symptoms in humans, including anaphylaxis, a severe and potentially life-threatening reaction.
Structure
The structure of IgE is similar to that of other antibodies, consisting of four polypeptide chains. It has two heavy chains and two light chains, which are linked together by disulfide bonds. The heavy chains of IgE contain an extra domain, compared to other antibodies, which is involved in binding to Fc receptors on the surface of certain immune cells.
Function
The primary function of IgE is to protect the body against parasitic infections. It does this by binding to the surface of the parasite, which signals other immune cells to attack and destroy the parasite. IgE also plays a crucial role in the body's immune response to allergens. When an allergen enters the body, it triggers the production of IgE antibodies, which bind to the allergen and signal immune cells to release chemicals that cause allergic symptoms.
Role in Allergic Reactions
IgE is primarily known for its role in allergic reactions. When the body is exposed to an allergen, it triggers the production of specific IgE antibodies. These antibodies bind to the surface of mast cells and basophils in the body. When the allergen enters the body again, it binds to the IgE antibodies on the surface of these cells, triggering them to release chemicals such as histamine. This causes the symptoms of an allergic reaction, which can range from mild symptoms such as sneezing and itching, to severe reactions such as anaphylaxis.
Role in Immune Response
In addition to its role in allergic reactions, IgE also plays a crucial role in the body's immune response to parasitic infections. It does this by binding to the surface of the parasite, which signals other immune cells to attack and destroy the parasite. This is particularly important in the body's defense against helminth parasites, which are large multicellular organisms that can cause serious infections in humans.
Clinical Significance
The level of IgE in the blood can be a useful indicator of several health conditions. Elevated levels of IgE can indicate an allergic reaction or a parasitic infection. However, it can also be a sign of certain immune disorders, such as Hyper IgE Syndrome, a rare genetic disorder characterized by high levels of IgE, recurrent skin and lung infections, and certain skeletal and dental abnormalities.