Allergic reaction (hypersensitivity reaction) represent the reaction of the immune system, accompanied by damage to the body's own healthy tissues. The mechanisms by which the immune system protects the body from the «strange», and the mechanisms of hypersensitivity reactions, in which damaged «their» tissue are similar. Thus, antibodies, lymphocytes and other cells, which are components of normal immune system, in addition to combat infections are involved in the development of allergic reactions, as well as in reactions to blood transfusion in autoimmune diseases and rejection of transplanted organs.
Generally, the term allergic reaction indicate processes that are involved in antibody class immunoglobulin E (IgE).
These antibodies combine with the specialized cells, such as basophilic in the blood and mast cells in tissues. When meeting with the antigen (in this case it is called the allergen) cells associated with IgE, are beginning to provide substance, damaging the surrounding tissue. Theoretically allergen can be anything that acts as an antigen, causing the immune response: dust, plant pollen, medicine or food.
Sometimes, to describe a group of diseases, which is involved in the development of IgE, for example allergic rhinitis and allergic asthma (often hereditary), use the term a topic disease. Such diseases are characterized by the development of IgE in response to various substances in the air, like pollen, mold, animal fur, as well as the mites present in the dust. Eczema (atopic dermatitis) is also related to a topic diseases, although the role of IgE in the development of the disease less clear. A person with a topic disease, however, not increased risk of IgE in the ingestion of allergens in the skin (ex, drugs or insect venom).
Allergic reactions are mild and severe.
Typically, they are limited and itching eye irritation, lacrimation, and sneezing, but may become a threat to life if suddenly impeded respiration, heart function is disrupted and drastically reduces arterial blood pressure (eg, is a shock). This condition is called anaphylaxis and may occur in sensitive people in a variety of situations, for example, shortly after the consumption of certain products of certain medications or bee sting.