The immune system produces five kinds of antibodies, each with its own function. Allergic reactions involve the IgE antibody. Allergic persons form IgE antibodies against substances that are harmless in most individuals, such as certain types of food and pollen, called antigens or allergens. Once the IgE antibodies are formed against a specific allergen, they bind to certain mast cells and basophils which circulate in the blood. This process is called allergic sensitisation. When a person is exposed to that specific allergen again, the IgE antigens attached to mast cells and basophils bind to the allergen, causing a reaction that makes the mast cell burst. When the mast cell bursts (also called degranulation of mast cells), it releases chemicals such as histamine. These chemicals make the blood vessels dilate and smooth muscles contract. For example, the smooth muscles of the bronchi contract and the air passage narrows, which may lead to asthma. These chemicals also attract eosinophils to that area. The eosinophils release chemicals that neutralise the chemicals released by the mast cells.
When the allergic reaction is severe, so much histamine is released that the person’s blood pressure drops, blood circulation slows down and the bronchi contract, causing respiratory distress. Such a severe allergic reaction is called anaphylactic shock and may cause death. Fortunately this is rare.
(published with permission in writing from:http://www.health24.com)
