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How do antibodies and allergens trigger mast cells to release histamine?
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antihistamine
Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H1 receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.
In the context of an allergic reaction, the process by which mast cells release histamine is a specific immune response known as a Type I hypersensitivity reaction.1
The mechanism functions as follows:
- Antibody Binding: The immune system produces specialized antibodies, specifically immunoglobulin E (IgE), in response to an allergen. These IgE antibodies become bound to the surface of mast cells, which are found throughout the body's connective tissues.512
- Allergen Interaction: When an individual is exposed to the specific allergen again, the allergen enters the body and binds to the IgE antibodies already attached to the mast cells.21
- Degranulation: Once a sufficient amount of the allergen has bound to these antibodies, the mast cells are stimulated to undergo a process called [degranulation]. During this process, the mast cells release the contents of their granules—including histamine—into the surrounding tissues.321
The released histamine then acts on nearby tissues, causing the characteristic symptoms of an allergic reaction, such as inflammation, swelling, and the constriction of bronchial passages.231