Illustration depicting an allergic reaction leading an asthma attack. In the lighter area of the background, an antigen (such as a pollen grain) sensitizes a B lymphocyte to initiate production of immunoglobulin E or IgE antibody. People predisposed to allergies make this antibody in response to exposure to certain allergens. The antibody then binds to mast cells in the tissues lining the nose and bronchi, and also in the skin. On re-exposure, the allergen is bound to the IgE antibody on the surface of the mast cell. This triggers the mast cell to release chemicals, like histamine, that cause inflammation of nasal mucosa (highlighted) and the swelling, mucus secretion, and other changes that lead to narrowing of the airways indicative of an asthma attack.