Final answer:
Asthma leads to a decrease in airway diameter. In some patients, an allergen binds to IgE antibodies on mast cells and triggers the release of inflammatory mediators, including histamine, prostaglandins, and leukotrienes.
Step-by-step explanation:
An allergen binds to IgE antibodies on mast cells and promotes the release of inflammatory mediators. These mediators include histamine, prostaglandins, and leukotrienes. These substances are responsible for the symptoms associated with asthma, such as airway constriction and inflammation.