Which mediator is primarily involved in bronchoconstriction during an allergic reaction?

• A. Epinephrine
• B. Histamine
• C. Leukotrienes
• D. Sepsis

Answer: (C)

In allergic bronchoconstriction, the main players are the cysteinyl leukotrienes produced from arachidonic acid through the 5-lipoxygenase pathway. These mediators—LTC4, LTD4, and LTE4—bind to receptors on airway smooth muscle and cause strong, sustained constriction, which tightens the airways and also promotes mucus secretion and vascular leakage that worsen obstruction. Histamine can contribute to bronchial narrowing, but its effect is typically shorter-lived and less influential on sustained bronchoconstriction compared with leukotrienes. Epinephrine would reverse constriction by activating beta-2 receptors, so it’s a rescue agent rather than the mediator driving the response. Sepsis has no role here.