What triggers rapid release of chemicals from mast cells upon re-exposure to an allergen?

• A. Degranulation of mast cells
• B. Activation of neutrophils
• C. Production of leukotrienes by platelets
• D. Suppression of cytokines

Answer: (A)

Cross-linking of IgE antibodies that are bound to high-affinity FcεRI receptors on sensitized mast cells triggers rapid degranulation. When an allergen re-enters, it binds and cross-links these IgE molecules, activating a signaling cascade that causes the stored mediators in granules to be released quickly, producing the immediate allergic symptoms. Neutrophil activation and platelet-derived leukotriene production are parts of later inflammatory processes or separate pathways, not the trigger for the immediate release from mast cells. Suppressing cytokines would dampen the response rather than initiate rapid mediator release.