In the pathophysiology of anaphylaxis, the binding of an allergen to IgE antibodies on the surface of mast cells and basophils triggers the immediate release of preformed mediators. Which of the following is the most significant preformed mediator responsible for the initial, acute symptoms?
- Leukotrienes
- Prostaglandins
- Histamine (correct answer)
- Bradykinin
Explanation: During an IgE-mediated allergic reaction, the primary preformed mediator released from mast cell granules is histamine. Histamine is responsible for the classic, immediate signs of anaphylaxis: vasodilation, increased capillary permeability (leading to edema and hypotension), and smooth muscle contraction (leading to bronchospasm). Leukotrienes and prostaglandins are newly synthesized mediators that contribute to the inflammatory response but act later. Bradykinin is the primary mediator in ACE-inhibitor angioedema, not IgE-mediated anaphylaxis.