Within minutes of a bee sting, the affected skin shows redness and a wheal. Which mediator accounts for the immediate transient increase in vascular permeability at this site?
- A C3b deposited on endothelial basement membrane
- B Leukotriene B4 acting on neutrophil G-protein receptors
- C Histamine acting on H1 receptors of postcapillary venules ✓
- D Transforming growth factor beta released by platelets
Correct answer: C. Histamine acting on H1 receptors of postcapillary venules
Explanation
Histamine, preformed in mast cell granules, binds H1 receptors on postcapillary venular endothelium and causes rapid endothelial contraction with gap formation, producing the immediate transient permeability response within minutes. Leukotriene B4 is a chemoattractant, not a permeability mediator, and A3b is an opsonin. The slow, prolonged permeability response is mediated by leukotrienes A4, D4 and E4, not histamine.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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