What kind of hypersensitivity reaction does this represent?

A 24-year-old man with no past medical history develops urticaria and angioedema within 2 hours of taking aspirin for a headache. It is the first time he has taken aspirin in years, but he does not recall having an adverse reaction to it in the past. What kind of hypersensitivity reaction does this represent?

Cell-mediated
Cytotoxic
IgA-mediated
IgE-mediated
Immune complex-mediated

Correct answer
IgE-mediated
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correct answer: D

This represents an IgE-mediated (also called anaphylactic or type I) hypersensitivity reaction, where mast cells release histamine and other substances that result in vasodilation and increased vascular permeability, resulting in urticaria (hives) and angioedema (the same mechanism as urticaria, but affecting subcutaneous tissue).