A 25-year-old woman presents with acute eczema of the earlobes after wearing costume jewelry. A patch test is performed. At 48 hours, the test site shows erythema, edema, and papulovesicles. This reaction is mediated by which type of hypersensitivity?
- A Type I
- B Type II
- C Type IV ✓
- D Type III
Correct answer: C. Type IV
Explanation
Allergic contact dermatitis is a delayed-type hypersensitivity reaction mediated by sensitized T lymphocytes. Patch test reactions peak at 48 to 72 hours, which is characteristic of a delayed immune response. Type I is immediate IgE-mediated, Type II is cytotoxic, and Type III is immune complex-mediated.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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