A 30-year-old woman develops intensely itchy vesicles on the dorsum of her hands two days after wearing new costume jewellery earrings. Skin biopsy shows a perivascular lymphocytic infiltrate with spongiosis. Which mechanism underlies this lesion?

• A CD8+ cytotoxic T cell killing of keratinocytes after hapten presentation by Langerhans cells ✓
• B IgE-mediated mast cell degranulation triggered by a protein antigen
• C Deposition of circulating antigen-antibody complexes in dermal vessels
• D Complement-mediated lysis of keratinocytes by autoantibodies to desmoglein

Explanation

Allergic contact dermatitis is a Type IV reaction in which a small chemical hapten such as nickel binds self proteins, is carried by Langerhans cells to regional nodes, and primes CD8+ cytotoxic T cells that attack hapten-bearing keratinocytes on re-exposure. The 48 hour delay and lymphocytic spongiosis fit delayed hypersensitivity. Option B describes immediate urticaria within minutes, and option C describes serum sickness or Arthus-type vasculitis, neither of which produces this pattern.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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