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Review Question - QID 210798

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QID 210798 (Type "210798" in App Search)
A 22-year-old woman presents to her primary care physician because she has been having severe pruritus on her left leg. She says the symptoms started 1 week ago after she went on a hiking trip with her friends. She wore shorts during the hike and felt as if something brushed her skin on the front of her leg just below the knee. She has no past medical history and no family history of autoimmune diseases. On physical exam, she has red pruritic papules and vesicles on her left leg. Which of the following mechanisms was most likely involved in the development of this patient's symptoms?

Activation of cell surface receptors by antibodies

3%

8/258

Cross-linking of IgE antibodies

15%

38/258

Cytotoxicity due to antibodies

2%

5/258

Cytotoxicity due to T-cells

69%

178/258

Immune complex deposition

3%

9/258

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This patient with pruritic papules and vesicles most likely has poison ivy-triggered contact dermatitis, which is a type IV hypersensitivty reaction involving T-cell activation.

Contact dermatitis is an erythematous and pruritic rash caused by cutaneous exposure to allergens or irritants. For example, poison ivy releases urushiol, which can penetrate the skin and modify endogenous proteins in the body. These modified proteins then become allergenic and activate a T-cell mediated response. This is a delayed reaction so symptoms will not present until 12-48 hours after exposure to the allergen. Notably, since this reaction is mediated by activation of T-cells, contact dermatitis is classified as a type IV hypersensitivity reaction.

Incorrect Answers:
Answer 1: Activation of cell surface receptors by antibodies is consistent with type II hypersensitivity; however, contact dermatitis is a type IV hypersensitivity reaction.

Answer 2: Cross-linking of IgE antibodies is consistent with type I hypersensitivity; however, contact dermatitis is a type IV hypersensitivity reaction.

Answer 3: Cytotoxicity due to antibodies is consistent with type II hypersensitivity; however, contact dermatitis is a type IV hypersensitivity reaction.

Answer 5: Immune complex deposition is consistent with type III hypersensitivity; however, contact dermatitis is a type IV hypersensitivity reaction.

Bullet Summary:
Contact dermatitis is a type IV hypersensitivity reaction mediated by T-cell activation.

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