Hypersensitivity and Autoimmunity · USMLE Step 1

Contact dermatitis due to poison ivy exposure is caused by which immune mechanism?

  1. IgE-mediated mast cell activation
  2. Antibody-mediated cell lysis
  3. Immune complex deposition
  4. Delayed T-cell hypersensitivity
Show answer and explanation

Correct answer: Delayed T-cell hypersensitivity

Poison ivy causes a Type IV delayed hypersensitivity reaction. Sensitized T cells trigger inflammation upon re-exposure.

Difficulty: Medium Question 7 of 20

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