Immunology USMLE Step 1 Practice Question
A 29-year-old woman presents with intensely pruritic vesicular lesions on her wrists and forearms 48 hours after hiking through poison ivy. Vital signs show BP 118/76, HR 82, RR 16, Temp 37.2°C, SpO2 98% on room air. Examination reveals erythematous linear streaks with small vesicles; no systemic lymphadenopathy noted. Patch testing confirms urushiol sensitization. Which mediator primarily drives this delayed-type hypersensitivity reaction?
Answer choices
- APreformed IgE on mast cells
- BSensitized T lymphocytes releasing cytokinesCorrect answer
- CIgG against basement membrane antigens
- DImmune complex deposition in vessel walls
- EAutoantibodies stimulating the TSH receptor
- FComplement anaphylatoxin (C3a/C5a)-mediated mast cell activation
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.