Immunology USMLE Step 1 Practice Question
A 20-year-old woman with no prior shellfish exposure develops acute onset wheezing, diffuse urticaria, and angioedema within 3 minutes of ingesting shrimp. Vital signs show BP 88/52 mmHg, HR 118 bpm, RR 22/min, temp 37.2°C. Serum tryptase is elevated at 12 ng/mL. She denies previous allergic reactions and takes no medications. She improves rapidly after intramuscular epinephrine 0.3 mg. Which immunologic mechanism best explains this acute reaction?
Answer choices
- AIgE mediated cross linking on mast cells with release of histamineCorrect answer
- BIgG directed against cell surface antigens with complement activation
- CAutoantibody stimulation of a hormone receptor
- DT cell mediated tissue injury from sensitized lymphocytes
- EImmune complex deposition with neutrophilic inflammation
- FNon-IgE mast cell degranulation via complement anaphylatoxins C3a and C5a
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.