Immunology USMLE Step 1 Practice Question
A 6-year-old unvaccinated boy presents with fever (39.2°C), sore throat, and progressive stridor. Vital signs show HR 118/min, RR 28/min, BP 102/68 mmHg, SpO2 94% on room air. Examination reveals cervical lymphadenopathy and a gray pharyngeal pseudomembrane that bleeds when touched. Gram stain shows gram-positive bacilli. He denies recent travel. The responsible bacterial toxin most directly causes disease by which mechanism?
Answer choices
- AInactivation of the 60S ribosomal subunit
- BCleavage of SNARE proteins in motor neurons
- CADP ribosylation of elongation factor 2Correct answer
- DCross linking T cell receptor and MHC class II molecules
- EActivation of adenylate cyclase via Gs
- FADP ribosylation of Gi to prevent inhibition of adenylate cyclase
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