Immunology USMLE Step 1 Practice Question
A 19-year-old man presents with arthralgias and malar rash. Vital signs: BP 128/82, HR 92, RR 16, Temp 37.2°C, SpO2 98%. Labs reveal ANA 1:640 with anti-dsDNA antibodies; complement C3 level is low. He denies photosensitivity. Genetic testing shows a mutation preventing thymocyte apoptosis after high-affinity binding to self-peptide MHC complexes. Failure of which normal thymic process best explains his increased autoimmunity risk?
Answer choices
- ANegative selection in the thymic medullaCorrect answer
- BPositive selection in the thymic cortex
- CClass switching in activated B cells
- DAffinity maturation in germinal centers
- EAnergy in peripheral B cells
- FRegulatory T cell development in the thymic medulla
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