Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 32-year-old woman presents with a 3-month history of polyarthralgia, photosensitivity, and a malar rash. Vital signs show BP 128/82 mmHg, HR 88/min, RR 16/min, temp 37.2°C, SpO2 98% on room air. Laboratory studies reveal positive antinuclear antibodies, anti-double-stranded DNA antibodies, and decreased serum complement C3 levels (45 mg/dL). Urinalysis is negative for proteinuria. Which pathologic mechanism best explains the complement depletion?
Answer choices
- ADirect destruction of complement-producing cells by cytotoxic T lymphocytes
- BAntibody-mediated blockade of complement receptor expression
- CBacterial endotoxin activation of the alternative complement pathway
- DImmune complex deposition activating the classical complement cascadeCorrect answer
- EHereditary deficiency of complement regulatory proteins
- FAutoantibodies against complement C3 convertase preventing complement activation
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