Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 32-year-old woman with a 3-year history of systemic lupus erythematosus presents to the emergency department with acute onset dyspnea, pleuritic chest pain, and low-grade fever. She reports recent medication non-adherence. Vital signs: BP 128/82 mmHg, HR 102/min, RR 22/min, temperature 37.8°C, SpO2 98% on room air. Chest X-ray shows bilateral pleural effusions. Pleural fluid analysis demonstrates: LDH 320 U/L (serum LDH 240 U/L), protein 3.2 g/dL, glucose 68 mg/dL, positive ANA, positive anti-dsDNA antibodies, and decreased complement C3 (42 mg/dL; normal 80-160). Serum creatinine is 0.9 mg/dL and urinalysis shows no proteinuria. Which of the following best explains the pathophysiology of pleural inflammation in this patient?
Answer choices
- ADeposited immune complexes activate the complement cascade, generating C5a chemotaxins that recruit neutrophils, which release proteolytic enzymes causing tissue damageCorrect answer
- BAutoreactive T cells directly infiltrate the pleura and release interferon-gamma, causing delayed hypersensitivity tissue damage
- CAnti-pleural mesothelial cell antibodies directly bind mesothelial cells and activate complement-dependent cellular cytotoxicity
- DCirculating anti-dsDNA antibodies cross-react with pleural surface antigens, initiating mast cell degranulation and local histamine release
- ENeutrophil elastase released from activated neutrophils causes direct proteolytic damage independent of immune complex deposition
- FAberrant expression of HLA-DR on pleural mesothelial cells activates autoreactive CD4+ T cells via molecular mimicry
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