Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 19-year-old male college student presents to the emergency department with a 12-hour history of fever (39.4°C), severe headache, and photophobia. On examination, he has a petechial rash on his trunk and lower extremities, nuchal rigidity, and altered mental status. Vital signs show HR 128/min, RR 24/min, BP 94/62 mmHg, and SpO2 92% on room air. Cerebrospinal fluid analysis reveals: WBC 450/µL (90% neutrophils), protein 210 mg/dL, glucose 18 mg/dL (serum glucose 98 mg/dL), and Gram stain shows gram-negative diplococci. The patient is otherwise healthy with no history of recent infections or antibiotic use. Which of the following best explains why individuals with deficiency in a particular complement component are at highest risk for disseminated infection with this organism?
Answer choices
- ADeficiency of C1q prevents lectin pathway activation and opsonization of the capsule
- BDeficiency of C3 prevents both classical and alternative pathway amplification, eliminating opsonization and MAC formationCorrect answer
- CDeficiency of C5a impairs chemotaxis of neutrophils to the site of infection
- DDeficiency of Factor H allows uncontrolled alternative pathway activation leading to complement exhaustion
- EDeficiency of properdin prevents alternative pathway activation exclusively
- FDeficiency of C4 prevents immediate recognition of polysaccharide antigens on the bacterial capsule
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