Immunology USMLE Step 1 Practice Question
A 6-year-old boy presents with recurrent skin abscesses and pneumonia. Vital signs show HR 110/min, BP 105/68 mmHg, RR 22/min, temperature 38.2°C, SpO2 98% on room air. Prior cultures grew Serratia and Staphylococcus aureus. Chest X-ray reveals right lower lobe infiltrate. He has granulomatous lesions on colonoscopy. Nitroblue tetrazolium test is negative. Lymph node biopsy shows normal architecture. Which defective immune process best explains his clinical presentation?
Answer choices
- AFusion of phagosomes with lysosomes
- BAdhesion of neutrophils to endothelium via integrins
- CExpression of Fc receptors on neutrophils
- DFormation of myeloperoxidase within azurophilic granules
- EGeneration of reactive oxygen species by NADPH oxidaseCorrect answer
- FChemotaxis of neutrophils toward bacterial pathogens
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