Immunology USMLE Step 1 Practice Question
A 2-week-old male newborn presents with fever (38.9°C), tachycardia (165 bpm), and omphalitis with erythematous umbilical skin that has separated incompletely. The mother denies antibiotic use during pregnancy. Laboratory studies reveal marked neutrophilia (WBC 28,000/μL with 89% neutrophils) and elevated CRP. Blood culture remains sterile after 48 hours. The patient has experienced recurrent skin and soft tissue infections despite appropriate antibiotic therapy. Which of the following best explains this patient's susceptibility to infection?
Answer choices
- ADeficient terminal complement proteins leading to recurrent Neisseria infections
- BImpaired neutrophil chemotaxis due to absent C5a
- CDefective B cell maturation due to tyrosine kinase mutation
- DDefective respiratory burst caused by absent superoxide generation
- EFailure of neutrophils to adhere to endothelium because of CD18 deficiencyCorrect answer
- FSelectin ligand deficiency causing impaired neutrophil rolling (LAD type II)
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