Bacteriology USMLE Step 1 Practice Question
A 2-year-old boy with functional asplenia secondary to sickle cell disease (hemoglobin S on electrophoresis) presents for preventive vaccination against encapsulated bacteria. Vital signs are stable: BP 95/60, HR 110, RR 24, Temp 37.2°C, SpO2 98% on room air. He has no active infection and takes hydroxyurea daily. His pediatrician selects a conjugate vaccine formulation rather than a pure polysaccharide vaccine to enhance immunogenicity. Which mechanism best explains this advantage?
Answer choices
- AThe conjugate vaccine bypasses antigen presentation and directly activates cytotoxic T cells
- BThe conjugate vaccine works by passive transfer of preformed antibodies
- CThe conjugate vaccine stimulates only innate immunity and avoids memory formation
- DThe conjugate vaccine prevents antigenic drift in the pathogen
- EProtein conjugation converts the response into a T cell dependent processCorrect answer
- FThe conjugate vaccine enhances opsonization by directly blocking the bacterial capsule's resistance to complement deposition
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