Immunology USMLE Step 1 Practice Question
A formula-fed, 1-month-old male is exposed to his sister with active varicella (vesicular rash, fever 38.5°C). Despite exposure, he remains asymptomatic with no cutaneous lesions. His mother contracted varicella 5 years ago. Maternal serum shows varicella-specific antibodies at 1:512 titer. The infant's cord blood contained transplacental antibodies but demonstrates no active viral replication on PCR. Which immunoglobulin class provided passive protection against varicella in utero?
Answer choices
- AIgM
- BIgE
- CIgGCorrect answer
- DIgD
- EIgA
- FIgG and IgM equally
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