Immunology USMLE Step 1 Practice Question
A 6-year-old girl receives a protein-based vaccine booster. Six weeks later, she presents with high-affinity IgG antibodies against the vaccine antigen, confirmed by serum immunoglobulin electrophoresis showing elevated IgG levels (1800 mg/dL). Her temperature is 37°C, vital signs stable, and she reports no recent infections. She has not received immunosuppressive medications. Which enzyme in B cells is most directly required for both immunoglobulin class switching to IgG and somatic hypermutation of antibody variable regions?
Answer choices
- ATyrosine kinase encoded by BTK
- BAdenosine deaminase
- CTerminal deoxynucleotidyl transferase
- DActivation induced cytidine deaminaseCorrect answer
- ERAG recombinase
- FPurine nucleoside phosphorylase
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