USMLE Step 1 Quiz
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IMMUNOLOGY
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A 2-year-old boy presents with a history of recurrent severe bacterial infections of the sinuses and lungs, as well as an episode of Pneumocystis jirovecii pneumonia. Laboratory studies show markedly elevated serum IgM levels but almost undetectable levels of IgG, IgA, and IgE. T-cell and B-cell counts are normal.
This patient's clinical presentation is most likely caused by a genetic defect affecting the function of which of the following molecules?
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