Bacteriology USMLE Step 1 Practice Question
A 23 year old woman comes to the clinic because of recurrent sinus infections and 3 episodes of bacterial pneumonia over the past 2 years. She has chronic diarrhea and notes that infections became more frequent during late adolescence. Physical examination is unremarkable. Laboratory studies show low levels of IgG, IgA, and IgM with a normal number of circulating B lymphocytes. Which of the following is the most likely underlying defect?
Answer choices
- AFailure of B cells to differentiate into plasma cellsCorrect answer
- BDefect in CD40 ligand on T helper cells
- CDeficiency of the NADPH oxidase complex
- DMutation in the BTK tyrosine kinase gene
- EAbsence of thymic development from the third and fourth pharyngeal pouches
- FSelective IgA deficiency with normal IgG and IgM levels
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