Virology USMLE Step 1 Practice Question
A 32-year-old woman with a 3-month history of progressive exertional dyspnea and nonproductive cough presents to the emergency department. She reports unintentional weight loss and night sweats for 2 months. She denies prior HIV testing or antiretroviral therapy. Vital signs show tachypnea (respiratory rate 28/min) and oxygen saturation of 88% on room air. Chest X-ray reveals bilateral interstitial infiltrates with a ground-glass appearance. Bronchoalveolar lavage demonstrates foamy macrophages and Pneumocystis jirovecii organisms. Laboratory values show CD4+ T cell count of 48 cells/μL (normal 500-1500), HIV viral load of 450,000 copies/mL, and normal absolute neutrophil and B cell counts. She is started on TMP-SMX, prednisone, and antiretroviral therapy. Which of the following mechanisms best explains this patient's inability to mount an adequate immune response to Pneumocystis jirovecii?
Answer choices
- ADirect infection of macrophages by HIV prevents effective antigen presentation to T cells
- BProgressive loss of CD4+ T helper cells through HIV-mediated cell lysis and apoptosis impairs coordinated immune responsesCorrect answer
- CPreferential infection of CD8+ cytotoxic T cells by HIV results in loss of cytotoxic function against infected cells
- DHIV-induced thymic involution prevents generation of new naive T cells to replace infected cells
- EDecreased production of granulocyte-macrophage colony-stimulating factor due to loss of Th1 CD4+ T cell function impairs fungal clearance
- FB cell dysfunction from chronic HIV antigenic stimulation prevents antibody-mediated opsonization of Pneumocystis organisms
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