Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 3-year-old boy presents with recurrent severe bacterial infections, failure to thrive, and oral candidiasis. Flow cytometry shows absent CD4+ T cells. Genetic testing reveals mutations in the IL2RG gene encoding the common gamma chain of cytokine receptors. Which of the following mechanisms best explains the immunodeficiency in this patient?
Answer choices
- AMutation in RAG1/RAG2 genes preventing V(D)J recombination
- BImpaired signaling through IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21 receptors preventing T cell, B cell, and NK cell developmentCorrect answer
- CDefective NADPH oxidase preventing respiratory burst in neutrophils
- DImpaired complement cascade due to early complement protein deficiencies
- EDirect destruction of lymphocytes by defective thymic epithelial cells
- FAdenosine deaminase deficiency causing similar SCID through toxic purine metabolite accumulation in lymphocytes
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