A 20-year-old woman has recurrent mucocutaneous infections with Candida albicans despite normal neutrophil counts. Neutrophil superoxide generation in the nitroblue tetrazolium test is normal, but killing of ingested Candida is impaired. What is the defect?
- A Deficiency of the p47phox cytosolic component of NADPH oxidase
- B Deficiency of myeloperoxidase in azurophilic granules ✓
- C Deficiency of CD11b preventing fungal binding to CR3
- D Deficiency of lactoferrin in specific granules
Correct answer: B. Deficiency of myeloperoxidase in azurophilic granules
Explanation
Myeloperoxidase converts hydrogen peroxide and chloride into hypochlorous acid, the main microbicidal oxidant of the phagolysosome. In myeloperoxidase deficiency the NADPH oxidase pathway is intact, so superoxide generation tests are normal, but candidacidal killing is selectively impaired, giving recurrent Candida infections. p47phox deficiency defines a form of chronic granulomatous disease in which the NBT test is abnormal.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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