Within the phagolysosome of a stimulated neutrophil, hydrogen peroxide generated by the respiratory burst is converted by myeloperoxidase into the most potent microbicidal oxidant. What is this product?

• A Hypochlorous acid (HOCl) ✓
• B Superoxide anion
• C Singlet oxygen
• D Hydrogen peroxide dimer

Explanation

Myeloperoxidase uses chloride ion as substrate to convert H2O2 into hypochlorous acid, which kills bacteria far more efficiently than H2O2 alone; it also reacts with amines to form chloramines. Superoxide is the initial product of NADPH oxidase upstream of this step, and singlet oxygen is not the defined MPO product. Inherited MPO deficiency causes recurrent candidal infections despite normal bacterial killing.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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