Immunology: myeloperoxidase deficiency: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Immunology: myeloperoxidase deficiency

Sample item

Routine blood counts on an automated peroxidase-based analyser reveal neutrophils that lack peroxidase staining in an otherwise healthy adult. The cells generate superoxide normally but kill Candida slowly. Which microbicidal product is missing?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Hypochlorous acid

Myeloperoxidase in azurophilic granules converts hydrogen peroxide and chloride into hypochlorous acid, a potent microbicide. Deficiency is the commonest inherited phagocyte defect and is usually asymptomatic, but candidal infections can occur, especially in diabetics. The respiratory burst itself is intact.

Option by option

  • A. Superoxide anion

    Superoxide is made normally by NADPH oxidase in this condition.

  • B. Nitric oxide

    Nitric oxide is produced by inducible nitric oxide synthase in macrophages and is separate from this enzyme.

  • C. Hydrogen peroxide

    Hydrogen peroxide is produced normally and accumulates because it is not consumed by myeloperoxidase.

  • D. Hypochlorous acid (correct)

    Correct. Without myeloperoxidase, hypochlorous acid cannot be generated.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Hypochlorous acid. Myeloperoxidase in azurophilic granules converts hydrogen peroxide and chloride into hypochlorous acid, a potent microbicide.

Why is "Superoxide anion" not the answer?

Superoxide is made normally by NADPH oxidase in this condition.

Why is "Nitric oxide" not the answer?

Nitric oxide is produced by inducible nitric oxide synthase in macrophages and is separate from this enzyme.

Why is "Hydrogen peroxide" not the answer?

Hydrogen peroxide is produced normally and accumulates because it is not consumed by myeloperoxidase.

What concept does this question test?

It tests Immunology: myeloperoxidase deficiency in Microbiology. Deficiency is the commonest inherited phagocyte defect and is usually asymptomatic, but candidal infections can occur, especially in diabetics. The respiratory burst itself is intact.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Immunology: myeloperoxidase deficiency?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.