Immunopathology: mendelian susceptibility to mycobacterial disease: practice question

A Pathology 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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Pathology · Immunopathology: mendelian susceptibility to mycobacterial disease

Sample item

A 3-year-old develops disseminated infection with a weakened mycobacterium after BCG vaccination, with poorly formed granulomas. T and B cell numbers and immunoglobulins are normal. Which pathway is most likely defective?

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

The answer and the reasoning

D. The IL-12 and interferon-gamma axis

Defects of IL-12, the IL-12 receptor, interferon-gamma or its receptor prevent Th1 cells and macrophages from activating each other, so intracellular mycobacteria and Salmonella are not contained. Granuloma formation is poor and the immunoglobulins are normal.

Option by option

  • A. The classical complement pathway

    Classical complement deficiency predisposes to immune complex disease.

  • B. The IgE receptor on mast cells

    The IgE receptor is involved in allergic, not mycobacterial, responses.

  • C. The NADPH oxidase respiratory burst

    NADPH oxidase defect gives chronic granulomatous disease, with catalase-positive bacteria and fungi.

  • D. The IL-12 and interferon-gamma axis (correct)

    Correct. Without IL-12 and interferon-gamma signalling, macrophages cannot kill mycobacteria.

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 Pathology question

What is the answer to this Pathology question?

The best answer is D, The IL-12 and interferon-gamma axis. Defects of IL-12, the IL-12 receptor, interferon-gamma or its receptor prevent Th1 cells and macrophages from activating each other, so intracellular mycobacteria and Salmonella are not contained.

Why is "The classical complement pathway" not the answer?

Classical complement deficiency predisposes to immune complex disease.

Why is "The IgE receptor on mast cells" not the answer?

The IgE receptor is involved in allergic, not mycobacterial, responses.

Why is "The NADPH oxidase respiratory burst" not the answer?

NADPH oxidase defect gives chronic granulomatous disease, with catalase-positive bacteria and fungi.

What concept does this question test?

It tests Immunopathology: mendelian susceptibility to mycobacterial disease in Pathology. Granuloma formation is poor and the immunoglobulins are normal.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Immunopathology: mendelian susceptibility to mycobacterial disease?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.