Immunology: IL-12 and interferon-gamma axis: 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: IL-12 and interferon-gamma axis

Sample item

A 7-year-old boy develops disseminated infection after BCG vaccination, followed by recurrent non-tuberculous mycobacterial infection and Salmonella bacteraemia. HIV is negative, immunoglobulins and lymphocyte counts are normal, and the dihydrorhodamine oxidation test is normal. Which defect is most likely?

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

The answer and the reasoning

A. Defect in the IL-12 and interferon-gamma pathway of Th1 immunity

Intracellular pathogens are controlled when IL-12 from macrophages drives Th1 cells to produce interferon-gamma, which activates macrophage killing. Mutations in IL-12Rbeta1, IL-12p40 or the interferon-gamma receptor cause Mendelian susceptibility to mycobacterial disease, with severe BCG, atypical mycobacteria and Salmonella infection. A normal oxidative burst test argues against chronic granulomatous disease.

Option by option

  • A. Defect in the IL-12 and interferon-gamma pathway of Th1 immunity (correct)

    Impaired IL-12 and interferon-gamma signalling selectively cripples control of mycobacteria and Salmonella.

  • B. Defect in the integrin CD18 chain

    CD18 deficiency causes leukocyte adhesion deficiency with delayed umbilical cord separation and neutrophilia.

  • C. Defect in Bruton tyrosine kinase

    BTK deficiency causes agammaglobulinaemia, in which immunoglobulins would be low.

  • D. Defect in phagocyte NADPH oxidase

    NADPH oxidase deficiency causes chronic granulomatous disease, which would give an abnormal dihydrorhodamine test.

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 A, Defect in the IL-12 and interferon-gamma pathway of Th1 immunity. Intracellular pathogens are controlled when IL-12 from macrophages drives Th1 cells to produce interferon-gamma, which activates macrophage killing.

Why is "Defect in the integrin CD18 chain" not the answer?

CD18 deficiency causes leukocyte adhesion deficiency with delayed umbilical cord separation and neutrophilia.

Why is "Defect in Bruton tyrosine kinase" not the answer?

BTK deficiency causes agammaglobulinaemia, in which immunoglobulins would be low.

Why is "Defect in phagocyte NADPH oxidase" not the answer?

NADPH oxidase deficiency causes chronic granulomatous disease, which would give an abnormal dihydrorhodamine test.

What concept does this question test?

It tests Immunology: IL-12 and interferon-gamma axis in Microbiology. Mutations in IL-12Rbeta1, IL-12p40 or the interferon-gamma receptor cause Mendelian susceptibility to mycobacterial disease, with severe BCG, atypical mycobacteria and Salmonella infection. A normal oxidative burst test argues against chronic granulomatous disease.

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 Immunology: IL-12 and interferon-gamma axis?

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.