Immunology: cytokine pathways: 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: cytokine pathways

Sample item

A 6-year-old child develops disseminated disease with a non-tuberculous mycobacterium after BCG vaccination. Immunoglobulins, CD4 count and neutrophil function are normal. Which pathway defect should be suspected?

AThe TGF-beta signalling pathwayBThe IL-4 and IL-13 pathwayCThe IL-12 and interferon-gamma pathwayDThe IL-2 and common gamma chain pathway

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

The answer and the reasoning

C. The IL-12 and interferon-gamma pathway

Mendelian susceptibility to mycobacterial disease arises from defects in IL-12, its receptor, interferon-gamma receptor or STAT1. Macrophages cannot be activated by Th1-derived interferon-gamma, so weakly virulent mycobacteria and BCG disseminate, while other immunity is normal. Interferon-gamma therapy may help in some defects.

Option by option

A. The TGF-beta signalling pathway
TGF-beta is mainly regulatory and not linked to selective mycobacterial susceptibility.
B. The IL-4 and IL-13 pathway
IL-4 and IL-13 drive IgE and allergic responses, not mycobacterial control.
C. The IL-12 and interferon-gamma pathway (correct)
Correct. Macrophage activation through IL-12 and interferon-gamma is needed to control mycobacteria.
D. The IL-2 and common gamma chain pathway
IL-2 and common gamma chain defects cause SCID with broad infections and low lymphocytes.

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.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, The IL-12 and interferon-gamma pathway. Mendelian susceptibility to mycobacterial disease arises from defects in IL-12, its receptor, interferon-gamma receptor or STAT1.

Why is "The TGF-beta signalling pathway" not the answer?

TGF-beta is mainly regulatory and not linked to selective mycobacterial susceptibility.

Why is "The IL-4 and IL-13 pathway" not the answer?

IL-4 and IL-13 drive IgE and allergic responses, not mycobacterial control.

Why is "The IL-2 and common gamma chain pathway" not the answer?

IL-2 and common gamma chain defects cause SCID with broad infections and low lymphocytes.

What concept does this question test?

It tests Immunology: cytokine pathways in Microbiology. Macrophages cannot be activated by Th1-derived interferon-gamma, so weakly virulent mycobacteria and BCG disseminate, while other immunity is normal. Interferon-gamma therapy may help in some defects.

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: cytokine pathways?

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.