Immunology: type IV hypersensitivity: 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: type IV hypersensitivity

Sample item

A positive tuberculin skin test 48 hours after injection is mediated primarily by which mechanism?

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

The answer and the reasoning

C. T-cell-mediated delayed hypersensitivity

The tuberculin reaction is a type IV hypersensitivity response driven by sensitised T lymphocytes and macrophage recruitment. Its delayed timing contrasts with immediate IgE-mediated reactions.

Option by option

  • A. IgG against cell-surface antigen

    Type II reactions target cells or extracellular matrix with antibody.

  • B. IgE-mediated mast-cell degranulation

    Type I hypersensitivity is immediate and IgE mediated.

  • C. T-cell-mediated delayed hypersensitivity (correct)

    Correct. Cell-mediated immunity produces the delayed induration.

  • D. Immune-complex deposition

    Type III reactions involve circulating immune complexes.

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 C, T-cell-mediated delayed hypersensitivity. The tuberculin reaction is a type IV hypersensitivity response driven by sensitised T lymphocytes and macrophage recruitment.

Why is "IgG against cell-surface antigen" not the answer?

Type II reactions target cells or extracellular matrix with antibody.

Why is "IgE-mediated mast-cell degranulation" not the answer?

Type I hypersensitivity is immediate and IgE mediated.

Why is "Immune-complex deposition" not the answer?

Type III reactions involve circulating immune complexes.

What concept does this question test?

It tests Immunology: type IV hypersensitivity in Microbiology. Its delayed timing contrasts with immediate IgE-mediated reactions.

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: type IV hypersensitivity?

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.