Immunity: delayed hypersensitivity: practice question

A Physiology 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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Physiology · Immunity: delayed hypersensitivity

Sample item

A tuberculin skin test is read at 48 to 72 hours rather than within minutes. What is the basis of this time course?

AAntigen–antibody complexes deposit in vessel walls and fix complementBSensitised CD4 Th1 cells and macrophages must be recruited and activatedCPreformed IgE on mast cells releases histamine on re-exposureDAntibody binds a cell-surface antigen and activates complement

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

The answer and the reasoning

B. Sensitised CD4 Th1 cells and macrophages must be recruited and activated

The tuberculin reaction is a type IV hypersensitivity. Memory Th1 cells in the skin release interferon-gamma, which activates macrophages and recruits more cells, producing induration that peaks at 48 to 72 hours. It is cell-mediated and cannot be transferred by serum.

Option by option

A. Antigen–antibody complexes deposit in vessel walls and fix complement
Immune complex disease is type III, as in the Arthus reaction, peaking at 4 to 10 hours.
B. Sensitised CD4 Th1 cells and macrophages must be recruited and activated (correct)
Correct. Cell-mediated recruitment takes days rather than minutes.
C. Preformed IgE on mast cells releases histamine on re-exposure
IgE-mediated mast cell degranulation is type I and occurs within minutes.
D. Antibody binds a cell-surface antigen and activates complement
Antibody against cell-surface antigen is type II, as in transfusion reactions.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Sensitised CD4 Th1 cells and macrophages must be recruited and activated. The tuberculin reaction is a type IV hypersensitivity.

Why is "Antigen–antibody complexes deposit in vessel walls and fix complement" not the answer?

Immune complex disease is type III, as in the Arthus reaction, peaking at 4 to 10 hours.

Why is "Preformed IgE on mast cells releases histamine on re-exposure" not the answer?

IgE-mediated mast cell degranulation is type I and occurs within minutes.

Why is "Antibody binds a cell-surface antigen and activates complement" not the answer?

Antibody against cell-surface antigen is type II, as in transfusion reactions.

What concept does this question test?

It tests Immunity: delayed hypersensitivity in Physiology. Memory Th1 cells in the skin release interferon-gamma, which activates macrophages and recruits more cells, producing induration that peaks at 48 to 72 hours. It is cell-mediated and cannot be transferred by serum.

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 Immunity: delayed hypersensitivity?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.