Immunology: haptens: 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: haptens

Sample item

A patient develops urticaria after penicillin, although penicillin is too small to be immunogenic by itself. How does it provoke an antibody response?

AIt acts as a hapten by binding covalently to a host carrier proteinBIt acts as a superantigen by cross-linking MHC class II and the T cell receptorCIt acts as an alloantigen that differs between individuals of one speciesDIt acts as an adjuvant that enhances unrelated antigen presentation

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

The answer and the reasoning

A. It acts as a hapten by binding covalently to a host carrier protein

A hapten is a small molecule that is antigenic but not immunogenic alone. Once bound to a carrier protein, such as serum albumin, it forms a conjugate that T and B cells can recognise, which is how drug allergies arise.

Option by option

A. It acts as a hapten by binding covalently to a host carrier protein (correct)
Correct. Penicillin conjugates to carrier proteins and then becomes immunogenic.
B. It acts as a superantigen by cross-linking MHC class II and the T cell receptor
Superantigens such as TSST-1 bind outside the peptide groove and activate many T cells nonspecifically.
C. It acts as an alloantigen that differs between individuals of one species
An alloantigen is a genetic variant between members of one species, as in blood groups.
D. It acts as an adjuvant that enhances unrelated antigen presentation
An adjuvant boosts responses to a co-administered antigen but is not itself the antigen.

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 A, It acts as a hapten by binding covalently to a host carrier protein. A hapten is a small molecule that is antigenic but not immunogenic alone.

Why is "It acts as a superantigen by cross-linking MHC class II and the T cel…" not the answer?

Superantigens such as TSST-1 bind outside the peptide groove and activate many T cells nonspecifically.

Why is "It acts as an alloantigen that differs between individuals of one spe…" not the answer?

An alloantigen is a genetic variant between members of one species, as in blood groups.

Why is "It acts as an adjuvant that enhances unrelated antigen presentation" not the answer?

An adjuvant boosts responses to a co-administered antigen but is not itself the antigen.

What concept does this question test?

It tests Immunology: haptens in Microbiology. Once bound to a carrier protein, such as serum albumin, it forms a conjugate that T and B cells can recognise, which is how drug allergies arise.

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: haptens?

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.