Immunology: vaccine immunology: 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: vaccine immunology

Sample item

A pure capsular polysaccharide vaccine gives a poor, short-lived response in infants under 2 years, but the same polysaccharide linked to a protein carrier is effective. What is the reason?

AThe conjugate is a live attenuated organism that replicatesBThe protein carrier acts as a toll-like receptor agonist that activates B cells directlyCThe protein carrier prolongs antigen half-life by blocking antibodyDThe conjugate recruits T helper cells, converting a T-independent response to a T-dependent one

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

The answer and the reasoning

D. The conjugate recruits T helper cells, converting a T-independent response to a T-dependent one

Polysaccharides are T-independent antigens that elicit mainly IgM with little memory, particularly in infants. In a conjugate vaccine, B cells specific for the sugar internalise the conjugate and present carrier peptides to T helper cells, which provide help for class switching, affinity maturation and memory.

Option by option

A. The conjugate is a live attenuated organism that replicates
Conjugate vaccines are inactivated and cannot replicate.
B. The protein carrier acts as a toll-like receptor agonist that activates B cells directly
The carrier works by T cell help, not as a toll-like receptor agonist.
C. The protein carrier prolongs antigen half-life by blocking antibody
Antigen half-life is not the mechanism, and the carrier does not block antibody.
D. The conjugate recruits T helper cells, converting a T-independent response to a T-dependent one (correct)
Correct. Carrier-specific T cell help yields memory and IgG responses.

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 D, The conjugate recruits T helper cells, converting a T-independent response to a T-dependent one. Polysaccharides are T-independent antigens that elicit mainly IgM with little memory, particularly in infants.

Why is "The conjugate is a live attenuated organism that replicates" not the answer?

Conjugate vaccines are inactivated and cannot replicate.

Why is "The protein carrier acts as a toll-like receptor agonist that activat…" not the answer?

The carrier works by T cell help, not as a toll-like receptor agonist.

Why is "The protein carrier prolongs antigen half-life by blocking antibody" not the answer?

Antigen half-life is not the mechanism, and the carrier does not block antibody.

What concept does this question test?

It tests Immunology: vaccine immunology in Microbiology. In a conjugate vaccine, B cells specific for the sugar internalise the conjugate and present carrier peptides to T helper cells, which provide help for class switching, affinity maturation and memory.

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: vaccine immunology?

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.